Class 10

Balbharti Maharashtra State Board Class 10 Science Solutions Part 1 Chapter 3 Chemical Reactions and Equations Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 Science Solutions Part 1 Chapter 3 Chemical Reactions and Equations

Question 1.
Choose the correct option from the bracket and explain the statement giving reasons :
(Oxidation, displacement, electrolysis, reduction, zinc, copper, double diplacement, decomposition)

a. To prevent rusting, a laver of ……… metal is applied on iron sheets.
Answer:
To prevent rusting, a layer of zinc metal is applied on iron sheets.
The rusting of iron is an oxidation process. Due to corrosion of an iron a deposit of reddish substance (Fe₂O₃.H₂O) is formed on it. This substance is called rust. To prevent corrosion, a layer of zinc metal (galvanisation) is applied on iron sheets.

b. The conversion or ferrous sulphate to ferric sulphate is …….. reaction.
Answer:
The conversion of ferrous sulphate to ferric sulphate is an oxidation reaction.
When ferric ion is formed. from ferrous ion, the positive charge is increased by one unit. while this happens the rerrous ion loses one electron. A process in which a metal or its ion loses one or more electrons is called an oxidation.
2FeSO₄ → Fe₂(SO₄)₃
Fe₂ + SO₄^2- → 2Fe³⁺ + SO₄^2-

c. When electric current is passed through acidulated water …….. of water takes place.
Answer:
when electric current is passed through acidulated water decomposition of water takes place. In this reaction. hydrogen and oxygen gas are formed.

This decomposition takes place with the help of an electric current, it is also called electrolytic decomposition.

d. Addition of an aqueous solution of ZnSO₄ to an aqueous solution of BaCl₂ is an example of ……… reaction.
Answer:
Addition of an aqueous solution of ZnSO₄ to an aqueous solution or BaCl₂ is an example or double displacement reaction.

Barium chloride reacts with zinc sulphate to form a white precipitate of barium sulphate. white precipitate is formed by exchange of ions Ba⁺⁺ and SO₄^— between the reactants.

Question 2.
a. What is the reaction called when oxidation and reduction take place simultaneously? Explain with one example.
Answer:
The reaction which involves simultaneous oxidation and reduction is called an oxidation-reduction or redox reaction.
In a redox reaction, one reactant gets oxidised while the other gets reduced during a reaction.
Redox reaction = Reduction + Oxidation

In redox reaction, the reductant is oxidized by the oxidant and the oxidant is reduced by the
reductant.
Example:CuO_(s) + H_2(g) → Cu_(s) + H₂O
In this reaction, oxygen is removed from copper oxide therefore it is a reduction of CuO, while hydrogen accepts oxygen to form water that means oxidation of hydrogen takes place. Thus oxidation and reduction reactions occur simultaneously.

Other examples of redox reactions:

b. How can the rate of the chemical reaction, namely, decomposition of hydrogen peroxide be increased?
Answer:
At room temperature, the decomposition of hydrogen peroxide into water and oxygen takes place slowly. However, the same reaction occurs at a faster rate on adding manganese dioxide (MnO₂),
powder in it.

c. Explain the term reactant product giving examples.
Answer:

1. The substance which undergoes bond breaking while taking part in a chemical reaction is called reactant.
2. The substance formed as a result of a chemical reaction by formation of new bonds is called product.
3. Example: In a chemical reaction, the formation of carbon dioxide gas takes place by combustion of coal in air. In this reaction, coal (carbon) and oxygen (from air) are the reactants while carbon dioxide is the product.

d. Explain the types of reactions with reference to oxygen and hydrogen. Illustrate with examples.
Answer:
With reference to oxygen and hydrogen, there are two types of reaction

1. Oxidation reaction
2. Reduction reaction.

1. Oxidation reaction:
Examples:
(1) When carbon burns in air, it forms carbon dioxide. In this reaction carbon accepts oxygen, therefore, this is an oxidation reaction.
C_(s) + O_2(g) → CO_2(g)

(2) When sodium reacts with ethyl alcohol, sodium ethoxide and hydrogen gas is formed. In this reaction, hydrogen is removed from ethyl alcohol, therefore this is an oxidation reaction.

(3) Acidified potassium dichromate (K₂Cr₂O₇ / H₂SO₄) oxidises ethly alcohol to acetic acid.

2. Reduction reaction:
Examples:
(1) When hydrogen gas is passed over black copper oxide a reddish coloured layer of copper is
formed.
In this reaction an oxygen atom removed from CuO to form copper, hence, this is reduction.

(2) when hydrogen gas is passed over red hot coke, methane is obtained.
Here, hydrogen is added to coke (carbon). Hence, this is reduction.

e. Explain the similarity and difference in two events, namely adding NaOH to water and adding CaO to water.
Answer:
Similarity : Both NaOH and CaO, when dissolved separately in water, solid NaOH dissolves releasing heat, resulting in rise in temperature. This reaction is exothermic reaction. When solid CaO dissolves in water, Ca(OH)₂ is formed, large amount of heat is evolved. This reaction is also exothermic reaction. Both reactions are combination reactions and single product is obtained.
NaOH_(s) + H₂O → NaOH_(aq) + Heat
CaO_(s) + H₂O → Ca(OH)_2(aq) + Heat
Difference:

1. Aqueous solution of NaOH is considered as a strong alkali.
2. Aqueous solution of Ca(OH)₂ is considered as a weak alkali.

Question 3.
Explain the following terms with examples.
a. Endothermic reaction
Answer:
Endothermic reaction: The reaction in which heat is absorbed is called an endothermic
reaction.
when KNO_3(s) dissolves in water, there is absorption of heat during the reaction and the temperature of the solution falls.
KNO_2(s) + H₂O_(l) + Heat → KNO_3(aq)

b. Combination reaction
Answer:
When two or more reactants combine in a reaction to form a single product, it is called a combination reaction.
Examples:
1. The ammonia gas reacts with hydrogen chloride gas to form the salt in gaseous state, immediately it condenses at room temperature and gets transformed into the solid state.

2. Magnesium burns in air to form white powder of magnesium oxide as a single product.

3. Iron reacts with sulphur to form iron sulphide.

c. Balanced equation
Answer:
In a chemical reaction, the number of atoms of the elements in the reactants is same as the number or atoms of those elements in the product, such an equation is called a balanced equation.
Example: AgNO₃ + NaCl → AgCl + NaNO₃
In the above reaction, the number of atoms of the elements in the reactants is same as the number of atoms of elements in the products.

d. Displacement reaction
Answer:
The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by the formation of its own ions is called displacement reaction.

When zinc granules are added to the blue coloured copper sulphate solution, the zinc ions formed from zinc atoms take the place of Cu²⁺ ions in CuSO₄, and copper atoms, formed from Cu²⁺ ions comes out i.e. the more reactive zinc displaces the less reactive Cu from copper sulphate.

4. Give scientific reason:
a. When the gas formed on heating lime stone is passed through freshly prepared lime water, the lime water turns milky.
Answer:
when lime stone is heated, calcium oxide and carbon dioxide are formed. This carbon dioxide gas is passed through freshly prepared lime water, insoluble calcium carbonate and water are formed. In this reaction, lime water turns milky.

b. It takes time for pieces of Shahabud tile to disappear in HCl, but its powder disappears rapidly.
Answer:
The rate of a reaction depends upon the size of the particles of the reactants taking part in the reaction. The smaller the size of the reactants particles, the more is their total surface area and the faster is the rate of reaction.

In the reaction of dil. HCl with pieces of Shahabad tile, CO₂ effervescence is formed amid the tile disappears slowly. On the other hand. CO₂ effervescence forms at faster rate with Shahabad tile powder and it disappears rapidly.

c. While preparing dilute sulphuric acid from concentrated sulphuric acid in the laboratory, the concentrated sulphuric acid is added slowly to water with constant stirring.
Answer:
(1) The preparation of dilute sulphuric acid falls in the category of extreme exothermic process.

(2) During the preparation of dilute sulphuric acid. large amount of water is taken in a glass container which is surrounded by ice. Cool it for twenty minutes, Now small quantity of conc. H₂SO₄ is added slowly with stirring. Therefore, only a small amount of heat is liberated at a time. In this way dilute sulphuric acid is prepared.

(3) On the other hand, in the process of dilution or conc. sulphuric acid with water, very large amount of heat is liberated. As a result, water gets evaported instantaneously, if it is poured in to conc. H₂SO₄ which may cause an accident.

d. It is recommended to use air tight container for storing oil for long time.
Answer:

1. If edible oil is allowed to stand for a long time, it undergoes air oxidation, it becomes rancid and its smell and taste changes.
2. Rancidity in the rood stuff cooked in oil or ghee is prevented by using antioxidants. The process of oxidation reaction of food stuff can also be slowed down by storing it in air tight container.

Question 5.
Observe the following picture a write down the chemical reaction with explanation.

Answer:
The rusting of iron is an oxidation process. The rust on iron does not form by a simple reaction between oxygen and iron surface. The rust is formed by an electrochemical reaction. Fe oxidises to Fe₂O₃. H₂O on one part of iron surface while oxygen gets reduced to H₂O on another part or surface, Different regions on the surface of iron become anode and cathode.
(1) Fe is oxidised to Fe²⁺ in the anode region.
Fe_(s) → Fe²⁺ _(aq) + 2e^–
(2) O₂ is reduced to form water in the cathode region.
O_2(g) + 4H⁺ _(aq) + 4e— → 2H₂O_(l)

When Fe²⁺ ions migrate from the anode region they react with water and futher get oxidised to form Fe³⁺ ions.
A reddish coloured hydrated oxide is formed from Fe³⁺ ions. It is called rust. It collects on the
surface.
2Fe³⁺ _(aq) + 4H₂O_(l) → Fe₂O₃. H₂O_(s) + 6H⁺ _(aq)…
Because of various components in the atmosphere, oxidation of metals takes place, consequently resulting in their damage. This is called ‘corrosion’. Iron rusts and a reddish coloured layer is formed on it. This is corrosion of iron.

Question 6.
Identify from the following reactions the reactants that undergo oxidation and reduction.
a. Fe + S → FeS
Answer:
Fe + S → FeS
In this reaction, Iron (Fe) undergoes oxidation
and sulphur. (S) undergoes reduction.

b. 2Ag₂O → 4Ag + O₂↑
Answer:
2Ag₂O → 4Ag + O₂↑
In this reaction, reduction of Ag₂O takes place.

c. 2Mg + O₂ → 2MgO
Answer:
2Mg + O₂ → 2MgO
In this reaction, oxidation of Mg takes place.

d. NiO + H₂ → Ni + H₂O
Answer:
NiO + H₂ → Ni + H₂O
In this reaction, reduction of NiO takes place and oxidation of H₂ takes place.

Question 7.
Balance the following equation stepwise.
a. H₂S₂O_7(l) + H₂O_(l) → H₂SO_4(l)
Answer:
Step 1: Rewrite the given equation as it is
H₂S₂O7_(l) + H₂O_(l) → H₂SO_4(l)
Step 2: write the number or atoms of each element in the unbalanced equation on both sides of equations.

Element	Number of atoms in reactant (left side)	Number of atoms in products (right side)
H	4	2
S	2	1
O	8	4

Step 3: To equalise the number of hydrogen atoms, sulphur atoms and oxygen atoms we use 2 as the coemficient or factor in the product.

Element	Number of atoms in reactant (left side)	Number of atoms in products (right side)
H	4	2 × 2
S	2	1 × 2
O	8	4 × 2
Total	14	14

Now the equation becomes H₂S₂O₇ + H₂O → 2H₂SO₄
Now, count the atoms of each element on both sides of the equation. The number of atoms on both sides are equal. Hence, the balanced equation is
H₂S₂O₇ + H₂O → 2H₂SO₄
Now indicate the physical states of the reactants and products.
H₂S₂O_7(l) + H₂O_(l) → 2H₂SO_4(l)

b. SO_2(g) + H₂S_(aq) → S_(s) + H₂O_(l)
Answer:
Step 1:
Rewrite the given equation as it is
SO_2(g) + H₂S_(aq) → S_(s) + H₂O_(l)

Step 2:
Write the number of atoms of each element in the unbalanced equation on both sides of equations.

Element	Number of atoms in reactants (left side)	Number of atoms in products (right side)
S	2	1
O	2	1
H	2	2

The number of hydrogen atoms on both sides of the equation is same, therefore, equalise the number of sulphur atoms and oxygen atoms.

Step 3: To balance the number of sulphur atoms:

Number of atoms of sulphur	In reactants		In products
	S2O	H2S	(S)
Initially	1	1	1
To balance	1	1	1 × 2

To equalise the number of sulphur atoms, we use 2 as the factor in the product, now the equation becomes
SO₂ + H₂S → 2S + H₂O

Step 4:
To equalise the number of oxygen atoms in the unbalanced equation.

Number of atoms of oxygen	In reactants (SO2)	In products H2O
Initially	2	1
To balance	2	1 × 2

To equalise the number of sulphur atoms, we use 2 as the factor in the product i.e. H₂O, now the unbalanced equation becomes
SO₂ + H₂S → 2S + 2H₂O

Step 5:
To equalise the number of hydrogen atoms in unbalanced equation:

Number of atoms of hydrogen	In reactants (H2S)	In products (H2O)
Initially	2	4
To balance	2 × 2	4

To equalise the number of hydrogen atoms we use 2 as the factor in the reactant i.e, H₂S, now the unbalanced equation become
SO₂ + 2H₂S → 2S + 2H₂O
Now, count the atoms of each element on both sides of the equation, there are less number of sulphur atoms in the product. Now equalise the sulphur atoms, the balanced equation becomes,
SO₂ + 2H₂S → 3S + 2H₂O
Now indicate the physical states of reactants and products.
SO_2(g) + 2H₂S_(aq) → 3S_(s) + 2H₂O_(l)

c. Ag_(s) + HCl_(l) → AgCl ↓ + H₂ ↑
Answer:
Step 1:
Rewrite the given equation as it is
Ag_(s) + HCl_(l) → AgCl ↓ + H₂ ↑

Step 2:
write the number of atoms or each element in the unbalanced equation on both sides of equations.

Element	Number of atoms in reactants (left side)	Number of atoms in products (right side)
Ag	1	1
H	1	2
Cl	1	1

The number of silver and chlorine atoms on both sides of the equation are same, therefore, equalise the number of hydrogen atoms.

Step 3:
To balance the number of hydrogen atoms.

Number of atoms of hydrogen	In reactants HCl	In products H2
Initially	1	2
To balance	1 × 2	2

To equalise the number of hydrogen atoms, we use 2 as the factor in the product HCl, now the unbalanced equation become
Ag_(s) + 2HCl → AgCl + H₂

Step 4:
To balance the number of chlorine atoms:

Number of atoms of chlorine	In reactants (2HCl)	In products (AgCl)
Initially	2	1
To balance	2	2 ×1

To equalise the number of chlorine atoms, we use 2 as the factor in the product AgCl. now the unbalanced equation becomes
Ag + 2HCl → 2AgCl + H₂
Now count the atoms of each element on both sides of the equation, there are less number of silver atoms in the reactant. Now equalise the silver atoms, the balanced equation becomes
2Ag + 2HCl → 2AgCl + H₂
Now indicate the physical states of the reactunts and products
2Ag_(s) + 2HCl_(l) → 2AgCl ↓ + H₂ ↑

d. H₂SO_4(aq) + NaOH_(aq) → Na₂SO_4(aq) + H₂O_(l)
Answer:
Step 1:
Rewrite the given equation as it is
H₂SO_4(aq) + NaOH_(aq) → Na₂SO_4(aq) + H₂O_(l)

Step 2:
write the number of atoms of each element in the unbalanced equation on both sides of the equation.

Element	Number of atoms in reactants	Number of atoms in products
Na	1	2
S	1	1
O	5	5
H	3	2

The number of oxygen atoms involved in different compounds on both sides (reactants and products) are equal. Therefore, balance the number of atoms of the second element, sodium.

Step 3:
To balance the number of sodium atoms:

Number of atoms of sodium	In reactants	In products
To begin with	1 (in NaOH)	2 (in Na2SO4)
To balance	1 × 2	2

To equalise the number of sodium atoms, we use 2 as the factor of NaOH in the reactants. Now, the partly balanced equation becomes as follows
H₂SO₄ + 2NaOH → Na₂SO₄ + H₂O

Step 4:
Now, balance the number of hydrogen atoms:

Number of atoms of hydrogen	In reactants	In products
To begin with	(in H2SO4) 2 (in NaOH)	2 (in H2O)
To balance	4	2 × 2

To equalise the number of hydrogen atoms, we use 2 as the factor or H₂O in the products. The equation then becomes
H₂SO₄ + 2NaOH → Na₂SO₄ + H₂O
Now, count the atoms of each element on both sides of the equation. The number of atoms on both sides are equal. Hence, the balanced equation is
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
Now indicate the physical states of the reactants and the products.
H₂SO_4(aq) + 2NaOH_(aq) → Na₂SO_4(aq) + 2H₂O_(l)

Question 8.
Identify the endothermic and exothermic reaction.
a. HCl + NaOH → NaCl + H₂O + heat
Answer:
Exothermic reaction.

b. \(2 \mathrm{KClO}_{3}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow} 2 \mathrm{KCl}(\mathrm{s})+3 \mathrm{O}_{2} \uparrow\)
Answer:
Exothermic reaction.

c. CaO + H₂O → Ca(OH)₂ + heat
Answer:
Exothermic reaction.

d. \(\mathrm{CaCO}_{3}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow} \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2} \uparrow\)
Answer:
Exothermic reaction.

Question 9.
Match the column in the following table:

Reactants	products	Type of chemical reaction
BaCl2(aq) + ZnSO4(aq)	H2CO3(aq)	Displacement
2 AgCl(s)	FeSO4(aq) + Cu(s)	Combination
CuSO4(aq) + Fe(s)	BaSO4↓ + ZnCl2(aq)	Decomposition
H2O(l) + CO2(g)	2Ag(s) + Cl2(g)	Double displacement

Answer:

Reactants	products	Type of chemical reaction
BaCl2(aq) + ZnSO4(aq)	BaSO4↓ + ZnCl2(aq)	Double displacement
2 AgCl(s)	2Ag(s) + Cl2(g)	Decomposition
CuSO4(aq) + Fe(s)	FeSO4(aq) + Cu(s)	Displacement
H2O(l) + CO2(g)	H2CO3(aq)	Combination

Project:
Do it your self:
1. Prepare aqueous solutions or various solid salts available in the laboratory. Observe what happens when aqueous solution of sodium hydroxide is added to these. Prepare a chart of double displacement reactions based on these observation.

2. Observe and note the physical and chemical changes experienced in various incidents in your day to day 1ife.

Can you recall? (Text Book Page No.16)

Question 1.
what are the types of molecules of elements and compounds?
Answer:
Elements are divided into three classes i.e. metals, nonmetals and metalloids. When two or more elements combine chemically in a fixed proportion by weight, a compound is formed. The properties of a compound are altogether different from those of the constitutional elements.

Question 2.
what is meant by valency of element?
Answer:
The number of electrons that an atom of an element gives away or takes up while forming an ionic bond, is called the valency or that element.

Question 3.
What is the requirement for writing molecular formulae of different compounds?
How are the molecular formulae of the compounds written?
Answer:
while writing the molecular formulae of different compounds, the symbol of the radicals and their valence should be known.
The number of the ions is written as subscript on the right of the symbol or the ion. By cross multiplication of valenceies chemical formula is obtained.

Find out (Text Book Page No. 44)
Question1.
How are the blackened silver utensils and patinated (greenish) brass utensils cleaned?
Answer:
The blackened silver utensils and patinated (greenish) brass utensils are cleaned using baking soda, vinegar and lemon mix.

Use your brain power! (Text Book Page No. 35)

Question 1.
write down the physical states of reactants and products in the reaction
SO₂ + 2H₂S → 3S + 2H₂O
Answer:
Reactants : SO_2(g), 2H₂S_(g)
Products : 3S_(s), 2H₂O_(l).

Question 2.
write down the physical states of reactants and products in the reaction
2Ag + 2HCl → 2AgCl + H₂
Answer:
Reactants: 2Ag_(s), 2HCl_(l)
Products: 2AgCl ↓, H₂ ↑

Question 3.
Identify the reactants and products of the following equation.

Answer:
Reactants: vegetable oil, H₂(g)
Product: Vanaspathi ghee

Use your brain power! (Text Book Page No. 42)

Question 1.
Which is the oxidant used for purification of drinking water?
Answer:
The chlorine based oxidants are used in the purification of drinking water.

Question 2.
Why is potassium permanganate used during cleaning water tanks?
Answer:
Potassium permanganate is an oxidising agent. It oxidises dissolved iron, manganese and hydrogen sulphide into solid particles that are filtered out of the water tank. It is used to control iron bacteria growth in tank.

Can you tell? (Text Book Page No. 43)

Question 1.
what is the type of this reaction, in which Vanaspathi ghee is formed from vegetable oil?
Answer:

In the preparation of vanaspathi ghee from vegetable oil hydrogen gas is used. This process is known as hydrogenation. This is reduction reaction.

Find out (Text Book page No. 33)

What are the other uses of silver nitrate in every day life?
Answer:
Silver nitrate is used in the voters-ink. It is used as reactant in the laboratory. Silver nitrate is used to prevent infection in wounds and skin burns.

Use your brain power! (Text Book Page No. 35)

Question 1.
N_2(g) + H_2(g) ⇌ NH_3(g)
Answer:
Step 1:
Rewrite the given equation as it is
N_2(g) + H_2(g) ⇌ NH_3(g)

Step 2:
Write the number of atoms of each element in the unbalanced equation on both sides of equations

Element	Number of atoms in reactants	Number of atoms in products
N	2	1
H	2	3

Step 3:
In the given equation. NH₃ is a compound and it contains hydrogen element. On the left hand side there are two H atoms and on the right side 3H atoms. Equalise H atoms on both sides.

Hydrogen atoms	In reactants	In products
Initially	2	3
To balance	3 × 2	2 × 3

To equalise the number of hydrogen atoms, we use 3 as the factor in the reactant and 2 as the factor in the products. Now the equation becomes
N₂ + 3H₂ → 2NH₃
Now, count the atoms of each element on both sides of the equation. The number of atoms on both sides are equal. Hence, the balanced equation is
N₂ + 3H₂ → 2NH₃
Now indicate the physical states of the reactants and products
N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

Question 2.
Calcium chloride + Sulphuric acid → Calcium sulphate + Hydrogen chloride.
Answer:
Step 1:
Write the chemical equation from the given word equation.
CaCl₂ + H₂SO₄ → CaSO₄ + HCl

Step 2:
Write the number of atoms of each element in the unbalanced on both sides of equation.

Element	Number of atoms in reactants	Number of atoms in products
Ca	1	1
Cl	2	1
H	2	1
S	1	1
O	4	4

Step 3:
In the given equation H₂SO₄ is a compound and it contains hygrogen element. On the left hand side there are two hydrogen atoms and on the right side one hydrogen atom. Equalise H atoms on both sides.

Hydrogen atoms	In reactants (H2SO4)	In products (HCl)
Initially	2	1
To balance	2	2  × 1

To equalise the number of hydrogen atoms we use 2 as the factor in the product so that the number of H atoms on both sides are equal. Therefore, the equation becomes
CaCl₂ + H₂SO₄ → CaSO₄ + 2 HCl
Now, count the atoms of each element on both sides of the equation. The number of atoms on both sides are equal hence, the balanced equation is
CaCl₂ + H₂SO₄ → CaSO₄ + 2 HCl
Now, indicate the physical state of the reactants and products.
CaCl_2(s) + H₂SO_4(l) → CaSO_4(s) + HCl_(l)

Can you tell? (Text Book Page No. 39)

Take into account the time required for following processes. Classify them into two groups and give titles to the groups.
(1) Cooking gas starts burning on ignition.
(2) Iron article undergoes rusting.
(3) Erosion of rocks takes place to form soil.
(4) Alcohol is formed on mixing yeast in glucose solution under proper condition.
(5) Effervescence is formed on adding baking soda into a test tube containing dilute acid.
(6) A white precipitate is formed on adding dilute sulphuric acid to barium chloride solution.
Answer:
The above processes are classified into two groups (a) slow speed reactions (b) fast speed reactions.
Slow speed reactions: (2), (3) and (4).
Fast speed reactions: (1),(5) and (6).

Use your brain power! (Text Book Page No. 43)

Question 1.
Some more examples of redox reaction are as follows. Identify the reductants and oxidants from them.
(1) 2H₂S + SO₂ → 3S↓ + 2H₂O
(2) MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂↑
Answer:
Oxidants: SO₂, MnO₂
Reductants: H₂S, HCl

Question 2.
If oxidation means losing electrons, what is meant by reduction.
Answer:
Reduction means gaining one or more electrons.

Question 3.
Write the reaction of formation of Fe²⁺ by reduction Fe³⁺ by making use of the symbol (e^–).
Answer:
Fe³⁺ + e^– → Fe²⁺ (reduction)

Think about it (Text Book Page No. 43)

Question 1.
The luster of the surface of the aluminium utensils in the house is lost after a few days. Why does this happen?
Answer:
The aluminium utensils when kept in the house for a few days, oxidation of aluminium takes place, a thin laver aluminium oxide (Al₂O₃) is deposited on the surface. Hence, aluminium utensils lose their lustre in a few days.

Question 3.
How many products are formed in each of the above reactions?
Answer:
A single product is formed in each of the above reaction.

Use your brain power! (Text Book Page No. 39)

Question 1.
What is the difference in the process of dissolution and a chemical reaction.
Answer:
In the process of dissolution, new substance is not necessarily formed. Whereas in a chemical reaction a new substance is definitely formed.

Question 2.
Does a new substance form when a solute dissolves in a solvent?
Answer:
It is not necessary that a new substance is always formed.

Fill in the blanks:

Question 1.
Organic waste is decomposed by micro-organism and as a result manure and……..are formed.
Answer:
Organic waste is decomposed by micro-organism and as a result manure and bio gas are formed.

Question 2.
……….is formed on mixing yeast in glucose solution under proper condition.
Answer:
Alcohol is formed on mixing yeast in glucose solution under proper condition.

Question 3.
The chemical reaction during which H_2(g) is lost is termed as………
Answer:
The chemical reaction during which H_2(g) s lost is termed as oxidation.

Question 4.
Corrosion can be prevented by using………
Answer:
Corrosion can be prevented by using antirust solution.

Question 5.
The chemical reactions in which heat is liberated are called………..reactions.
Answer:
The chemical reactions in which heat is liberated are called exothermic reactions.

Question 6.
The chemical formula of rust is………
Answer:
The chemical formula of rust is Fe₂O₃.H₂O.

Question 7.
A reaction in which heat is absorbed is called………reaction.
Answer:
A reaction in which heat is absorbed is called endothermic reaction.

Question 8.
The process of rusting or iron is………process.
Answer:
The process of rusting of iron is oxidation process.

Question 9.
when oil and fats are oxidised or even allowed to stand in air for a long time, they become ……….
Answer:
when oil and fats are oxidised or even allowed to stand in air for a long time, they become rancid.

Question 10.
……… are used to prevent oxidation of food.
Answer:
Antioxidants are used to prevent oxidation of food.

Question 11.
Carbon dioxide is passed through water. The reaction is a………reaction.
Answer:
Carbon dioxide is passed through water. The reaction is a combination reaction.

Question 12.
Calcium carbonate is heated. The reaction is a………..reaction.
Answer:
Calcium carbonate is heated. The reaction is a decomposition reaction.

Question 13.
Zinc strip is dipped in a CuSO₄ solution. The reaction is a……….reaction.
Answer:
Zinc strip is dipped in a CuSO₄ solution. The reaction is a displacement reaction.

Question 14.
Silver nitrate solution is added to NaCl solution. The reaction is a……….reaction.
Answer:
Silver nitrate solution is added to NaCl solution. The reaction is a double displacement reaction.

Question 15.
The slow process of decay or destruction of a metal due to effect of air, moisture and acids on it is known as……….
Answer:
The slow process of decay or destruction of a metal due to effect of air, moisture and acids on it is known as corrosion.

Rewrite the following statements by selecting the correct options:

Question 1.
The reaction of iron nail with copper sulphate solution is………reaction. (March 2019)
(a) double displacement
(b) displacement
(c) combination
(d) decomposition
Answer:
(b) displacement

Question 2.
Reddish brown deposit formed on iron nails kept in a solution of copper sulphate is
(a) Cu₂O
(b) Cu
(c) CuO
(d) CuS
Answer:
(b) Cu

Question 3.
The reaction CuSO_4(aq) + Zn_(s) → ZnSO_4(aq) + Cu_(s) is a……..reaction.
(a) displacement
(b) double displacement
(c) decomposition
(d) combination
Answer:
(a) displacement

Question 4.
………is a combination reaction.
(a) Cu + H₂SO₄ → CuSO₄ + H₂
(b) H₂ + Cl₂ → 2HCl
(c) \(2 \mathrm{HgO} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{Hg}+\mathrm{O}_{2}\)
(d) \(\mathrm{CaCO}_{3} \stackrel{\Delta}{\longrightarrow} \mathrm{CaO}+\mathrm{CO}_{2}\)
Answer:
(b) H₂ + Cl₂ → 2HCl

Question 5.
………..a decomposition reaction.
(a) \(\mathrm{CaCO}_{3} \stackrel{\Delta}{\longrightarrow} \mathrm{CaO}+\mathrm{CO}_{2}\)
(b) H₂O + CO₂ → H₂CO₃
(c) CaS + 2HCl → CaCl₂ + H₂S
(d) 2H₂ + O₂ → 2H₂O
Answer:
(a) \(\mathrm{CaCO}_{3} \stackrel{\Delta}{\longrightarrow} \mathrm{CaO}+\mathrm{CO}_{2}\)

Question 6.
In a chemical equation the……….are written on the left hand side.
(a) products
(b) reactants
(c) catalysts
(d) elements
Answer:
(b) reactants

Question 7.
The Δ sign written above the arrow indicates………..of the reaction.
(a) reactant
(b) product
(c) heat
(d) direction of the reaction
Answer:
(c) heat

Question 8.
The reaction KNO_3(S) + H₂O_(l) + Heat → KNO_3(aq) is a/an……….reaction.
(a) exothermic
(b) endothermic
(c) oxidation
(d) reduction
Answer:
(b) endothermic

Question 9.
The reaction NaOH_(S) + H₂O_(l) → NaOH_(aq) is a/an……..reaction.
(a) exothermic
(b) endothermic
(c) oxidation
(d) reduction
Answer:
(a) exothermic

Question 10.
A solution of Al₂(SO₄)₃ in water is……….
(a) blue
(b) pink
(c) green
(d) colourless
Answer:
(d) colourless

Question 11.
Carbon dioxide………..
(a) turns lime water milky
(b) is odourless
(c) is colourless
(d) All the three (a), (b) and (c) are correct
Answer:
(d) All the three (a), (b) and (c) are correct

Question 12.
……….is the correct set up to pass CO₂ through lime water.

Answer:
Correct set up D.

Question 13.
when……..is passed through fresh lime water, it turns milky.
(a) H₂
(b) CO
(c) CO₂
(d) SO₂
Answer:
(c) CO₂

Question 14.
Magnesium reacts with con. HCl to form………..salt.
(a) copper chloride
(b) ferrous chloride
(c) calcium chloride
(d) magnesium chloride
Answer:
(d) magnesium chloride

Question 15.
Zinc reacts with hydrochloric acid. The reaction is a reaction.
(a) combination
(b) decomposition
(c) displacement
(d) double decomposition
Answer:
(c) displacement

Question 16.
In a double displacement reaction,………… (Practice Activity Sheet – 1)
(a) ions remain at rest
(b) ions get liberated
(c) ions are exchanged
(d) ions are not created
Answer:
(c) ions are exchanged

State whether the following statements are True or False:

Question 1.
Rusting of iron is a fast reaction.
Answer:
False. (Rusting of iron is a slow reaction.)

Question 2.
Milk is set into curd is a chemical change.
Answer:
True.

Question 3.
The reaction between salt and water is an example of exothermic reaction.
Answer:
False. (The reaction between salt and water is an example of endothermic reaction.)

Question 4.
The speed of a chemical reaction depends on the catalyst used in the chemical reaction.
Answer:
True.

Question 5.
The simple form of representation of a chemical reaction in words is known as word reaction.
Answer:
True.

Question 6.
Nascent oxygen is always denoted by showing the symbol of oxygen.
Answer:
False. (Nascent oxygen is always denoted by showing symbol of oxygen [0] in square brackets.)

Question 7.
Antioxidants are used to prevent oxidation or food containing fats and oils.
Answer:
True.

Question 8.
When oils and fats are allowed to stand for a long time, they become rancid.
Answer:
True.

Question 9.
The chemical formula of rust is Fe₃O₄ .xH₂O.
Answer:
False. (The chemical formula or rust is Fe₂O₃ .xH₂O.)

Question 10.
Glucose combines with oxygen in our body and provides energy. The reaction is an endothermic reaction.
Answer:
False. (Glucose combines with oxygen in our body and provides energy. The reaction is an exothermic reaction.)

Question 11.
Chemical reactions in which reactants gain oxygen are reduction reactions.
Answer:
False. (Chemical reactions in which reactants gain oxygen are oxidation reactions.)

Question 12.
CuSO_4(aq) + Znl_(s) → ZnlSO_4(aq) + Cu_(s) is an example of decomposition reaction.
Answer:
False. (It is an example of displacement reaction.)

Question 13.
The chemical reactions in which heat is liberated are called endothermic reactions.
Answer:
False. (The chemical reactions in which heat is liberated are called exothermic reactions.)

Question 14.
The product or insoluble solid in chemical reaction is indicated by an arrow pointing upwards.
Answer:
False. (The product or insoluble solid in chemical reaction is indicated by an arrow ↑ pointing downwards.)

Question 15.
The rate of a reaction increases on increasing the temperature.
Answer:
True.

Question 16.
The digestion of food is a chemical decomposition process.
Answer:
True.

Question 17.
The reaction between sodium hydroxide and hydrochloric acid is a slow reaction.
Answer:
False (The reaction between sodium hydroxide and hydrochloric acid is a fast reaction.)

Question 18.
When calcium carbonate is heated, it decomposes into calcium oxide and oxygen gas.
Answer:
False (when calcium carbonate is heated. it decomposes into calcium oxide and carbon dioxide gas.

Question 19.
The rate of a chemical reaction changes in presence of catalyst.
Answer:
True.

Question 20.
Chlorines is an oxidant.
Answer:
True.

Taking into consideration the relationship in the first pair, complete the second pair. (OR) Complete the following:

Question 1.
2H₂ + O₂ → 2H₂O Combination reaction :: 2HgO → 2Hg + O₂ :……….
Answer:
Decomposition reaction

Question 2.
NH₃ + HCl → NH₄Cl : Combination reaction :: Fe + CuSO₄ → FeSO₄ + Cu :……..
Answer:
Displacement reaction

Question 3.
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂ : Oxidation :: CuO + H₂ → Cu + H₂O :……….
Answer:
Reduction

Question 4.
CuCl₂ + 2KI → CuI₂ + 2KCl : Double displacement :: Zn + 2HCl → ZnCl₂ + H₂ :……….
Answer:
Displacement reaction

Question 5.

Answer:
Combination reaction

Question 6.
CuI₂ : Brown :: AgCl :……….
Answer:
White.

Match the column in the following table:

Question 1.

Reactants	products	Type of chemical reaction
Fe + S	NaCl + H2O	Oxidation
CuSO4 + Zn	2CuO	Neutralization
2Cu + O2	ZnSO4 + Cu	Displacement
HCl + NaOH	FeS	Combination

Answer:

Reactants	products	Type of chemical reaction
Fe + S	FeS	Combination
CuSO4 + Zn	ZnSO4 + Cu	Displacement
2Cu + O2	2CuO	Oxidation
HCl + NaOH	NaCl + H2O	Neutralization

Rewrite the second column so as to match the item from first column or Match the following:

Question 1.

Column I	Column II
1. Reduction	(a) Type of a chemical reaction
2. Oxidation	(b) Combination with hydrogen
3. Double displacement	(c) Losing hydrogen
4. Displacement	(d) Exchange of ions

Answer:
(1) Reduction – Combination with hydrogen
(2) Oxidation – Losing hydrogen
(3) Double displacement – Exchange of ions
(4) Displacement – Type of chemical reaction.

Question 2.

Column I	Column II
1. Oils and fats are allowed to stand in air for a long time	(a) Slow  reaction
2. NaOH dissolves in water	(b) Rancid
3. Zinc is added to CuSO4 solution	(c) Exothermic reaction
4. Rusting of water	(d) Colourless Solution

Answer:
(1) Oils and fats are allowed to stand in air for a long time – Rancid
(2) NaOH dissolves in water – Exothermic reaction
(3) Zinc is added to CuSO₂ solution – Colourless solution
(4) Rusting of iron – Slow reaction.

Question 3.

