Class 8 – Page 2 – Maharashtra Board Solutions

Pollution Class 8 Science Chapter 8 Questions And Answers Maharashtra Board

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 8 Pollution Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 8 Pollution Question Answer Maharashtra Board

Class 8 Science Chapter 8 Pollution Question Answer Maharashtra Board

1. Following are some statements about pollution. Which type of pollution do those express:

Question a.
Fog seems to be appearing in Delhi during day hours.
Answer:
Air pollution-Smog
(The sentence should have the word Smog and not fog. Smog is fog with smoke. Only fog cannot be polluting, but the smog is.)

Question b.
Many times, vomiting and dysentery occurs after eating ‘panpuri’.
Answer:
Water pollution-Contaminated food and water due to bacteria or virus

Question c.
Problem of sneezing occurs sometimes during visit to garden.
Answer:
Air pollution due to pollens

Question d.
Crop does not grow up in some areas.
Answer:
Soil pollution

Question e.
People living in the busy squares face the problems like short breathing and other respiratory problems.
Answer:
Air pollution due to traffic

2. Read the passage and identify the sentences expressing types of pollution.

Question a.
Nilesh is a student of Std. VII and lives in urban area. It takes about an hour to go to the school by bus. He faces the heavy traffic of two wheelers, four wheelers, rickshaws, buses while going to school. He is facing the problem of asthma since last few days, Doctors recommended him to stay away from urban area. Since then, his mother sent him to the village of his maternal uncle, Nilesh saw the heaps of garbage at many places in village. Foul smell of human and animal wastes was present at many places. Blackish water with foul smell was flowing in a stream. He developed some abdominal disease within few days.
Answer:

It takes about an hour to go to the school. (Due to traffic jam, Nilesh is spending more time in polluted, contaminated air.)
He faces the heavy traffic. (Large scale combustion of fossil fuel.)
He is facing the problem of asthma. (Air pollution – Harmful to human health.)
The heaps of garbage at many places. (Solid waste – Land pollution.)
Foul smell of human and animal wastes. (Biological pollution, air pollution.)
Blackish water with foul smell was flowing in a stream. (Improper sewage management – Water pollution.)
He developed some abdominal disease within few days. (Water pollution – Effect on human health.)

3. Match the pairs from ‘A’ and ‘B’ columns and explain the effect of pollution on human health.

Question a.

Column ‘A’	Column ‘B’
1. Water containing cobalt	a. Mental retardation
2. Methane gas	b. Paralysis
3. Water containing lead	c. Inflammation of lungs
4. Sulphur dioxide	d. Skin cancer
5. Nitrogen dioxide	e. Irritation of eyes

Answer:

Column ‘A’	Column ‘B’
1. Water containing cobalt	b. Paralysis
2. Methane gas	d. Skin cancer
3. Water containing lead	a. Mental retardation
4. Sulphur dioxide	e. Irritation of eyes
5. Nitrogen dioxide	c. Inflammation of lungs

4. True or false.

Question a.
Water does not get polluted by washing the clothes in running water of river.
Answer:
False. (Even if washing of soiled clothes is done in running water, it will cause pollution as the dirt and the waste materials will be added to water. This certainly will cause water pollution.)

Question b.
More the use of electric appliances, more will be the pollution.
Answer:
True. (Most of the electricity is generated in India by burning coal. The power generation plants thus cause lots of air pollution. More the electricity is used by using more appliances, there will be more pollution. However, only power generation through solar energy cannot cause pollution.)

5. Answer the following:

Question a.
What is pollution?
Answer:
Contamination of natural environment that can harmfully affect the environment is called pollution.

Question b.
What are Pollutants?
Answer:
The products which affect the normal functioning of ecosystem and have an adverse effect on plants, animals and humans are called pollutants.

Question c.
What is acid rain?
Answer:
1. When rainwater contains harmful amounts of nitric and sulphuric acids, it is called acid rain.
2. Burning of fossil fuels such as coal, wood, petroleum, etc. releases nitrogen oxide and sulphur oxide into the atmospheric air.
3. Since these oxides are soluble in water, they dissolve in rainwater. Nitrogen and sulphur oxides dissolved in large quantities of water vapour form acids like nitric acid, nitrous acid, sulphurous acid and sulphuric acid.
4. These acids mix with mist, drops of rainwater and snow. They change their composition and fall back on the ground in the form of acid rain.
5. Effects of acid rain are as follows:

Increase in the acidity of soil and water bodies.
Damage to the trees.
Water becomes unsuitable for fish and wildlife.
Buildings, statues, sculptures, bridges, monuments and fences are corroded due to acid rain. Thus, acid rain damages our national assets.
Acid rain affects agriculture and crop lands.

Question d.
What is greenhouse effect?
Answer:

Greenhouse effect is the ; phenomenon due to which global warming and climate change occur.
The earth receives solar energy in the form of heat from the sun. The surface of earth absorbs this heat and reflects it back to the atmosphere as infrared radiation. Some of this heat energy goes directly into space.

Question e.
Which are visible pollutants known to you?
Answer:
1. The polluting substances that are seen easily with the naked eyes can be called as visible pollutants. E.g. Solid wastes, plastic articles, plastic bags, the suspended things in the water, metal refuse, etc.

Question f.
Which are invisible pollutants?
Answer:
The pollutants which are completely dissolved in water or mixed in the air, cannot be seen and hence they can be called invisible pollutants. Since they are not seen, we remain unaware about the presence of these pollutants. E.g. the insecticides spread f on the crops. Aerosols, many hazardous gases in the air, toxic compounds that are totally soluble in water, etc.

6. Answer the following.

Question a.
Give two examples of each of water, soil and air pollution from your residential area.
Answer:
Air pollution:

New buildings are constructed. Old structures are demolished. This is creating lots of dust pollution. The air is full of particulate matter.
The number of vehicles on the road has tremendously increased. This causes smoky environment.

Water pollution:

The sea shows lots of floating plastic and decaying flowers, etc. When beaches are visited it is a common sight.
Many fishes are seen dying in great numbers and are washed off to the shore.

Soil pollution :

Everywhere garbage heaps are seen. In that plastic bags, needles, old medicine vials and cartons are seen in abundance.
The sludge brought by rainwater is spread everywhere and that causes stink.

Question b.
How does the pollution occur due to vehicles? Give the names of vehicles causing least pollution.
Answer:

More than 50% of the air pollution is caused by vehicular traffic.
Particulate matter, unburnt hydrocarbons, CO, nitrogen oxides and carcinogenic hydrocarbons are present in the automobile exhausts.
Fossil fuels like petrol, diesel, natural gas, gasoline, etc. which are burnt to run the automobiles lead to the emission of CO₂ and other gases.
Therefore, vehicles are said to be the major contributors to air pollution.
The only vehicle which is non¬polluting is bicycle. The four-wheelers which are battery operated are also manufactured recently.

These two types of vehicles are eco-friendly. The cars that run on C.N.G. are also said to be lesser polluting.

Question c.
What are natural reasons causes for water pollution?
Answer:
The natural causes of the water pollution:
1. If organic pollutants are added to the water there is an overgrowth of weeds such as Eichhornia. The growth of algae also makes the water unsuitable for consumption. These aquatic plants release oxygen during daytime but by night they require oxygen thus depleting the dissolved oxygen level. The natural characters of water are then changed.

2. The decomposing matter when added to the water make it polluted and stinking.

3. Due to deposition of sludge or eroded soil, the rivers change their path and divert from original flow. The