Answer:
(1) Combination reaction – 2Cu +O₄ → 2CuO
(2) Double displacement reaction – AgNO₃ + NaCl → AgCl ↓ + NaNO₃
(3) Decomposition reaction – \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11(\mathrm{s})} \stackrel{\Delta}{\longrightarrow} 12 \mathrm{C}_{(\mathrm{s})}+11 \mathrm{H}_{2} \mathrm{O}_{(\mathrm{g})}\)
(4) Displacement reaction – Zn+ 2HCl → ZnCl₂ + H₂ ↑

Classify each of the following reactions as combination, decomposition, displacement or double displacement reactions:

Answer:
Combination reaction

Answer:
Decomposition reaction

Answer:
Displacement reaction

Answer:
double displacement reaction

Answer:
Combination reaction

Answer:
double displacement reaction

Name the following:

Question 1.
The product formed in the thermal decomposition of sugar.
Answer:
Carbon is formed in the thermal decomposition of sugar.

Question 2.
The gas evolved when sorghum metal reacts with ethanol.
Answer:
Hydrogen (H₂) gas is evolved when sodium metal reacts with ethanol.

Question 3.
The precipitate formed when barium sulphide reacts with zinc sulphate.
Answer:
When barium sulphide reacts with zinc sulphide, a precipitate of barium sulphate is formed.
\(\mathrm{BaS}+\mathrm{ZnSO}_{4} \longrightarrow \underset{\text { precipitate }}{\mathrm{BaSO}_{4}}+\mathrm{ZnS}\)

Question 4.
The reducing agent used for the reduction of copper oxide.
Answer:
Hydrogen is used for the reduction of copper oxide.

Question 5.
The catalyst used to accelerate the rate of decomposition of hydrogen peroxide.
Answer:
Manganese dioxide (MnO₂) is used as a catalyst to accelerate the rate of decomposition of hydrogen peroxide.

Question 6.
which oxidising agent is used to oxidise ferrous sulphate.
Answer:
Potassium permanganate (KMnO₄) is used as an oxidising agent to oxidise ferrous sulphate.

Question 7.
The product formed in the oxidation of ethyl alcohol.
Answer:
Acetic acid is formed in the oxidation of ethyl alcohol.

Answer the following questions in one sentence each:

Question 1.
what is meant by a chemical equation?
Answer:
The simple representation or a chemical reaction in a condensed form with the help of chemical formulae is called a chemical equation.

Question 2.
what is meant by a word equation?
Answer:
The simple form or representation or a chemical reaction in words is known as word equation.

Question 3.
what happens in a combination reaction?
Answer:
A single compound (product) is formed from two or more substances during a combination reaction.

Question 4.
what happens in a displacement reaction?
Answer:
In a displacement reaction. a more reactive element displaces another element, having less reactivity, from its compound.

Question 5.
what happens in a decomposition reaction?
Answer:
A single substance is broken down and two or more substances are formed during a decomposition reaction.

Question 6.
what happens in a double displacement reaction?
Answer:
A precipitate is formed by exchange of ions between the reactants during a double displacement reaction.

Question 7.
IdentIry the type of following reaction:
\(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11} \stackrel{\Delta}{\longrightarrow} 12 \mathrm{C}+11 \mathrm{H}_{2} \mathrm{O}\) (Practice Activity Sheet – 2)
Answer:
The above reaction is a decomposition reaction.

Question 8.
what happens in an endothermic reaction?
Answer:
In an endothermic reaction, the reactants absorb heat to form products.

Question 9.
State the use of antioxidants in food containing fats and oils.
Answer:
Antioxidants are used to prevent oxidation of food containing fats and oils.

Question 10.
What are edible oils?
Answer:
Edible oils are compounds of alcohols and organic acids (carboxylic acids). The compounds formed are known as esters of carboxylic acids.

Question 11.
Is rancidity a phenomenon of oxidation or reduction?
Answer:
Rancidity is a phenomenon of oxidation.

Answer the following questions:

Question 1.
What do you understand by a physical change?
OR
Define physical change.
Answer:
The change in which only the physical state of a substance is changed; no new substance is formed. This change is temporary. During this change the composition of the substance does not change.

Question 2.
Explain giving two examples or physical change.
Answer:
(1) Conversion of ice into water is a physical change. On heating, ice melts into water. when the water is cooled, it freezes into ice. Thus, we get ice from water by a simple method and no new substance is formed. Hence, conversion of ice into water is a physical change.

(2) Magnetization of iron nail is a physical change. An iron nail magnetized by induction loses its magnetism as soon as it is detached from the magnet which induces magnetism in it. An iron nail magnetized by some other methods can also be demagnetized by simple means such as hammering or heating it. Thus, the magnetization of an iron nail can be easily reversed to get original nail. Hence, it is a physical change.

Question 3.
what do you understand by a chemical change?
OR
Define Chemical change.
Answer:
The change in which a substance or substances are converted into a new substance or substances, possessing properties altogether different from the original ones, is called a chemcial change. During this change, the original substance cannot be recovered by any simple means. This change is permanent.

Question 4.
Explain giving two examples of chemical change.
Answer:
(1) When carbon is burnt, carbon dioxide is formed. In this process carbon combines with oxygen, therefore carbon and oxygen are reactants, while curbon dioxide is a product. This change is permanent.
\(\mathrm{C}_{(\mathrm{s})}+\mathrm{O}_{2(\mathrm{g})} \stackrel{\text { Heat }}{\longrightarrow} \mathrm{CO}_{2(\mathrm{g})}\)

(2) When a magnesium wire is burnt in air, a white powder of magnesium oxide is formed. We cannot obtain magnesium from magnesium oxide by simple methods. Properties of magnesium oxide are altogether different from those of magnesium. A new substance MgO is formed in the reaction. Hence, this change is a chemical change.
\(\begin{array}{c}
2 \mathrm{Mg} \\
\text { Magnesium }
\end{array}+\mathrm{O}_{2} \stackrel{\Delta}{\longrightarrow} \begin{array}{c}
2 \mathrm{MgO} \\
\text { Magnesium oxide }
\end{array}\)

Question 5.
What is meant by a chemical reaction?
Answer:
A process in which some substances undergo bond breaking and are transformed into new substances by formation of new bonds is called a chemical reaction.

Question 6.
What is the importance of a chemical equation?
Answer:

1. Reactants are converted into products.
2. Mass is conserved.
3. Atoms are conserved.
4. The properties and compositions of the products of a chemical reaction are different from those of its reactants.
5. Generally, energy is either absorbed or evolved.

Question 7.
What are the conventions used in writing a chemical equation?
Answer:
Conventions used in writing a chemical equation:
(1) The reactants are written on the left hand side (LHS), while the products are written on the right hand side (RHS).

(2) Whenever there are two or more reactants, a plus sign (+) is written between each two of them. Similarly, if there are two or more products, a plus sign is written between each two of them.

(3) Reactant side and product side are connected with an arrow (→) pointing from reactants to products. The arrow represents the direction of the reaction. Heat is to be given from outside to the reaction, it is indicated by the sign Δ written above the arrow.

(4) The conditions like temperature, pressure, catalyst, etc., are mentioned above the arrow (→) pointing towards the product side.

(5) The physical states of the reactants and products are also mentioned in a chemical equation. The notations g, l, s, and aq are written in brackets as a subscript along with the symbols / formulae of reactants and products. The symbols g, l, s, and aq stand for gaseous, 1iquid. solid and aqueous respectively.

If the product is gaseous, instead of (g) it can be indicated by an arrow ↑ pointing upwards. If the product formed is insoluble solid, then instead of (s) it can be indicated by an arrow ↓ pointing downwards.

(6) Special information or names of reactants/products are written below their formulae.

Write the balanced equations for the following reactions:

Question 1.
Ba(OH)₂ + HBr → BaBr₂ + H₂O
Answer:
Step 1:
Rewrite the given equation as it is
Ba(OH)₂ + HBr → BaBr₂ + H₂O

Step 2:
write the number of atoms of each element in the unbalanced equation on both sides of the equation.

Element	Number of atoms in reactants	Number of atoms in products
Ba	1	1
Br	1	2
O	2	1
H	3	2

Step 3:
To balance the number of oxygen atoms:

Number of atoms of oxygen	In reactants	In products
To begin with	2 [in Ba(OH)2]	1 (in H2O)
To balance	2	1 × 2

To equalise the number of oxygen atoms, we use 2 as the coefficient of H₂O in the product.
Now, the partly balanced equation become as follows
Ba(OH)₂ + HBr → BaBr₂ + 2H₂O

Step 4:
Now, balance the number of hydrogen atoms.
In the partly balanced equation:

Number of atoms of hydrogen	In reactants	In products
To begin with	2 [in Ba(OH)2] 1 (in HBr)	4 (in 2H2O)
To balance	1 × 2 + 2	4

To equalise the number of hydrogen atoms, we use 2 as the coefficient of HBr in the reactants. Now, the equation becomes
Ba(OH)₂ + 2HBr → BaBr₂ + 2H₂O
Now, count the atoms or each element on both sides of the equation. The number of atoms on both
sides are equal. Hence, the balanced equation is
Ba(OH)₂ + 2HBr → BaBr₂ +2H₂O
Now indicate the physical states of the reactants and products.
Ba(OH)_2(aq) + 2HBr_(aq) → BaBr_2(aq) +2H₂O_(l)

Question 2.
KCN + H₂SO₄ → K₂SO₄ + HCN
Answer:
Step 1:
Rewrite the given equation as it is
KCN + H₂SO₄ → K₂SO₄ + HCN

Step 2:
Write the number of atoms of each element or group in the unbalanced equation on both sides of the equation.

Element	Number of atoms in reactants	Number of atoms in products
K	1	2
CN (group)	1	1
O	4	4
H	2	1
S	1	1

The number of oxygen atoms involved in different compounds on both sides (reactants and products) are equal. Therefore, balance the number of atoms of the second element, potassium.

Step 3:
To balance K atoms:

Number of atoms of Potassium	In reactants	In products
To begin with	2 (KCN)	2 (in K2SO4)
To balance	1 × 2	2

To equalise the number of potassium atoms, we use 2 as the coefficient of KCN in the reactants.
Now, the partly balanced equation becomes
2KCN + H₂SO₄ → K₂SO₄ + 2HCN
Now, count the atoms of each element on both sides of the equation. The number of atoms on both sides are equal. Hence, the balanced equation is
2KCN + H₂SO₄ → KgSO₄ + 2HCN
Now indicate the physical states of the reactants and the products.
2KCN_(aq) + H₂SO_4(aq) → K₂SO_4(aq) + 2HCN_(g)

Question 3.
CH₄ + O₂ → 4CO₂ + H₂O
Answer:
Step 1:
Rewrite the given equation as it is
CH₄ + O₂ → 4CO₂ + H₂O

Step 2:
Write the number of atoms of each element in the unbalanced equation on both sides of the equation.

Element	Number of atoms in reactants	Number of atoms in products
C	1	1
O	2	3
H	4	2

Step 3:
To balance the number of oxygen atoms:

Number of atoms of oxygen	In reactants	In products
To begin with	2 (in O2)	1 (in H2O) 2 (in CO2)
To balance	2 × 2	1 × 2 + 2

To equalise the number of oxygen atoms, we use 2 as the coefficient of O₂ in the reactants and 2 as the coefficient of H₂O in the product.
Now, the partly balanced equation becomes
CH₄ + 2O₂ → CO₂ + 2H₂O
Now, count the atoms of each element on both sides of the equation. The number of atoms on both sides are equal. Hence, the balanced equation is,
CH₄ + 2O₂ → CO₂ + 2H₂O
Now, indicate the physical states of the reactants and the products.
CH_4(g) + 2O_2(g) → CO_2(g) + 2H₂O_(l)

Answer the following questions:

Question 1.
what are the different types of chemical reaction?
Answer:
Types of chemical reaction

1. Combination reaction
2. Decomposition reaction
3. Displacement reaction
4. Double displacement reaction.

Question 2.
What is meant by a combination reaction?
OR
Define: combination reaction.
Answer:
When two or more reactants combine in a reaction to form a single product, it is called a combination reaction.

Question 3.
Give two examples of combination reaction.
Answer:
Examples of combination reaction :
(1) The ammonia gas reacts with hydrogen chloride gas to form the salt in gaseous state, immediately it condenses at room temperature and gets transformed into the solid state.

(2) Magnesium burns in air to form white powder of magnesium oxide as a single product.

(3) Iron reacts with sulphur to form iron sulphide.

Question 4.
What Is meant by a decomposition reaction?
Answer:
The chemical reaction in which two or more products are formed from a single reactant is called decomposition reaction.

Question 5.
what is meant by a thermal decomposition?
Answer:
The reaction in which a compound is decomposed by heating it to a high temperature is called thermal decomposition.

Question 6.
What is meant by a electrolytic decomposition?
Answer:
The reaction in which a compound is decomposed by passing an electric current through its solution or molten mass is called an electrolytic decomposition.

Question 7.
Give two examples of thermal decomposition.
Answer:
(1) At high temperature, calcium carbonate decomposes into calcium oxide and carbon dioxide.

(2) At high temperature sugar decomposes into black mass of carbon and water vapour.

Question 8.
Give an example of electrolytic decomposition.
Answer:
When an electric current is passed through acidified water, it is electrolysed giving hydrogen
and oxygen.

Question 9.
Study the following reaction and answer the questions asked.

(a) State the type of reaction.
(b) Define this reaction. (Practice Activity Sheet – 1)
Answer:
(a) The type of reaction is electrolytic decomposition reaction.
(b) The reaction in which a compound is decomposed by passing an electric current through its solution or molten mass is called an electrolytic decomposition.

Question 10.
what is meant by a displacement reaction?
Answer:
The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by formation of its own ions, is called displacement reaction.

Question 11.
Give an example of displacement reaction.
Answer:
when zinc granules are added to the blue coloured copper sulphate solution, the zinc ions formed from zinc atoms take the place or Cu²⁺ ions in CuSO₄, and copper atoms, formed from Cu²⁺ ions comes out i.e. the more reactive zinc displaces the less reactive Cu from copper sulphate.

Question 12.
Observe the reaction and answer the following questions.
CuSO_4(aq) + Fe_(s) → FeSO_4(aq) + Cu_(s)
(a) Identify and write the type of chemical reaction.
(b) write the definition of above reaction. (Practice Activity Sheet – 3)
Answer:
(a) When iron powder is added to the blue coloured copper sulphate solution, the iron ions formed from iron atoms take the place or Cu²⁺ ions in CuSO₄, and copper atoms, formed from Cu²⁺ ions comes out i.e. the more reactive iron displaces the less reactive Cu from copper sulphate. Therefore this reaction is a displacement reaction.

(b) The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by formation of its own ions, is called displacement reaction.

Question 13.
what is meant by a double displacement reaction?
Answer:
The reaction in which the ions in the reactants are exchanged to form a precipitate is called double displacement reaction.

Question 14.
Give two examples of double displacement reaction.
Answer:
(1) Solutions of sodium chloride and silver nitrate react with each other forming a precipitate of silver chloride and a solution of sodium nitrate.

White precipitate of AgCl is formed by exchange of ions Ag⁺ and Cl^– between the reactants.

(2) Barium suiphide reacts with zinc sulphate to form zinc sulphide and a white precipitate of barium sulphate.

white precipitate is formed by exchange of ions Ba⁺⁺ and SO₄^— between the reactants.

Question 15.
Write down what you understand from the following chemical reaction:
AgNO_3(aq) + NaCl_(aq) → AgCl ↓ + NaNO_3(aq)
Answer:
(i) The above reaction is a double displacement reaction.
(ii) AgNO₃ and NaCl are the reactants while AgCl and NaNO₃ are the products.
(iii) The reactants and the product NaNO₃ are in aqueous state. The product AgCl is formed in the form of precipitate.

Question 16.
Study the following chemical reaction and answer the questions given below:
AgNO_3(aq) + NaCl_(aq) → AgCl_(s)↓ + NaNO_3(aq)
(i) Identiry and write the type of chemical reaction.
(ii) write the definition of above type of chemical reaction.
(iii) Write the names of reactants and products of above reaction. (March 2019)
Answer:
(i) The type of chemical reaction: Double displacement reaction.
(ii) The reaction in which the ions in the reactants are exchanged to form a precipitate is called double displacement reaction.
(iii)

1. The above reaction is a double displacement reaction.
2. AgNO₃ and NaCl are the reactants while AgCl and NaNO₃ are the products.
3. The reactants and the product NaNO₃ are in aqueous state. The product AgCl is formed in the form of precipitate.

Question 17.
When sodium chromate solution is mixed with barium sulphate solution, a precipitate is formed.
(i) What is the colour of the precipitate formed?
(ii) Name the precipitate.
(iii) What is the type of chemical reaction?
Answer:
(i) The colour of the precipitate is yellow.
(ii) The yellow precipitate formed is barium chromate.
(iii) The type of chemical reaction is double displacement.

Question 18.
Explain the term Exothermic reaction.
Answer:
Exothermic reaction : The process in which heat is given out is called an exothermic reaction.
When NaOH_(s) dissolves in water, there is evolution of heat leading to a rise in temperature.
NOH_(s) + H₃O_(l) → NaOH_(aq) + Heat

Question 19.
State whether the following reactions are exothermic or endothermic:
(i) 3CaO. Al₂O_3(s) + 6H₂O_(l) → 3CaO. Al₂O₃. 6H₂O_(s) + Heat
Answer:
Exothermic reaction

(ii) 2CaSO₄. H₂O + 3H₂O → 2CaSO₄. 2H₂O + Heat
Answer:
Exothermic reaction

(iii) KNO_3(aq) + H₂O_(l) + Heat → KNO_3(aq)
Answer:
Endothermic reaction

(iv) NaOH_(s) + H₂O_(l) → NaOH_(aq) + Heat
Answer:
Exothermic reaction

(v) Transformation of ice into water.
Answer:
Endothermic reaction

(vi) Water turns into ice.
Answer:
Exothermic reaction

(vii) Cooking of food.
Answer:
Endothermic reaction

(viii) Burning candle.
Answer:
Exothermic reaction

Question 20.
What do you mean by slow speed reaction?
OR
Define: Slow speed reaction.
Answer:
The reaction which requires long time for completion i.e. occurs slowly is called slow speed reaction.

Question 21.
What do you mean by fast speed reaction?
OR
Define: Fast speed reaction.
Answer:
The reaction which is completed in short time i.e. occurs rapidly is called fast speed reaction.

Question 22.
Give two examples of slow speed reactions.
Answer:
(1) On heating potassium chlorate (KClO₃) it decomposes slowly into potassium chloride and oxygen gas.

This reaction requires long time for completion, therefore it is slow speed reaction.

(2) Rusting of iron is a slow speed reaction. In this reaction iron reacts with oxygen from air to form iron oxide.

Question 23.
Give two examples of fast speed reactions.
Answer:
(1) The reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) is a neutralization reaction and it is fast speed reaction.
NaOH_2(aq) + HCl_(aq) → NaCl_(aq) + H₂O_(l)
This neutralizaton reaction is completed in short time, therefore it is fast speed reaction.

(2) Aqueous solution of sodium chloride reacts with silver nitrate solution to form white precipitate of silver chloride (NaCl) and sodium nitrate.
NaCl_(aq) + AgNO_3(aq) → NaNO_3(aq) + AgCl ↓
This reaction is completed in short time, therefore it is fast reaction.

Question 24.
Write a short note on slow speed and fast speed reactions.
Answer:
Slow speed reaction:
The reaction which requires long time for completion i.e. occurs slowly is called slow speed reaction.
Examples:
(1) On heating potassium chlorate (KClO₃) it decomposes slowly into potassium chloride and oxygen gas.

This reaction requires long time for completion, therefore it is slow speed reaction.

(2) Rusting of iron is a slow speed reaction. In this reaction iron reacts with oxygen from air to form iron oxide.

This reaction requires long time for completion.

Fast speed reaction:
The reaction which is completed in short time i.e., occurs rapidly is called fast speed reaction.
Examples:
(1) The reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) is a neutralization reaction and it is fast speed reaction.
NaOH_(aq) + HCl_(aq) → NaCl_(aq) + H₂O_(l)
This neutralizaton reaction is completed in short time, therefore it is fast speed reaction.

(2) Aqueous solution of sodium chloride reacts with silver nitrate solution to form white precipitate of silver chloride (NaCl) and sodium nitrate.

This reaction is completed in short time, therefore it is fast reaction.

Question 25.
State the factors which affect the speed (or rate) of a reaction.
Answer:
The factors which affect the rate of a reaction are

1. Nature of the reactants.
2. Size of the particles of the reactants.
3. Concentration of the reactants.
4. Temperature of the reaction.
5. Catalyst.

Question 26.
How does the rate of reaction depend on the nature of the reactants? Illustrate with suitable example.
Answer:
(1) when the reactant combines with two or more other reactants then the rate of a chemical reaction depends on the nature of the reactants.

(2) Both Al and Zn reacts with dilute hydrochloric acid, H₂ gas is liberated and water soluble salts of these metals are formed. However, aluminium metal reacts faster with dil. HCl as compared to zinc metal.

(3) Al is more reactive than Zn. Therefore, the rate of reaction of Al with hydrochloric acid is higher than that of Zn. Hence, the nature of the reactant affect the rate of a reaction.

Question 27.
How does the rate of a reaction depend on the size of the particles of reactants?
Answer:
(1) In the reaction of dil. HCl and Shahabad tile, CO₂ effervescence is formed slowly. On the other hand, C₂ effervescence forms at faster speed with the powder of Shahabad tile.

(2) The above observation indicates that the rate of a reaction depends upon the size of the particles of the reactants taking part in the reaction. Smaller the size of the reactant particles taking part in a reaction faster will be the rate of reaètion.

Question 28.
How does the rate of a reaction depend upon the concentration of the reactants? Give suitable example.
Answer:
(1) A chemical reaction takes place due to collisions of the reactant molecules. Higher the concentrations of the reactants more will be the frequency of collisions and faster wifi be the rate of the reaction.

(2) In the reaction of dil. HCl and CaCO₃, CaCO₃ disappears slowly and CO₂ also liberates slowly. On the other hand the reaction with concentrated HCl takes place rapidly and CaCO₃ disappears fast.

(3) Concentrated acid reacts faster than dilute acid, that means the rate of a reaction is proportional to the concentration of reactants.

Slow reaction:
CaCO₃ + dli.2HCl → CaCl₂ + CO₂ + H₂O
Fast reaction:

Question 29.
How does the rate of a reaction depend upon the temperature of reactants? Give suitable example.
Answer:
(i) (1) When the temperature of the reactants is increased, the reactant molecules start moving with more velocity and their kinetic energy increases. As a result, the number collisions increases. Hence, the rate of chemical reaction increases.

(2) Lime stone on heating decomposes to give CO₂, which turns 1ime water milky. On the other hand, the lime water does not turn milky before heating the lime stone: because of the zero rate of reaction. The above observation indicates that the rate of a reaction increases on increasing the temperature.

(ii) Solid CaCO₃ does not decompose at room temperature when heated, it decomposes to give CaO and CO₂ that means the rise in temperature increases the rate of reaction. CaCO₃ room temperature No chemical reaction.

Question 30.
How does the rate if a reaction depend upon the catalyst? Give suitable example.
Answer:
(1) The substance in whose presence the rate of a chemical reaction changes, without causing any chemical change to it is called a catalyst.

(2) On heating potassium chlorate (KClO₃) decomposes into potassium chloride and oxygen slowly.
\(2 \mathrm{KClO}_{3} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{KCl}+3 \mathrm{O}_{2}\)
The rate of the above reaction neither increases by reducing the particle size nor by increasing the reaction temperature. However in the presence of manganese dioxide, KClO₃ decomposes at a comparatively lower temperature and oxygen is produced more briskly. No chemical change takes place in MnO₂ in this reaction. It acts as catalyst.

Question 31.
State the Importance of rate in a chemical reaction.
Answer:

1. The use of strong acid and strong base in a chemical reaction increases the rate of reaction.
2. In a chemical reaction, if the smaller size of the reactant particles, the concentrated solution, high temperature and use of catalyst increases the rate of chemical reaction.
3. The rate of chemical reaction is important with respect to environment.
4. If the rate of chemimal reaction is fast it is profitable for the chemical factories.
5. The ozone layer in the earth’s atmosphere protects the life of earth from the ultraviolet radiation of the sun. The process of depletion or maintenance of this layer depends upon the rate of production or destruction of ozone molecules.

Question 32.
Define Oxidation reaction.
Answer:
Oxidation: The chemical reaction in which a reactant combines with oxygen or loses hydrogen to form the product is called oxidation reaction.

Question 33.
Give examples of oxidation.
Answer:
(1) when carbon burns in air, it forms carbon dioxide. In this reaction carbon accepts oxygen, therefore, this is an oxidation reaction.
C_(s) + O_2(g) → CO_2(g)

(2) when sodium reacts with ethyl alcohol, sodium ethoxide and hydrogen gas is formed. In this reaction, hydrogen is removed from ethyl alcohol, therefore this is an oxidation reaction.

(3) Acidified potassium dichromate: (K₂Cr₂O₇/H₂SO₄) oxidises ethly alcohol to acetic acid.

Question 34.
What do you mean by oxidant? Explain with suitable example.
Answer:
The chemical substances which bring about an oxidation reaction by making oxygen available are called oxidants or oxidizing agents.

1. In the combustion of carbon, oxygen is an oxidant.
2. In the oxidation of ethly alcohol, potassium dichromate is used as oxidant.

Question 35.
Name the various oxidants. How nascent oxygen is liberated from these oxidants?
Answer:
K₂Cr₂O₇/H₂SO₄, KMnO₄/H₂SO₄ are the commonly used chemical oxidants. Hydrogen peroxide (H₂O₂) is used as a mild oxidant. Ozone (O₃) is also a chemical oxidant. Nascent oxygen is generated by chemical oxidants and it is used for the oxidation reaction.
O₃ → O₂ + [O].
H₂O₂ → H₂O + [O]
K₂Cr₂O₇ + 4H₂SO₄ → K₂SO₄ + Cr₂(SO₄)₃ + 4H₂O + 3[O]
2KMnO₄ + 3H₂SO₄ → K₂SO₄ + 2MnSO₄ + 3H₂O + 5[O]
Nascent oxygen is a state prior to the formation of the O₂ molecule. It is the reactive form of oxygen and is represented by the symbol as [O]

Question 36.
Acidified potassium permanganate (KMnO₄) is a chemical oxidant and explain, how acidified potassium permanganate oxidise ferrous sulphate (FeSO₄). Accordingly write a new definition of oxidation and reduction.
Answer:
Acidified KMnO4 oxidises ferrous sulphate (FeSO₄) to ferric sulphate Fe₂(SO₄)₃ and in addition to above K₂SO₄ and MnSO₄ by-products are formed.
2KMnO₄ + 10 FeSO₄ → 8H₂SO₄ → K₂SO₄ + 2MnSO₄ + 5Fe₂(SO₄)₃ + 8H₂O
2FeSO₄ → Fe₂(SO₄)₃
Ionic reaction :
2Fe₂ + 2SO₄²⁺ → 2Fe³⁺ + 3SO₂^2-
Net Ionic equation Fe²⁺ → Fe³⁺ + e^–
When ferric ion is formed from ferrous ion the positive change is increased by one unit. While this happens the rerrous ion loses one electron.

When metal or its ion loses electron, it is called an oxidation and gain of electron is called reduction.

Question 37.
Define reduction reaction.
Answer:
The chemical reaction in which a reactant gains hydrogen and loses oxygen to form the product is called the reduction reaction.

Question 38.
Give two examples of reduction.
Answer:
(1) When hydrogen gas is passed over black copper oxide a reddish coloured layer of copper is formed.
In this reaction an oxygen atom removed from CuO to form copper, hence, this is reduction.

(2) When hydrogen gas is passed over red hot coke, methane is obtained.
Here, hydrogen is added to coke (carbon). Hence, this is reduction.

Question 39.
What do you mean by reductant? Explain with suitable example.
Answer:
The chemical substances which bring about reduction by making hydrogen available are called reductant. In the preparation of methane from carbon, hydrogen is a reductant.

Question 40.
What are redox reactions? Identify the substances that are oxidised and the substances that are reduced in the following reactions:
(1) 2H₂S_2(g) + SO_2(g) → 3S_(s) + 2H₂O_(l)
(2) CuO_(s) + H_2(g) → CU_(s) + H₂O_(l)

Answer:
When oxidation and reduction take place simultaneously in a given chemical reaction, it is known as a redox reaction.
(1)

H₂S is oxidised and SO₂ is reduced.

(2)

CuO is reduced and H₂ is oxidised.

(3)

(1) Oxidation: H₂S, H₂O and HCl.
(2) Reduction: SO₂, CuO and MnO₂

Question 41.
Observe the following reaction and answer the questions given below:
BaSO₄ + 4C → BaS + 4CO
(1) what type of reaction is it? Justify.
(2) Give one more example.
Answer:
(1) This is a redox reaction. In this reaction the reduction of BaSO4 and oxidation of carbon take place simultaneously.

(2) Example
CuO+H₂ → Cu + H₂O
2H₂S + SO₂ → 3S + 2H₂O

Question 42.
What is corrosion?
Answer:
The slow process of decay or oxidation of metals due to various components of atmosphere is known as corrosion.
Iron rusts and a reddish coloured layer is collected on it. This is corrosion of iron.

Question 43.
How does rusting of iron occur?
Answer:
Iron when exposed to moist air forms a reddish layer of hydrated ferric oxide.

Question 44.
How can corrosion be prevented?
Answer:

1. Corrosion damages buildings, bridges, automobiles, ships, iron railings and other articles made of iron.
2. It can be prevented by using an anti-rust solution, coating the surface by a paint, processes like galvanising and electroplating with other metals.

Question 45.
What is corrosion? Do gold ornaments corrode? Justify.
Answer:
The slow process of decay or oxidation or metal due to the effect of air, moisture and acids on
it is known as corrosion.
(1) Gold is a noble metal. There is no effect or moist air or action of acid on it at any temperature.
(2) Pure gold is a very soft metal. it breaks and gets bent easily. Hence, in gold ornaments, gold is alloyed with other metals 1ike copper or silver in appropriate proportion to make it hard and resistant to corrosion. Hence gold ornaments do not get corroded.

Question 46.
Complete the process of iron rusting by filling the blanks. Suggest a way to prohibit the process.
The iron rust is formed due to reaction. Different regions on iron surface become anode and cathode.
Reaction on anode region:
Fe_(s) → Fe²⁺ _(aq) + 2e^–
Reaction on cathode region:
O_2(g) + 4H⁺ _(aq) +………→ 2H₂O_(l)
when Fe²⁺ ions migrate from anode region they react with……..to fomm Fe³⁺ ions.
A reddish coloured hytirated oxide is formed from……….ions. It is called rust.
2Fe³⁺ _(aq) + 4H₂O_(l) → +………+ 6H⁺ _(aq)
A way to prevent rusting………..
(Practice Activity Sheer – 2)
Answer:
The iron rust is formed due to electrochemical reaction. Different regions on iron surface become unode and cathode.
Reaction on anode region:
Fe_(s) → Fe²⁺ _(aq) + 2e^–
Reaction on cathode region:
O_2(g) + 4H⁺ _(aq) + 4e^– → 2H₂O_(l)
when Fe²⁺ ions migrate from anode region they react with water to form Fe³⁺ ions.
A reddish coloured hydrated oxide is formed from Fe³⁺ ions. It is called rust.
2Fe³⁺ (aq) + 4H₂O_(l) → + Fe₂O₃. H₂O_(s) + 6H⁺_(aq)
A way to prevent rusting by colouring with acrylic paints, Zn plating, galvanizing, anodizing, alloying, etc.

Question 17.
Deifne: Rancidity.
Answer:
When oil or fat or left over cooking oil for making food stuff undergoes oxidation ir stored for a long time and it is found to have foul odour called rancidity.

Distinguish between the following:

Question 1.
Combination reaction and Decomposition reaction.

Combination reaction	Decomposition reaction
1. In a combination re­action, two or more reactants take part in the chemical reaction.	1. In a decomposition reaction there is only one reactant in the chemical reaction.
1. In the combination reaction, only one product is formed.	2. In a decomposition reaction, two or more products are formed.

Question 2.
Oxidation and reduction
Answer:

Oxidation	Reduction
1. The chemical reaction in which reactants gain oxygen or lose hydrogen is called oxidation.	1. The chemical reaction in which reactants gain hydrogen or lose oxygen is called reduction.
2. A reducing agent undergoes oxidation.	2. An oxidising agent undergoes reduction.

Question 3.
Exothermic and Endothermic reaction.
Answer:

Exothermic reaction	Endothermic reaction
1. The reaction in which heat is evolved is called an exothermic reaction.	1. The reaction in which heat is absorbed is called an endothermic reaction.
2. The evolution of heat leads to a rise in the temperature of the solution.	2. The absorption of heat leads to a fall in the temperature of the solution.

Give scientific reasons:

Question 1.
Grills of doors and windows are always painted before they are used.
Answer:

• Grills of doors and windows are made from iron. Iron has a tendency to undergo corrosion.
• Paint does not allow air or moisture to come in contact with iron surface.
  Therefore, to prevent rusting of iron. grills of doors and windows are always painted before they are used.

Question 2.
Physical states of reactants and products are mentioned while writing a chemical equation.
Answer:
(1) while writing a chemical equation, gaseous, 1iquid and solid states are symbolised as (g), (l) and (s) respectively.

(2) This is done to make it more informative and to emphasise that those reactions occur in that manner only under those conditions. Hence, physical states of reactants and products are mentioned while writing a chemical equation.

Question 3.
Iron articles rust readily whereas steel which is also mainly made of iron does not undergo corrosion.
Answer:
(1) Iron articles rust readily as iron reacts with oxygen and moisture of air to convert into its hydroxide and oxide (Fe₂O₃. x H₂O), while steel is an alloy of iron, carbon and chromium.

(2) The properties of an alloy are different from the properties of its constituents. The added metals increase its resistance to corrosion. It is more durable and clean.

Question 4.
Concentrated hydrochloric acid reacts more vigorously with calcium carbonate than dilute hydrochloric acid.
Answer:

1. The rate of a reaction increases with the concentration of the reactant.
2. As concentrated hydrochloric acid contains more number of HCl molecules than those in an equal volume of dilute HCl, concentrated HCl reacts more vigorously with calcium carbonate.

Question 5.
Zinc powder reacts much faster with dil. H₂SO₄ than does granulated zinc of the Same mass.
Answer:
(1) In a reaction. the rate of the reaction depends upon the particle size of the solid reactant as the reaction takes place on the surface only. Smaller the particles are, the more will be their total surface area and faster will be the rate of the reaction.
(2) Hence, zinc powder reacts much faster with dil. H₂SO₄ than does granulated zinc.

Question 6.
When copper articles exposed to air for a long time, gets corroded.
Answer:
Copper oxidises to form black coloured laver of copper oxide. when copper oxide combines with carbon dioxide from air, copper loses its lustre due to formation of greenish layer of copper carbonate on its surface. Thus, copper articles exposed to air for a long time get corroded.

Question 7.
When silver vessels exposed to air turns blackish after sometime.
Answer:
On exposure to air, silver vessels turns blackish after sometime. This is because of the layer of silver sulphide (Ag₂S) formed by the reaction or silver with hydrogen suphide in air.

Explain the following reactions giving their balanced chemical equations:

Question 1.
Calcium carbonate (Lime stone) is heated.
Answer:
When calcium carbonate (Lime stone) is heated at high temperature it decomposes to form quicklime and carbon dioxide gas.

Question 2.
Copper reacts with dil. nitric acid.
Answer:
When copper reacts with dil. nitric acid, nitric oxide gas is formed.

Question 3.
Copper reacts with conc. nitric acid.
Answer:
When copper reacts with conc. nitric acid, reddish coloured poisonous nitrogen dioxide gas is formed.

Question 4.
Ammonia gas reacts with hydrogen chloride gas.
Answer:
When ammonia gas reacts with hydrogen chloride gas, it forms the salt ammonium chloride in gaseous state, but immediately it got transformed into the solid state.

Question 5.
Magnesium strip is burnt in air.
Answer:
When magnesium strip is burnt in air, a white powder of magnesium oxide is formed.

Question 6.
Calcium oxide is mixed with water.
Answer:
When calcium oxide (slaked lime) is mixed with water, calcium hydroxide is formed with evolution of large amount of heat.

Question 7.
Sugar is heated.
Answer:
When sugar is heated, it decomposes to form carbon (black substance).

Question 8.
Electric current is passed through acidulated water.
Answer:
When an electric current is passed through acidulated water, it decomposes into hydrogen and
oxygen gas.

Question 9.
Zinc powder is added to copper sulphate solution.
Answer:
When zinc powder is added to copper sulphate solution, more reactive zinc displaces less reactive copper from copper sulphate solution. The colourless zinc sulphate is formed with evolution of heat.

Question 10.
Iron powder is added to copper sulphate solution.
Answer:
When iron powder is added to copper sulphate solution, more reactive iron displaces less reactive copper from copper sulphate. The colourless ferrous sulphate solution is formed with evolution of heat.

Question 11.
Lead is added to copper sulphate solution.
Answer:
When lead is added to copper sulphate solution, more reactive lead displaces less reactive copper from copper sulphate. The colourless lead sulphate solution is formed with evolution of heat.

Question 12.
Potassium chromate solution is added to barium sulphate solution.
Answer:
When potassium chromate solution is added to barium sulphate solution, yellow precipitate of barium chromate is formed.

Question 13.
Calcium chloride solution is added to sodium carbonate solution.
Answer:
When calcium chloride solution is added to sodium carbonate solution, white precipitate of calcium carbonate is formed.

Question 14.
Sodium chloride solution is mixed with silver nitrate solution.
Answer:
When sodium chloride solution is mixed with silver nitrate solution, white precipitate or silver chloride is formed.

Question 15.
Dilute sulphuric acid is added to barium chloride solution.
Answer:
When dilute sulphuric acid is added to barium chloride solution, white precipitate of barium sulphate is rormed.

Question 16.
Calcium carbonate (Lime stone) is treated with dil. hydrochloric acid.
Answer:
When calcium carbonate (lime stone) is treated with dil. hydrochloric acid, carbon dioxide gas is formed.

Question 17.
Aluminium is treated with dil. hydrochloric acid.
Answer:
When aluminium is treated with dilute hydrochloric acid, hydrogen gas is liberated.

Question 18.
Magnesium is treated with hydrochloric acid.
Answer:
When magnesium is treated with hydrochloric acid, hydrogen gas is liberated.

Question 19.
Hydrogen peroxide is decomposed in the presence of manganese dioxide (MnO₂).
Answer:
When hvdrogen peroxide is decomposed in the presence of manganese dioxide (MnO₂), water and oxygen are formed.

Question 20.
Ethyl alcohol is treated with acidified potassium dlchromate.
Answer:
When ethly alcohol is treated with acidified potassium dichromate, acetic acid is formed. This is oxidation reaction.

Question 21.
Hydrogen gas is passed over black copper oxide.
Answer:
When hydrogen gas is passed over black copper oxide, a reddish coloured layer of copper is formed.

Balbharti Maharashtra State Board Class 10 History Solutions Chapter 7 Sports and History Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 History Solutions Chapter 7 Sports and History

Question 1.
(A) Choose the correct option from the given options and complete the statement.
(1) The ancient event of Olympic competitions used to be held at ………………………… .
(a) Olympia, Greece
(b) Rome
(c) India
(d) China
Answer:
(a) Greece

(2) The wooden dolls made in Maharashtra are known as ………………………… .
(a) Thaki
(b) Kalichandika
(c) Gangavati
(d) Champavati
Answer:
(a) Thaki

(B) Identify and write the wrong pair in the following set.
(1) Mallakhamb – Outdoor game based on physical skills
(2) Water polo – Water sport
(3) Skating – Adventurous ice sport
(4) Chess – Outdoor game
Answer:
(4) Chess – Outdoor game

Question 2.
Write notes :
(1) Toys and Festivals
Answer:

• Toys and festivals are inter-related since ancient times.
• Toys are used for decoration in different cultures and religions during festivals.
• In some cultures toys are distributed as gifts. Santa Claus gifts children toys during Christmas.
• As part of Diwali celebration in Maharashtra, model forts are made displaying images of Chhatrapati Shivaji Maharaj, his soldiers and animals which are toys.
• Clay images of snakes and bullocks are- sold during festivals like Bail pola and Nagpanchami.

(2) Sports and movies
Answer:

• The presence of sports was limited to a scene in the movies made earlier.
• In recent times, biographical movies are made on sportspersons and on sports.
• Movies like Lagaan and Dangal are made related to cricket and wrestling respectively.
• Biographical movies are made on Mary Kom, and the Phogat sisters.
• Movies are made on careers of famous sprinter Milkha Singh.
• Bharat Ratna Sachin Tendulkar and Cricketer Mahendra Singh Dhoni.
• Overall, movies and sports are related from the silent era till date.

Question 3.
Explain the following statements with reasons.
(1) Currently the structure of sports economy has been significantly affected.
Answer:

• The process of globalisation has influenced the field of sports in the 20th-21st century.
• International matches of various sports like Cricket, Football, etc. are*telecast in every corner of the world.
• Fans watch these matches for entertainment,r and aspiring players to learn more.
• The citizens of the non-participating countries also watch these matches.
• Retired players get a chance on television channels as commentators.
• Matches garner a large audience, hence the commercial companies look at it as an opportunity to advertise and sell their products.
• All these factors have led to change in the structure of sports economy.

(2) Toys can tell us about cultural history.
Answer:
A tradition of making different type of toys for entertainment is going on since ancient time.

• Toys give us an idea about the cultural and religious development of that period.
• Clay models of forts and the images of Chhatrapati Shivaji Maharaj placed on fort gives us an idea about the structures of forts during that period.
• An ivory doll found at Pompeii, an ancient city in Italy, sheds light on Indo-Roman trade and cultural relations.
• The mention of games, toys and flying and dancing dolls in Kathasaritsagara give us an idea about cultural history of toys. In this way, we come to know about cultural history from toys.

Question 4.
Write detailed answers to the following questions.
(1) Write about the history of sports equipment and toys in ancient India.
Answer:

1. The history of sports equipment and toys dates back to epic age. The ancient Indian literature and epics mention various games such as games of dice, wrestling, horse and chariot race.
2. Sports are of two types ‘Indoor Games’ and ‘Outdoor Games’. Indoor games such as chess, card games, dice, carrom, kachkavadya or Indian ludo, Bhatukli were very popular. It can be noted that all of them required equipment to play.
3. Cards to play card games, dice to play game of dice, a board and pieces to play chess, bunch of seeds or stones to play sagargote; (playing house) to play Bhatukli.
4. Likewise, Outdoor games like marbles, lagori (seven stones), vitti-dandu, bhavare (tops) all require material like marbles, stones, tops, a small and large stick to play.
5. A Sanskrit play by Shudraka is named as Mrichchhakatika. It means a clay cart. A clay cart was a toy used to play during Harappan period.
6. Kathasaritsagara has very interesting descriptions of games and toys. There are descriptions of flying dolls. There is a mention that on pressing a key some dolls used to fly, some used to dance and some used to make sounds.

(2) Explain the close tie between sports and history.
Answer:
Sports and history are closely related with each other.

1. It is a must for a sports writer to know the history of the game he chooses to write on.
2. In order to write a review on any sport competition, the critic should have knowledge of competitions held in the past.
3. A comparative study of the skills, techniques and strategies used in the past and developments or improvements in the present makes the review comprehensive.
4. The writer has to resort to history while writing columns or articles on sports events like Olympics or Asiad or any national or international matches.
5. While commentating on Akashvani and Doordarshan, an expert commentator needs to have good knowledge of the history of the game, previous records of illustrious and eminent players, statistical analysis and historical anecdotes related to the game and players.
6. Coaches, special experts, selection committee should have information of the players, their strength and weakness and also history of the players in the opposing team. Even players should know history of their competitors.
   In short, it is essential to know the history of all the aspects related to sports.

(3) Explain the difference between indoor and outdoor games.
Answer:

Indoor games	Outdoor games
1. Most of the indoor games are played by sitting at one place. They are played in a closed environment.	1. Outdoor games are played on a field.
2. Indoor games require skills but physical exercise is negligible.	2. Outdoor games need more physical exercise and skill.
3. As there is no exertion in indoor games, so it is not essential to develop stamina.	3. Outdoor games require stamina and strength.
4. Indoor games do not involve adventure.	4. Outdoor games involve adventures at times, e.g.. Auto racing
5. Indoor games includes Chess, Indian Ludo (Playing house) Bhatukli and many more.	5. Outdoor games involve national and international games like Kabaddi, Kho-kho, Hockey, Cricket, etc.
6. With the exception of chess and carrom no competitions are held for rest of the Indoor games.	6. National and international competitions are held of almost all outdoor games.

Project
(1) Collect information about your favorite sports and its players.
(2) Discuss the hardships the sportspersons have to face while training for the sport with the help of information gathered through movies and literature.

Question 5.
Complete the sentences by choosing the correct option:
(a) The activity which combines physical exercise and entertainment is ……………………….. .
(a) Show
(b) Attitude
(c) Sports
(d) Competition
Answer:
(c) Sports

(b) ……………………….. was looked upon as a game and entertainment by ancient people.
(a) Dancing
(b) Playing
(c) Singing
(d) Hunting
Answer:
(d) Hunting

(c) ……………………….. and its various tactics were devised by Balambhat Deodhar, the physical trainer of Peshwa Bajirao II.
(a) Kabaddi
(b) Atyapatya
(c) Khokho
(d) Mallakhamb
Answer:
(d) Mallakhamb.

(d) The Indian Government has honoured Sachin, Tendulkar with ……………………… for his illustrious achievements in the field of cricket.
(a) Padma Shri
(b) Khel Ratna
(c) Arjuna Award
(d) Bharat Ratna
Answer:
(d) Bharat Ratna

(e) ……………………… is the national game of India.
(a) Hockey
(b) Cricket
(c) Football
(d) Kabaddi
Answer:
(a) Hockey

(f) The National Sports Day of India is celebrated on 29th August which is the birth date of …………………….. .
(a) Khashaba Jadhav
(b) Sachin Tendulkar
(c) Major Dhyan Chand
(d) Bal J. Pandit
Answer:
(c) Major Dhyan Chand

(g) Vishnubhat Godse in his book Maza Pravas wrote that sports and physical activity had great importance in the daily schedule of ………………………
(a) Tatya Tope
(b) Queen of Jhansi Lakshmibai
(c) Bahadur Shah Jaffar
(d) Nanasaheb Peshwa
Answer:
(b) Queen of Jhansi Lakshmibai

(g) Maruti Mane is known for …………………….. .
(a) Hockey
(b) Kabaddi
(c) Marathon
(d) Wrestling
Answer:
(d) Wrestling.

(h) …………………….. wrote the play Mrichchhakatika which means a clay cart.
(a) Harshvardhan
(b) Shudraka
(c) Bhavbhuti
(4) Kalidas
Answer:
(b) Shudraka

(i) The findings in the excavations of …………………….., an ancient city in Italy includes an ivory doll made by Indian craftsmen.
(a) Rome
(b) Athens
(c) Sparta
(d) Pompeii
Answer:
(d) Pompeii

(j) An interesting description of games and toys is found in ……………………. .
(a) Shakuntal
(b) Panchatantra
(c) Mrichchhakatika
(d) Kathasaritsagara
Answer:
(d) Kathasaritsagara

(k) Major Dhyan Chand was honoured in 1956 with …………………….. for his marvellous achievements in hockey.
(a) Padma Shri
(b) Padma Bhushan
(c) Padma Vibhushan
(d) Bharat Ratna
Answer:
(c) Padma Bhushan

(l) …………………….. was the first Indian female boxer to win a bronze medal in the Olympics.
(a) P 7 Sindhu
(b) Mary Kom
(c) Geeta Phoghat
(d) Saina Nehwal
Answer:
(b) Mary Kom.

Question 6.
Identify the wrong pair in the following and write it:
(1)

(1) Mallakhamb	Outdoor game based on physical skills
(2) Water Polo	Water sport
(3) Skating	Adventure ice sports
(4) Chess	Outdoor game

Answer:
Wrong pair: Chess – Outdoor game

(2)

(1) Mallakhamb trainer	Balambhat Deodhar
(2) Wizard of Hockey	Milkha Singh
(3) First Indian female boxer	Mary Kom
(4) First Indian female wrestlers	Phogat sisters

Answer:
Wrong pair: Wizard of Hockey – Milkha Singh

Question 7.
Do as directed
(A) Complete the graphical description:
(1)

Answer:

Answer:

Answer:

Answer:

(B) Prepare a Tree-Diagram on typs of games:
Answer:

Question 8.
Write short notes:

(a) Indigenous Games:
Answer:

1. The games which have their origin in India and are an important part of Indian culture are indigenous games.
2. They are of two types – ‘Indoor Games’ and ‘Outdoor Games’. Indoor Games are played within a closed environment and a number of them are played by sitting at one place. Chess, card games, dice, carrom, etc. are indigenous indoor games.
3. An open space or preferably a playground is required to play outdoor games. Kabaddi, Atyapatya, Kho-kho etc. are indigenous outdoor games.
4. The special feature of indigenous games is that they do not require high cost material and hence are less expensive. Phugadi, Zimma, Bhatukali are some of the indigenous games played by girls. In modern times, all national and international games are played by both girls and boys.

Question 9.
Explain the following statements with reasons:

(a) Major Dhyan Chand is called the Wizard of Hockey.
Answer:

• Major Dhyan Chand was part of hockey teams as a player in 1928 and 1932 which won gold medal at Olympics.
• He was also captain of the Indian Hockey team which won a Gold Medal at the Berlin Olympics in 1936.
• He shot 25 goals against America and Japan in the 1932 Olympics.
• He shot more than 400 goals in his entire career which include national and international matches. Owing to his brilliant achievement he is called the ‘Wizard of Hockey’.

(b) Globalisation has influenced sports.
Answer:

1. No sport is limited to any one country. Television and other media channels telecast matches widening the reach of sports in all comejcs, of the world.
2. International competition Asiad, Paralympics, Cricket Wc watched by people irrespective r
   part of the world.
3. World Cup matches of cricket, hockey and football are held.
4. No country has a monopoly on any sport which means that globalisation has influenced sports.

(c) A commentator should know the history of the game.
Answer:

• The mere description of a live match is not enough for commentators.
• A commentator should have good knowledge of the history of the game, previous records (who made or who broke) and eminent players in the past as well as events related to different competitions.
• Along with the history and information of the playground, commentator should narrate records made by the players in different matches.
• It will make his commentary interesting. Therefore, it is essential for the commentator to know the history of the game.

Question 10.
Answer the following questions in 25-30 words:
(a) Explain the importance of sports.
Answer:
Sports has gained great importance for the following reasons:

• Sports helps us to overcome our pains, worries and sufferings. We feel relaxed and refreshed by playing games.
• Games which involve a lot of physical activity not only provide good exercise but also help in building a tenacious and strong body.
• One. can develop courage; determination and sportsmanship playing games. A sense of cooperation and teamspirit develops when we participate in games which require collective participation.
• Team games also help in developing a leadership! quality.

(b) Write about the history of sports.
Answer:

• It is a natural instinct in human beings to play. From beginning of civilisation till date man has played different types of games for his entertainment.
• Hunting was a way of obtaining food for the ancient people as well as considered a game.
• Horse and chariot races, wrestling, game of dice (dyut) are mentioned in ancient Indian literary texts and epics.
• Dolls, whistles, toy carts were discovered in the excavations at Harappa. So, it can be said that the history of sports is as old as the history of man.

(c) Write about the importance of sports in education field.
Answer:

• Sports are an integral part „ of education. The making of a player begins at school level.
• Many types of sports events are held at the international level. To make the players competent they are given opportunity to play at district, state and national level.
• They are promoted and sponsored by the government and private sectors. Talented and ranking players get State scholarship or National scholarship.
• Seats are reserved for them in colleges and Universities. It has been observed that the foundation of successful players is laid in school life.

(d) What do we need to know while making movies on sports?
Answer:
While making a movie on sports the makers should have complete information of the. sport as well as its history.

1. Nowadays special research teams are appointed by production houses which do thorough research on the subject of the movie.
2. In order to gather information on the sportsperson or the sport it is essential to study books, articles, columns written by eminent sports writers.
3. If the movie is on a sportsperson, all interviews published in national and international magazines and newspapers should be read.
4. Factors such as period, type of equipment used, sports wear, dressing style, social life needs to be studied.
5. General understanding of the people about the game, practises and famous sportspersons is required.

Question 11.
Read the following passage and answer the following questions:

(a) Complete the Concept Map:

Answer:

(b) How are the experts in history helpful regarding international sports competition?
Answer:
Experts in history are helpful to write and critically analyse the game.

(c) How are professional opportunities available in field of sports?
Answer:
There are many professional opportunities available in the field of sports.

• Writers are in demand who can write on sports and critics to write reviews are in demand.
• Commentators are in demand on Television, radio and various other private channels. Experts and assistants are needed to provide information regularly.
• Coaches train the players, playground staff to maintain the field, umpires, etc.
• Cameramen, computer experts and team of assistants to have uninterrupted transmission. Trained and qualified referees are required to work at district, national and international levels.
• Overall, a great number of job opportunities are available in the field of sports.

Question 12.
Write a detailed answer to the following:

(a) Write about the history of sports literature and toys in ancient India.
Answer:
A new enterprise is developing in publishing related to sports in India. There is extensive written work on various sports.

• Many books related to sports and biographies are published. Encylopaedias are being written on sports.
• An independent encyclopaedia is written on exercise. The History of Mallakhamb is recently published.
• Sports magazines are published fortnightly and monthly.
• Many newspapers have allotted a separate section or last pages for news related to sports.
• ‘Shatkar’ was a sports magazine published some years ago. There is ample of literature available on sports.

(b) Trace the development of toys and their importance.
Answer:

• Toys and games have been essentially part of entertainment from ancient times. Every I developing society has made toys for the 8 entertainment and education of their children.
• Toys were found at archaeological sites at various places. The toys were made of clay, baked clay, terracotta and ivory.
• Either a mould was used to make the toy or it was fashioned by hand.
• Toys and the material used to make them were indicators of the development and advancement of civilisations.
• An interesting description of flying dolls is found in Kathasaritsagara. The dolls used to fly, made some sound and some danced when a key was pressed.
• Toys give us information about the period it was made, how they were made, religious and 8 cultural practices and technical know-how of the 8 people. ’

Question 13.
Observe the picture and write information about the event it is related to:

Answer:

1. This picture is the logo of the modern Olympic Games. The five interlocked rings represent the five continents of the world.
2. The rings coloured blue, yellow, black, green and red on a white field are known as the ‘Olympic rings’. The symbol was originally designed in 1912 by Pierre de Coubertin.
3. Olympic rings are the symbol of games which were first played in the ancient city of Olympia. They were held after every four years.
4. The ancient Olympics had fewer events than the modern games and only Greek men were allowed to participate. Events such as Horse and Chariot race, Footrace, Wrestling, Boxing, Discus Throw, Pentathlon were held.
5. The Greeks standardised rules of the sports were laid which was helpful to organise the games systematically.
6. The modern Olympic games are also held every four years. It is a great honour for sportspersons to participate and win the Olympic medals.

Memory Map

Balbharti Maharashtra State Board Class 10 Political Science Solutions Chapter 2 The Electoral Process Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 Political Science Solutions Chapter 2 The Electoral Process

Question 1.
Choose the correct option from the given options and complete the sentences.
(1) The Election Commissioner is appointed by the …………………………. .
(a) President
(b) Prime Minister
(c) Speaker of Loksabha
(d) Vice President
Answer:
(a) President

(2) …………………………. was appointed as the first Chief Election Commissioner of independent India.
(a) Dr. Rajendra Prasad
(b) T.N. Sheshan
(c) Sukumar Sen
(d) Neela Satyanarayan
Answer:
(c) Sukumar Sen

(3) Constituencies are created by …………………………. committee of the Election Commission.
(a) Selection
(b) Delimitation
(c) Voting
(d) Timetable
Answer:
(b) Delimitation

Question 2.
State whether the following statements are true or false. Give reasons for your answer.
(1) The Elections Commission lays down the code of conduct during elections.
Answer:
The above statement is True. Reasons:

• It ensures free and fair elections.
• Maipractices during the election come under control.
• Due to the strict observance of the code of conduct in the last few’ elections, the common voters have become confident.

(2) Under special circumstances the Election Commission holds re-elections in a particular constituency for a second time.
Answer:
The above statement is True. Reasons :

• Sometimes, the representative of Lok Sabha, Vidhan Sabha or the local self governmènt resigns from his/her constituençy.
• In some cases, death of the representative occurs.
• In such special situations, the Election Commission has to conduct an election for a second time. It is called By-elections.

(3) The state government decides as to when and in how many stages the elections would be held in a particular State.
Answer:
The above statement is False. Reasons :

• The entire process of conducting elections is entrusted upon and managed by the Election Commission.
• If this responsibility is given to the state government it may adopt a biased approach.
• Hence, the Constitution has formed the Election Commission an independent body to carry out the responsibility.

Therefore, it is decided by the Election Commission as to when and in how many stages it will conduct elections.

Question 3.
Explain the concept.
(1) Reorganising the constituencies
Answer:
(1) The Election Commission of India formed constituencies for Lok Sabha and Legislative Assembly.
(2) The Election Commission had decided upon the constituencies before the first election. As the years passed, there was a lot of migration of the people for business and other activities from the villages to cities.
(3) This changed the demography to large extent. Number of voters in some constituencies reduced while in some it increased to a very great extent. This disturbed the ratio of- seats allotted as compared to population in those constituencies.
(4) Hence, the need to readjust the constituencies arose. The Delimitation Commission of the election commission does the work of reorganising or restructuring of constituencies.

(2) Midterm Elections

Question 4.
Complete the following picture.

Answer:


Answer:

Answer:

Answer:

Question 5.
Answer in brief.
(1) Explain the functions of the Election Commission.
Answer:
The functions of the Election Commissipn are:
(1) Prepare the voters’ list.
(2) Decide election timetable and decide the entire process of holding elections.
(3) Scrutinize the applications of the candidates.
(4) Conduct free and fair elections and do all the work related to it.
(5) Give recognition and also de-recognize political parties.
(6) Resolve all the disputes and complaints regarding elections.

(2) Write some additional information about post of the Election Commissioner.
Answer:
(1) The Election Commission in India has one Chief Election Commissioner and two other Chief Commissioners.
(2) All the commissioners are appointed by the President.
(3) The Chief Election Commissioner of India is usually a member of the Indian Civil Service or. Indian Administrative Service.
(4) The responsibility of conducting free and fair elections to the Parliament and State Legislatures lies with the Election Commissioner.
(5) In order do safeguard the independence of the Election Commissioner, he cannot be easily removed from the post for any political reasons.

(3) Explain the meaning of Code of Conduct.
Answer:
(1) After the announcement of elections till the declaration of results, the Election Commission enforces the Code of Conduct.
(2) It explains the rules to be followed by the government, political parties candidates and voters before and during elections.
(3) Code of conduct is adopted to control malpractices during elections. It ensure free and fair ecections.

Project
Organise a mock poll in the school to understand the process of voting.
Answer:

Memory Map

Question 6.
Choose the correct option from the given options and complete the sentences:
(a) Article of Indian Constitution created the independent body of Election Commisšion.
(a) 351
(b) 370
(c) 324
(d) 301
Answer:
(c) 324

(b) system exists in India.
(a) Single-party
(b) Two-party
(c) Multi-party
(d) No-party
Answer:
(c) Multi-party.

(c) The right to give recognition or de-recognize a political party lies with ……………….. .
(a) President
(b) Election Commission
(c) Parliament
(d) Vice-President
Answer:
(b) Election Commission

(d) There are constituencies of Lok Sabha at present.
(a) 288
(b) 350
(c) 500
(d) 543
Answer:
(d) 543

(e) from the present state of Himachal Pradesh was the first voter.
(a) Sukumar Sen
(b) Sham Sharan Negi
(c) Prem Kumar Ghumal
(d) P N. Chadda
Answer:
(b) Sham Sharan Negi

(f) Due to EVM, people can also vote easily.
(a) elder
(b) salaried
(c) Divyanga
(d) Transgender
Answer:
(c) Divyanga

(g) The first elections in India were held in
(a) 1948-49
(b) 1949-50
(c) 1950-51
(d) 1951-52
Answer:
(d) 1951-52.

Question 7.
State whether following statements are True or False. Give reasons for your answer :
(a) There should be secrecy in Election process.
Answer:
The above statement is False. Reasons :

• Election should be conducted in a free and fair environment.
• If the elections are not held in free environment then there are chances of malpractices and corruption.
• Then, it will be impossible to elect the honest and efficient candidates.

(b) The Election Commission has started awareness campaign for registration of voters.
Answer:
The above statement is True. Reasons :

• The responsibility of preparing and updating electoral roll lies with the Election Commission.
• The Election Commission starts an awareness campaign to create awareness among new eligible voters so that they register themselves in the voter’s list.
• The Indian voter is not -much aware about the election process.
• Special voter’s awareness campaign is run for voter’s registration.
• For their awareness National Voter’s Day is celebrated every year.

(c) Every candidate who fills the nomination form can contest election.
Answer:
The above statement is False. Reasons :

• Every candidate of a party or independent candidate has to be personally present to fill the nomination form.
• It is necessary for him or her to give complete information in the nomination form as decided by the Election Commission.
• The nomination forms are then scrutinized. If there are irregularities in a nomination paper and if the information is found to be false the nomination forms are rejected.

Therefore, it is not possible for every candidate who fills the nomination form to contest election.

(d) Sometimes, the Election Commission has to conduct mid-term elections. OR Explain the concept : Mid-Term Elections.
Answer:
The above statement is True. Reasons :

• If the elected government in power loses its majority before completing its term.
• If no party gets complete majority, then two or more parties come together and form a coalition government.
• Such coalition government collapses if any party withdraws the given support.
• In such situations, the government is left with no option other than resigning.
• If there is no alternative available to form government then the Parliament or Vidhan Sabha is dissolved before completing its term. In such a scenario, the Election Commission has to conduct mid-term elections.

Question 8.
Explain the following concepts :

(a) What is representation?
Answer:
Modern democracy is a representative democracy. In a democracy it is not possible to involve the entire population in the ecision-making process. This resulted in the starting of the practice of electing some people on behalf of entire population
as representatives who would run the government. The representatives who form the government are expected to be responsible to the people and give preference to the welfare of the people.

• Direct and Indirect or representative democracy rire two types of democracy.
• In modem nation-states; the population has increased to a great èxtent.
• So it is impossible to involve all the people in decision-making process.
• Thus, th practice of electing some people on behalf of entire population as representatives started.
• The elected representatives form government and work for the welfare of the people.

(b) Election Commission :
Answer:
In India, the Election Commission is central to the process of elections. Art. 324 of the Indian Constitution has established this autonomous body which consists of one Chief Election Commissioner and two other commissioners.

1. One of the most important features of a democratic nation is elections at regular intervals. Holding free and fair elections at regular intervals is essential for a democratic system.
2. Under the Article 324 of the Constitution, Election Commission was formed in 1950. The President appoints one Chief Election Commissioner and two additional commissioners. It is an autonomous body.
3. The rank and powers of all the three commissioners are the same. The declaration of dates of the elections to the announcement of the results the entire procedure is monitored by the Election Commission.
4. The Election Commission does not have its own staff to carry out this procedure. So they carry out the work with help of government employees and teachers. Special provisions are made for all finances incurred by the Election Commission.

Question 9.
Write short notes :
(a) Journey from Ballot box to EVM machine :
Answer:

1. From the first election in 1951-52 till 1999, elections were held using ballot box. Twenty lakh ballot boxes were used in the first election. Voters used to cast his or her vote by stamping in front of the candidate’s name and put them in the metal boxes.
2. Electronic Voting Machines (EVMs) were first used for 5 seats in Rajasthan, 5 seats in Madhya Pradesh and 6 seats in New Delhi 1998 in Legislative Assembly.
3. EVM machines were used at all polling booths in the general elections held in 2004. It proved to be a very useful device.
4. It has been improvised since its first use. Due to the use of EVMs the results are declared early and at a very fast rate.

(b) Recognition to Political Parties :
Answer:

• India has a multi-party system with recognition accorded to national, state and regional level parties by the Election Commission.
• Their recognition depends on the voting percentage received by them in the assembly elections and number of elected representatives of their party.
• If any party does not fulfill these criteria, its recognition is cancelled.
• The Election Commission allots appropriate symbols to parties and independent candidates. All political parties should have recognition of the Election Commission.

Question 10.
Complete the concept map :

(a) Prepare a flow chart on the process of election.
Answer:

(b) Which two conditions among following is the violation of code of conduct?
(1) The candidate distributes items of household use. –
(2) Promises made to resolve the water problem if elected.
(3) To go from door to door to meet voters and request them to vote.
(4) To appeal on the basis of caste and religion to get support.
Answer:
(1) The candidate distributes items of household use.
(2) To appeal on the basis of caste and religion to get support.

Question 11.
Answer in brief :
(a) Why is it important to conduct elections?
Answer:
It is important to conduct elections because of the following reasons :

• The existence and working of democracy depends on elections.
• All political parties get a chance to rule.
• Elections help to bring a change in power through peaceful meAnswer:
• It not only changes government policies but also society.

(b) What are the conditions for voting?
Answer:
The following are the conditions for voting:

• The person should be a citizen of India.
• He should have completed 18 years of age.
• His name should appear in voters’ list.
• The person should have photo identity card issued by the Election Commission of India.

(c) What action is taken by the Election Commission if disputes arise regarding elections?
Answer:

• If any disputes arise regarding the elections, the Election Commission is empowered to take final decisions.
• The Election Commission conducts a thorough inquiry about the said dispute.
• If there is evidence of any malpractices during elections, in any constituency, it declares the elections invalid and announces re-polls.
• If any candidate breaks the code of conduct and contests elections, he/she is barred by the Election Commission from contesting elections.

(d) What challenges are faced by the Election Commission to conduct free and fair elections?
Answer:
The following challenges are faced by the Election Commission tcx conduct free and fair elections :

• Managing the large geographical landscape and huge electoral population.
• To stop misuse of money and muscle power during elections.
• Barring candidates with criminal background from contesting elections.
• Conducting elections successfully in politically criminalised environment.
• Conducting elections in spite of increasing instances of violence and making them a success.

(e) What are the advantages of EVM machines?
Answer:
The battery operated Electronic Voting Machine (EVM) has more advantages than the ballot box. They are as follows :

• It saves tonnes of paper used to make ballot paper.
• So, it conserves the environment as it stops the reckless cutting of trees required to make paper.
• If the voter does not wish to cast his vote in favour of any candidate contesting, he can make use of NOTA (None Of The Above).
• It makes counting of the votes much faster which enables the election officer to declare result in a short time.
• It is helpful for disabled (Divyanga) people to cast vote.

(f) Explain the features of procedures of voting during the first Lok Sabha Election.
Answer:

• It was a challenge to prepare voters’ list at the time of the first election. Illiteracy rate was very high in our country. Therefore, the procedure to vote and making the voter list was a challenge.
• 20 lac steel boxes were made and election symbols of political parties were stuck on it.
• Blank ballot papers were given to the voters and they were supposed to drop in the box having the election symbols of the party they decide to vote for.
• Even the illiterate people could vote because of this system.

Question 12.
Give your opinion :
(a) When candidates have only the condition of age, why should they give other information to Election Commission? Answer:

• While filling the form candidates should reveal information about his property assets and if there are any criminal charges against him.
• When candidates have only the condition of age as eligibility, why should they give other information to election commission?
• Why are the candidates required to give the information of their property to Election Commission?
• Such candidates if elected can misuse power and amass wealth with corrupt practices.
• With criminal background they can even threaten voters to vote for him.
• His nomination could get cancelled based on the information.

(b) Why is it so?
(A) Some constituencies are reserved for scheduled castes and scheduled tribes.
Answer:

• It is difficult for the people of scheduled castes and scheduled tribes to get representation as they are scattered in different parts.
• Without a representative it is difficult to discuss their problems in Parliament.
• Lack of representative will hinder their progress. Hence some constituencies are reserved for scheduled castes and scheduled tribes.
• Some constituencies are kept reserved for Scheduled caste and Scheduled tribes.
• Every political party has an election symbol.
• At the time of voting and counting of votes, the official representatives of political parties remain present.
• Recognised parties have equal opportunity to present their side before media such as television and radio.

(B) Why every political party has an election symbol?
Answer:

• After independence, the literacy rate was quite low in India.
• It was not possible for the voters to read the name of the candidate and vote.
• Therefore, the Election Commission gave symbols to political parties and independent candidates which helped the voters to identify and decide whom to vote for.

(C) At the time of voting and counting of votes, the official representatives of political parties remain present.
Answer:

• There are incidences of duplicate voters who register in multiple constituencies.
• There are cases of rigging of EVM or booth capturing.
• Such incidences are brought to light by representatives who are present at polling centres.
• During the counting process, if the EVM machine looks tampered, the representative can raise an objection.

(D) All recognised parties should get an equal opportunity to express their opinion on media such as television and radio.
Answer:

• All political parties should get a fair chance to express their agenda.
• Their ideas and philosophy should reach the people.
• Television and radio are owned by the government.
• Political parties have equal right on both.
• Hence, all the recognised parties can express their opinion on Doordarshan and Radio.

(c) Think!
(A) How political parties suffer due to family monopoly in the party? OR What are the disadvantages of dynasty rule?
Answer:

1. If only one family has domination on the political party because of dynasty rule then others are not given leadership opportunity.
2. It is impossible to have all the members of the family efficient. An inefficient heir can cause damage to the party.
3. The growth and expansion of party comes to a halt because of such heir. His faults seep into the party making it weak in the long term.
4. The nature of such a party become dictatorial. Opposing views are suppressed and the internal democracy in the party vanishes.
5. If the heir does not have progressive thoughts then the party becomes regressive and of obsolete ideology.
6. How political parties suffer due to family monopoly in the party?
7. What do you understand by the system of ‘one vote one value’?

(B) What do you understand by the system ‘One Vote One Value’?
Answer:

• There is great importance in political and social equality in democracy.
• According to this ideology, ‘One Vote One Value’ is very important.
• In a democracy, each vote has the same value. The value of the vote of a Prime Minister and a common man is same.
• Under military rule or dictatorship or during monarchy the value of a vote for privileged classes was more. There was no importance given to the vote of the common man.
• ‘One Man One Vote’ indicates all the people in the country have same status. This is the gift of democracy.

(d) Voting is our duty as well as responsibility to vote.
Answer:

• It is enshrined in the fundamental principles of our Constitution to vote.
• It is not only our duty but also responsibility.
• Democracy exists because of elections. People should elect honest and efficient representatives through election.
• If voters show no interest in voting then the government will ignore people’s welfare.
• Hence I feel it is not only the duty of every citizen to vote but also his responsibility.
• Government has to observe the code of conduct declared by the Election commission.

(e) What measures should be taken to increase the credibility of elections?
Answer:
To increase the credibility of elections the following measures should be taken :

• 50% seats should be reserved for women candidates by every party.
• Candidates with a criminal background should be permanently barred from contesting any elections.
• The misuse of money should be stopped during elections. The government should incur the expenditure.
• Candidates who resort to malpractices should be immediately booked. A strict inquiry and action should be taken against them by the court.
• Laws and regulations should be followed strictly by the political parties before giving election tickets.
• If the political parties do not co-operate with the above terms, the Election Commission should cancel their recognition.

(f) Which rules would you include in Code of Conduct for voters?
Answer:
The following rules should be included in Code of Conduct for voters :

• The voters who abstain from voting should be fined and government should suspend all the facilities given to them.
• If it is proved that the voter has accepted money or any kind of gifts, he should be punished.
• The action of voters should not instigate common people.
• They should not involve in bogus voting.
• They should not resort to illegal means for voting.
• The candidate distributes items of household use.
• Promise made to resolve the water problem if elected.
• To go from door to door to meet voters and request them to vote.
• To appeal on the basis of caste and religion to get support.

 

Balbharti Maharashtra State Board Class 10 Political Science Solutions Chapter 5 Challenges faced by Indian Democracy Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 Political Science Solutions Chapter 5 Challenges faced by Indian Democracy

Question 1.
Choose the correct option from the given options and complete the sentences.
(1) In a democracy …………………….. participate in elections and get political power.
(a) political parties
(b) courts
(c) social organisations
(d) none of the above
Answer:
(a) political party

(2) The major challenge faced by all democratic nations in the world is ……………………. .
(a) Religious conflicts
(b) Naxal activities
(c) Deepening the roots of democracy
(d) Importance to muscle power
Answer:
(c) Deepening the roots of democracy

Question 2.
State whether following statements are true or false. Give reasons for your answer.
(1) Alertness is required to sustain democracy.
Answer:
The above statement is True.

1. In order to make democracy successful it should be practised by people in all aspects of their life. It should not remain limited at the government level.
2. Conscious effort should be taken to keep the rights of the people intact.
3. The different challenges faced by democracy like corruption,violence and criminalisation should be tackled timely and strictly. It is necessary that people and the government should remain alert for the sustenance of democracy.

(2) Importance of the problems of farmers and tribals has increased in the left extremist movement.
Answer:
The above statement is False.

• Landlords confiscated lands of farmers and tribals.
• Naxalite movement was started to remove injustice against the landless farmers and tribals.
• But later the problems of farmers and tribals lost its focus and became violent.
• They adopted violent ways like to attack army, police and oppose the government.
• The importance of farmers and tribals decreased in the leftist movement.

(3) People may lose confidence in the democratic process due to corruption during elections.
Answer:
The above statement is True.

• In order to strengthen democracy, it is important to conduct elections in a free and fair atmosphere.
• There are instances of .the election process getting affected by corruption.
• Bogus voting, bribing the voters, abducting voters and ballot boxes, distributing articles to lure voters and other such things take place.
• All these things make people lose faith in the democratic process.

Question 3.
Explain the concept.
(1) Left-extremism
(2) Corruption
Answer:

• It is a form of dishonest or unethical conduct for personal gain by people at influential position.
• It is found at all levels economic, political, social and at government levels. The misuse power is also corruption.
• Bogus voting, giving bribe to voters, are examples of corruption in the election process.
• Hoarding of goods and then selling them at price more than the market yalue is also a way of corruption.
• Corruption in the public and private sector is the biggest problem in India.
• People develop distrust and dissatisfaction about the entire system. They lose trust in democracy because of corruption.

Question 4.
Answer the following questions in brief.
(1) Which factors are required for the success of democracy in India?
Answer:
The following factors are required for the success of democracy in India:

• Though democracy is the government of majority the opinions of minorities, religious, ethnic and lingustic should be included in the decision-making process.
• Stringent laws must be implemented to stop criminalisation of politics.
• Efforts should be made not only at the level of the government but also at social and personal level.
• Decisions about important public policies should be taken after interaction with the people.. Participation of people should increase in all government undertakings.

(2) What are the effects of criminalisation of politics?
Answer:
The following effects are seen due to criminalisation of politics:

• Money and muscle power gets undue importance.
• Violence increases during elections and it becomes difficult to hold elections in free and fair environment.
• Terror seizes the mind of people and their participation becomes less in administration.
• People lose their tolerance and the development of democracy does not take place.

(3) What efforts are undertaken to bring transparency in political process?
Answer:
The following efforts are made to bring transparency in political process:

• An independent Election Commission is appointed to hold free and fair elections.
• Stringent laws are made to stop criminalisation of politics.
• Laws are formed to stop corruption in politics and elections.
• Courts have banned people who are corrupt and those having criminal background or criminal allegations from taking part in political process.

Project
(1) What measures will you suggest to control corruption? Make a list of it.
(2) Organise a group discussion in your class on the problem of terrorism in India.
(3) Present a street play on ‘how to get rid of addiction?
Answer:

Memory Map

Question 5.
Choose the correct option from the given options and complete the sentences:
(a) ………………….. is a continuous and living process.
(a) Military rule
(b) Democracy
(c) Dictatorship
(d) Monarchy
Answer:
(b) Democracy

(b) The main objective of democracy is ………………….. .
(a) to hold elections
(b) public welfare
(c) public campaigns
(d) social work
Answer:
(b) public welfare

(c) Voting, elections, government structure, etc. is only ………………….. form of democracy.
(a) economic
(b) political
(c) social
(d) all-inclusive
Answer:
(b) political

(d) In order to make democracy meaningful the Government of India adopted …………………. .
(a) internal party elections
(b) public welfare schemes
(c) decentralisation of power
(d) protection of democratic values.
Answer:
(c) decentralisation of power

(e) Naxalite movement began to remove injustice done to …………………. .
(a) workers and dalits
(b) middle and lower class
(c) poor and common class
(d) landless farmers and tribals
Answer:
(d) landless farmers and tribals

(f) The …………………. in India is making conscious efforts to make political process transparent,
(a) Parliament
(b) Government
(c) Judiciary
(d) Political parties
Answer:
(c) Judiciary

(g) Due to increase in ………………….., there is increase in religious conflict.
(a) communalism
(b) terrorism
(c) corruption
(d) casteism
Answer:
(a) communalism

(h) In order to make democracy successful in India, participation of …………………. should increase.
(a) government
(b) people
(c) political parties
(d) social organization
Answer:
(b) people

Question 6.
Explain with reasons whether the following statements are true or false:

(a) Communalism does not cause much harm to the nation.
Answer:
The above statement is False.

• Increase in communalism leads to religious conflict in the country.
• Increasing conflicts in turn create frictions in society and destroy social unity.
• It creates division in society resulting in terrorist activities.
• People’s participation also reduces in the democratic process.
• This ultimately creates instability in society and democracy comes in danger.

Hence communalism harms the nation to a great extent.

(b) The opinion of the minorities should not be taken into consideration.
Answer:
The above statement is False.

1. Even though the government of the majority community comes to power, it should adhere to the democratic principle that government should work for the welfare of all communities.
2. In democracy, opinion of all the communities should be valued instead of giving importance only to the majority community.
3. All religious, linguistics, ethnic and caste groups should be part of the decision-making process of the government. Hence, to avoid injustice to minorities their opinion should also be taken into consideration.

(c) Democracy is the best form of governance.
Answer:
The above statement is True.

• The freedom and rights of the people remain intact in democracy.
• In democracy, values like liberty, equality, social justice, secularism and fraternity are nurtured in the real sense.
• Welfare of the people is the main aim of’ democracy.
• People do not enjoy so much freedom in any other form of government. Hence, democracy is the best form of governance.

(d) Majority opinion has a lot of importance in Democracy.
Answer:
The above statement is True.

• In a democracy, the political party getting majority of votes comes to power.
• Parliament takes all the decisions by majority.
• Democracy aims at the welfare of the majority of the people.

Therefore, majority opinion has a lot of importance in Democracy.

Question 7.
Explain the concept:
(a) Decentralisation:
Answer:

• If complete power rests in the hands of government it gives rise to dictatorship.
• Therefore division of power between legislature, executive and judiciary is essential.
• This division of power is known as Decentralisation.
• Decentralisation safeguards the freedom of the people.
• People participate in the functioning of the government.
• With increased participation, people become aware of their responsibilities.
• Decentralisation has great importance in democracy.

(b) Criminalisation of politics:
Answer:

• Participation of criminals in political process is criminalisation of politics. It is a serious problem and a threat to our democratic system.
• Political parties or candidates spread terror among people using money and muscle power.
• Political parties who give candidature to people with criminal background are responsible for violence during elections.
• Such candidates after coming to power continue their criminal activities.

They create financial scams and trouble the opponents. Criminalisation of politics weakens democracy.

Question 8.
Write short notes:
(a) Communalism and Terrorism:
Answer:

• Communalism and Terrorism causes great harm to nation. Communalism emerges out of narrow religious pride.
• Increasing communalism triggers religious conflict in the country. Religious conflict hampers social stability.
• Society gets divided on communal lines. Communalism gives rise to terrorism.
• People’s participation in democratic process in reduced to a great extent due to terrorism.
• It causes great damage to our nation.

Question 9.
Do as directed:
(1)

Answer:

(2)

Answer:

(3)

Asnwer:

(4)

Answer:

Question 10.
Answer the following questions in brief:
(a) What challenges are faced at global level by democracy?
Answer:
The following challenges are faced by democracy at global level:

• Many democratic countries in the world face the threat of military regime.
• It becomes important to propagate democracy which safeguards people’s rights and freedom.
• All-inclusive democracy is real democracy which should be adopted and practised instead of adopting just political form of democracy.

(b) What improvements are required for democracy to be deep rooted?
Answer:
The following improvements are required for democracy to be deep rooted:

• Values like freedom, equality, fraternity, justice, peace and humanitarianism should be practised and nurtured by all sections in the society.
• Autonomy should be given to various social organisation and assimilqje all the sections of the society.
• Empowerment to the citizens, free and fair elections and independent judiciary is necessary.
• Adoption of a form of democracy which gives preference to public welfare.

(c) What measures are adopted by India to strengthen democracy?
Answer:
In order to strengthen democracy following measures are adopted by India:

• Decentralisation of power.
• Reservation for minorities and women so that they get a share in power.
• The values of liberty, equality, secularism and social justice adopted by our Constitution.
• At administrative level various projects like Education for all, Clean Bharat campaign.
• Gram Samruddhi Yojana, Mahatma Gandhi National Rural Employment Guarantee Scheme are undertaken.

Question 11.
Give your opinion:
(a) What is your opinion about participation of people in various undertakings of the government?
Answer:

• There will be change in the public policies of the government.
• There will be interaction between all sections of society and exchange of ideas.
• There will be transparency in government administration and problems like corruption will be tackled.
• More public welfare schemes will get implemented and no one will feel that injustice is done to them or they are left out.

(b) Are internal elections held by political parties?
Answer:

• It is mandatory to hold internal elections in a political party.
• Elections are held for various posts like president, treasurer and secretary.
• Elections are held after every 3 years as per the niles laid down by the Election Commission of Itdia.
• The paity which does not abide by the rule loses recognition.
• Because of such elections, there can never be dominance of any single person on a party.
• Democracy sustains within the party. In Indian democracy the internal elections are held by all the parties regularly.
• Another challenge before democratic nations is to ensure that democracy becomes deep rooted.
• Freedom, equality, fraternity and justice, peace, development and humanitarianism are the values that should be practiced at all levels of the society.
• The mass support for this purpose can be gathered only through democratic means.

(c) In spite of economic reforms China accepted dominance of only one party. Is China a democratic nation?
Answer:

• After the Communist revolution in 1948 China became a republic.
• After the formation of the republic, the Communist party of China became a dominant party.
• All the offices in the party are elected through internal elections.
• But in practice, there is dictatorship of the Communist party. Democracy is for namesake in China.
• In such a situation, the people do not enjoy freedom as in true democracy.
• However, China accepted economic reforms and became part of World Trade Organization.
• Another challenge before democratic nations is to ensure that democracy becomes deep rooted.
• Freedom, equality, fraternity and justice, peace, development and humanitarianism are the values that should be practiced at all levels of the society.
• The mass support for this purpose can be gathered only through democratic means.

(d) Do you think there should be family monopoly in politics?
Answer:

• There is no place for family monopoly in politics.
• The elected representatives serve the people till their term lasts.
• People vote out the inefficient representatives out of power in next election.
• If there is monopoly of one family, the perspective of democracy becomes narrow, common people cannot share power.
• If any inefficient heir comes to power, he or she could be a great loss for the party, people as well as the nation.
• Family monopoly in politics is a major problem before democracy in India.
• Monopoly of just one family in politics reduces democratic space. Common people cannot participate in the public sector.

Hence there should be no family monopoly in politics.

Balbharti Maharashtra State Board Class 10 History Solutions Chapter 6 Entertainment and History Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 History Solutions Chapter 6 Entertainment and History

Question 1.
(A) Choose the correct option from the given options and complete the statement.
(1) ……… are supposed to be the first keertankar in Maharashtra.
(a) Saint Dnyanehshwar
(b) Saint Tukaram
(c) Saint Namdev
(d) Saint Eknath
Answer:
(c) Saint Namdev

(2) Baburao painter made the movie, …………………….. .
(a) Pundalik
(b) Raja Harischandra
(c) Sairandhri
(d) Bajirao-Mastani
Answer:
(c) Sairandhri

(B) Identify and write the wrong pair in the following set.
(1) Raigadala Jevha Jag Yete – Vasant Kanetkar
(2) Tilak Ani Agarkar – Vishram Bedekar
(3) Sashtang Namaskar – Acharya Atre
(4) Ekach Pyala – Annasaheb Kirloskar
Answer:
(4) Wrong Pair: Ekach Pyala – Annasaheb Kirloskar

Question 2.
Complete the following chart.

	Bhajan	Keertan	Lalit	Bharud
Characteristics
Examples

Answer:

Sr.No.	Point	Bhajan	Keertan	Lalit	Bharud
1	Characteristics	Singing songs in praise of God and chanting his name accompanied by Taal (Cymbals), Pakhvaj and Mridangam	(1) Naman and Nirupanacha Abhang and Nirupan comprise the Poorvarang (2) Narration of a story to illustrate main theme is Uttarrang	(1) Deity is invoked during festival to fulfill desire (2) It is performed in a theatrical style. Stories of Krishna, Rama and great devotees are presented during performances	It is a metaphorical song with spiritual and ethical teachings.
2	Examples	Bhajans of Saint Tulsidas, Saint Tukadoji Maharaj and Saint Namdev	Naraadiya Keertan and Mahatma Phule’s Keertan	Popular in Konkan and Goa	Bharuds of Saints Eknath, Namdev and Dnyaneshwar.

Question 3.
Write short notes:
(1) Need of entertainment
Answer:

• Entertainment of excellent quality is essential for healthy growth of a person as it is an integral part of one’s life?
• To break the boredom of routine life and keep the mind lively and fresh we need gome entertainment.
• It makes us feel more energetic and our efficiency at- work improves.
• Hobbies and games are pursued for entertainment which eventually develops personality.
• Entertainment refreshes our mind and helps to distress.
• Lack of entertainment in one’s life will lead to monotonous life and boredom.

(2) Marathi Theatre
Answer:

• Theatre is a place devoted to performances either solo or collective, of performing arts.
• The 19th century saw a great development of the Marathi Theatre.
• Vishnudas Bhave was known as the father of the Marathi Theatre.
• In the initial years historical, mythological plays were performed along with light farcical plays.
• The plays had no written script.
• The tradition of having a complete written script began with the play ‘Thorale Madhavrao Peshwe’ in 1861.
• At the end of 19th century,„ the tradition of musical plays started.
• Historical themes and social problems were presented through these plays.
• The popular plays by Acharya Atre like Udyacha Sansar, Gharabaher helped the Marathi theatre to sustain through a temporary decline. Vasant Kanetkar, Vishram Bedekar, Acharya Atre, enriched the Marathi theatre.

(3) Entertainment and professional opportunities
Answer:

• There are many professions associated with theatre and cinema.
• Professional hairstylists, costume designers, make-up artists, art directors who put up stage backdrops are required in theatre.
• Directors, technicians, actors, lightmen, costume and jewellery designers and assistants are required too. Experts in music and script writers, singers are required.
• Cinema requires all of them along with dance directors, singers, cameramen, dialogue writers and story writers. Scholars of history can work in this field as art directors.

Question 4.
Explain the following statements with reasons.
(1) Expertise in history is important in the film industry.
Answer:
It is essential to have knowledge of history while making films on historical’ events or a person. .

• If the movie has a historical theme then art directors are required to create backdrop designs showcasing the atmosphere of that period.
• To write movie dialogues, the knowledge of the culture and language as spoken in that period is necessary.
• It is important to have knowledge of appropriate hairstyles, costumes, jewellery make¬up of that era.
• Scholars of history are required who can work as art directors or as consultants to the art director.
• Experts in field of history can find many professional opportunities.

(2) Bharuds composed by Saint Eknath are popular in Maharashtra.
Answer:

• Saint Eknath composed Bharuds with the purpose of educating people on various aspects of life.
• Bharuds composed by Saint Eknath had a wide range of subjects, dramatic quality, easy rhythm and humour.
• People liked the way it was performed.
• A message was given in a humorous way.

Question 5.
Answer the following questions in detail.
(1) Why is Maharashtra known as the land that nurtured the Indian film industry?
Answer:

1. The contribution of Madanrao Madhavrao Pitale, the Patwardhan family of Kalyan and Harishchandra Sakharam Bhatvadekar is very important in the development of Indian movies.
2. Dadasaheb Torane, A. E Karandikar, S. N. Patankar, V. E Divekar sought help from foreign technicians and made a movie entitled Pundalik. It was released in Mumbai in 1912.
3. ‘Raja Harischandra’ was the first movie to be processed completely in India. It was released in Mumbai in 1913.
4. The credit of making a full-length movie goes to Maharashtra.
   Therefore Maharashtra is known as the land that nurtured the Indian film industry.

(2) What is Powada?
Answer:

1. Powada is a dramatic narration by altematingly reciting poetry and prosaic extracts. Powada narrates great deeds of heroic men and women in a very forceful and inspiring style.
2. The Powada composed by – Adnyandas, a contemporary poet of Chhatrapati Shivaji Maharaj which narrated the incident of Afzal Khan’s death and battle of Simhgarh composed by Tulsidas are very famous.
3. In the British period, Powadas narrating the stories of Umaji Naik, Chaphekar brothers and Mahatma Gandhi were composed.
4. During the Samyukta Maharashtra Movement the Powadas were used as medium of creating public awareness.

Project
Get the lyrics of any one of Saint Eknath’s Bharud, and enact it in the cultural programme of your school.

Question 6.
Complete the sentences by choosing the correct option:
(a) In the 18th century, ………………………. started a Phad of Dashavatara artists which used to perform all over Maharashtra.
(a) Saint Gadge Maharaj
(b) Adnyandas
(c) Tulsidas
(d) Shyamiji Naik Kale
Answer:
(d) Shyamji Naik Kale

(b) Traditionally, ………………………. is supposed to be the founder of keertan tradition.
(a) Saint Namdev
(b) Saint Eknath
(c) Naradmuni
(d) Saint Gadge Maharaj
Answer:
(c) Naradmuni

(c) The Powada composed by the poet ………………………. on the incident of the killing of Afzal Khan is well-known.
(a) Adnyandas
(b) Tulsidas
(c) Ramdas
(d) Surdas
Answer:
(a) Adnyandas.

(d) Compositions of ………………………. are not part of Bhajans sung in Karnataka.
(a) Purandardas
(b) Surdah
(c) Bodhendraguruswami
(d) Thyagraj
Answer:
(b) Surdas

(e) Varkari sect has developed a glorious tradition of ………………………. by chanting God’s name.
(a) Powada
(b) Dashavatari Natak
(c) Bhajan-Keertan
(d) Bharud
Answer:
(c) Bhajan-Keertan

(f) Powada composed by Tulsidas on the battle of ………………………. is very well known.
(a) Panhala
(b) Raigarh
(c) Pratapgad
(d) Simhgarh
Answer:
(d) Simhgarh

(g) Powadas composed by ………………………. were not the part of Samyukta Maharashtra Movement.
(a) Amarsheikh
(b) Patthe Bapurao
(c) Annabhau Sathe
(d) Gawankar
Answer:
(b) Patthe Bapurao

(h) ………………………. is known as the Father of Marathi theatre.
(a) V. J. Kirtane
(b) Dattopant Patwardhan
(c) Vishnudas Bhave
(d) Annasaheb Kirloskar
Answer:
(c) Vishnudas Bhave.

(i) started the tradition of having a complete written script.
(a) V. J. Kirtane
(b) Vishnudas Bhave
(c) Shripad Krishna Kolhatkar
(d) Govind Ballal Deval
Answer:
(a) V. J. Kirtane

(j) In the latter half of the 19th century, made special efforts to introduce classical khyal music in Maharashtra.
(a) Bhimsen Joshi
(b) Kumar Gandharva
(c) Kishori Amonkar
(d) Balkrishnabuva Ichalkaranjikar
Answer:
(d) Balkrishnabuva Ichalkaranjikar

(k) In India, is the first one to make a cine camera.
(a) Anandrao Painter
(b) Baburao Painter
(c) Dadasaheb Torne
(d) Dadasaheb Phalke
Answer:
(a) Anandrao Painter

(l) In 1925, made a movie Bajirao Mastani, which was later on banned by the British Government under the suspicion of spreading nationalistic sentiments.
(a) Sanjay Leela Bhansali
(b) Dadasaheb Phalke
(c) Baburao Painter
(d) Bhalaji Pendharkar
Answer:
(d) Bhalaji Pendharkar

(m) was the first woman producer of: Marathi movies.
(a) Kamalabai Mangarulkar
(b) Devika Rani
(c) Amirbai Karnataki
(d) Kanandevi
Answer:
(a) Kamalabai Mangalurkar.

Question 7.
Identify the wrong pair in the following and write it:
(1)

Name of the Play	Playwright
(1) Raygadala Jevha Jag Yete	Vasant Kanetkar
(2) Tilak Ani Agarkar	Vishram Bedekar
(3) Sashtang Namaskar	Acharya Atre
(4) Ekach Pyala	Annasaheb Kirloskar

Answer:
Wrong pair: Ekach Pyala – Annasaheb Kirloskar

(2)

First release	Movie
(1) First full length movie released in India	Raja Harishchandra
(2) First historical film in India	Simhgarh
(3) Movie dealing with real social issues	Savkari Pash
(4) Indian movie which got international acclaim	Saint Dnyaneshwar

Answer:
Wrong pair: Indian movie which got international acclaim — Saint Dnyaneshwar

(3)

Film producer	Produced Biographical Movies on
(1) Acharya Atre	Ram Shastri
(2) Vishram Bedekar	Vasudev Balwant Phadke
(3) Dinakar D. Patil	Dhanya te Santaji Dhanaji
(4) Prabhakar Pendharkar	Bal Shivaji

Answer:
Wrong Pair: Acharya Atre – Ram Shashtri

(4)

(1) Keechakvadh	Krishnaji Prabhakar Khadilkar
(2) Ekach Pyala	Ram Ganesh Gadkari
(3) Ithe Oshalala Mrutyu	Vasant Kanetkar
(4) Natasamrat	Vijay Tendulkar

Answer:
Wrong Pair: Natasamrcrt -Vijay Tendulkar

(5)

Work	Saint
(1) Gave momentum to the Bhakti movement in Gujarat	Saint Kabir
(2) First Keertankar of Maharashtra	Saint Namdev
(3) Popularised Khanjiri Bhajan	Saint Tukdoji Maharaj
(4) Tradition of Rashtriya Keertan was started	Dattopant Patwardhan

Answer:
Wrong Pair: Gave momentum to Bhakti movement in Gujarat — Saint Kabir

(6)

(1) The first play in Marathi	Seetaswayamvar
(2) First play having  complete written script	Thorale  Madhavrao
(3) Metaphorical Drama	Udyacha Sanskar
(4) Play based on Shakespeare’s King Lear	Natasamrat

Answer:
Metaphorical Drama-Udyacha Sanskar.

(7)

Name of the Play	Playwright
(1) Thorale Madhavrao Peshwe	V. J. Kirtane
(2) Ekach Pyala	Annasaheb Kirloskar
(3) Sangeet Sharada	Shripad Krishna Kolhatkar
(4) Sangeet Manapaman	Krishnaji Prabhakar Khadilkar

Answer:
Wrong Pair: Sangeet Sharada – Shripad Krishna Kolhatkar

Question 8.
Complete the graphical presentation:
(a) Prepare concept map on:
(1) Types of Puppets:

Answer:

(2) Saints who popularised Bhajans:

Answer:

(3) Plays by famous Playwrights:

Answer:

(4) Saints who popularised Bhajans in North India:

Answer:

(b) Prepare a flow chart on the development of Marathi Theatre:
Answer:
Development of Marathi Theatre:

Question 9.
Explain the concept:
(1) Dashavatara Theatre:
Answer:

• The stories presented in Dashavatara shows are based on the ten incarnations of Vishnu.
• The method of acting, make-up, costumes in Dashavatara show is set by the tradition.
• It is mostly a musical show but there may be a few spontaneous dialogues.
• At the beginning of the show, Sutradhar, the narrator invokes Lord Ganesha, for its successful run.
• Dashavatara is part of the folk theatre in Maharashtra which has its origin in mythological plays.

(2) Bhajan:
Answer:

• Singing songs in praise of God and chanting God’s name accompanied by instruments like taal (cymbals), mridangam, pakhavaj is known as Bhajan.
• Bhajan is an important element of devotional music for those who are on the path of devotion.
• Varkari sect made Bhajans accessible to all.
• There are two types of Bhajans, Chakri and Songi BhajAnswer:
• Devotees keep moving in circular fashion and without break in Chakri Bhajan.
• In Songi Bhajan, singer-actors act as devotees and deliver dialogues in the form of devotional songs.

(3) Bharud:
Answer:

• Bharud can be described as a metaphorical song that has spiritual and ethical lessons. Bharud is similar to road show.
• Bharud is popular because of its wide range of subjects, humorous presentation, dramatic quality and easy rhythm.
• Bharuds are composed with the purpose of educating people on various aspects of life.
• Even though Bharuds of Saint Eknath are famous, bharuds were composed by many saints including Saint Dnyaneshwar.

(4) Keertan.
Answer:

• Keertan involves oratory, singing, acting, dancing and story telling.
• Naradmuni is assumed to be the founder of Keertan tradition.
• It is pure glorification of god. It is also a medium to educate the masses about good values of life and very purpose of human life.
• There are two parts in Naraadiya keertan Poorvarang and Uttarrang. Poorvarang comprises of Naman.
• Nirupanacha Abhang and Nirupan; Uttarrang comprises of narration of a story to illustrate the main theme.
• Keertan has two traditions in Maharashtra – Naraadiya and Varakari.

(5) Documentaries: (You would like to know this: Textbook page 44)
Answer:

• A film which gives information, inspires and educates people and is a short film is a documentary.
• Documentaries were made on freedom struggle, national leaders, social issues and superstitions, forts, animal species, sports, etc.
• They were aimed at creating public awareness about various issues.
• They are shown in the cinema theatres before the start of the main movie.

Question 10.
Write short notes:
(a) Means of Entertainment:
Answer:

• Entertainment is an integral part of man’s life. Man has developed many means of entertainment since ancient times.
• Ancient times saw the rise of festivals, fairs, sports, dance-music, etc.
• The means of entertainment changed with times.
• Television, mobiles, video games and movies and such other modem means of entertainment were introduced.
• Folk music, classical music, plays, books, newspapers, magazines are some mediums of entertainment which are available. Different types of sports, hobbies and travel too are means of entertainment.

(b) Lalit:
Answer:

1. Lalit is an old form of entertainment popular in Konkan, Maharashtra and Goa. It belongs to the tradition of Naaradiya Keertan.
2. It is presumed that the presiding deity is present on the throne. It is invoked by the people as it is widely believed that the deity fulfils all the wishes.
3. Stories of Krishna, Rama and of great devotees are presented during the performance.
4. Lalit forms a part of the backdrop of modem Marathi theatre.

(c) Keechakvadh: (Do You Know? Textbook page 43)
Answer:

• Krishnaji Prabhakar Khadilkar wrote Keechakvadh in the pre-independence era. It was a metaphorical drama.
• It was based on the incident of Keechakvadh described in the epic, Mahabharata.
• Draupadi represented helpless Mother India, while Yudhishthira represented the moderates and Bheem the extremists.
• Keechak represented the insolent Viceroy Lord Curzon.
• The audience used to perceive characters in this fashion and feel* enraged about the imperialistic British rule.

(d) Natashmrat: (Do You .Know? Textbook page 43)
Answer:

• The renowned author-poet Vishnu Waman Shirwadkar, also knpwn as Kusumagraj wrote Natasctmrat.
• It is styled after Shakespeare’s well known play ‘King Lear’.
• Ganpatrao Belvalkar, the tragic protagonist of Natasamrat represents a blend of two well-known personalities of early Marathi stage Ganpatrao Joshi and Nanasaheb.
• The traits of both great actors are found in the main character of Natasamrat.
• Natasamrat is a tragic story of an aging actor who gives his entire wealth to his sons and is humiliated by them.
• This play was very popular and created history on stage performance and in playwriting.

(e) Tamasha (Folk theatre):
Answer:

1. Tamasha is a Persian word which means a pleasing sight. Tamasha emerged as an independent form in the 18th century absorbing the traits of folk theatre and classical arts.
2. Tamasha is classified into ‘Sangeet Bari’ and ‘Dholakicha Phad’. Dance and music are more important than drama in Sangeet Bari. Tamasha with drama as main part was developed later. It included Vag, the dramatic part a little later.
3. The show begins by singing the praise of Lord Ganesha, known as Gana. It is followed with the presentation of Gavalan.
4. The second part of Tamasha presents the Vag. The plays like ‘Vichchha Mazi Puri Kara’ or ‘Gadhavache Lagna’ were very popular.

Question 11.
Explain the following statements with reasons:
(a) Puppetry is an oldest form of entertainment.
Answer:

• Puppet show was an important form of entertainment.
• The remains of clay dolls have been found in the excavations at the archaeological sites of Harappa, Egypt and Greece civilisations.
• Information on puppets is found in the texts like Mahabharata and in Panchatrantra stories.
• The ancient text Mahabharat has a mention that puppetry was one of the 64 arts.

(b) Vishnudas Bhave is known as the Father of Marathi Theatre.
Answer:

• The origins of the Marathi theatre can be traced to Dashavatara tradition. Lalit forms a backdrop of Marathi theatre.
• Seetaswayamvar, the first play, written and presented by Vishnudas Bhave was very successful.
• The movement of stage plays started by Vishnudas Bhave was followed in Maharashtra by historical, mythological and also light farcical stage plays.
• The farcical plays dealt with social issues in a humorous way. Therefore, he is known as the Father of Marathi theatre.

Question 12.
Answer the following questions in 25 – 30 words:
(a) Make a list of various types of entertainment and classify them into different categories. (Try to do it: Textbook Page 39)
Answer:

• Entertainment can be classified into two categories, active and passive.
• Active entertainment means an individual’s mental-physical participation. In passive entertain-ment, a person may not be an actual participant.
• To play cricket is active form of entertainment but to watch a cricket match is passive entertainment.
• To participate in festivals, fairs, celebrations is active entertainment but to watch as audience is passive entertainment.

(b) Write about Dashavatara form of folk theatre.
Answer:

• The stories presented in Dashavatara are based on the 10 incarnations of Lord Vishnu.
• The method of acting, make-up, costumes in Dashavatara shows is set by the tradition.
• The show is mostly musical but sometimes there may be a few spontaneous dialogues.
• The characters representing gods use wooden masks. At the start of the show, the sutradhara invokes Lord Ganesha.
• The show ends by breaking dahihandi, followed by aarati, praising the God.
• This is part of folk theatre in Maharashtra.
• Dashavatara shows are presented in the regions of Konkan and Goa after the harvesting season is over.

(c) What is required to be a Keertankar?
Answer:
The following qualities are required to be a Keertankar:

• A Keertankar also known as Haridas or Kathekaribuva needs to be very well informed.
• He should have wide experience and knowledge of the world.
• He should be well-versed in mythological and social subjects.
• He needs to train himself in qratory, singing, musical instruments, dance and humour. .
• He should dress in a traditional way.

(d) Write about the contributions of Bhosale family to drama.
Answer:

• The Bhosale family of Tanjore were successors of Chhatrapati- Shivaji Maharaj. They were patrons of arts.
• The rulers of the Bhosale family encouraged dramas in Marathi and in southern languages.
• Some of them have written a few plays and also translated Sanskrit plays.

(e) What is the contribution of Vishnudas Bhave and V. J. Kirtane to Marathi theatre?
Answer:

1. Vishnudas Bhave presented the first play, Seetaswyamwar, on stage. Initially no written scripts were used for plays. Only the lyrics were written and dialogues were spontaneous.
2. The movement started by him was followed in Maharashtra by historical, mythological and also light farcical stage plays. He is known as the Father of the Marathi theatre.
3. V. J. Kirtane was the first author who wrote the script of Thorale Madhavrao Peshwe in 1861 and its printed copy was made available.
4. It was the beginning of the tradition of having a complete written script ready before staging the play.

(f) Explain the nature of Rashtriya Keertan.
Answer:

• During the independence movement, a new type of Keertan was developed known as Rashtriya Keertan.
• It is performed in the same way as Naradiya Keertan.
• It placed more importance on creating awareness by narrating the life stories of great leaders of the Indian independence movement, scientists, social reforms, etc.
• Dattopant Patwardhan of Wai started Rashtriya Keertan.

Question 13.
Read the following passage and answer the questions:
(a) Who presented the play ‘Seetaswayamvar’?
Answer:
‘Seetaswayamvar’ was the first play presented by Vishnudas Bhave.

(b) Who wrote the musical play ‘Sharada’?
Answer:
Govind Ballal Deval wrote the musical play Sharada.

(c) How can plays bring about social awakening?
Answer:

• As theatre is an audio-visual medium, it creates a strong impact on the audience.
• They commented on evil customs, traditions, superstitions in our society. This started the reformation process.
• Sharada, a musical play, written by Govind Ballal Deval shed light on the evil custom of marrying young girls to aged men in a humorous style.
• ‘Ekach Pyala’ by Ram Ganesh Gadkari made the society aware about the evil effects of drinking.

Question 14.
Answer the following questions in detail:
(a) Write about the art of Puppetry.
Answer:

• The Kathputali is a traditional art of puppetry which has two styles.
• One that developed in Rajasthan and the other in South India.
• In ancient India, materials like wood, wool, leather, horns and ivory were used to make puppets.
• The role of the narrator known as Sutradhar is very crucial in stage show.
• The stage for this puppetry show is very small but the puppeteers use light and sound effects in an ingenious way.
• Shadow puppets, hand puppets, string puppets and wooden puppets are used in Kathputali shows.
• The artists who perform Kathputali shows are found in Uttar Pradesh, Maharashtra, Rajasthan, Telangana, Karnataka and Kerala.

(b) Write about the development of Indian film industry.
Answer:

1. Cinema is a medium that brings together art and technology. With the advent of the technology of motion pictures the film industry came into being. It gave rise to the era of silent movies.
2. The technology of sound recording paved the way for talkies. Dadasaheb Torane, A. P Karandikar, S. N. Patankar and V. E Divekar made the movie Pundalik with help from foreign techniciAnswer: This was a great step in the development of the art.
3. Dadasaheb Phalke made a full length movie, completely processed in India. He made silent movies and documentaries also.
4. Baburao Painter’s cousin, Anandrao Painter made the first cine-camera. Baburao Painter made many historical movies and a movie on realistic social issues. Bhalaji Pendharkar made movies invoking nationalist sentiments.
5. Kamalabai Mangarulkar was the first woman producer, who made movies in Marathi as well as Hindi.
6. Prabhat Film Company made many religious, historical, mythological and social movies. Production studios like Bombay Talkies, Rajkamal Productions, R. K. Studios, Navketan played significant role in development of the Indian film Industry. Period from 1961 to 1981 is the golden period of Indian film industry.

Question 15.
Identify the given picture and write about his contribution:

Answer:

1. The given picture is of Dadasaheb Phalke who is known as the Father of Indian Film Industry.
2. He released the first movie ‘Raja Harishchandra’ in Mumbai in 1913. He directed the movie which was entirely processed in India for the first time.
3. He made silent movies named as Mohini- Bhasmasur, Savitri-Satyavana.
4. He also made documentaries on the rock cut caves of Verul and pilgrim centres of Nashik and Tryambakeshwar. Later, he made historical and mythological movies.
5. The Government of India has honoured him by instituting Dadasaheb Phalke Award given for lifetime contribution to cinema, which is considered one of the most prestigious awards.

Balbharti Maharashtra State Board Class 10 Political Science Solutions Chapter 1 Working of the Constitution Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 Political Science Solutions Chapter 1 Working of the Constitution

Question 1.
Choose the correct option from the given options and complete the sentences.
(1) In Maharashtra …………………… seats are reserved for women in local self-governing institutions.
(a) 25%
(b) 30%
(c) 40%
(d) 50%
Answer:
(d) 50%

(2) Which of the following laws created a favorable environment for women to secure freedom and self-development?
(a) Right to Information Act
(b) Dowry Prohibition Act
(c) Food Security Act
(d) None of the above
Answer:
(b) Dowry Prohibition Act

(3) The essence of democracy is ……………………
(a) universal adult franchise.
(b) decentralisation of power.
(c) policy of reservation of seats.
(d) judicial decisions.
(d) Judicial decisions
Answer:
(b) decentralization of power

Question 2.
State whether the following statements are true or false. Give reasons for your answer.

(1) Indian democracy is considered the largest democracy in the world.
Answer:
The above statement is True.

• Indian Constitution cancelled all the conditions which were put for voting before independence thereby increasing the number of voters.
• The Constitution adopted adult suffrage which has facilitated all adult men and women to cast their vote.
• The age limit to vote was reduced to 18 years from 21 years which gave opportunity of political participation to the young generation. No other democratic country in the world has voters- in such large numbers.

Hence, Indian democracy is the largest democracy in the world.

(2) Secrecy in the working of Government has increased due to the Right to Information.
Answer:
The above statement is False.

• To strengthen democracy and increase mutual trust between the government and the people, it is very important that the people should know about ‘the functioning of the government.
• Transparency and accountability are the hallmarks of good governance.
• With Right to Information given to the citizens, Government became more transparent. Thus, the Right to Information has reduced element of secrecy in administration.

(3) The nature of the Constitution is seen as a living document.
Answer:
The above statement is True.

• Parliament has the powers to make changes in the Constitution according to the changing circumstances and conditions.
• However, it should be done without tampering or changing the basic structure of the Constitution.
• As it has kept itself abreast with the changes, S the Constitution became a live and dynamic document instead of a rigid one

Question 3.
Explain the following concepts.

(1) Right based approach
Answer:

• India adopted democracy after independence. Each government which came to power took efforts to make the democratisation process more profound.
• In the initial stages, these governments considered citizens as ‘beneficiaries’.
• After the year 2000, the approach towards citizens changed. Democratic reforms were considered as ‘rights’ of citizens.
• Hence, the Right to Information, Education and Food Security was granted not as beneficiaries but as rights of the citizens. This approach is known as Rights Based Approach.

(2) Right to information
Answer:

• In order to bring transparency in the administration and make it accountable, Indian citizens are given Right to Information.
• Right to Information helped in promoting harmony between government and people and empowered the citizens.
• It brought transparency in administration, made the government realise that they are answerable to people.
• It has helped to reduce the element of secrecy which surrounded the functioning of the government. It made the government open and transparent.

(3) Women representation in the Loksabha.
Answer:

• The Constitution of India empowers women by granting them equal status with men and equal political rights.
• 22 women were elected in the Lok Sabha elections held in 1951-52. Their number increased to 66 in 2014 elections.
• Reservation has been increased to 50% in local self-governing institutions in Maharashtra and in many other states.
• If the number of women representative increased in Lok Sabha, it will help in reducing incidents of violence against women and increase their involvement in the decision-making process.

Question 4.
Answer in brief.
(1) What are the effects of reducing the voting age from 21 years to 18 years?
Answer:

• Earlier the Indian Constitution had fixed the voting age of 21 years.
• The voting age was lowered to 18 years.
• The young voters secured the right to vote and the increased number of voters was unparalleled. ‘
• They got the right to decide how their representative should be. ,
• Moreover, it provided to the unrepresented youth an opportunity to become part of political process being literate and politically conscious.
• It increased the scope of democracy by including the youth of the country thus making it the largest democracy in the world.

(2) What is meant by establishment of social justice?
Answer:
Establishing social justice means:

• To eliminate the practices and beliefs which are responsible for injustice towards a person or a community and which hampers collective progress of society should be eliminated.
• Government policies should be all inclusive which means it should aim at accommodating different sections of society.
• There should not be any discrimination based on caste, creed, religion, gender, language, property, region or place of birth.
• All should get equal opportunities for development.

(3) Which decision of the Court has resulted in protection of honour and dignity of women?
Answer:

• The apex court has given several judgments which have helped in protection of honour and prestige of women.
• Court gave judgement on Right to alimony as well as Right to equal remuneration.
• Women have an equal share in the property of husband and father. This gave them financial security. Dowry prohibition Act was a measure for women empowerment.
• The Act against sexual harrassment. Domestic Violence Prohibition Act are also very important in the direction of women empowerment.
• All these acts emphasised the need to protect women and protect their self-esteem and dignity rejecting the traditional forms of domination and authoritarianism.

Project
(1) Which information can be secured with the help of the right to information? Find out with the help of your teachers.
(2) Make a list of concessions given by the Government for the students of minority communities?
(3) Visit the official website of the National election commission and collect more information about it.
(4) Take an interview of women representations from local self-governing institutions from your area.

Memory Map

Q. Complete the sentences by choosing the correct option:

1. Right to Information came into force from
(a) 2002
(b) 2004
(c) 2005
(d) 2006
Answer:
(c) 2005

2. The Indian government has been working in accordance with principle of the
(a) Parliament
(b) President
(c) Constitution
(d) Party
Answer:
(c) Constitution

3. Men and women above years of age can vote in India.
(a) 15
(b) 18
(c) 21
(d) 25
Answer:
(b) 18

4. can make amendments to the Constitution.
(a) President
(b) Prime Minister
(c) Council of Ministers
(d) Parliament
Answer:
(d) Parliament

5. got recognition because of 73rd and 74th Amendments to the Constitution.
(a) Parliament
(b) Local self-governing institutions
(c) Legislative council
(d) Cooperative societies
Answer:
(b) Local self- governing institutions

6. ………………….. has made the government more transparent.
(a) Equality
(b) Freedom
(c) Right to Information
(d) Social Justice
Answer:
(c) Right to Information

7. and are two features of good governance.
(a) Popular, populist
(b) Efficient, democratic
(c) Transparent, responsible
(d) Equality, decentralization
Answer:
(c) Transparency, responsible.

Q. State whether the following statements are true or false:

1. Indian democracy is evidently unsuccessful.
Answer:
The above statement is False.

• India has the largest number of voters as compared to any other democratic nation in the world.
• Free and fair elections which are held regularly is the key for successful democracy.
• Recurring elections have helped in understanding the political process. As the voting age was reduced from 21 to 18 years, the political participation has increased.
• Increasing participation of the people in the political process and political contest shows that Indian democracy is successful.

2. There is less friction in all inclusive democracy.
Answer:
The above statement is True.

• To establish social justice and equality is the aim of democracy. .
• If all the sections of society are given equal opportunities without any discrimination then all 8 components come into the main stream.
• In fact, democracy is the process of accommodating different sections of society which ultimately reduces the social conflict.

Q. Explain the following concepts:

1. Decentralisation:
Answer:

• Division of power within, a country is known as Decentralisation.
• Under dictatorship and military rule, the power is centred around one person or a group of individuals.
• But in democracy the power is divided among Centre, State and Local Self-governing institutions. Decentralisation is the core of democracy.
• Decentralisation can stop the misuse of power and facilitate common people to participate in democracy.

2. Provisions regarding Minorities:
Answer:

• Constitution has adopted several measures for the protection of the rights of minorities.
• Several policies have been adopted by the government to provide them the opportunities in education and employment.
• The Constitution has prohibited any form of discrimination on the basis of caste, creed, religion, language and region.
• The Constitution provided rights to the minorities to protect and conserve their language, culture and establish educational institutions

3. Policy of Reservation of Seats:
Answer:

• Some sections of Indian society were denied social justice.
• They were deprived of educational and employment opportunities. It was essential to bring them in the main stream of society.
• The policy was adopted to give reservation to Scheduled Castes and Scheduled Tribes in educational institutions and public employment.
• Seats were also reserved for Other Backward Classes. Reservation policy gave the deprived classes justice and opportunities for development.

Q. Complete the Concept Map:

1. Complete the Concept Map:

Answer:

2. important to understand:

Answer:

3. please understand:

Answer:

Q. Answer the following questions in brief:

1. What are the provisions made in the Directive Principles regarding decentralization?
Answer:
The Directive Principles of the Indian Constitution has made provisions for decentralization of power. It means:

• Indian Constitution has divided the power between the centre, state and local self-governing institutions.
• The guidelines about empowering the local self-governing bodies are given in the Constitution.
• After independence, 73rd and 74th Amendment to the Constitution in 1992 has given constitutional status to the local self-governing bodies.
• Due to this, there is increase in the participation by the people at grass root level. Democracy was put into practice which eventually got strengthened. Decentralisation curbed the misuse of power.

2. What were the measures taken to increase the number of women in politics?
Answer:

• The 73rd and 74th Constitutional Amendment provided reservation of 33% seats for women in local self governing institutions.
• This reservation has been increased to 50% in Maharashtra and many other states.
• One-third seats and the offices (posts) of Sarpanch, Mayor, etc. are reserved for women. Several policies have been adopted to remove illiteracy among women and to make available opportunities for their development.
• A bill is tabled in the house to reserve 50% seats in Legislative Assembly and Parliament.

3. The Judiciary in India has played an important role in strengthening democracy. Explain.
Answer:

• The Judiciary has always taken into consideration the fundamental objectives of the Constitution and also the intention of its framers.
• While interpreting the Constitution, it has taken care that its basic structure is not altered as Constitution is foundation of our democracy.
• The important role played by judiciary is in strengthening and helping democracy to achieve the objectives of social justice and equality.

4. Which particular Laws/Acts created a favourable environment for the protection of freedom of women and secure their development?
Answer:

1. Several policies have been adopted in the post-independence period for empowering women.
2. Provisions were made in the Constitution to provide opportunities for progress.
3. Many laws were passed to empower them. They are:
   • Right to have equal share in the property of father and husband.
   • Dowry Prohibition Act.
   • Act against Sexual Harassment.
   • Domestic Violence Prohibition Act.

Q. Give your opinion:

1. What measures should be adopted to increase the number of women in representative democracy?
Answer:
Several restrictions were imposed in the name of traditions and practices, making’ the workspace of women limited to home.

• To curb injustice the representation of women should increase in all institutions. The 73rd and 74th Amendment reserved 33% of seats for women in local self governing institutions.
• Access to more and more social and political fields should be made available for women. They should be involved in the decision-making process and work for their betterment.
• This would ultimately lead to eliminating injustice done to them and will enhance their self respect and status.

2. Do you agree that Indian democracy has become profound?
Answer:
I entirely agree that Indian democracy has become profound.

• The Indian Constitution has laid down representative structure of democracy.
• The actual practice of the principles of democracy is the essence of representative system.
• People have direct representation in Lok Sabha, Rajya Sabha and Local Self-Government Institutions.
• Free and fair elections are held at regular intervals to elect representatives.
• Citizens cast their votes weighing the public issues and policies related to it. All the above factors show that Indian democracy has become profound.

3. Do you think that citizens in India should 8 have the right to employment? (Discuss – Textbook page 70)
Answer:
I agree that all Indian citizens should get I employment.

• If they are deprived of employment opportunities their families would face hunger and starvation.
• Incident of crime will increase in society.
• Democracy will collapse leading to chaos.
• More and more employment opportunities S should be generated for their progress.

4. According to you, if everyone gets the right to shelter, how will it affect democracy in 8 India?
Answer:

• Food, clothing and shelter are the basic necessities of a man.
• Shelter is not only his necessity but also his right.
• A permanent need is to get settled in life. 8 If a man gets a home, a large part of his struggle 8 in life will come to an end.
• The financial burden will be low and he will x work with honesty and will contribute in nation’s X progress.
• Home for all creates a healthy society. It has an all-round social, economical and psychological effect to strengthen democracy and make it 8 profound.

5. What steps should be taken to stop injustice done to the Backward Classes? OR What efforts should be made to prevent x atrocities?
Answer:
The backward classes have suffered for thousands of years. I feel the following measures x will remove injustice done to the backward classes:

• Atrocities laws should be made stringent.
• Fast courts should be set up to handle such cases.
• Stringent punishment should be given if 8 found guilty.
• Efforts should be made to improve economic 8 status of the backward classes.
• The Government should make efforts to establish social justice and equality. .

6. What efforts should be made to bring in all the features of good governance in democracy?
Answer:
For the successful functioning of democracy, good governance is very essential.

• People should elect good and professional candidates.
• People should keep watch on the work done by them.
• Corrupt candidates should not be elected or re-elected.
• People should respond to various policies which are beneficial for society.
• People should pressurise the government to start various developmental policies for country’s progress.

Q. B Can you tell the reasons for the following changes?

1. Some seats were reserved for women to increase their participation in political process.
Answer:

• Women empowerment movement started after independence.
• All the countries in the world started increasing number of women representatives.
• The 73rd and 74th constitutional amendment reserved 33% seats for women in local self- governing institutions.
• Some seats are kept reserved for women to increase their participation in political process.
• Some seats are kept reserved for weaker sections of the society so that they can get a share in political power.
• The State Election Commission has been established. The 11th and 12th schedule was added to the constitution.

2. Some seats are kept reserved for weaker sections of the society so that they can get a share in political power.
Answer:

• The weaker sections suffered injustice for thousand of years.
• The opportunities of education and employment had been denied to them.
• In order to establish social justice and equality, reservations are now given to the weaker sections.

3. The State Election Commissions were set up.
Answer:

• Elections for the Parliament and State Assemblies are conducted by the National Election Commission.
• It was impossible to put upon the local self government bodies the responsibility of conducting elections. Hence the State Election Commissions were formed.

4. 11th and 12th Schedule was added to the Constitution.
Answer:

• The 11th schedule of Indian Constitution was added in 1992 by the 73rd Constitution Amendment Act. This schedule contains 29 subjects related to panchayat.
• The 74th Amendment to the Constitution added 12th schedule and covered 18 subjects related to the Municipalities.
• ”It gave constitutional status to Municipalities and Panchayats and aimed to strengthen rural and urban governments so that they can function efficiently.

Balbharti Maharashtra State Board Class 10 Science Solutions Part 2 Chapter 5 Towards Green Energy Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 Science Solutions Part 2 Chapter 5 Towards Green Energy

Question 1.
Remake the table taking into account relation between entries in three columns.

I	II	III
Coal	Potential energy	Wind electricity plant
Uranium	Kinetic energy	Hydroelectric plant
Water reservoir	Nuclear energy	Thermal plant
Wind	Thermal energy	Nuclear power plant

Answer:

I	II	III
Coal	Thermal energy	Thermal plant
Uranium	Nuclear energy	Nuclear power plant
Water reservoir	Potential energy	Hydroelectric plant
Wind	Kinetic energy	Wind electricity plant

Question 2.
Which fuel is used in thermal power plant? what are the problems associated with this type of power generation?
Answer:
(1) The fuel used in the thermal power plant is coal. Coal contains chemical energy. Upon burning it releases heat energy. This heat is used for generation of electricity in the thermal power plants.

(2) Problems associated with power 8enerations by thermal power plant:
(a) Air pollution: Due to burning of coal, there is emission of carbon dioxide, carbon monoxide, sulphur dioxide and nitrogen dioxide gases. These are harmful and toxic to health.
(b) Soot particles emitted during combustion can cause severe respiratory problems such as asthma.

Question 3.
Other than thermnl power plant. which power plants use thermal energy for power generation? In what different ways is the thermal energy obtained?
Answer:
(1) The power plant based on natural gas and the nuclear power plants also used thermal energy for the power generation. Apart from these, solar energy is also used to produce heat and thereby create the power.
(2) In nuclear power plant, the energy is released by carrying out fission of nuclei of atoms like Uranium or Plutonium. This energy is used to generate the steam of high temperature and high pressure. The steam rotates the turbine. The kinetic energy in steam drives the turbine and turbine in turn drives the generator.
(3) The combustion of natural gas produces gas, which is used to run the turbine. This gas is under high pressure and high temperature. This is used to produce thermal energy.
(4) In solar thermal power plant, thermal energy is generated with the help of solar radiation. For this reflectors and absorbers are used for concentrating solar radiation and converting it into thermal energy.

Question 4.
Which type/types of power generation involve maximum number of steps of energy conversion? In which power generation is the number minimum?
Answer:
The steps of energy conversion are maximum in the thermal power generation. They are minimum in wind energy generation.

Question 5.

a. Maximum energy generation in India is done using …………… energy.
Answer:
Maximum energy generation in India is done using thermal energy.

b. ………. energy is a renewable source of energy.
Answer:
wind energy is a renewable source of energy.

c.Solar energy can be called ……. energy.
Answer:
Solar energy can be called clean energy.

d. ……. energy of wind is used in wind mills.
Answer:
kinetic energy of wind is used in wind mills.

e. ………. energy of water in darns is used for generation of electricity.
Answer:
Potential energy of water in darns is used for generation of electricity.

Question 6.
Explain the difference.
a. Conventional and Non-conventional Sources of energy.
Answer:
Conventional Sources of energy:

1. Conventional sources of energy are largely polluting, they release lot of carbon through its emissions.
2. Conventional sources of energy are not eco¬friendly.
3. The fuels produced from the conventional sources of energy are comparatively costlier.
4. Conventional energy power plants require less area and its management cost is also less.
5. Conventional source of energy are non-renewable.
6. Conventional sources of energy are in the form of limited reserves. After few years they will be completely over. e.g. Fossil fuels, coal, crude oil, diesel, petrol, natural gas, etc.

Non-conventional Sources of energy:

1. Non-conventional sources of energy are not polluting, They do not release carbon or other toxic gases.
2. Non-conventional sources of energy are eco-friendly.
3. The energy obtained from the non-conventional sources of energy are comparatively cheaper.
4. Non-conventional energy power plants require more area and its management cost is also more.
5. Non-conventional source of energy are renewable.
6. Non-conventional energy sources qre in abundance on the earth. They are persistent and sustainable. Thus they will not get over. e.g. Solar energy, wind energy, etc.

b. Thermal electricity generation and Solar thermal electricity generation.
Answer:
Thermal electricity generation:

1. After burning the coal, the heat that is produced is used in the generation of thermal electricity.
2. For producing heat, the coal is burnt in the boilers.
3. The combustion of coal produces heat. This heat converts water into steam, which is under very high temperature and pressure. By its force the turbines move. The turbines in turn are connected to generator which rotates and produces energy.
4. Thermal energy is polluting and not eco-friendly.
5. The fuel here is coal, its reserves are limited.

Solar thermal electricity generation:

1. Solar radiations are used in solar thermal electricity production.
2. For production of heat, many reflectors are used which reflect the radiations of the sun into the absorbent.
3. Sun’s heat convert the water into steam that rotates the turbine. The turbines then rotate the generators. This generates the electricity.
4. Solar energy is not polluting, it is eco-friendly.
5. The solar radiations are in abundance and are sustainable and persistent.

Question 7.
What is meant by green energy? Which energy sources can be called green energy sources and why? Give examples.
Answer:
(1) Green energy means eco-friendly form of energy which does not cause environmental problems and are non-exhaustible, perpetual and sustainable.
(2) These sources of energy do not produce toxic gases or other pollutants, therefore they are safe.
(3) Examples of green energy: (i) Hydroelectric energy (ii) Wind energy (iii) Solar energy (iv) Energy obtained biofuels.

Question 8.
Explain the following sentences.
a. Energy obtained from fossil fuels is not green energy.
Answer:
Fossil fuels like petrol, diesel or natural gas when burnt, emit toxic gases and soot particles. Thus, fossil fuels cause air pollution. Burning of fossil fuels cause increased levels of carbon dioxide, carbon monoxide and nitrogen dioxide. The increased carbon dioxide emission results in global warming. Nitrogen oxide results later in acid-rain. Soot particles generated through burning of fuels cause respiratory problems iike asthma.

Moreover, the fossil fuels are non-renewable and exhaustible fuels. They have to be explored from the
deeper layers of the earth causing lots of environmental problems. Green energy is sustainable, renewable and abundant. It never creates any environmental problems and is non-polluting. Thus, energy obtained from fossil fuels is not at all a green energy.

b. Saving energy is the need of the hour.
Answer:
In modern civilization, continuous energy supply is needed for the technology and development. The energy has become a basic need for man. Most of the energy used in India is obtained from thermal power plant. For this energy generation, various fuels are used. The coal and fossil fuels are limited. Due to over-exploitation, these reserves are getting fast depleted. Use of fossil fuels is also resulting in pollution and climate change.

Nuclear energy can be very hazardous. Lot of research is being done in the field of green energy, but the tremendous human population always is in need of more energy. Therefore, each and every person should save the energy, as saving energy is the need of the hour.

Question 9.
Answer the following questions.
a. How can we get the required amount of energy by connecting solar panels?
Answer:

• The photovoltaic solar cells can be connected in a series or in parallel to make a solar panel.
• When solar cells are connected in a series, the potential difference of individual cells are added in the combination, however the currents from individual cells are not added.
• When solar cells are connected in parallel, the currents of the individual cells are added in the combination, but the potential differences from individual cells are not added.
• Through such connections the required potential difference and current can be obtained.
• Many such solar panels are connected in series and in parallel to generate required current and potential difference.
• When many solar panels connected in series they form a solar string. Many solar strings connected in parallel make a solar array. In such manner we can get the required amount of energy by connecting solar panels.

b. What are the advantages and limitations of solar energy?
Answer:
I. Advantages:

• While generating the power through solar radiations, no fuel is burnt.
• Solar energy generation thus does not create any type of pollution. The technology can be completely utilized in regions with abundant sunlight.
• Solar energy is eco-friendly, green energy.

II. Limitations:

• Sunlight is available only during day time. Thus solar cells can generate power only during day.
• In rainy season and in cloudy conditions, solar power generation suffers.
• The power present in the solar cells is DC while most of the domestic equipments work on AC.

Question 10.
Explain with diagram step-by-step energy conversion in
a. Thermal power plant.
Answer:

In thermal power plant the turbines are rotated using steam. Here the coal is burnt. The heat energy liberated from this burning is used to heat the water in the boiler. This water produces steam of very high temperature and pressure. The kinetic energy in the steam rotates the turbines. The rotation of turbines produces its own mechanical kinetic energy.

The generators connected to turbines produce electrical energy. The steam is condensed in a condenser and converted back into water. In this way in thermal power plant, thermal energy to kinetic energy, kinetic energy into mechanical energy and mechanical energy to electrical energy, are the conversions that take place.

b. Nuclear power plant.
Answer:

In nuclear power plant, the energy is releasdd by fission of nuclei of atbms like Uranium or Plutonium. This energy is used to generate the steam or high temperature ind high pressure. The kinetic energy in the steam rotates the turbine. The turbine in turn drives the generator to produce electricity.

c. Solar thermal power plant.
Answer:

Solar radiation is used to produce thermal energy. For this purpose, many reflectors are used which concentrate the solar radiation on absorbers. The heat energy created due to solar radiations is used to make steam. The steam possesses kinetic energy. This kinetic energy drives turbine and generator. The electrical energy is thus created from this kinetic energy.

d. Hydroelectric power plant:
Answer:

In hydroelectric plant the water stored in the reservoir is used as a source or potential energy. This water is made to fall at a great speed and hence there is production of kinetic energy in flowing water. This fast flowing water ralling down from the reservoir is brought to the turbine at the lower levels. The kinetic energy of the flowing water in turn drives the turbine, The turbine then drives the generator and electrical energy is produced.

Question 11.
Give scientific reasons:
a. The construction of turbine is different for different types of power plants.
Answer:

• Generators work on the principles of electromagnetic induction.
• For this the generator must be rotated.
• For this purpose, there is a turbine for each generator.
• This rotation needs energy. The turbines are different according to the type of energy source that is used for its rotation.
• Therefore, the construction of turbine is different for each power plant.

b. It is absolutely necessary to control the fission reaction in nuclear power plants.
Answer:

• Nuclear fission reaction is a type of chain reaction.
• In nuclear power plants these reactions are closely controlled.
• If these reactions are not managed properly, there can be more production of neutrons in an uncontrolled way.
• Each released neutron further causes fission of 3 Uranium (U-235) atoms, such uncontrolled reactions can cause hazardous accidents, hence ft is absolutely necessary to control the fission reaction in nuclear power plants.

c. Hydroelectric energy, solar energy and wind energy are called renewable energies. (July ’19, Board’s Model Activity Sheet)
Answer:

• Hydroelectric energy, solar energy and wind energy is obtained respectively from flowing water, solar radiations and flowing wind.
• These sources, i.e. water reservoirs, sun and the wind are inexhaustible and sustainable. They will not be finished.
• On the contrary, the conventional energy sources such as coal and fossil fuels have limited reserves.
• They cannot be renewed and may get exhausted in future. Hydroelectric energy, solar energy and wind energy can be replenished and hence they are called renewable.

d. It is possible to produce energy from mW to MW using solar photovoltaic cells.
Answer:

1. Solar panels can be constructed by connecting solar photovoltaic cells in either series or in parallels.
2. The combinations are done in such a way that it can give the desired potential difference and the current.
3. Solar strings are then made by joining solar panels in a series.
4. When solar strings are joined in parallel; they form solar array.
5. Therefore, by proper combinations, it becomes possible to produce energy from mW to MW using solar photovoltaic cells.

Question 12.
Draw a Schematic diagram of Solar thermal electric energy generation.
Answer:

Question 13.
Give your opinion about whether hydroelectric plants are environment-friendly or not?
Answer:

• Hydroelectric plants are advantageous in some respect while in some aspects it does create problems.
• Hydroelectric power generation does not need burning of fuels. Therefore, there is no problem regarding combustion of fuels and release of toxic pollutants.
• Electricity can be obtained as and when required if there is enough water in the reservoir.
• Water is replenished every time when there is sufficient rainfall.
• All the above facts give an impression that hydroelectric power generation is eco-friendly but it is not.
• Many villages and settlements are submerged when a dam and reservoir is constructed. The displaced people are given re-settlement, but it causes lot of emotional trauma to people.
• Biodiversity is affected as forest lands is submerged. The river flow is obstructed by the dam which affects the aquatic organisms residing in such water.
• Due to excessive pressure of water on land, it is said that the region gets prone to earthquakes.

Question 14.
Draw a neat labelled diagrams.
a. Energy transformation in solar thermal electric energy generation.
Answer:

b. One solar panel produces a potential difference of 18 V and current of 3A. Describe how you can obtain a potential difference of 72 Volts and current of 9 A with a solar array using solar panels. You can use sign of a battery for a solar panel.
Answer:
Given Potential difference is 18 V and current is 3A. The requirement is potential difference of 72 V and current is 9A Voltage remains the same if connected in parallel and gets added it they are connected in series. Current remains the same if connected in series but adds if connected in parallel.

Question 15.
Write a short note on Electrical energy generation and environment.
Answer:
The energy obtained through the fossil fuels as well as nuclear energy can cause degradation of the environment. If such energy sources are used, they can cause harm to the environment.

(1) The burning of fossil fuels cause air pollution. The incomplete combustion of fossil fuels cause release of carbon monoxide. Some more toxic gases and soot particles cause various respiratory diseases. The carbon dioxide produced is creating global warming and climate change. The nitrogen dioxide released through burning is responsible for acid rains.

(2) Fossil fuels are limited. They are getting fast depleted. It has taken millions of years for the fossil fuels to form. The exploration of such fuels also cause environmental degradation and marine pollution too.

(3) In production of nuclear energy, there is a great risk of accidents. The safe disposal of nuclear waste is also a problem.

(4) Hydroelectric power from water reservoirs, wind power from wind, solar energy from sun and electricity from biofuels are eco-friendly alternatives.

Projects: (Do it your self)

Project 1.
Gather information about solar light, solar water heating system and solar cooker.

Project2.
Gather information about a power plant near your locality by visiting the plant.

Can you recall? (Text Book Page No. 47)

Question 1.
What is Energy?
Answer:
The capacity to do work is called energy.

Question 2.
What are different types of Energy?
Answer:
Potential energy and kinetic energy are the two types of energy.

Question 3.
What are different forms of Energy?
Answer:
Heat, light, electric energy, solar energy, chemical energy, nuclear energy, mechanical energy, etc. are different forms of energy.

Use your brain power! (Text Book Page No. 54)

Question 1.
The schematic of hydroelectric plant is shown in Figure 5.17 on text book page no. 54. Water from about middle of the total height of the dam is taken to the turbine, as shown by point B in the diagram.

(i) With reference to point B, potential energy of how much water reservoir in the dam will be converted into kinetic energy?
Answer:
When the sluice gate at point B is opened, the water from reservoir will start flowing. The potential energy of the stored water will become kinetic energy of the quantity of water that is let out through the sluice gates.

(ii) What will be the effect on electricity generation, if the channel taking water to turbine starts at point A?
Answer:
If the channel taking water to turbine starts at point A, then the water will flow with a greater speed. Since point A is at hSight, water will acquire speed. This will result into more efficient rotation of the blades of turbine. The electricity generation will thus become more efficient.

(iii) What will be the effect on electricity generation, if the channel taking water to turbine starts at point C?
Answer:
If the channel taking water to turbine starts at point C, it will affect the electricity generation adversely. Point C is on the lower height as compared to the channel that carries water to the turbine. The flow of the water thus will be affected resulting into improper rotation of blades of turbine. This will certainly affect the electricity generation.

Choose the correct alternative and write its alphabet against the sub-question number:

Question 1.
Large ……….. are used in commercial power generation plants.
(a) machines
(b) generators
(c) turbines
(d) pannels
Answer:
(b) generators

Question 2.
The principle of electromagnetic ……….. was invented by Michael Faraday.
(a) induction
(b) attraction
(c) repulsion
(d) expulsion
Answer:
(a) induction

Question 3.
………… is used to rotate the magnet in the generator.
(a) fan
(b) Generator
(c) Turbine
(d) Panels
Answer:
(c) Turbine

Question 4.
In thermal power plants, the ………… energy in the coal is converted into electrical energy through several steps.
(a) physical
(b) biological
(c) kinetic
(d) chemical
Answer:
(d) chemical

Question 5.
At ………. in Andhra Pradesh power plant based on natural gas has been installed.
(a) Hyderabad
(b) Vishakhapatnam
(c) Samaralkota
(d) Kakinada
Answer:
(c) Samaralkota

Question 6.
Burning of coal may cause serious health problems related to ……….. system.
(a) digestive
(b) respiratory
(c) nervous
(d) excretory
Answer:
(b) respiratory

Question 7.
Incomplete combustion of fuels leads to formation of ……….
(a) carbon dioxide
(b) carbon monoxide
(c) carbon tetrachloride
(d) All the above
Answer:
(b) carbon monoxide

Question 8.
Solar cells are made of a special type of material called semiconductor such as ………..
(a) silicon
(b) uranium
(c) borosilicate
(d) hydrogen
Answer:
(a) silicon

Question 9.
……….. of the following is eco-friendly energy resource. (Board’s Model Activity Sheet)
(a) Coal
(b) Hydroelectric power
(c) Fossil fuel
(d) Atomic energy
Answer:
(b) Hydroelectric power

Question 10.
Which is the most abundant and renewable energy?
(a) Thermal power
(b) Solar energy
(c) Fossil fuels
(d) Atomic power
Answer:
(b) Solar energy

Question 11.
What are the two technologies for harnessing solar energy?
(a) Solar photovoltaics and solar thermal
(b) Solar cooker and solar lamp
(c) Heat capturing and Heat conversation
(d) Active and passive technologies
Answer:
(a) Solar photovoltaics and solar thermal

Question 12.
Which of the following is used in solar cooker to harvest the solar energy?
(a) Solar panels
(b) Silicon cell
(c) Mirrors
(d) Glass lid
Answer:
(c) Mirrors

Question 13.
Which of the following is not the source of green energy?
(a) Wind
(b) Natural gas
(c) Sunlight
(d) Fossil fuel
Answer:
(d) Fossil fuel

Question 14.
The solar lamp uses the energy.
(a) Heat
(b) Wind
(c) Light
(d) Sound
Answer:
(c) Light

State whether the following statements are true or false with proper explanation:

Question 1.
In thermal power plants, the turbines work on solar energy.
Answer:
False. (In thermal power plant, the turbines work on steam. The turbines working on solar energy are not used.)

Question 2.
How to dispose the nuclear waste safely is a big challenge before the scientists.
Answer:
True. (Nuclear waste disposal is the greatest problem. It produces highly toxic effects in any ecosystem. Therefore, disposing such radioactive substances becomes a major challenge.)

Question 3.
The efficiency of power generation using coal plant is higher than that of power generation plant based on natural gas.
Answer:
False. (The efficiency of power generation using natural gas plant is higher than that of power generation plant based on coal.)

Question 4.
Energy obtained from nuclear fission is eco-friendly.
Answer:
False. (Energy obtained from nuclear fission is not eco-friendly, because if accidents happen it leads to hazardous accidents.)

Question 5.
In hydroelectric power plant, the kinetic energy in water stored in dam is converted into potential energy of water.
Answer:
False. (In hydroelectric power plant, the potential energy in water stored in dam is converted into kinetic energy of water. The forceful downpour of flowing water causes this kinetic energy.)

Question 6.
The turbine is connected to electric generator, therefore the magnet rotates and electric energy is thus produced.
Answer:
True. (The rotating wheels of turbine cause mechanical energy. This energy helps to produce electrical energy.)

Question 7.
Use of energy is unavoidable in our daily life, but we must use it carefully and only in the required amount.
Answer:
True. (The energy Supply for everyday use results into lot of pollution. This causes harmful effects in the surrounding environment. Therefore, energy should be used in minimal amount and with great care.)

Question 8.
The machine which converts the potential energy of wind to electrical energy is called wind-turbine.
Answer:
False. (When wind blows, the kinetic energy is present in it. This kinetic energy is converted into electricity. The flowing wind never has a potential energy.)

Question 9.
The potential difference available from a solar cell is independent of its area.
Answer:
True. (The potential difference available from a solar cell is independent of its area. However, it is dependent on the way in which solar cells are connected.)

Question 10.
The power available from the solar cells is AC.
Answer:
False. (The power available from solar cells is always DC while the domestic appliances that we use work on AC.)

Match the columns:

Question 1.

Column I	Column II
(1) Polluting energy	(a) Soot particles
(2) Eco-friendly energy	(b) Thermal energy
	(c) Nuclear energy
	(d) Wind energy

Answer:
(1) Polluting energy – Thermal energy
(2) Eco-friendly energy – Wind energy

Question 2.

Column I	Column II
(1) Pollutants	(a) Soot particles
(2) Hazard to ecosystem	(b) Thermal energy
	(c) Nuclear energy
	(d) Wind energy

Answer:
(1) Pollutants – Soot particles
(2) Hazard to ecosystem – Nuclear energy

Question 3.

Type of energy	Problem
(1) Nuclear energy	(a) Rehabilitation of displaced people
(2) Natural gas	(b) Rainy season and darkness
	(c) Limited reserves
	(d) Disposal of wastes

Answer:
(1) Nuclear energy – Disposal of wastes
(2) Natural gas – Limited reserves

Question 4.

Type of energy	Problem
(1) Solar energy	(a) Rehabilitation of displaced people
(2) Hydroelectric  energy	(b) Rainy season and darkness
	(c) Limited reserves
	(d) Disposal of wastes

Answer:
(1) Solar energy – Rainy season and darkness
(2) Hydroelectric energy – Rehabilitation of displaced people

Find the odd one out:

Question 1.
Kudankulam, Tarapur, Ravatabhata, Anjanvel
Answer:
Anjanvel. (All others are places having nuclear power plants.)

Question 2.
Samaralkota, Kudankulam, Bavanaa, Kondapalli
Answer:
Kudankulam. (All others are places having power plants based on natural gas.)

Question 3.
Tehari, Koyana, Srishailam, Tarapur
Answer:
Tarapur. (All others are places having hydroelectric projects.)

Question 4.
Edible oil, crude oil, LPG, CNG
Answer:
Edible oil. (All others are fossil fuels.)

Question 5.
Hydroelectric energy, Solar energy, Nuclear energy, Wind energy
Answer:
Nuclear energy. (All others are eco-friendly green energy types.)

Explain with diagram step-by-step energy conversion in:

Question 1.
Power plant based on natural gas.
Answer:

In a power plant based on natural gas, there are three main sections of the plant. There is combustion chamber with compressor in which the steam under pressure is introduced. The natural gas burns in the presence of air in this combustion chamber. This results in a production of a gas which is at very high temperature and pressure. This generated gas from the chamber runs the turbine. The kinetic energy of the turbine drives the generator. The generator produces electrical energy.

Question 2.
Power plant based on wind energy.
Answer:

Wind energy is used for moving turbines. The wind with specific speed is used to rotate the large fins of wind turbine. The kinetic energy in these fins is transferred to generator which then produces electrical energy.

Explain the following questions in detail:

Question 1.
What are the advantages of hydroelectric power generation? (March 2019)
Answer:

1. Hydroelectric energy does not cause pollution.
2. Generation of hydroelectric energy does not involve burning of fossil fuel.
3. If sufficient water storage is available then electricity generation can be done as per requirement.
4. Rainwater can replenish the water storage and power generation can thus be done uninterrupted.

Question 2.
How is nuclear fission reaction carried out in nuclear power plants?
Answer:

• In nuclear power plants neutrons are bombarded on atom of Uranium – 235.
• This causes conversion of Uranium – 235 into its isotope U – 236.
• U-236 is very unstable and thus forms atoms of Barium and Krypton by nuclear fission. This forms 3 neutrons and 200 MeV energy.
• In a similar way three more Uranium – 235 atoms are subjected to nuclear fission which then releases energy.
• The neutrons released are again used for further nuclear fission reactions. In this way nuclear fission reactions are carried out in controlled manner in nuclear power plants.

Question 3.
Draw schematic of power plant based on natural gas and answer the following questions: (July 2019)
(a) At which place natural gas power plant is situated in Maharashtra?
(b) How is pollution reduced in natural gas based power plant?
(c) Give two examples of eco-friendly electricity process.
Answer:
(a) Natural gas power plant is situated at Anjanvel in Maharashtra.
(b) Natural gas does not contain sulfur. Burning of such natural gas does not produce pollution.
(c) Solar energy and wind energy are two examples of eco-friendly energy.

Complete the paragraph by choosing the appropriate words given in the brackets:

Question 1.
(marginal, array, cell, panel, string, current, power station, potential difference).
Many solar panels are connected in series and in parallel to generate required ………… and ……… Solar …………. is the basic unit in solar electric plant. Many solar cells come together to form a solar …………… Many solar panels connected in series form a solar ………., and many solar strings connected in parallel form a solar …………. As we can obtain as much electrical power as needed, they are used in applications which need ……….. power (e.g. calculators that run on solar energy) to ……….. of MW capacity.
Answer:
Many solar panels are connected in series and in parallel to generate required current and potential difference. Solar cell is the basic unit in solar electric plant. Many solar cells come together to form a solar panel. Many solar panels connected in series form a solar string, and many solar strings connected in parallel form a solar array. As we can obtain as much electrical power as needed, they are used in applications which need marginal power (e.g. calculators that run on solar energy) to power station of MW capacity.

Read the paragraph and answer the questions given below:

1. Renewable energy is, energy produced from sources that do not deplete or can be replenished within a human’s life time. The most common examples include wind, solar, geothermal, biorhass, and hydroelectric power. This is in contrast to non-renewable sources such as fossil fuels. Most renewable energy is derived directly or indirectly from the sun. Sunlight can be captured directly using solar technologies. The sun’s heat drives winds, whose energy is captured with turbines. Plants also rely on the sun to grow and their stored energy can be utilized for bioenergy. Not all renewable energy sources rely on the sun. For example, geothermal energy utilizes the Earth’s internal heat, tidal energy relies on the gravitational pull of the moon, and hydroelectric power relies on the flow of water.

Questions and Answers :
Question1.
What is renewable energy?
Answer:
Renewable energy is energy that is produced from sources which will not get exhausted within a human’s life time.

Question 2.
Give the examples of renewable energy.
Answer:
Wind, solar, geothermal, biomass and hydroelectric power are some examples of renewable energy.

Question 3.
Why will energy from fossil fuel be over soon?
Answer:
Fossil fuels are exhaustible in their amount. We have been using these extensively in the past 100 years and hence it may get over soon. It is a non-renewable resource.

Question 4.
Name the renewable sources of energy which are not dependent on sun. What are they dependent upon?
Answer:
Geothermal energy, tidal energy and hydroelectric power are renewable energy resources which are not dependent on sun. Geothermal energy utilizes the Earth’s internal heat, tidal energy relies on the gravitational pull of the moon, and hydropower relies on the flow of water.

Question 5.
Which type of energy do we mostly use in India?
Answer:
The most used energy resource is coal, i.e. fossil fuel based energy followed by hydroelectric energy.

2. Read the information given below and solve the questions based on it.
Electric energy is produced in various ways like hydroelectric, wind power, solar energy, bio-fuel, etc. These energy sources are inexhaustible, sustainable. Besides, it does not cause any environmental problem.

Questions and Answers:
Question 1.
Above information is about which type of energy?
Answer:
From the above information, we understand about green energy.

Question 2.
Whether the fossil fuel is an example of this energy?
Answer:
Fossil fuels are not green energy.

Question3.
Draw the flow chart of production of electric energy.
Answer:

Diagram based questions:

Question 1.
Observe the connections of cells shown in the following images.


(i) Which connection will give maximum potential difference?
Answer:
The solar cells shown in the diagram 5.19 (a) are connected in series. This gives maximum potential difference.

(ii) Give one advantage and one disadvantage of this energy.
Answer:
Advantage of Solar energy: Solar energy is eco-friendly which does not create pollution. It is boundless source.
Disadvantage of solar energy: Solar energy is available only when sun is in the sky. Therefore, it has to be stored in batteries.

Question 2.
Answer the following questions:
(a) Write the name of the device shown in the above diagram.
Answer:
Steam turbine is the device shown in the above diagram.

(b) Write briefly the work of this device.
Answer:
Turbine is a device with the blades. When the flow of liquid or gases is directed on the blades of the turbine, they rotate. The rotation produces kinetic energy. This turbine is then used to rotate the magnet in the electric generator. For this purpose, turbines are connected with the generators. The magnets rotate and produce electric energy by electromagnetic induction. The turbines working on steam are used in large commercial power generation plants.

Question 3.
Label the given diagram of Electromagnetic induction.
Answer:

Question 4.
Answer the questions with the help of picture.

(a) Which type of energy is produced?
(b) This power plant is based on which energy source.
(c) Is this power plant eco-friendly? How?
Answer:
(a) In the picture, it is shown that using wind energy electricity is produced.
(b) The power plant shown here is based on kinetic energy of wind which is converted to electric energy by utilizing kinetic energy from rotating turbines.
(c) This power plant is eco-friendly because it does not cause pollution. Wind energy is green energy which is non-exhaustible and perpetual.

Question 5.
Observe the figure and answer the questions given below.

Answer:
(a) Name the reaction.
Answer:
The reaction shown in nuclear fission or chain reaction.

(b) Where is this reaction used?
Answer:
This reaction is used in nuclear power plants where electricity is generated.

(c) Which element is used in it?
Answer:
Uranium-235 is used in the nuclear fission reactions.

(OR)

Identify the process shown in figure and name it. (March 2019)
Answer:
The above figure shows nuclear fission chain reaction of Uranium – 236.

Question 6.
Observe the diagram and answer the questions : (March 2019)

(a) Which energy is generated from the power plant?
Answer:
The diagram shows electricity generated from natural gas.

(b) State its source.
Answer:
The energy is generated from natural gas.

(c) Which is more eco-friendly – Power generation from coal or Power generation from natural gas? Why?
Answer:
Power generation from natural gas is more eco-friendly. Natural gas does not contain sulfur and hence its burning does not cause major pollution by forming sulphur dioxide. The efficiency of power generation by natural gas is also high.

Question 7.
Write the names of apparatus that is used in thermal power plant.
Answer:

Question 8.
Label correctly the diagram of Nuclear power plant.
Answer:

Question 9.
Label correctly the diagram of power plant baded on natural gas.
Answer:

Question 10.
Label correctly the structures seen in Windmill.
Answer:

Question 11.
Sketch two ways in which solar cells can be connected. Also draw the diagrams to show the arrangement of solar cells to form solar? panel and solar array.
a. Solar cells in series.
Answer:

(b) Solar cells in parallel.
Answer:

(c) Solar panel.
Answer:

(d) Solar array.
Answer:

Question 12.
Observe the figure given below and answer the given questions:

(a) Identify the type of energy generation process shown in this picture.
(b) Name any four equipments which use this type of energy. (Board’s Model Activity Sheet)
Answer:
(a) In this figure solar energy is converted into electrical energy. Solar energy is also called clean energy.
(b) Solar energy is used in following equipment:

• Solar cooker
• Solar heater
• Calculator
• Solar Photovoltaic cell.

Activity based questions.

Question 1.
Make a table: (Text Book Page No. 47)
Make a table based on forms of energy and corresponding devices.
Answer:

Forms of energy	Devices based on this type of energy
(1) Electric	Electric iron, Geyser, Heater, Oven, Refrigerator, Fans, Lights, Elevator.
(2) Mechanical	Sewing machine, Car, Bicycle, Different machines.
(3) Thermal	Chulha, Furnace, Steam engine
(4) Solar	Solar cooker, Solar heater.

Question 2.
Let’s Think: (Text Book Page No. 52)
Which electricity generation process is eco-friendly and which not?
Answer:
Electricity generated through solar energy and wind energy are truly eco-friendly. Though it is said that hydroelectricity is non-polluting and eco-friendly, it is not true. Hydroelectric project cause destruction of biodiversity and displacement of the local people. Thermal energy, nuclear energy and energy obtained through natural gas are not at all eco-friendly.

Question 3.
Find out: (Text Book Page No. 55)
What is lake tapping? Why it takes place?
Answer:
A lake tap involves excavating a tunnel at the bottom of the lake. Dynamites are planted therein and blasted carefully. The water flows with greater force through the tunnel after such blasting is done. This increased flow of water is then driven to the hydroelectric power generation plant for increased electricity production. This technique is done to establish waterways for hydropower, for making drinking water available, for irrigation water purposes and also for the landing of oil and gas pipes from offshore fields.

Question 4.
Get information: (Text Book Page No. 56)
Get information about major wind-power stations in India and their capacity. Make a table of their location, state and their power generation capacity in MW.
Answer:

Location	State	Power generation capacity in MW
Muppandal, Kanyakumari	Tamil Nadu	7,684.31
Dhule, Satara, Sangli, Dhalgaon	Maharashtra	4,664.08
Bhuj	Gujarat	4,227.31
Dangiri Wind Farm Jaisalmer Wind Park	Rajasthan	4,123.35
Jogmatti BSES	Karnataka	3,082.45
Bhopal at Nagda Hills near Dewas	Madhya Pradesh	2,288.60
Tirumala hills	Andhra Pradesh	1,866.35
	Telangana	98.70
Kanjikode in Palakkad	Kerala	43.50
	Others	4.30
	Total	28, 082.95

Question 5.
Find out: (Text Book Page No. 58)
Gather information about major solar photovoltaic power generating plants and their capacity in India.
Answer:
List of solar power stations:

Project:

Project 1.
Let’s Discuss: (Text Book Page No. 47)
Make a list of the work that we do in our day-to-day life using energy. Which forms of energy do we use to do this work? Discuss with your friends.

Project 2.
Compare: (Text Book Page No. 51)
Observe the schematic of thermal power plant and the nuclear power plant. Discuss what are the similarities and differences between the two.

Project 3.
Use of ICT: (Text Book Page No. 49)
Prepare a presentation about thermal power plant using computerized presentation, animation, video, pictures, etc. Send it to others and upload on YouTube.

Project 4.
Internet is my friend: (Text Book Page No. 51)
Complete the following table for some important nuclear power plants in India.

Balbharti Maharashtra State Board Class 10 History Solutions Chapter 3 Applied History Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 History Solutions Chapter 3 Applied History

Question 1.
(a) Choose the correct option from the given options and complete the statement.
(1) The earliest museum in the world was discovered in the excavations at the city of ……………..………. .
(a) Delhi
(b) Harappa
(c) Ur
(d) Kolkata
Answer:
(c) Ur

(2) The National Archives of India is in ……………..………. .
(a) New Delhi
(b) Kolkata
(c) Mumbai
(d) Chennai
Answer:
(a) New Delhi

(b) Identify and write the wrong pair in the following set.
(1) Kootiyattam- Sanskrit theatre, Kerala
(2) Ramman- Dance form in West Bengal
(3) Ramlila- Traditional Performance of the Ramayana in Uttar Pradesh
(4) Kalbelia- Folk songs and dances of Rajasthan.
Answer:
(2) Wrong pair: Ramman – Dance form in West Bengal

Question 2.
Explain the following concepts :
(1) Applied History
Answer:

•  When one subject is applied to different fields and conclusions are derived, it is known as application of that subject.
• When objectives of History are applied to other subjects; new conclusions are obtained.
• This is known as ‘Applied History’. It is also known as Public History.
• We get insights of the events that took place in the past through history.
• Applied History is concerned with application of knowledge of history to provide guidance in finding solutions.
• Contemporary social issues and include them in social planning.
• Thus Applied History’ is a field of study concerned with the application of history for the benefit of people in contemporary and future times.

(2) Archives
Answer:

•  A place where historical documents are preserved is called an ‘Archive’.
• Many old documents, official records, old films, records of treaties are kept at this place.
• We get references of original documents because of Archives.
• A study of historical events of a particular period is possible.
• We come to know about language, script used in a particular period/era.
• The National Archives of India is in Delhi. It is the largest Archive in Asia.
• Every state in India maintains its archives independently.

Question 3.
Complete the following concept chart.

Answer:

Question 4.
Explain the following statements with reasons.
(1) It is essential to study the history of technology.
Answer:

• Man acquired different skills at various stages in his evolution process.
• From mxking stone tools to developing new techniques of agriculture production, he learnt many skills and entered in the age of science.
• Agricultural production, commodity production, architecture, engineering, etc.
• underwent several changes. Production increased manifold bcause of technology.
• Hence, it is necessary to know the history of technology in order to understand the development in mechanisation and mutual dependence between science and technology.

(2) The list of world Heritage Sites is announced by UNESCO.
Answer:

• Cultural heritage is a form of human creation. It is a cultural treasure that has been inherited from our ancestors.
• We feel connected to it and hence preserve and conserve it.
• This heritage is our asset that binds us to our past and hence we should preserve it for the benefit of future generations.
• In order to save this heritage, UNESCO has announced some directives.
• On the basis of those directives, list of sites, and traditions are declared as ‘World Heritage’.
• It has helped us in promoting these sites as tourist places.

Question 5.
Write elaborate answers
(1) How is the method of history useful in the research of
(a) Science
(b) Arts
(c) Management Studies
Answer:
Each field has its own history of building’ knowledge. The direction of development in every field is dependent on the stcrte of available knowledge in that field. The method of history has proved valuable in the research of various fields.

(a) Science: Scientific discoveries /invenfions take place because of humdn efforts to satisfy needs and curiosity. These efforts are based on scientific knowledge that already existed. Knowledge of the history of science helps in understanding the reasons, chronology and factors that facilitated a scientific invention/discovery. Knowledge of history of science helps in every field.

(b) Art: Development of any style of art lies in their expression through intellectual, emotional and cultural traditions. While studying any art form we have to understand the history of its traditions, the key to the expressions in it, and emotional temperament of the artist. Prevalent art style in the given period can be understood with the help of cultural history.

(c) Management Studies: All components like means of production, human resources, processes of production, the chain of market and sales, etc. are interrelated and require management.

Different social and economic institutions are involved in these industrial and commercial processes. Knowledge of similar functional systems of the past is essential to bring about changes, improvements and make the management smooth and efficient. It becomes necessary to know its history.

(2) How can we correlate applied history with our present?
Answer:
History gives us knowledge about the events that happened in past. Applied history helps us in understanding how the knowledge can be put to use for our benefit as well as for the benefit of future generations. Applied history is correlated with our present in the following ways:

(1) Knowledge of our past helps us in deciding our course of action in present. The.heritage of our ancestors exists in tangible and intangible- form. We have the curiosity to know more about our part because they represent the creative thoughts and traditions of that period.

(2) With the help of applied history we can not only come to know about the heritage but also conserve and preserve it.

(3) We can be better equipped to face social challenges in the present because the knowledge of history can provide guidance in finding solutions to contemporary social issues and incorporate them in the ’social planning.

(4) The direction of future development is S decided when we rightly analyse our present with our knowledge of the past acquired through applied history.

(3) Suggest at least 10 solutions for the preservation of the sources of history.
Answer:
There are three types of sources which are used to study history. They are written, oral and material sources. These sources are preserved in different ways. According to me, the following measures should be taken to preserve the sources:

1. A regular repair and maintenance work of forts, memorials and palaces should be carried out. Timely action should be taken to avoid vandalisation of historic and public places.
2. Historical coins, weapons should be handled with precaution and utmost care. They should be kept in a safe place to avoid the possibility of theft.
3. Social awareness regarding the conservation and preservation of our cultural and natural heritage should be created. People will develop affinity towards the heritage and feel connected.
4. Variations in environment and climatic conditions pose a threat to monumental structures. Humidity, dampness, moulds and pollution cause irrevocable damage to manuscripts, rare artefacts, statues, coins, etc.
5. To protect them, special arrangements have to be made like rooms with controlled temperature or sanitising and detoxing the rooms.
6. Oral literature like owis, folk songs should be compiled and written down.
7. Public training programmes should be conducted for understanding the importance of history.
8. Experts from different fields should be involved in preservation and conservation projects. S Stringent laws should be enacted to protect the monuments.
9. Above all, people’s participation in conservation and preservation process is paramount.

(4) What objectives can be fulfilled through the heritage projects.
Answer:
The following objectives can be fulfilled through the heritage projects:

• Preservation, conservation and development of heritage sites can be done without any change in its original state/ structure.
• The local social structure and psychology of the local people, challenges they face in the present situations and their expectations can be surveyed.
• In the process of completing the project of conservation, preservation and development of a heritage site due precaution should be taken to avoid hurting the sentiments of the local people.
• Participation of the local people in the proposed project can be facilitated.
• In order to engage and employ the local skills in a creative way and create better opportunities of livelihood, it becomes easier to design systematic plans.

Project
Show the Indian heritage sites on the map of India.
Answer:

Memory Map

Question 6.
Complete the sentences by choosing the correct option:
(a) ……………………… Institute of Art, Design and Technology at Bengaluru has an independent department named ‘Centre for Public History’.
(a) Pitch
(b) INTACH
(c) Shrushti
(d) AIMS
Answer:
(c) Shrushti

(b) ……………………… is the mother of science and all other branches of knowledge.
(a) Philosophy
(b) History
(c) Technology
(d) Mythology
Answer:
(a) Philosophy

(c) In order to preserve and conserve cultural and natural heritage for the benefit of future generations ……………………… has given directives.
(a) UNICEF
(b) UN
(c) UNESCO
(d) INTACH
Answer:
(c) UNESCO

(d) The ……………………… in the Satara District of the Western Ghats is included in the list of World Natural Heritage.
(a) Balaghat Mountain
(b) Melghat
(c) Masai Plateau
(d) Kas Plateau
Answer:
(d) Kas Plateau

(e) The main office of the National Film Archives of India is situated at ……………………… .
(a) Delhi
(b) Mumbai
(c) Pune
(d) Nagpur
Answer:
(c) Pune

(f) Excavations at the city of ‘Ur’ in Mesopotamia were conducted by ……………………… .
(a) Nathaniel Wallick
(b) Ennigaldi
(c) Leonard Wolley
(d) Sir John Marshall
Answer:
(c) Leonard Wolley.

Question 7.
Identify the wrong pair in the following, and write it:

(1) Kootiyattam	(a) Sanskrit theatre, Kerala
(2) Ramman	(b) Dance form in West Bengal
(3) Ramlila	(c) Traditional performance of Ramayana in Uttar Pradesh
(4) Kalbelia	(d) Folk songs and dances of Rajasthan

Answer:
Wrong pair: Ramman – Dance form in West Bengal

(2)

Cultural Heritage	Place
(1) Red Fort	(a) Udaipur
(2) Jantar Mantar	(b) Jaipur
(3) Brihadeeshvara Temple	(c) Thanjavur
(4) Capital Complex	(d) Chandigarh

Answer:
Wrong pair: Red Fort – Udaipur

Question 8.
Complete the graphical presentation:
(1)

Answer:

(2)

Answer:

(3)

Answer:

Question 9.
Explain the following concept:
(a) Natural Heritage:
Answer:

• In Cultural heritage what we inherit is man-made but Natural heritage is bestowed upon us by Nature.
• The concept of natural heritage gives importance to the thought of biodiversity.
• The following things are included in natural heritage:
  • Fauna
  • Flora
  • Ecology required for sustaining animal and plant life, flora and fauna of a particular region.
  • Geomorphic characteristics, sanctuaries, mountain ranges, river valleys, lakes and dams are all part of natural heritage.

Question 10.
Write short notes:
(a) Importance of Applied History:
Answer:

• Applied History is a field of study which helps us understand our ancient heritage.
• We realise the importance of preserving our heritage.
• The process of preservation and conservation of tangible and intangible heritage sites generate employment opportunities.
• The study of Applied History help us to get a better understanding of the present and can provide guidance for the future.

(b) Preservation of cultural heritage of India:
Answer:
Conservation and preservation of India’s cultural heritage is done at different levels:

1. Archaeological Survey of India (ASI) is an important body of Indian government which mainly does the work of conservation and preservation along with State Departments of Archaeology.
2. INTACH (Indiqn National Trust for Art and Cultural Heritage) is actively working in this field.
3. Local self-government bodies, social institutions all over India, people who have love for history are seen involved in the work of preservation of our heritage.
4. The work of conservation and preservation of cultural and natural heritage requires participation of experts from various fields as well as local people.

(c) Indian Museum:
Answer:

• The Indian Museum at Kolkata is the oldest museum and one of the important heritage sites of India.
• Nathaniel Wallich, a Danish botanist, founded the museum in 1814 C.E. He was also its first curator.
• The museum has three main departments Arts, Archaeology and Anthropology.
• Other affiliated departments are conservation, publication, photography, exhibition- presentation, model-making, training, library and security.

(d) National Film Archives:
Answer:

• The main office of the National Rim Archives of India is located at Pune and was established in 1964.
• It functions as the Media Unit of the Ministry of Information and Broadcasting of the Indian Government.
• It was established with the view of three objectives. They are:
  • To search and obtain the rare Indian films and preserve our heritage for the benefit of future generations.
  • To categorise important aspects of films, create documentation and do research.
  • To establish a centre for dissemination of ‘films culture’.

Question 11.
Explain the following statements giving reasons:
(a) It is essential to study the history of philosophy.
Answer:

• With the passage of time, many schools of thought came into existence with different ideologies.
• These ideologies had their effect on people and society as a whole.
• What led to the origin of various ideologies, the intellectual tradition giving rise to those ideologies and their historical development needs to be researched.
• To know about the progress of those ideologies, their development and expansion or downfall we need to have knowledge of the history of philosophy.

(b) It is important to know the history of Industry and Commerce.
Answer:

• With the growth of industry and trade, the field of mutual social transactions also expand.
• It promoted development of the network of cultural interactions.
• As the nature of market and commerce changed sp did the nature of human relationships and the social organisation.
• This series of changes is influenced by prevalent culture, social structure and economic system.
• All this is an integral part of the industrial and commercial management.

Therefore, it becomes important to know the history of Industry and Commerce.

(c) It is necessary to preserve and conserve our natural and cultural heritage.
Answer:

• The visible and invisible relics of the past exist in the present.
• They represent the thought and traditions of our ancestors.
• We nurture some kind of curiosity and attraction towards them.
• The history of our heritage links us with our origin.

Therefore, it becomes necessary to preserve and conserve for our future benefit as well as for the benefit of future generations.

Question 12.
Answer the following in 25-30 words:
(a) Explain the concept of ‘Public History’.
Answer:

• Public History also known as ‘Applied History’ is a field of study concerned with the application of history for the benefit of people in the contemporary and future life.
• It provides solutions to the contemporary social issues and incorporate them in social planning.
• It helps to overcome misgivings about history and makes history meaningful in everyday life connecting people to history.

(b) What is the role of UNESCO in the context of heritage sites?
Answer:
The role of UNESCO, the global agency of United Nations, is as follows:

• For preservation and conservation of natural and cultural heritage which is in a ruined state because of years of neglect, UNESCO has announced some directive principles.
• The organisation announces list which includes the names of sites and traditions which meet the criteria.
• On the basis of those directives it declares a list of site and traditions of world heritage.

(c) Find out the cultural heritage sites located in Maharashtra and write their names.
Answer:
The following places in Maharashtra are included in the list of cultural heritage sites declared by UNESCO:

• Ajanta Caves
• Verul (Ellora) Caves and Kailas Temple
• Elephanta Caves
• Chhatrapati Shivaji Maharaj Terminus, Mumbai.

Many forts like the Raigad, Devgiri, Janjira and Sindhudurg are part of the cultural heritage Of Maharashtra though they are not included in the list.

(d) What are the misgivings about history among the people?
Answer:
There are many misgivings about history among the people:

• History is a subject only for historians and students who pursue higher studies in history.
• It has no relevance or applicability in our day-to-day life.
• History is nothing but piece of information about the battles fought by kings and politics.
• History cannot be connected to an economically productive field.

(e) Where can we trace the roots of philosophy?
Answer:

• Ancient people all over the world tried to speculate the relationship between the universe and human existence.
• This gave rise to various myths about origin of this world, universal order, human life.
• Imagination about gods and goddesses, rituals to please them and philosophical explanation of rituals.
• Thus, the roots of philosophy can be traced in these speculations and ponderings of mythological stories.

(f) What are the opportunities created by affiliated professional fields of Applied History?
Answer:
Affiliated fields of Applied History which include museums, archives, tourism ‘and hospitality, entertainment, mass media, etc. needs the following professionals:

• Experts like Historians, Archaeologists, Sociologists, legal experts, etc. are assigned new projects.
• Officers like Managers, Secretaries and Directors are taken into service.
• Technicians like engineers, architects, skilled photographers, laboratory assistants, archive management professionals are hired.
• Tourist guides, boarding and lodging, food services, entertainment and related business get a wide scope for flourishing.

(g) What are the main objectives of ‘National Film Archives’?
Answer:
The main objectives of ‘National Rim Archives’ are as follows:

• To research and obtain the rare Indian films.
• To preserve such films for the benefit of future generations.
• To categorise the important aspects of films to create documentation, catalogue them -and carry out research in the field.
• To establish a centre for dissemination of films culture.

(h) How can we increase people’s participation in the field of applied history?
Answer:

• The field of applied history includes museums, archives, collection and maintenance of artefacts.
• Tourism creates interest in history.
• Awareness is created among people to preserve ancient monuments and sites in their vicinity.
• This realisation increases people’s participation in the field of applied history.

(i) Write information on World Heritage sites in Maharashtra.
Answer:
Maharashtra is endowed with many natural and historical sites. Among them the prominent ones are Ajanta caves, Verul caves, Gharapuri/Elephanta caves and Chhatrapati Shivaji Maharaj Terminus Railway Station at Mumbai.

Chhatrapati Shivaji Maharaj Terminus is finest example of Indo-Gothic architecture emerged in India during British rule. It stands witness to the British empire, freedom struggle and transformation of our country into a modern nation. It needs conservation as it a architectural marvel which stood the test of times recently when there was a terror attack on Mumbai city.

(j) What is the role of Applied History?
Answer:
The role of Applied History is as follows:

• In public training programmes for understanding the importance of history.
• Using knowledge of history, to create awareness regarding the conservation and preservation of our cultural and natural heritage.
• To facilitate participation of people in various projects and programmes related to applied history even in their capacity as tourists.
• To enhance professional skills of people and to develop industrial commercial field.
• To carry out preparatory work and plan for effective implementation of heritage projects.

Question 13.
Read the given passage carefully and answer the questions given below:
(a) Who built this museum?
Answer:
This museum was built by Ennigaldi, the princess of Mesopotamia.

(b) Where was the earliest museum in the world discovered? Who discovered it?
Answer:
The earliest museum in the world was discovered in the city of ‘Ur’ in Mesopotamia. It was discovered by Leonard Woolley.

(c) What is a noteworthy feature of this museum?
Answer:
A noteworthy feature of this museum is the clay tablets inscribed with the descriptions of exhibited artefacts.

Question 14.
Write elaborate answers: OR Answer in detail:
(a) Who does the work of conservation and preservation of the cultural heritage of Indian?
Answer:
The preservation and conservation of Indian cultural heritage is done at various stages:

• The work of preservation and conservation primarily falls under jurisdiction of the Archaeological Survey of India.
• In addition, INTACH (Indian National Trust for Art and Cultural Heritage) is also actively working .in this field.
• Experts from various fields and local people too participate in the work of conservation and preservation of natural and cultural heritage.

Question 15.
Observe the picture and write information about it:

Answer:

• This picture is of the largest Indian rock-cut ancient Hindu temple located in the Ellora cave.
• This famous rock-cut Shiva temple was constructed during the reign of Rashtrakuta king Krishna I.
• It is regarded as a marvel of architecture.
• It bears an eloquent testimony to the high level skill attained by India in the arts of sculpture and architecture under the Rashtrakuta patronage.
• A sculpture of an elephant and a pillar can be seen in the picture.
• The famous rock cut temple in Maharashtra was declared as a world heritage site by UNESCO in 1983.

Brain Teaser

Hints:
Across:
(1) Queen’s stepwell at Patan
(2) Dancing, singing, drumming ritual of Manipur
(3) Religious festival and ritual theatre of Garhwal
(4) Archaeological site of Nalanda University
(5) World famous monument at Agra
(6) Famous city built by emperor Akbar marking his victory
(7) Sanskrit Theatre: Kerala

Down:
(1) The traditional performance of Ramayan in Uttar Pradesh
(2) Ellora caves also known as caves
(3) Observatory at Jaipur, Rajasthan
(4) Group of monuments at (place) in Karnataka
(5) Archaeological park at Pavagadh
(6) Folk songs and dances of Rajasthan
(7) A ritual theatre of Kerala

Balbharti Maharashtra State Board Class 10 Science Solutions Part 1 Chapter 7 Lenses Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 10 Science Solutions Part 1 Chapter 7 Lenses

Question 1.
Match the columns in the following table and explain them:

Column 1	Column 2	Column 3
Farsightedness	Nearby object can be seen clearly	Bifocal  lens
Presbyopia	Faraway object can be seen clearly	Concave  lens
Nearsightedness	Problem of old age	Convex  lens

Answer:

Column 1	Column 2	Column 3
Farsightedness	Faraway object can be seen clearly	Convex  lens
Presbyopia	Problem of old age	Bifocal  lens
Nearsightedness	Nearby object can be seen clearly	Concave  lens

1. Farsightedness:
Hypermetropia or farsightedness is the defect of vision in which a human eye can see distant objects clearly but is unable to see nearby objects clearly.
In this case the image of a nearby object would fall behind the retina instead of on the retina.

Possible reasons for hypermetropia:
(1) Curvature of the cornea and the eye lens decreases. Hence, the converging power of the eye lens becomes less.
(2) The distance between the eye lens and retina decreases (relative to the normal eye) and the focal length of the eye lens becomes very large due to the flattening of the eyeball.

2. Presbyopia:
Presbyopia is the defect of vision in which aged people find it difficult to see nearby objects
comfortably and clearly without spectacles.

Reason of presbyopia: The power of accommodation of eye usually decreases with ageing. The muscles near the eye lens lose their ability to change the focal length of the lens.

Therefore, the near point of the eye lens shifts rarther from the eye, This defect is corrected using a. convex lens of appropriate power. The lens converges light rays before they fall on the eye lens such that the action of the eye lens forms the image on the retina.

3. Nearsightedness:
Myopia or nearsightedness is the defect of vision in which a human eye can see nearby objects distinctly but is unable to see distant objects clearly as they appear indistinct.
In this case the image of a distant object is formed in front of the retina instead of on the retina.
[Figs. 7.29 (a), 7.29 (b)]

Possible reasons for myopia:
(1) The curvature of the cornea and the eye lens increases. The muscles near the lens cannot relax so that the converging power of the lens remains large. (2) The distance between the eye lens and the retina increases as the eyeball elongates.

Myopia is corrected using a suitable concave lens. Light rays are diverged by the concave lens before they strike the eye lens. A concave lens of proper focal length is chosen to produce the required divergence. Hence, after the converging action of the eye lens, the image is formed on the retina. [Fig. 7.29 (c)]

Question 2.
Draw a figure explaining various terms related to a lens.
Answer:
(1) Centre of curvature (C): The centres of the spheres whose parts form the surfaces of a lens are called the centres of curvature of the lens. A lens has two centres of curvature C₁, and C₂ for its two spherical surfaces.

(2) Radii of curvature (R₁, R₂): The radii of the spheres whose parts form surfaces of a lens are called the radii of curvature of the lens.

(3) Principal axis: The imaginary straight line passing through the two centres of curvature of a lens is called the principal axis of the lens.

(4) Optical centre (O): The point inside a lens on the principal axis, through which light rays pass without changing their path is called the optical centre (O) of the lens.

(5) Principal focus (F): When light rays parallel to the principal- axis are incident on a convex lens, they converge at a point on the principal axis. This point is called the principal focus (F) of the convex lens. Light rays travelling parallel to the principal axis of a concave lens diverge after refraction in such a way that they appear to be coming out of a point on the principal axis. This point is called the principal focus of the concave lens. A lens has two principal foci F₁ and F₂.
[Note: In this chapter, the terms focus and the principal focus are used in the same sense.]

(6) Focal length (f): The distance between the optical centre and the principal focus of a lens is called the focal length (f) of the lens.

C₁, C₂: Centres of curvature, R₁, R₂: Radii of curvature, O: Optical centre.
The cross sections of convex and concave lenses are shown in parts (a) and (b) of Fig. 7.4. The surface marked as 1 is part of sphere S₁ while the surface marked as 2 is part of sphere S₂.

P₁, P₂, P₃: Incident rays of light,
Q₁, Q₂, Q₃: Refracted rays of light, O: Optical centre

F₁, F₂: Principal foci of the lens, f: Focal length of the lens

Question 3.
At which position will you keep an object in front of a convex lens so as to get a real image of the same size as the object? Draw a figure.
Answer:
At 2F₁.

Question 4.
Give scientific reasons:
a. A simple microscope is used for watch repairs.
Answer:
(1) when an object is placed within the focal length of a magnifying glass or simple microscope (convex lens), its larger and erect image is obtained on the same side of the lens as that of the object.

(2) By adjusting the distance between the object and the lens, the image can be obtained at the minimum distance of distinct vision. Thus, a watch repairer can see the minute parts of a watch more clearly with the aid of a magnifying glass (a simple microscope) than with the naked eye, without any stress on the eye. Hence, watch repairers use a magnifying glass (a simple microscope) while repairing the watches.

b. One can sense colours only in bright light.
Answer:
(1) The retina in the eye is made of many light sensitive cells. The rod-shaped cells respond to the intensity of light while the cone-shaped cells j respond to various colours.
(2) The cone-shaped cells do not respond to faint light. They function only in bright light. Hence, one can sense colours only in bright, light.

c. We cannot clearly see an object kept at a distance less than 25 cm from the eye.
Answer:
(1) When we try to see a nearby object, the eye lens becomes more rounded and its focal length decreases. Then a clear image of the object is formed on the retina of the eye.
(2) The focal length of the eye lens cannot be decreased beyond some limit. Therefore we cannot clearly see an object kept at a distance less than 25 cm from the eye.

Question 5.
Explain the working of an astronomical telescope using refraction of light.
Answer:
Construction of a refracting telescope: It consists of two convex lenses called the objective lens (directed towards the object) and the eyepiece (directed towards the eye). The focal length and diameter of the objective lens are respectively greater than the focal length and diameter of the eyepiece. The objective lens is fitted at one end of a long metal tube.

A metal tube of smaller diameter is fitted in this metal tube and the eyepiece is fitted at the outer end of the smaller tube. With the help of a screw it is possible to change the distance between the eyepiece and the objective lens by sliding the tube fitted with the eyepiece. The principal axes of the objective lens and the eyepiece are along the same line. A telescope is usually mounted on a stand.

Working: When the objective lens is pointed towards the distant object to be observed, the rays of light from the distant object, which are almost parallel to each other, pass through the objective lens. The objective lens collects maximum amount of light as it is large in size. It forms a real, inverted and diminished image in the focal plane of the objective lens. Now, the position of the eyepiece is adjusted such that this image falls just within the focal length of the eyepiece and serves as the object for the eyepiece which works as a simple microscope.

The final image is highly magnified, virtual, on the same side as that of the object and inverted with respect to the original object. The final image can be observed by keeping the eye close to the eyepiece. If the image formed by the objective lens lies in the focal plane of the eyepiece, the final image is formed at infinity.

Question 6.
Distinguish between the following:
a. Farsightedness (Hypermetropia) and Nearsightedness (Myopia).
Answer:
Farsightedness:

1. In hypermetropia, a human eye can see distant distinctly but is unable to see nearby objects clearly.
2. In this case, the image of a nearby object would be formed behind the retina.
3. This defect can be corrected using a convex lens of appropriate power.

Nearsightedness:

1. In myopia, a human eye can see near objects distinctly, but is unable to see distant objects clearly.
2. In this case, the image of a distant object is formed in front of the retina.
3. This defect can be corrected using a concave lens of appropriate power.

b. Concave lens and Convex lens.
Answer:
Concave lens:

1. A concave lens has its surfaces curved inwards.
2. It is thicker at the edges than in the middle.
3. It can form only a virtual image.
4. It can form only a diminished image.

Convex lens:

1. A convex lens has its surfaces puffed up outwards.
2. It is thicker in the middle than at the edges.
3. It can form a real image as well as a % virtual image.
4. It can form a magnified, diminished or the same sized image (relative to the object) depending on the position of the object.

Question 7.
What is the function of the iris and the muscles connected to the lens in the human eye?
Answer:
When the incident light is very bright, the muscles of the iris stretch to reduce the size of the pupil. When the incident light is dim, the muscles of the iris relax to increase the size of the pupil. Thus, the iris controls the size of the pupil and thereby regulates the amount of light entering the eye. (Fig. 7.26)

When a distant object is to be observed, the ciliary muscles relax so that the eye lens becomes flat. This increases the focal length of the lens. Therefore, a sharp image of the distant object is formed on the retina.
Thus, we can see a distant object clearly. (Fig. 7.27)

when an object closer to the eye is to be observed. the ciliary muscles contract increasing the curvature. of the eye lens. The eye lens, therefore, becomes rounded. This decreases the focal length of the lens. Therefore, a sharp image of the nearby object is formed on the retina. Thus, we can see a nearby object clearly. (Fig. 7.27)

Question 8.
Solve the following examples:
i. Doctor has prescribed a lens having I power + 1.5 D. What will be the focal length of the lens? What is the type of the lens and what must be the defect of vision?
Solution:
Data: P = + 1.5 D, f = ?
Focal length of the lens, f = \(\frac{1}{P}=\frac{1}{1.5 \mathrm{D}}\)
= \(\frac{10}{15}\) m = 0.6667 m = 0.67 m
P is positive. This shows that the lens is convex. The defect of vision is farsightedness (hypermetropia).

ii. 5 cm high object is placed at a distance of 25 cm from a converging lens of focal length of 10 cm. Determine the position, size and type of the image.
Solution:
Data: Converging lens, f = 10 cm
u = – 25 cm, h₁ = 5 cm, v = ?, h₂ = ?


The height of the image = -3.3 cm (inverted image ∴ minus sign).
(iii) The image is real, inverted and smaller than the object.

iii. Three lenses having powers 2, 2.5 and 1.7 D are kept touching in a row. What is the total power of the lens combination?
Solution:
Data: P₁ = 2 D, P₂ = 2.5 D, P₃ = 1.7 D, P = ?
Total power of the lens combination,
P = P₁ +P₂ + P₃
= 2 D + 2.5 D + 1.7 D
= 6.2 D.

iv. An object kept 60 cm from a lens gives a virtual image 20 cm in front of the lens. What is the focal length of the lens? Is it a converging lens or diverging lens?
Solution:
Data: u = -60 cm, v = -20 cm, f = ?

∴ The focal length of the lens, f = – 30 cm. As f is negative, it is a diverging lens.

Project:

Question 1.
Make a Powerpoint presentation about the construction and use of binoculars. (Do it your self)

Can you recall? (Text Book Page No. 80)

Question 1.
Indicate the following terms related to spherical mirrors in figure 7.1: pole, centre of curvature, radius of curvature, principal focus.

Answer:

Question 2.
How are concave and convex mirrors constructed?
Answer:
The given part of a hollow spherical glass can be converted into a concave mirror by (i) polishing (silvering) its inner side (inner surface or concave surface) to make it reflecting or (ii) coating its outer side with a thin layer of silver and painting it with red colour to protect the silver coating.
[Note: Case (i) corresponds to the front surface silvered concave mirror.]

The given part of a hollow spherical glass can be converted into a convex mirror by (i) polishing (silvering) its outer side (outer surface or convex surface) to make it reflecting or (ii) coating its inner side with a thin layer of silver and painting it with red colour to protect the silver coating.
[Note: Case (i) corresponds to the front surface silvered convex mirror. ]

Use your brain power! (Text Book Page No. 85)

Question 1.
From equations (1) and (2) what is the relation between h₁, h₂, u and v?
Answer:
M = \(\frac{h_{2}}{h_{1}}\) …….(1)
Also, M = \(\frac{v(\text { image distance })}{u \text { (object distance) }}\)……(2)
\(\frac{h_{2}}{h_{1}}\) = \(\frac{v}{u}\)

Try this (Text Book Page No. 88)

(1) Try to read a book keeping it very far from your eyes.
(2) Try to read a book keeping it very close to your eyes.
(3) Try to read a book keeping it at a distance of 25 cm from your eyes.
At which time do you see the alphabets clearly? Why?
Answer:
Minimum distance of distinct vision: Though the focal length of the eye lens is adjustable, it cannot be decreased below a certain limit. Hence, if an object is very close to the eye, it cannot be seen clearly. For a normal human eye, the minimum distance from the eye at which an object is clearly visible without stress on the eye, is called the minimum distance of distinct vision. For the normal human eye, it is 25 cm.

Use your brain power! (Text Book Page No. 89)

Question.
(1) Why do we have to bring a small object near the eyes in order to see it clearly?
(2) If we bring an object closer than 25 cm from the eyes, when can we not see it clearly even though it subtends a bigger angle at the eye?
Answer:
(1) when a small object is brought near the eyes, its apparent size increases. Therefore, it is
seen clearly.

(2) Minimum distance of distinct vision: Though the focal length of the eye lens is adjustable, it cannot be decreased below a certain limit. Hence, if an object is very close to the eye, it cannot be seen clearly. For a normal human eye, the minimum distance from the eye at which an object is clearly visible without stress on the eye, is called the minimum distance of distinct vision. For the normal human eye, it is 25 cm.

Try this (Text Book Page No. 91)

Question 1.
Take a burning incense stick in your hand and rotate it fast along a circle.
Answer:
A circle of red light is seen.

Question 2.
Draw a cage on one side of a cardboard and a bird on the other side. Hang the cardboard with the help of a thread. Twist the thread and leave It. What do you see and why?
Answer:
The bird appears to be inside the cage. This happens due to persistence of vision.
Persistence of vision: We see an object when its image is formed on the retina. The image disappears when the object is removed from our sight. But this is not instantaneous and the image remains imprinted on the retina for about \(\frac{1}{16}\) th of a second after the removal of the object. The sensation on the retina persists for a while. This effect is known as the persistence of vision.

It is due to persistence of vision that we continue to see the object in its position for about \(\frac{1}{16}\) th of a second after it is removed.
Example: When a burning stick of incense is moved fast in a circle, a circle of red light is seen.

Can you tell? (Text Book Page No. 91)

Question 1.
How do we perceive different colours?
Answer:
(1) In nature we field objects of various colours. Perception of colour means to be able to respond to colour.
(2) We can distinguish between various colours due to perception of colour.
(3) The cone-shaped cells on the retina of the eye respond to the various colours when light is bright and communicate to the brain about the colours of the image formed on the retina. This gives us the proper idea about the colours of the object.
(4) If, in the retina of a person, the cone-shaped cells responding to certain specific colours are absent, the person is unable to distinguish between the colours. As a result, he lacks perception of colour.

Fill in the blanks and rewrite the statements:

Question 1.
The focal length of a………..lens is positive.
Answer:
The focal length of a convex lens is positive.

Question 2.
The focal length of a………..lens is negative.
Answer:
The focal length of a concave lens is negative.

Question 3.
The magnification produced by a………..lens is always positive.
Answer:
The magnification produced by a concave lens is always positive.

Question 4.
The power of a………..lens is positive.
Answer:
The power of a convex lens is positive.

Question 5.
The power of a………..lens is negative.
Answer:
The power of a concave lens is negative.

Question 6.
The focal length of a lens with power 2.5 D is………..
Answer:
The focal length of a lens with power 2.5 D is 40 cm (0.4 m).

Question 7.
The power of a lens with focal length 20 cm is………..
Answer:
The power of a lens with focal length 20 cm is 5D.

Question 8.
The minimum distance of distinct vision for a normal human eye is………..
Answer:
The minimum distance of distinct vision for a normal human eye is 25 cm.

Question 9.
If two lenses with focal lengths 10 cm and 20 cm respectively are kept in contact with each other, the effective power of the combination is………..
Answer:
If two lenses with focal lengths 10 cm and 20 cm respectively are kept in contact with each other, the effective power of the combination is 15 D.

Question 10.
A………..lens is used as a simple microscope.
Answer:
A convex lens is used as a simple microscope.

Rewrite the following statements by selecting the correct options:

Question 1.
Inside water, an air bubble behaves………..
(a) like a flat plate
(b) like a concave lens
(c) like a convex lens
(d) like a concave mirror
Answer:
Inside water, an air bubble behaves like a concave lens.

Question 2.
…………represents the lens formula.

Answer:
(b) \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\) represents the lens formula.

Question 3.
The power of a convex lens of focal length 25 cm is………..
(a) +4.0 D
(b) 0.25 D
(c) -4.0 D
(d) -0.4D
Answer:
The power of a convex lens of focal length 25 cm is +4.0 D

Question 4.
A lens does not produce any deviation of a ray of light passing through………..
(a) it’s centre of curvature
(b) it’s optical centre
(c) it’s principal focus
(d) an axial point at a distance 2F from its centre
Answer:
A lens does not produce any deviation of a ray of light passing through its optical centre.

Question 5.
The image formed by a concave lens is always………..
(a) virtual and erect
(b) real and erect
(c) virtual and inverted
(d) real and inverted
Answer:
The image formed by a concave lens is always virtual and erect.

Question 6.
A convex lens forms a virtual image of an object placed………..
(a) at infinity
(b) at a distance 2F from the lens
(c) at a distance F from the lens
(d) between the principal focus and the optical centre of the lens.
Answer:
A convex lens forms a virtual image of an object placed between the principal focus and the optical centre of the lens.

Question 7.
When an object is placed at 2F₁ of a convex lens, its image is formed………..
(a) at F₁
(b) at 2F₂
(c) beyond 2F₂
(d) on the same side as the object
Answer:
When an object is placed at 2F₁ of a convex lens, its image is formed at 2F₂

Question 8.
To obtain an image of the same size as that of an object with the help of a convex lens, the object should be placed………..
(a) at infinity
(b) beyond F₁
(c) between F₁ and 2F₁
(d) at 2F₁
Answer:
To obtain an image of the same size as that of an object with the help of a convex lens, the object should be placed at 2F₁

Question 9.
When an object is placed between O and F₁ in front of a convex lens, the image formed is ………..
(a) enlarged and erect
(b) diminished and erect
(c) real and enlarged
(d) diminished and inverted
Answer:
When an object is placed between O and F₁ in front of a convex lens, the image formed is enlarged and erect.

Question 10.
When an object is placed at any finite distance from a concave lens, the image is formed ………..
(a) between F₁ and 2F₁
(b) beyond 2F₁
(c) at F₁
(d) between F₁ and O on the same side as the object.
Answer:
When an object is placed at any finite distance from a concave lens, the image is formed between F₁ and O on the same side as the object.

Question 11.
A student obtained a clear image of window grills on the screen. But the teacher told him to get the image of a tree far away, instead of the window. To get a clear image, the lens must be ……….. (Practice Activity Sheet – 2)
(a) moved towards the screen
(b) moved away from the screen
(c) moved behind the screen
(d) moved far away from the screen
Answer:
A student obtained a clear image of window grills on the screen. But the teacher told him to get the image of a tree far away, instead of the window. To get a clear image, the lens must be moved towards the screen.

Question 12.
The image obtained while finding the focal length of a convex lens is ……….. (Practice Activity Sheet – 3)
(a) real and erect
(b) virtual and erect
(c) real and inverted
(d) virtual and inverted
Answer:
The image obtained while finding the focal length of a convex lens is real and inverted.

Question 13.
Yash found out f₁ and f₂ of a symmetric convex lens experimentally. Then which of the following conclusions is true? (Practice Activity Sheet – 4)
(a) f₁ = f₂
(b) f₁ > f₂
(c) f₁ < f₂
(d) f₁ ≠ f₂
Answer:
(a) f₁ = f₂

State whether the following statements are true or false: (If a statement is false, correct it and rewrite it.)

Group (A)

Question 1.
Power of a lens, P = \(\frac{1}{f}\).
Answer:
True.

Question 2.
If the power of a lens is 2 D, its focal length = 0.5 m.
Answer:
True.

Question 3.
A concave lens is a converging lens. (March 2019)
Answer:
False. (A concave lens is a diverging lens.)

Question 4.
A convex lens is a diverging lens.
Answer:
False. (A convex lens is a converging lens.)

Question 5.
A concave lens always forms a virtual image.
Answer:
True.

Question 6.
A convex lens always forms a virtual image.
Answer:
False. (A convex lens forms a real image or a virtual image depending on the object distance.)

Question 7.
Due to the light sensitive cells in the eye, we get information about the brightness or dimness of the object and the colour of the object.
Answer:
True.

Question 8.
The focal length of a concave lens is negative.
Answer:
True.

Question 9.
The magnification produced by a concave lens is positive or negative depending on the object distance.
Answer:
False. (The magnification produced by a concave lens is always positive.)

Question 10.
The magnification produced by a convex lens is positive or negative depending on the object distance.
Answer:
True.

Question 11.
A concave lens is used as a magnifying glass.
Answer:
False. (A convex lens is used as a magnifying glass.)

Question 12.
A convex lens is used as a simple microscope.
Answer:
True.

Question 13.
A concave lens is used to correct myopia.
Answer:
True.

Question 14.
A convex lens is used to correct hypermetropia.
Answer:
True.

Group (B)

Question 1.
When red light falls on the eyes, the cells responding to red light get excited more than those responding to other colours and we get the sensation of red colour.
Answer:
True.

Question 2.
When an object is placed in front of a concave lens, its image is obtained on the opposite side of the object.
Answer:
False. (When an object is kept in front of a concave lens, its image is obtained on the same side of the lens as the object.)

Question 3.
The image formed by a concave lens is always virtual.
Answer:
True.

Question 4.
The principal focus of a convex lens is virtual.
Answer:
False. (The principal focus of a convex lens is real.)

Question 5.
An object of height 2 cm forms an image of height 3 cm when placed in front of a concave lens.
Answer:
False. (An object of height 2 cm forms an image of height less than 2 cm when placed in front of a concave lens.)

Question 6.
Absence of rod like cells results in colour blindness.
Answer:
False. (Absence of conical cells results in colour-blindness.)

Question 7.
Nearsightedness can be corrected using spectacles having convex lenses.
Answer:
False. (Nearsightedness can be corrected using spectacles having concave lenses.)

Question 8.
Farsightedness can be corrected using spectacles having convex lenses of suitable focal length.
Answer:
True.

Question 9.
As one grows old, ciliary muscles become weak.
Answer:
True.

Question 10.
In a simple microscope, the object is placed within the focal length of the convex lens.
Answer:
True.

Question 11.
A compound microscope forms an erect and real image of a small object.
Answer:
False. (A compound microscope forms an inverted and virtual image of a small object.)

Question 12.
In a compound microscope, a real image acts as an object for the eyepiece.
Answer:
True.

Question 13.
In television, we see a continuous picture due to persistence of vision.
Answer:
True.

Question 14.
The conical cells can respond differently to red, green and blue colours.
Answer:
True.

Question 15.
The rod like cells respond to colours and communicate the presence of colours in the retinal image of the brain.
Answer:
False. (The rod like cells respond to the intensity of light and communicate the degree of brightness and darkness, to the brain.)

Question 16.
The conical cells respond to the intensity of light and communicate the degree of brightness and darkness to the brain.
Answer:
False. (The conical cells respond to colours and communicate the presence of colours in the retinal image to the brain.)

Question 17.
Generally, using the same objective lens, but different eyepieces, different magnification can be obtained.
Answer:
True.

Find the odd one out and give the reason:

Question 1.
Simple microscope, Compound microscope, Telescope, Myopia.
Answer:
Myopia. It is a defect of vision; others are instruments.

Question 2.
Myopia, Presbyopia, Hypermetropia, Spectrometer.
Answer:
Spectrometer. It is an instrument; others are defects of vision.

Question 3.
Presbyopia, Retina, Nearsightedness, Farsightedness.
Answer:
Retina. It is a part of the eye; others are defects of vision.

Question 4.
Compound microscope, Kaleidoscope, Simple microscope, Astronomical telescope.
Answer:
Kaleidoscope. Others are optical instruments.

Question 5.
TV, Motion picture, Complete circle formed by a revolving burning incense stick, Colour blindness.
Answer:
Colour-blindness. Others are examples of persistence of vision.

Question 6.
Planets, Stars, Satellites, Rainbow.
Answer:
Rainbow. Others are celestial bodies.

Considering the correlation between the words of the first pair, pair the third word accordingly with proper answer:

Question 1.
Nearsightedness: Elongated eyeball :: Farsightedness:………
Answer:
Flattened eyeball

Question 2.
Convex lens : Converging :: Concave lens :………..
Answer:
Diverging

Question 3.
Object at 2F₁ of a convex lens : Image at 2F₂ :: Object at F₁ :………..
Answer:
Image on the opposite side at infinity

Question 4.
Magnification positive : Erect image :: Magnification negative :………..
Answer:
Inverted image

Question 5.
Convex lens : Positive power of the lens :: Concave lens:
Answer:
Negative power of the lens.

Question 6.
\(\frac{1}{f(\text { in metre })}\) : Power of the lens (in dioptre) :: \(\frac{\text { Image distance }}{\text { Object distance }}\)
Answer:
Magnification.

Question 7.
Focal length : Metre :: Power of a lens :………..
Answer:
Dioptre.

Question 8.
Iris : Pupil :: Ciliary muscles :……….
Answer:
Eye lens

Question 9.
Nearsightedness : Concave lens :: Farsightedness :………..
Answer:
Convex lens

Question 10.
Nearsightedness : Image in front of the retina :: Farsightedness :………..
Answer:
Image behind the retina

Question 11.
Observation of stars and planets : Telescope :: Repairing a watch :……….
Answer:
Simple microscope

Question 12.
Cinema : Persistence of vision :: Rainbow :………
Answer:
Refraction, dispersion and internal reflection of light.

Match the following:

Question 1.

Column A	Column B
(1) Conical cells	(a) Intensity of light
(2) Rod like cells	(b) Colour of an image
(3) Pupil	(c) Iris
(4) Cornea	(d) Aperture
	(e) Transparent

Answer:
(1) Conical cells – Colour of an image
(2) Rod like cells – Intensity of light
(3) Pupil – Aperture
(4) Cornea – Transparent.

Question 2.

Column A	Column B
(1) Magnification	(a) \(\frac{1}{f}\)
(2) Power of a lens	(b) \(\frac{h_{2}}{h_{1}}\)
(3) Focal length	(c) f
(4) Distance of an object from a lens	(d) u
	(e) \(\frac{h_{1}}{h_{2}}\)

Answer:
(1) Magnification: \(\frac{h_{2}}{h_{1}}\)
(2) Power of a lens: \(\frac{1}{f}\)
(3) Focal length: f
(4) Distance of an object from a lens: u.

Question 3.

Answer:
(1) Lens: \(\frac{1}{f}: \frac{1}{v}-\frac{1}{u}\)
(2) Magnification: \(\frac{h_{2}}{h_{1}}\)
(3) Refractive index: \(\frac{\sin i}{\sin r}\)

Question 4.

Column A	Column B
(Convex lens)	(a) Image virtual, erect and enlarged
(1) Object at 2F1	(b) Image real, inverted and of the same size
(2) Object between F1 and 2F1	(c) Image real, inverted and highly diminished
(3) Object between O and F1	(d) Image real, inverted and highly enlarged
(4) Object at infinity	(e) Image real, inverted and enlarged

Answer:
(1) Object at 2F₁ – Image real, inverted and of the same size
(2) Object between F₁ and 2F₁ – Image real, inverted and enlarged
(3) Object between O and F₁ – Image virtual, erect and enlarged
(4) Object at infinity – Image real, inverted and highly diminished

Question 5.

Column A	Column B
(1) Nearsightedness	(a) Ciliary muscles become weak
(2) Farsightedness	(b) Image in front of the retina
(3) Presbyopia	(c) Colour-blindness
	(d) Image behind the retina

Answer:
(1) Nearsightedness – Image in front of the retina
(2) Farsightedness – Image behind the retina
(3) Presbyopia – Ciliary muscles become weak

Question 6.

Column A	Column B
(1) Convex lens	(a) To see small objects clearly
(2) Astronomical telescope	(b) To observe minute objects
(3) Compound microscope	(c) To observe astronomical objects such as stars, planets, etc.
(4) Simple microscope	(d) Presbyopia
	(e) Power of a lens

Answer:
(1) Convex lens – Presbyopia
(2) Astronomical telescope – To observe astronomical objects such as stars, planets, etc.
(3) Compound microscope – To observe minute objects
(4) Simple microscope – To see small objects clearly.

Question 7.

Column A	Column B
(1) Persistence of vision	(a) Lenses and mirrors are used
(2) Reflecting telescope	(b) To see objects far away from us
(3) Telescope	(c) Motion picture
(4) Compound microscope	(d) To observe blood
	(e) Convex lens

Answer:
(1) Persistence of vision – Motion picture
(2) Reflecting telescope – Lenses and mirrors are used
(3) Telescope – To see objects far away from us
(4) Compound microscope – To observe blood corpuscles.

Name the following:

Question 1.
Name the lens which forms a real image or a virtual image depending on the position of the object.
Answer:
A convex lens.

Question 2.
Name the lens which produces magnification always less than 1.
Answer:
A concave lens.

Question 3.
Name the lens which always forms an image virtual and smaller than the object.
Answer:
A concave lens.

Question 4.
Name the lens used to obtain the image on a screen.
Answer:
A convex lens.

Question 5.
Name the lens for which the image always lies between the object and the lens.
Answer:
A concave lens.

Question 6.
Name the instrument used to observe bacteria.
Answer:
A compound microscope.

Question 7.
Name the instrument used to observe planets.
Answer:
An astronomical telescope.

Answer the following questions in one sentence each:

Question 1.
An object is placed at 60 cm from a convex lens of focal length 20 cm. State the nature and size of the image relative to that of the object.
Answer:
The image is real, inverted and smaller than the object.

Question 2.
If an object is placed at 50 cm from a convex lens of focal length 25 cm, what will be the image distance?
Answer:
The image distance will be.50 cm.

Question 3.
An object is placed at 40 cm from a convex lens of focal length 20 cm. State the nature and the size of the image relative to that of the object.
Answer:
The image is real, inverted and of the same size as that or the object.

Question 4.
An object is placed at 30 cm from a convex lens of focal length 20 cm. State the nature and the size of the image relative to that of the object.
Answer:
The image is real, inverted and larger than the object.

Question 5.
An object is placed at 15 cm from a convex lens of focal length 25 cm. State the nature and size of the image relative to that of the object.
Answer:
The image is virtual, erect and larger than the object.

Question 6.
State the type of lens that can be used to burn paper in sunlight at noon.
Answer:
A convex lens can be used to burn paper in sunlight at noon.

Question 7.
State the type of lens used to correct myopia.
Answer:
A concave lens is used to correct myopia.

Question 8.
State the type of lens used to correct hypermetropia.
Answer:
A convex lens is used to correct hypermetropia.

Question 9.
If two lenses with focal lengths 10 cm and – 20 cm respectively are kept in contact with each other, what will be the effective power of the combination of the lenses?
Answer:
The effective power of the combination of the lenses will be + 5 D.

Question 10.
If two lenses with focal lengths – 10 cm and 40 cm respectively are kept in contact with each other, what can you say about the behaviour of the combination of the lenses?
Answer:
The combination of the lenses will behave as a concave lens.

Answer the following questions:

Question 1.
What is a lens?
Answer:
A lens is a transparent material bound by two surfaces, out of which at least one surface is spherical.
[Note: A lens is normally made of glass or plastic.]

Question 2.
In which instruments have you seen a lens?
Answer:
We have seen a lens in a microscope and a telescope.

Question 3.
How is a lens different from a mirror?
Answer:
A mirror has one reflecting surface. By reflection of light, it forms an image of the object placed in front of it. A mirror is not transparent. A lens has two surfaces that form an image by refraction of light. A lens is transparent.

Question 4.
Make a list of optical devices you know.
Answer:
Microscope, telescope, binoculars, camera, projector.

Question 5.
Do you know which is the natural optical device?
Answer:
Yes. The eye is the natural optical device.

Question 6.
What is a convex lens?
Answer:
A lens having both spherical surfaces puffed up outwards is called a convex lens or double convex lens or biconvex lens. It is thicker in the middle than at the edges.
[Note: A convex lens is also called a converging lens.]

Question 7.
What is a concave lens?
Answer:
A lens having both spherical surfaces curved inwards is called a concave lens or double concave lens or biconcave lens. It is thicker at the edges than in the middle.
[Note: A concave lens is also called a diverging lens.]

Question 8.
Draw neat labelled diagrams: Types of lenses.
Answer:

[Note: Positive meniscus behaves as a convex lens as it is thicker in the middle than at the edges. Negative meniscus behaves as a concave lens as it is thicker at the edges than in the middle.]

Question 9.
In general, when a ray of light passes through a lens, there occurs a change in its direction of propagation. Why?
Answer:
The working of a lens is similar to that of a triangular prism. When a ray of light passes through a lens, it is refracted twice: When entering the lens and when emerging from the lens. There is a change 5 in its direction of propagation every time and as both the changes occur in the same sense, the direction of propagation of the emergent ray is different from that of the incident ray.

Question 10.
State the rules used for drawing ray diagrams for the formation of an image by a convex lens.
Answer:
Rules used for drawing ray diagrams for the formation of an image by a convex lens:
(1) When the incident ray is parallel to the principal axis, the refracted ray passes through the principal focus.

(2) When the incident ray passes through the principal focus, the refracted ray is parallel to the principal axis.

(3) When the incident ray passes through the optical centre of the lens, it passes without changing its direction.

Question 11.
In the case of a convex lens, show the path of the refracted ray when the incident ray of light (1) is parallel to the principal axis of the lens (2) passes through the focus of the lens (3) passes through the optical centre of the lens.
Answer:
1.

2.

3.

Question 12.
Draw neat and well labelled ray diagrams for image formation by convex lens when an object is (1) at infinity (2) beyond 2F₁ (3) at 2F₁ (4) between F₁ and 2F₁ (5) at focus F₁ (6) between focus F₁ and optical centre O. Also, in each case, state the position, nature and size of the image relative to that of the object.
Answer:
(1) Object at infinity:

In this case, the image is formed at focus F₂ of the convex lens. It is real, inverted and highly diminished (point-sized).

(2) Object beyond 2F₁:

In this case, the image is formed between F₂ and 2F₂. It is real, inverted and diminished.

(3) Object at 2F₁:

In this case, the image is formed at 2F₂. It is real, inverted and of the same size as that of the object.

(4) Object between F₁ and 2F₁:

In this case, the image is formed beyond 2F₂. It is real, inverted and magnified (enlarged).

(5) Object at focus F₁:

In this case, the image is formed at infinity. It is real, inverted and infinitely large (highly magnified).

(6) Object between focus F₁ and optical centre O:

In this case, the image is formed on the same side of the lens as the object. It is virtual, erect and larger than the object.
[Note: Here, the image is virtual. Hence, it is shown by a dotted line.]

Question 13.
Observe the following figure and complete the table: (March 2019)

Answer:

Point	Answer
(i) Position of the object	Between F1 and O
(ii) Position of the image	On the same side of the lens as the object
(iii) Size of the image	Very large
(iv) Nature of the image	Virtual and erect

Question 14.
At which position will you keep an object in front of a convex lens to get a real image smaller than the object? Draw a figure.
Answer:
The object should be placed beyond 2F₁.

Question 15.
State the rules used for drawing ray diagrams for the formation of an image by a concave lens.
Answer:

1. When the incident ray is parallel to the principal axis, the refracted ray, when extended backwards, passes through the principal focus.
2. When the incident ray is directed towards the principal focus F₂, the refracted ray is parallel to the principal axis.
3. When the incident ray passes through the optical centre of the lens, it passes without changing its direction.

Question 16.
State the characteristics of an image formed by a concave lens.
Answer:
The image formed by a concave lens is always virtual, erect and smaller than the object. It is on the same side of the lens as the object. Generally, it is formed between the optical centre of the lens and the principal focus F₁. If the object is at infinity, the image is a point image formed at F₁.

Question 17.
In the case of image formation by a concave lens, what can you say about the position, nature and size of the image relative to the size of the object?
Answer:
Image formation by a concave lens :
(1) If the object is at infinity, the image is formed at the focus of the lens, on the same side of the lens as the object. It is virtual, erect and much smaller than the object (point image).

(2) If the object is at any finite distance from the lens, the image is formed on the same side of the lens as the object and between the focus and the optical centre of the lens. It is virtual, erect and smaller than the object. The image distance is less than the object distance.

Question 18.
Draw a ray diagram to show image formation by a concave lens.
Answer:

PQ : Object
P’Q’ : Image (virtual, therefore shown by a dotted line),
O : Optical centre,
F₁ : Principal focus,
f : Focal length of the lens
[Note: If in a Board examination, incomplete diagram (as shown below) is given, students should complete it and label its parts as shown in Figure.]

Question 19.
State the Cartesian sign convention for refraction of light (image formation) by a lens.
Answer:
Cartesian sign convention for refraction of light (image formation) by a lens:
In this case, the optical centre (O) of the lens is taken as the origin and the principal axis of the lens is taken as X-axis of the coordinate system.

(1) The object is always placed at the left of the lens.
All distances parallel to the principal axis are measured from the optical centre of the lens.
(2) All distances measured to the right of the origin are taken as positive while distances measured to the left of the origin are taken as negative.
(3) Distances measured perpendicular to and above the principal axis are taken as positive.
(4) Distances measured perpendicular to and below the principal axis are taken as negative.
(5) The focal length of a convex lens is positive and that of a concave lens is negative. (Fig. 7.21)

Question 20.
(i) What is a lens formula? (ii) State it.
Answer:
(i) The relationship between the object distance (u), image distance (v) and focal length (J) of a lens is called the lens formula.
(ii) It is \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)
[Note: The lens formula holds good for all values of u and v and is applicable to a convex lens as well as a concave lens. The sign convention for u, v and f must tie used in solving numerical examples.]

Question 21.
What is meant by the magnification produced by a lens? State the formulae for it.
Answer:
The magnification (M) produced by a lens is the ratio of the height of the image (h₂) to the height of the object (h₁).
M = \(\frac{h_{2}}{h_{1}}\)……….(1)
Also M = \(\frac{v(\text { image distance })}{u \text { (object distance) }}\)……………(2)

Question 22.
When is the magnification produced by a lens (1) positive (2) negative?
Answer:
The magnification produced by a lens is
(1) Positive when the image is virtual (as it is erect)
(2) Negative when the image is real (as it is inverted).

Question 23.
Express the magnification produced by a lens in terms of the focal length of the lens and (1) the object distance (2) the image distance.
Answer:
Magnification (M) produced by a lens

where f is the focal length of the lens:

(2) From eq. (2), we have

Question 24.
An object is kept in front of a lens of focal length + 10 cm. Describe the nature of the image in the following cases: (1) The object” distance is 25 cm. (2) The object distance is 5 cm.
Answer:
Since, the focal length of the lens ( +10 cm) is positive, it is a convex lens.
(1) If an object is kept at 25 cm from the lens, the image will be real, inverted and smaller than the object.
(2) If an object is kept at 5 cm from the lens, the image will be virtual, erect and larger than the object.

Question 25.
Anu and Anand have concave and convex lenses respectively. They took lenses in sunlight and tried to burn two pieces of paper of equal areas and temperature. State which lens will burn the paper. Give the reason. Explain with the help of a diagram, why the other paper did not burn.
Answer:
(1) The convex lens will burn the paper. See Fig. 7.22 for reference. The ray of sunlight will converge at the principal focus of the lens. Hence, if the paper is held at the focus, it will burn due to concentration of heat energy.

(2) The paper held in front of the concave lens, will not burn. For reference, see Fig. 7.23. The concave lens will diverge the rays of sunlight falling on it. Hence, the paper will not burn.

Question 26.
To obtain a magnified real image of a small film strip, which type of lens is used? Where is the film strip placed to obtain the image on the screen?
Answer:
To obtain a magnified real image of a small film strip, a convex lens is used. The film strip is placed between F₁ and 2F₁ and the screen is placed on the other side of the lens.

Question 27.
When an object of height 2 cm is placed in front of a convex lens, the height of the image is found to be 3 cm. State the nature and position of the image giving reason.
Answer:
When an object is placed between the optical centre and the principal focus of a convex lens, the image formed by the lens is virtual and larger than the object. When an object is placed between F₁ and 2F₁ the image formed by the lens is real and larger than the object.

In the above case, if the image is virtual, it will be erect and on the same side of the lens as that of the object. If the image is real, it will be inverted and beyond 2F₂ on the other side of the lens with respect to the object.

Question 28.
You are given a lens which gives a virtual, erect and enlarged image. What type of lens is it?
Answer:
Since the lens gives a virtual, erect and enlarged image, it must be a convex lens.

Question 29.
When an object of height 3 cm is placed in front of a concave lens, the height of the image is found to be 6 cm. State, giving the reason, whether the given statement is true or false.
Answer:
When an object is placed in front of a concave lens, the image formed by the lens is always smaller than the object. In the statement given in the question, the height of the image is reported as greater than that of the object. Hence, the statement given in the question is false.

Question 30.
State two uses of a concave lens.
Answer:

1. A concave lens is used to correct myopia (nearsightedness).
2. In some optical instruments, a combination of a concave lens and a convex lens is used.

Question 31.
State two uses of a convex lens.
Answer:
A convex lens is used (1) to read words in small print (2) to correct hypermetropia (Far-sightedness).

Question 32.
An object is kept in front of a lens of j focal length – 20 cm. Describe the nature of the image when the object distance is 25 cm.
Answer:
Since the focal length of the lens (- 20 cm) is negative, it is a concave lens.
If an object is kept at 25 cm from the lens, the image will be virtual, erect and smaller than the object.
[Note: The nature of the image is independent of the object distance as it is a concave lens.]

Question 33.
An object is placed in front of a convex lens of focal length 20 cm. If the object distance is changed from 60 cm to 40 cm, what can you say about the size of the image relative to that of the object?
Answer:
In this case, the focal length (f) of the lens is 20 cm.
∴ 2f = 40 cm.
When the object distance is 60 cm (which is greater than 2f), the image will be smaller than the object. When the object distance becomes 40 cm (which is equal to 2f), the image will be of the same size as that of the object.

Question 34.
What is the power of a lens?
Answer:
The capacity of a lens to converge or diverge incident rays is called its power. The power (P) of a lens is the inverse of the focal length (f) of the lens.
P = \(\frac{1}{f}\)

Question 35.
What is the unit of power of a lens? Define it.
Answer:
The unit of power of a lens is the dioptre (D).
One dioptre is the power of a lens whose focal length is one metre.
1 dioptre (D) = \(\frac{1}{1 \text { metre }(\mathrm{m})}\)
[Note: The dioptre, the SI unit of power of a lens, is denoted by D.]

Question 36.
What is the sign of the power of (i) a convex lens (ii) a concave lens?
Answer:
The power of a convex lens is positive while that of a concave lens is negative.

Question 37.
If there is an increase or decrease in the focal length of a lens, what will be the effect on the power of the lens?
Answer:
The power of a lens is the inverse of its focal length. Hence, if there is an increase in the focal length of a lens, the power of the lens will decrease accordingly. Similarly, if there is a decrease in the focal length of a lens, the power of the lens will increase accordingly.

Question 38.
If two lenses of focal lengths f₁ and f₂ are kept in contact with each other, state the formula for the focal length of the combination. If P₁ and P₂ are the powers of these lenses, state the formula for the power of the combination.
Answer:
If two lenses of focal lengths f₁ and f₂ are kept in contact with each other, the focal length (f) of the combination is given by \(\frac{1}{f}=\frac{1}{f_{1}}+\frac{1}{f_{2}}\)

[Two lenses kept in contact with each other]
If P₁ and P₂ are the powers of these lenses, the power (P) of the combination is given by P = P₁ + P₂.
[Note: The figures are given only for reference.]

Question 39.
Draw a neat labelled diagram to show the structure of the human eye.
Answer:

Question 40.
What is cornea?
Answer:
The cornea is a thin and transparent cover (membrane) on the human eye through which light enters the eye. Maximum refraction of light rays entering the eye occurs at the cornea.

Question 41.
What is iris?
Answer:
The iris is a dark fleshy screen (muscular diaphragm) behind the cornea in the human eye. Its colours are different for different people.

Question 42.
What is pupil?
Answer:
The pupil is a small circular opening of changing diameter at the centre of the iris in the human eye.

Question 43.
What is the use of the pupil in the human eye?
Answer:
The pupil in the human eye is useful for controlling and regulating the amount of light entering the eye. The pupil contracts in the presence of too much light and dilates when light is insufficient, thus changing the amount of light entering the eye.

Question 44.
With reference to the functioning of the pupil in the human eye, what is adaptation?
Answer:
The tendency of the pupil in the human eye to adjust the opening for light, depending on the intensity of incident light, to control and regulate the amount of light entering the eye is called adaptation.

Question 45.
What is the shape and the size of the human eyeball?
Answer:
The human eyeball is approximately spherical in shape with a diameter of about 2.4 cm.

Question 46.
Name the part of the human eye that forms a transparent bulge on the surface of the eyeball.
Answer:
The cornea forms a transparent bulge on the surface of the eyeball.

Question 47.
Which part of the human eye is located just behind the pupil?
Answer:
A transparent biconvex crystalline lens is located just behind the pupil in the human eye.

Question 48.
What is retina?
Answer:
The retina is a light sensitive screen consisting of a delicate membrane with a large number of light sensitive cells.

Question 49.
What is the nature of the eye lens and what does the eye lens do?
Answer:
The eye lens is a double convex transparent crystalline lens, just behind the pupil. The eye lens provides small adjustment of focal length to form a real and inverted sharp image on the retina.

Question 50.
What happens when light falls on the retina?
Answer:
When light falls on the retina, light sensitive cells of the retina are activated. They generate electrical signals which are passed by optic nerves to the brain. The brain interprets the signals and processes the information such that we perceive the object as it is.

Question 51.
What are ciliary muscles?
Answer:
The muscles which hold the eye lens in its position, and bring about changes in the shape (curvature) of the eye lens, and hence of focal length are known as ciliary muscles.

Question 52.
What is the focal length of the eye lens of a normal eye in relaxed position of eye muscles?
Answer:
The focal length of the eye lens of a normal eye in relaxed position of eye muscles is about 2 cm.

Question 53.
Where does the second focal point of the eye lens of a normal eye in relaxed position of eye muscles lie?
Answer:
The second focal point of the eye lens of a normal eye in relaxed position of eye muscles lies on the retina.

Question 54.
What is meant by power of accommodation of the eye?
Answer:
The ability of the eye lens to adjust its focal length is called the power of accommodation of the eye.

Question 55.
Explain the term power of accommoda¬tion of the eye.
(OR)
Write a short note on the power of accommodation of the eye.
Answer:
Power of accommodation of the eye: The eye lens is held in its position by the ciliary muscles. When we look at a nearby object, the ciliary muscles compress the eye lens so that it becomes rounded. Hence, the focal length of the eye lens decreases. Therefore, the image is formed on the retina of the eye and hence the nearby object is seen clearly.

When we look at a distant object, the ciliary muscles relax so that the eye lens becomes flat. Hence, the focal length of the eye lens increases. Therefore, the image is formed on the retina of the eye and hence the distant object is seen clearly. This ability of the eye lens to adjust its focal length is called the power of accommodation of the eye.

Question 56.
What is meant by accommodation? How is it brought about?
Answer:
The process of focusing the eye on objects at different distances is called accommodation. It is brought about by changing the curvature of the f elastic eye lens making it thinner or thicker.

Question 57.
The human eye is very similar to a photographic camera. The figure given shows the main parts of a photographic camera. Now answer the following questions:

(1) Name the parts of the human eye similar to the following parts of the photographic camera :
(a) Photographic film (b) Aperture.
(2) State one difference between the human eye lens and camera lens.
(3) Name the muscles which adjust the curvature of the eye lens.
(4) Which phenomenon of light is responsible for the working of the eye?
Answer:
(1) (a) The retina in the human eye is similar to the photographic film in a camera.
(b) The pupil in the human eye is similar to the aperture in a camera.
(2) In a photographic camera, the focal length of the lens changes when the position of the lens is changed. In the human eye, the focal length of the eye lens is changed by the ciliary muscles and the distance of the image from the eye lens is fixed.
(3) The ciliary muscles adjust the curvature of the eye lens.
(4) The refraction of light is responsible for the working of the eye.

Question 58.
Have you seen a photographic camera in which a film is used? Compare the human eye with it. State similarities between them. State the points of difference between them.
Answer:
Yes, we have seen a photographic camera in which a film is used.
Cameras, in general, have various shapes and sizes. Some cameras are much bigger than the human eye while some are smaller than the human eye. Here we shall consider a simple camera.

Similarities: In the case of a camera as well as the human eye, it is possible to control the amount of incoming light with the help of a diaphragm and an aperture. Both use a convex lens for focusing. The photographic film in a camera is coated with a photosensitive material. The retina in the eye consists of a large number of light sensitive cells. The photographic film in a camera is processed using chemicals and then prints (photographs) can be obtained using the appropriate paper.

In the human eye, the electrical signals generated by light sensitive cells are passed by optic nerves to the brain which interprets them.

Differences: Cameras come in a variety of sizes and shapes unlike the human eye. Unlike the human eye, a wide variation in exposure time is possible in the case of cameras. The human eye is sensitive in the visible region (red to violet) of the electromagnetic spectrum, while a much wider range of the electromagnetic spectrum can be covered with cameras designed for specific J purposes. In comparison with the human eye, a wider view and range can be covered by a camera.

In comparison with the human eye, a wider intensity (of light) range can be covered with a camera. The retina is indispensable in the human eye, while cameras without a photographic film have been designed with the help of photosensitive materials and are in current use.

[Note: With advances in technology, improved cameras are designed all the time, and the list of differences between the human eye and a camera in general would be practically endless.]

Question 59.
What is meant by the minimum distance of distinct vision?
Answer:
The minimum distance from the normal eye, at which an object is clearly visible without stress on the eye is called the minimum distance of distinct vision.

Question 60.
Explain the term minimum distance of distinct vision.
(OR) Write a short note on distance of distinct vision.
Answer:
Minimum distance of distinct vision; Though the focal length of the eye lens is adjustable, it cannot be decreased below a certain limit. Hence, if an object is very close to the eye, it cannot be seen clearly. For a normal human eye, the minimum distance from the eye at which an object is clearly visible without stress on the eye, is called the minimum distance of distinct vision. For the normal human eye, it is 25 cm.

Question 61.
State four reasons related to problems of vision.
Answer:
Problems of vision are related to (i) weakening of ciliary muscles (ii) change in the size of the eyeball (iii) irregularities on the surface of cornea (iv) formation of a membrane over the eye lens.

Question 62.
What is myopia or nearsightedness? What are the possible reasons of myopia? How is myopia corrected? Explain with diagrams.
Answer:
Myopia or nearsightedness is the defect of vision in which a human eye can see nearby objects distinctly but is unable to see distant objects clearly as they appear indistinct.
In this case the image of a distant object is formed in front of the retina instead of on the retina. [Figs. 7.29 (a), 7.29 (b)]

Possible reasons of myopia: (1) The curvature of the cornea and the eye lens increases. The muscles near the lens cannot relax so that the converging power of the lens remains large. (2) The distance between the eye lens and the retina increases as the eyeball elongates.

Myopia is corrected using a suitable concave lens. Light rays are diverged by the concave lens before they strike the eye lens. A concave lens of proper focal length is chosen to produce the required divergence. Hence, after the converging action of the eye lens, the image is formed on the retina. [Fig. 7.29 (c)]

Question 63.
Observe the following diagram and answer the questions.
(a) Which eye defect is shown in this diagram?
(b) What are the possible reasons for this eye defect?
(c) How is this defect corrected? Write it in brief.

Answer:
(a) Myopia or Nearsightedness

(b) Possible reasons for the defect:
(i) The curvature of the cornea and the eye lens increases. The muscles near the lens cannot relax so that the converging power of the lens remains large.
(ii) The eyeball elongates so that the distance between the lens and the retina increases.

(c) Correction of the defect: This defect can be corrected using spectacles with concave lenses.
A concave lens diverges the incident rays and these diverged rays can be converged by the lens in the eye to form an image on the retina.

Question 64.
What is the sign of the power of the lens used to correct myopia?
Answer:
The power of the lens used to correct myopia is negative.
[Note: It is a concave lens. Negative focal length Negative power.]

Question 65.
In a Std. X class, out of 40 students, 10 students use spectacles, 2 students have ( positive power and 8 students have negative power of lenses in their spectacles.
Answer the following questions:
(1) What does the negative power indicate?
(2) What does the positive power indicate?
(3) Generally which type of spectacles do most of the students use?
(4) What defect of eyesight do most of the students suffer from?
(5) Give two possible reasons for the above defect.
Answer:
(1) The negative power indicates a concave lens or myopia.
(2) The positive power indicates a convex lens or hypermetropia.
(3) Generally, most of the students use spectacles with concave lenses.
(4) Most of the students suffer from myopia.
(5) Two possible reasons for myopia:

1. The curvature of the cornea and the eye lens increases. The muscles near the lens cannot relax so that the converging power of the lens remains large.
2. The distance between the eye lens and the retina increases as the eyeball elongates.

Question 66.
What is hypermetropia or farsightedness? What are the possible reasons of hypermetropia? How is hypermetropia corrected? Explain with figures.
Answer:
Hypermetropia or farsightedness is the defect of vision in which a human eye can see distant objects clearly but is unable to see nearby objects clearly.
In this case the image of a nearby object would fall behind the retina instead of on the retina.
[Figs. 7.31 (a), 7.31 (b)]

Possible reasons of hypermetropia:
(1) Curvature of the cornea and the eye lens decreases. Hence, the converging power of the eye lens becomes less. (2) The distance between the eye lens and retina decreases (relative to the normal eye) and the focal length of the eye lens becomes very large due to the flattening of the eyeball.

Hypermetropia is corrected using a suitable convex lens. Light rays are converged by the convex lens before they strike the eye lens. A convex lens of proper focal length is chosen to produce the required convergence. Hence, after the converging action of the eye lens, the image is formed on the retina. [Fig. 7.31 (c)]

Question 67.
What is the sign of the power of the lens used to correct hypermetropia?
Answer:
The power of the lens used to correct hypermetropia is positive.
[Note: It is a convex lens. Positive focal length ∴ Positive power.]

Question 68.
Given below is a diagram showing a defect of human eye.

Study it and answer the following questions:
(1) Name the defect shown in the figure. (Practice Activity Sheet – 3)
(2) Give two possible reasons for this defect of eye in human beings.
(3) Name the type of lens used to correct the eye defect.
(4) Draw a labelled diagram to show how the defect is rectified by using the lens.
Answer:
A lens having both spherical surfaces puffed up outwards is called a convex lens or double convex lens or biconvex lens. It is thicker in the middle than at the edges.
[Note: A convex lens is also called a converging lens.]

Question 69.
Observe the following figures and complete the table. (Practice Activity Sheet – 1)
Answer:

Question 70.
What is presbyopia? State the reason for this defect. How is presbyopia corrected?
Answer:
Presbyopia is the defect of vision in which aged people find it difficult to see nearby objects comfortably and clearly without spectacles.

Reason of presbyopia: The power of accommodation of eye usually decreases with ageing. The muscles near the eye lens lose their ability to change the focal length of the lens.
Therefore, the near point of the eye lens shifts farther from the eye.

This defect is corrected using a convex lens of appropriate power. The lens converges light rays before they fall on the eye lens such that the action of the eye lens forms the image on the retina.

Question 71.
What is a bifocal lens?
Answer:
A bifocal lens is a lens of which the upper part is a concave lens to correct myopia and the lower part is a convex lens to correct hypermetropia.

[Note: A person suffering from myopia as well as hypermetropia, uses a bifocal lens. Nowadays, the defects of vision such as myopia and hypermetropia can be corrected using contact lenses or by laser surgery.]

Question 72.
(A) Anil cannot see the blackboard writing clearly, but he can see nearby objects clearly.
(i) What is the eye defect he is suffering from?
(ii) How is it corrected?
(B) Anil’s uncle cannot see nearby objects clearly, but he can see distant objects clearly.
(i) What is the eye defect he is suffering from?
(ii) How is it corrected?
Answer:
(A) Anil cannot see the blackboard writing clearly, but he can see nearby objects clearly.
(i) This defect is called myopia (nearsightedness).
(ii) It is corrected using spectacles having concave lenses of appropriate power.

(B) Anil’s uncle cannot see nearby objects clearly, but he can see distant objects clearly.
(i) This defect is called hypermetropia (farsightedness).
(ii) It is corrected using, spectacles having convex lenses of appropriate power.

Question 73.
When are bifocal lenses used in spectacles?
Answer:
When a person cannot see nearby objects as well as distant objects clearly, bifocal lenses are used in spectacles.

Question 74.
Aniket from Std. X uses spectacles. The power of the lenses in his spectacles is -0.5 D. Answer the following questions:
(1) State the type of’ lenses used in his spectacles.
(2) Name the defect of vision Aniket is suffering from.
(3) Find the focal length of the lenses used in his spectacles.
Answer:
(1) Concave lenses are used in the spectacles used by Aniket.
(2) Aniket is suffering from myopia (near-sightedness).
(3) Focal length of the lenses used in his spectacles

= -2 m (Concave lens ∴ Minus sign)

Question 75.
Sunita from Std. X uses spectacles. Her spectacle number is -1.5 D. Answer the following questions:
(1) Name the defect of eye from which she is suffering.
(2) What type of lens is she using?
(3) Find the focal length of the lens.
Answer:
(1) Myopia.
(2) Concave.

(Concave lens ∴ minus sign)
This is the focal length of the lens.

Question 76.
Surabhi from Std. X uses spectacles. The power of the lenses in her spectacles is 0.5 D. Answer the following questions from the given information: (March 2019)
(i) Identify the type of lenses used in her spectacles.
(ii) Identify the defect of vision Surabhi is suffering from.
(iii) Find the focal length of the lenses used in her spectacles.
Answer:
(i) Convex lenses are used in the spectacles used by Surabhi.
(ii) Surabhi is suffering from hypermetropia (farsightedness).
(iii) Focal length of the lenses used in her spectacles

Question 77.
My grandfather uses a bifocal lens in his spectacles. Explain why.
Answer:
In old age, people usually suffer from both myopia and hypermetropia. Therefore, they need spectacles having bifocal lenses.

The upper part of a bifocal lens is a concave lens to correct myopia. The lower part of a bifocal lens is a convex lens to correct hypermetropia.

Question 78.
State uses of concave lens.
Answer:

1. Concave lenses are used for proper working of medical equipment, scanner, CD player – the instruments that employ laser rays.
2. One or more concave lenses are used in a small safety device, fitted in the peep hole in a door, due to which we can see a large area outside the door.
3. Concave lenses are used in spectacles to correct nearsightedness (myopia).
4. A concave lens is used to spread light emitted by the small bulb in a torch over a wide area.
5. A concave lens is used in front of the eyepiece or inside the eyepiece fitted in a camera, telescope and microscope – the instruments employing convex lenses.

Question 79.
State uses of a convex lens.
Answer:
Convex lenses are used in a simple microscope, compound microscope, refracting telescope, camera, projector, spectroscope, spectacles for correcting farsightedness (hypermetropia) and binoculars.

Question 80.
What is meant by the apparent size of an object? With a neat and labelled diagram, explain the relation between the apparent size of an object and the angle subtended by the object at the eye.
Answer:
An object appears small or big depending upon the size of its image formed on the retina of the eye. The size of an object as perceived by the eye is called the apparent size of the object. Consider two objects of the same size, one held near the eye and the other away from the eye as shown in the following figure (Fig. 7.34). The nearby object (PQ) appears larger than the distant object (P₁Q₁).

Also, the angle a subtended by the nearby object at the eye is larger than the angle β subtended by the distant object at the eye. This shows that the apparent size of an object depends upon the angle subtended by the object at the eye. The greater the angle subtended by the object at the eye, the greater is the apparent size of the object. Similarly, the smaller the angle subtended by the object at the eye, the smaller is the apparent size of the object.

Question 81.
With a neat labelled diagram, explain the working of a simple microscope. State uses of a simple microscope.
(OR)
What does a simple microscope consist of? What is the order of magnification obtained by a simple microscope? What is a simple microscope used for?
Answer:
A simple microscope consists of a convex lens of short focal length, usually fixed in a suitable frame with a handle or mounted on a stand.

The object is placed in front of the convex lens of short focal length such that the object distance is less than the focal length. The image is virtual and larger than the object. It is formed on the same side of the lens as the object.

A maximum magnification of about 20 can be obtained by a simple microscope. A simple microscope is used by watch repairers to observe small parts of a watch and by jewellers to examine ornaments. A simple microscope (also called a magnifying glass) is also used to read words in small print.

Question 82.
With a neat labelled diagram, explain the construction and working of a compound microscope.
Answer:
Construction of a compound microscope:

(1) A compound microscope consists of a metal tube fitted with two convex lenses at the two ends. These lenses are called the objective lens (the lens directed towards the object) and the eyepiece (the lens directed towards the eye). Both the lenses are small in size, but the cross section of the objective lens is less than that of the eyepiece. The objective lens has a short focal length. The focal length of the eyepiece is more than that of the objective lens.

(2) The metal tube is mounted on a stand. The principal axes of the objective lens and the eyepiece are along the same line. The distance between the object and the objective lens can be changed with a screw. It is possible to change the distance between the objective lens and the eyepiece.

Working :
(1) The object to be observed is illuminated and placed in front of the objective lens, slightly beyond the focal length of the objective lens. Its real, inverted and enlarged image is formed by the objective lens on the other side.

(2) This intermediate image lies within the focal length of the eyepiece. It serves as an object for the eyepiece. The eyepiece works as a simple microscope. The final image is virtual, highly enlarged and inverted with respect to the original object. It can be formed at the minimum distance of distinct vision from the eyepiece. The final image is observed by keeping the eye close to the eyepiece.

Question 83.
State two uses of a compound microscope.
Answer:
Uses of a compound microscope:

1. It is used to observe blood corpuscles, plant and animals cells, microorganisms like bacteria, etc.
2. It is used in a pathological laboratory to observe blood, urine, etc.
3. It is a part of a travelling microscope used for measurement of very small distance.

Question 84.
What will happen if in a compound microscope, the objective lens is large in size and has a focal length?
Answer:
If the objective lens of a compound microscope is large in size, in addition to the light coming from an object, other unwanted light will be incident on the objective lens. Hence, the image will not be seen clearly. If the objective lens has a large focal length, the magnification produced by it will be less.

Question 85.
(a) In which type of microscope do you find the lens arrangement as shown in the following diagram? (Practice Activity Sheet – 1)

(b) Write in brief, the working of this microscope.
(c) Where is this microscope used?
Answer:
(a) Compound microscope.

(b)
An object appears small or big depending upon the size of its image formed on the retina of the eye. The size of an object as perceived by the eye is called the apparent size of the object. Consider two objects of the same size, one held near the eye and the other away from the eye as shown in the following figure (Fig. 7.34). The nearby object (PQ) appears larger than the distant object (P₁Q₁).

Also, the angle a subtended by the nearby object at the eye is larger than the angle β subtended by the distant object at the eye. This shows that the apparent size of an object depends upon the angle subtended by the object at the eye. The greater the angle subtended by the object at the eye, the greater is the apparent size of the object. Similarly, the smaller the angle subtended by the object at the eye, the smaller is the apparent size of the object.

(c) A simple microscope is used by watch repairers to observe small parts of a watch and by jewellers to
examine ornaments. A simple microscope (also called a magnifying glass) is also used to read words in small print.

Question 86.
(i) Which type of microscope has the arrangement of lenses shown in the following figure?

(ii) Label the figure correctly.
(iii) Write the working of this microscope.
(iv) Where is this microscope used?
(v) Suggest a way to increase the efficiency of this microscope. (Practice Activity Sheet – 2)
Answer:
(i) Compound microscope.

(ii)

(iii) Working:
(1) The object to be observed is illuminated and placed in front of the objective lens, slightly beyond the focal length of the objective lens. Its real, inverted and enlarged image is formed by the objective lens on the other side.

(2) This intermediate image lies within the focal length of the eyepiece. It serves as an object for the eyepiece. The eyepiece works as a simple microscope. The final image is virtual, highly enlarged and inverted with respect to the original object. It can be formed at the minimum distance of distinct vision from the eyepiece. The final image is observed by keeping the eye close to the eyepiece.

(iv)

1. It is used to observe blood corpuscles, plant and animals cells, microorganisms like bacteria. etc.
2. It is used in a pathological laboratory to observe blood, urine, etc.
3. It is a part of a travelling microscope used for measurement of very small distance.

(v) Lenses with appropriate focal lengths should be selected.

Question 87.
State the use of a telescope.
Answer:
A telescope is used to observe a distant object such as mountain, moon, planet, star in the magnified form.

Question 88.
Observe the following figure and answer the questions. (Practice Activity Sheet – 3)
(a) Which optical instrument shows arrangement of lenses as shown in the figure?
(b) Write in brief the working of this optical instrument.

(c) How can we get different magnifications in this optical instrument?
(d) Draw the figure again and labelled it properly.
Answer:
(a) Refracting telescope.

(b) working: When the objective lens is pointed towards the distant object to be observed, the rays
of light from the distant object, which are almost parallel to each other. pass through the objective lens. The objective lens collects maximum amount of light as it is large in size. It forms a real, inverted and diminished image in the focal plane of the objective lens. Now, the position of the eyepiece is adjusted such that this image falls just within the focal length of the eyepiece and serves as the object for the eyepiece which works as a simple microscope.

The final image is highly magnified, virtual, on the same side as that of the object and inverted with respect to the original object. The final image can be observed by keeping the eye close to the eyepiece. If the image formed by the objective lens lies in the focal plane of the eyepiece, the final image is formed at infinity.

(c) We can get different magnifications by using the eyepiece with different focal lengths.

(d)

Question 89.
What is persistence of vision? Give one example of persistence of vision.
Answer:
Persistence of vision: We see an object when its image is formed on the retina. The image disappears when the object is removed from our sight. But this is not instantaneous and the image
remains imprinted on the retina for about \(\frac{1}{16}\) th of a second after the removal of the object.

The sensation on the retina persists for a while. This effect is known as the persistence of vision. It is due to persistence of vision that we continue to see the object in its position for about \(\frac{1}{16}\) th of a second after it is removed.
Example: When a burning stick of incense is moved fast in a circle, a circle of red light is seen.

Question 90.
Name two devices whose working is based on the phenomenon of persistence of vision.
(OR)
Name any two applications based on persistence of vision.
Answer:
The working of a television set and motion picture is based on the phenomenon of persistence of vision.
[Note: These are the examples of persistence of vision in daily life.

Question 91.
How is the phenomenon of persistence of vision used in motion pictures?
Answer:
In motion pictures, photographs of a moving object are taken at the rate of more than sixteen pictures per second. These photographs are projected on the screen at the same rate.
Each picture is slightly different from the other. As a result of persistence of vision, we get the impression of observing the object in continuous motion.

Question 92.
Name the two types of light sensitive cells present in the retina of the human eye. What are their functions?
Answer:
(1) The retina of the human eye contains a large number of light sensitive cells. These cells are of two shapes : (i) rods and (ii) cones.
(2) The rod-like cells respond to the intensity of light.
(3) The conical cells respond to various colours of light. They respond differently to red, green and blue colours. They do not respond to faint light.

Question 93.
When do you say that a person is colour blind?
Answer:
When a person is unable to distinguish between certain colours, he is said to be colour blind.
[Note: (i) Except for being colour-blind, their eyesight is normal, (ii) Rod-shaped cell ≡ rod-like cell, cone-shaped cell = Conical cell.]

Question 94.
Explain the perception of colour in the human eye.
(OR)
Explain in short perception of colour.
(OR)
Write a note on perception of colour.
Answer:
(1) In nature we firld objects of various colours. Perception of colour means to be able to respond to colour.
(2) We can distinguish between various colours due to perception of colour.
(3) The cone-shaped cells on the retina of the eye respond to the various colours when light is bright and communicate to the brain about the colours of the image formed on the retina. This gives us the proper idea about the colours of the object.
(4) If, in the retina of a person, the cone-shaped cells responding to certain specific colours are absent, the person is unable to distinguish between the colours. As a result, he lacks perception of colour.

Question 95.
What is colour-blindness?
Answer:
(1) The retina of the human eye contains a large number of light sensitive cells. These cells are of two shapes : (i) rods and (ii) cones.
(2) The cone-shaped cells respond to various colours of light when light is bright.
(3) Thus, the perception of colour is due to the presence of the cone-shaped cells in the retina.
(4) In the retina of some persons, cone-shaped cells responding to certain specific colours are absent. Hence, these persons are unable to distinguish between certain colours, i.e., they are colour-blind. This defect is known as colour¬blindness.

Question 96.
Why are some persons colour-blind? What is the cause of this defect?
Answer:
In the retina of some persons, cone-shaped cells responding to certain specific colours are absent. Hence, these persons are unable to distinguish between certain colours, i.e., they are colour-blind.

Question 97.
What are the difficulties faced by a colour-blind person?
Answer:
(1) A colour-blind person cannot distinguish between different colours. For example, he cannot distinguish between red and green colours. Also he cannot distinguish between blue and green colours. Red and green, both appear grey. Since a colour¬blind person cannot distinguish between red and green colours, it is difficult for him to cross a road. There is a possibility of an accident while crossing a road.

(2) A colour-blind person cannot distinguish between two objects of different colours, which are otherwise identical, e.g., clothes.

(3) A colour-blind person may have an inferiority complex and hence may find it difficult to mix with other persons.

Give scientific reasons:

Question 1.
A convex lens is known as a converging lens.
Answer:
When rays of light parallel to the principal axis of a convex lens pass through the lens, they converge to a point on the principal axis. Hence, a convex lens is known as a converging lens.

Question 2.
A concave lens is called a diverging lens.
Answer:
When rays of light parallel to the principal axis of a concave lens pass through the lens, they appear to diverge from a point on the principal axis. Hence, a concave lens is called a diverging lens.

Question 3.
In old age, a bifocal lens is necessary for some persons.
Answer:
(1) Some people, in old age, suffer from myopia (nearsightedness) as well as hypermetropia (farsightedness).
(2) Myopia is corrected using a concave lens of appropriate power. Hypermetropia is corrected using a convex lens of appropriate power. Therefore, they need a bifocal lens.

Question 4.
A person suffering from myopia (nearsightedness) uses spectacles of concave lenses.
Answer:
(1) A person suffering from myopia can see nearby objects clearly as the image of a nearby object is formed on the retina, but cannot see distant objects clearly as the image of a distant object is formed in front of the retina instead of on the retina.

(2) A concave lens diverges the rays of light passing through it. When spectacles of concave lenses of appropriate power are used, the parallel rays coming from a distant object are diverged to proper extent before they are incident on the eye lens. Therefore, after the converging action of the eye lens, the image of a distant object is formed on the retina of the eye and hence the distant object can be seen clearly.

Question 5.
A person suffering from hypermetropia (farsightedness) uses spectacles of convex lenses.
Answer:
(1) A person suffering from hypermetropia can see distant objects clearly as the image of a distant object is formed on the retina, but cannot see nearby objects clearly as the image of a nearby object would be formed behind the retina instead of on the retina.

(2) A convex lens converges the rays of light passing through it. When spectacles of convex lenses of appropriate power are used, the rays of light coming from a nearby object are converged to proper extent before they are incident on the eye lens. Therefore after the converging action of the j eye lens, the image of a nearby object is formed on j the retina of the eye and hence the nearby object | can be seen clearly.

Question 6.
You cannot enjoy watching a movie from a very short distance from the screen in a cinema hall.
Answer:
(1) The less the distance between the screen in a cinema hall and the person watching the movie, the more is the intensity of light falling on the eye.
(2) This results in great contraction of the pupil of the eye causing a strain. Hence, you cannot enjoy watching a movie from a very short distance from the screen in a cinema hall.

Question 7.
The rays of light travelling through the optical centre of a lens pass without changing their path.
Answer:
The portion of a lens near the optical centre is like a very thin slab of glass. Hence, the rays of light travelling through the optical centre of a lens pass without changing their path.

Question 8.
A convex lens converges the rays of light falling on it.
Answer:

• A convex lens can be regarded as made of a very large number of portions of triangular prisms. The bases of these prisms are towards the central thicker portion of the lens.
• A ray of light passing through a prism bends towards its base. Hence, a convex lens converges the rays falling on it.

Question 9.
A concave lens diverges the rays of light falling on it.
Answer:

• A concave lens can be regarded as made of a very large number of portions of triangular prisms. The bases of these prisms are towards the edges of the less, i.e, away from the central thinner portion of the lens.
• A ray of light passing through a prism bends towards its base. Hence, a concave lens diverges the rays of light falling on it.

Question 10.
When a burning stick of incense is moved fast in a circle, a circle of red light is seen.
Answer:
The impression of the image on the retina lasts for about \(\frac{1}{16}\) th of a second after the removal of the object. If a burning stick of incense is moved at a rate of more than sixteen revolutions per second, we see a circle of red light due to persistence of vision.

Question 11.
Colour-blind persons are unable to distinguish between different colours.
Answer:
(1) The cone-shaped cells in the retina of a person respond to colours. This makes the perception of colours possible.
(2) In the retina of colour-blind persons, cone-shaped cells responding to certain specific colours are absent. Hence, they are unable to distinguish between different colours.

Question 12.
It is risky to issue a driving license to a person suffering from colour-blindness.
Answer:
A colour-blind person cannot distinguish between different colours. If a driver is colour-blind, he will not be able to distinguish between the colours of the signal and the colours on different sign boards. This will lead to an accident. Hence, it is risky to issue a driving license to a person suffering from colour-blindness.

Distinguish the following:

Question 1.
Real image and Virtual image.
Answer:
Real image:

1. A real image is formed when the light rays starting from an object meet after reflection or refraction.
2. It can be projected on a screen.
3. It is inverted with respect to the object.

Virtual image:

1. A virtual image is formed when the light rays starting from an object (when extended backward) appear to meet after reflection or refraction.
2. It cannot be projected on a screen.
3. It is erect with respect to the object.

Question 2.
Simple microscope and Compound microscope.
Answer:
Simple microscope:

1. In a simple microscope, only one convex lens is used.
2. In this case, the object is placed within the focal length of the convex lens.
3. Its magnifying power is much less than that of a compound microscope.
4. It is used to observe minute parts of a watch, to read words in small print, etc.

Compound microscope:

1. In a compound microscope, two convex lenses, objective and eyepiece, are used.
2. In this case, the object is placed beyond the focal length of the objective lens.
3. Its magnifying power is much greater than that of a simple microscope.
4. It is used to observe blood corpuscles, plant and animal cells, etc.

Question 3.
Compound microscope and Astronomical refracting telescope.
Answer:
Compound microscope:

1. In a compound microscope, the focal length and cross section of the objective lens are respectively smaller than the focal length and cross section of the eyepiece.
2. In this case, to observe the object, the distance between the object and the objective lens is adjusted.
3. It forms a magnified image of a small object.
4. It is used to observe blood corpuscles, plant and animal cells, etc.

Astronomical refracting telescope:

1. In an astronomical refracting telescope, the focal length and cross section of the objective lens are respectively greater than the focal length and cross section of the eyepiece.
2. In this case, to observe the object, the distance between the objective lens and eyepiece is adjusted.
3. It forms a near image of a distant object.
4. It is used to observe sateulites, planets, stars, etc.

Question 4.
Simple microscope and Astronomical refracting telescope.
Answer:
Simple microscope:

1. In a simple microscope, only one convex lens is used.
2. In this case, the object is placed within the focal length of the convex lens.
3. In this case, the image is erect.
4. It is used to observe minute parts of a watch, to read words in small print, etc.

Astronomical refracting telescope:

1. In an astronomical refracting telescope, two convex lenses, objective lens and eyepiece are used.
2. In this case, the object is far away from the objective lens.
3. In this case, the image is inverted.
4. It is used to observe satellites, planets, stars, etc.

Read the following paragraph and answer the questions given below it:

Construction of a compound microscope:
(1) A compound microscope consists of a metal tube fitted with two convex lenses at the two ends. These lenses are called the objective lens (the lens directed towards the object) and the eyepiece (the lens directed towards the eye). Both the lenses are small in size, but the cross section of the objective lens is less than that of the eyepiece. The objective lens has a short focal length. The focal length of the eyepiece is more than that of the objective lens.(2) The metal tube is mounted on a stand. The principal axes of the objective lens and the eyepiece are along the same line. The distance between the object and the objective lens can be changed with a screw. It is possible to change the distance between the objective lens and the eyepiece.
Working:
(1) The object to be observed is illuminated and placed in front of the objective lens, slightly beyond the focal length of the objective lens. Its real, inverted and enlarged image is formed by the, objective lens on the other side.
(2) This intermediate image lies within the focal length of the eyepiece. It serves as an object for the eyepiece. The eyepiece works as a simple microscope. The final image is virtual, highly enlarged and inverted with respect to the original object. It can be formed at the minimum distance of distinct vision from the eyepiece. The final image is observed by keeping the eye close to the eyepiece.
Use: This microscope is used to observe blood cells, microorganisms, etc.

Question 1.
In a compound microscope, which lens has greater focal length?
Answer:
In a compound microscope, the eyepiece has greater focal length.

Question 2.
Where do you place the object to be observed with a compound microscope?
Answer:
In a compound microscope, the object to be observed is placed in front of the objective lens, slightly beyond the focus of the objective lens.

Question 3.
State which distance is adjusted to observe the object with a compound microscope.
Answer:
To observe the object with a compound microscope, the distance between the object and objective lens is adjusted.

Question 4.
State the nature of the final image in compound microscope relative to the object.
Answer:
In a compound microscope, the final image is highly enlarged, inverted and virtual relative to the object.

Question 5.
State the use of a compound microscope.
Answer:
A compound microscope is used to observe blood cells, microorganisms, etc.

Fill in the blanks for a convex lens:

Question 1.

f (m)	0.2	—————–	0.1
P (D)	—————	2	——————

Answer:
[P (D) = \(\frac{1}{f(\mathrm{m})}\)]

f (m)	0.2	0.5	0.1
P (D)	5	2	10

Question 2.

h1 (cm)	—————-	5	10
h2 (cm)	-30	-20	—————-
M	-2	—————–	-0.5

Answer:
[M = \(\frac{h_{2}}{h_{1}}\)]

h1 (cm)	15	5	10
h2 (cm)	-30	-20	-5
M	-2	-4	-0.5

Solve the following numerical problems:

Problem 1.
An object Is kept at 60 cm in front of a convex lens. Its real image is formed at 20 cm from the lens. Find the focal length or the lens.
Solution:
Data: Convex lens, u = -60 cm,

The focal length of the lens = 15 cm.

Problem 2.
The focal length of a convex lens is 20 cm. If an object of height 2 cm is placed at 30 cm from the lens, find (i) the position and nature of the Image (ii) the height of the image (iii) the magnification produced by the lens.
Solution:
Data: Convex lens, f = 20 cm,
u = -30 cm, h₁ = 2 cm, v = ?, h₂ = ?, M = ?

The image will be formed at 60 cm from the lens and on the other side of the lens with respect to the object. It is a real image.

h₂ is negative. This shows that the image is inverted.
The height of the image -4 cm.
(iii) M = \(\frac{h_{2}}{h_{1}}=\frac{-4 \mathrm{cm}}{2 \mathrm{cm}}\) = -2
M is negative, indicating that the image is inverted.
The magnification produced by the lens = -2.

Problem 3.
When a pm of height 3 cm is fixed at 10 cm from a convex lens, the height or the virtual image formed is 12 cm. Find the focal length of the lens.
Solution:
Data: Convex lens, h₁ =3 cm,
h₂ = 12 cm (virtual image), u = -10 cm, f = ?

The focal length of the lens = 13.33 cm [approximately]

Problem 4.
At what distance from a convex lens of focal length 2.5 m should a boy stand so that his image is half his height?
Solution:
Data: Convex lens, f= 2.5 m,
M= –\(\frac{1}{2}\), u=?

∴ u = -3f = -3 × 2.5 m = -7.5 m
This is the object distance.
The boy should stand at 7.5 m from the convex lens so that his image is half his height.

Problem 5.
A convex lens forms a real image or a pencil at a distance of 40 cm from the lens. The image formed is of the same size as the object. Find the focal length and power of the lens. At what distance is the pencil placed from the lens?
Solution:
Data: Convex lens, v = 40 cm,
M = -1, f = ?, h₁ = ?, u = ?
M = = -1 = \(\frac{v}{u}\)
∴ u = -v = -40 cm (object distance)
The pencil is placed at 40 cm from the convex lens.

The focal length of the lens 20 cm.

The power of the lens = 5 D.

Problem 6.
A spherical lens is used to obtain an image on a screen. The size of the image is four times the size of the object. What is the type of lens and at what distance is the screen placed from the lens?
Solution:
Data: M = -4, type of lens? v = ?
As the image formed by the lens is obtained on a screen, it is a real image. The lens is, therefore, a convex 1ens.

The distance of the screen from the lens = 5f.

Problem 7.
An object of height 5 cm Is held 20 cm away from a converging lens of focal length 10 cm. Find the position, nature and size of the image formed.
Solution:
Data: Converging lens (convex lens),
f = 10 cm, h₁ = 5 cm, u = -20 cm, v = ?, h₂ = ?

The image is real and inverted. it is formed at 20 cm from the lens and on the other side of the lens relative to the object.

The height of the image, h₂ = -5 cm
Thus, it is numerically the same as the height of the object.

Problem 8.
An object is placed at 10 cm from a convex lens of focal length 12 m. Find the position and nature of the image.
Solution:
Data: Convex lens, u = -10 cm,
f = 12 cm, v = ?


∴ v = -60 cm
It is negative.
The image is formed at 60 cm from the lens and on the same side of the lens relative to the object. It is virtual, erect, and enlarged.

Problem 9.
An object of height 4 cm is placed in front of a concave lens of focal length 40 cm. If the object distance is 60 cm, find the position and height of the image.
Solution:
Data: f = -40 cm (concave lens),
u = -60 cm, h₁ = 4 cm, v = ?, h₂ = ?

The image Is formed at 24 cm from the lens.
It is on the same side as the object.

The height of the image is 1.6 cm.

Problem 10.
What is the power of a convex lens having focal length 0.5 m?
Solution:
Data: Convex lens, f= 0.5 m, P = ?
P = \(\frac{1}{f}=\frac{1}{0.5 \mathrm{m}}\) = 2D
The power of the lens = 2D.

Problem 11.
The power of a convex lens is 2.5 dioptres. Find its focal length.
(OR)
Calculate the focal length of a corrective lens having power +2.5 D.
Solution:
Data: Convex lens, P = +2.5 D, f = ?
P = \(\frac{1}{f}\)
∴ 2.5 D = \(\frac{1}{f}\)
∴ f = \(\frac{1}{2.5 \mathrm{D}}\) = 0.4 cm = 40 cm
The focal length of the lens = 40 cm.

Problem 12.
Two convex lenses of focal length 20 cm each are kept in contact with each other. Find the power of their combination.
Solution:
Data: f₁ = 20 cm = 0.2 m,
f₂ =20 cm = 0.2 m, P (combination) = ?

∴ Focal length of the combination or the lenses, f = 0.1 m.
P = \(\frac{1}{f}=\frac{1}{0.1 \mathrm{m}}\) = 10 D
The power of the combination of the lenses, P = 10 D.

Problem 13.
Two convex lenses of equal focal lengths are kept in contact with each other. If the power of their combination is 20 D, find the focal length of each convex lens.
Solution:
Data: Convex lens, P = 20 D, f₁ = f₂ = ?
The focal length (f) of the combination of the lenses is given by

This gives the focal length or each convex lens.

Problem 14.
If a convex lens of focal length 10 cm and a concave lens of focal length 50 cm are kept in contact with each other, (i) what will be the focal length of the combination? (ii) what wiil be the power of the combination? (iii) what will be the behaviour of the combination (behaviour as a convex lens/concave lens)?
Solution:
Data: f₁ = +10 cm = +0.1 m (convex lens),
f₂ = -50 cm = -0.5 m (concave lens),
f (combination) = ?, P (combination) = ?

The focal length or the combination of the lenses = 0.125 m = 12.5 cm.

The power of the combination of the lenses 8.D.
(iii) The focal length of the combination of the lenses is positive. This shows that the combination will behave as a convex lens.

Numerical problems for practice:

Problem 1.
Find the focal length of a convex lens which produces a real image at 60 cm from the lens when an object is placed at 40 cm in front of the lens.
Answer:
24 cm

Problem 2.
Find the focal length of a convex lens which produces a virtual image at 10 cm from the lens when an object is placed at 5 cm from the lens.
Answer:
10 cm

Problem 3.
A real image is obtained at 30 cm from a convex lens of focal length 7.5 cm. Find the distance of the object from the lens.
Answer:
u = -10 cm

Problem 4.
An object is kept at 20 cm in front of a convex lens and its real image is formed at 60 cm from the lens. Find (1) the focal length of the lens (2) the height or the image if the height of the object is 6 cm.
Answer:
(1) 15 cm
(2) h₂ = -18 cm]

Problem 5.
An object is kept at 10 cm in front of a convex lens. Its image is formed on the screen at 15 cm from the lens. Calculate (1) the focal length of the lens (2) the magnification produced by the lens.
Answer:
(1) 6 cm
(2)M = -1.5

Problem 6.
An object is kept at 60 cm in front of a convex lens of focal length 15 cm. Find the image distance and the nature of the image. Also find the magnification produced by the lens.
Answer:
v = 20 cm. The image is real, inverted and smaller than the object. M = –\(\frac{1}{3}\)]

Problem 7.
An object of height 2 cm is kept at 30 cm from a convex lens. Its real image is formed at 60 cm from the lens. Find the focal length and power of the lens.
Answer:
f = 20 cm, P = 5 D

Problem 8.
If the power of a lens is 4 dioptres, find its focal length.
Answer:
25 cm

Problem 9.
Find the power of a convex lens of focal length 40 cm.
Answer:
2.5 D

Problem 10.
Find the power of a convex lens of focal length 12.5 cm.
Answer:
8 D

Problem 11.
If for a lens, f = – 20 cm, what is the power of the lens?
Answer:
-5 D

Problem 12.
An object of height 4 cm is kept in front of a concave lens of focal length 20 cm. If the object distance is 30 cm, find the position and the height of the image.
Answer:
v = -12 cm, h₂ = 1.6 cm

Problem 13.
If two convex lenses of focal lengths 10 cm and 5 cm are kept in contact with each other, what is their combined focal length?
Answer:
\(\frac{10}{3}\) cm [approximately 3.33 cm]

Problem 14.
If a convex lens of focal length 20 cm and a concave lens of focal length 30 cm are kept in contact with each other, (i) What will be the focal length of the combination? (ii) What will be the power of the combination? (iii) What will be the behaviour of the combination?
Answer:
(i) f = 60 cm
(ii) P = \(\frac{5}{3}\) D = 1.6667 D (approximately)
(iii) The combination will behave as a convex lens.

Problem 15.
A concave lens of focal length 12 cm and a convex lens of focal length 20 cm are kept in contact with each other, (i) Find the focal length of the combination, (ii) What will be the behaviour of the combination?
Answer:
(i) f = -30 cm
(ii) The combination will behave as a concave lens.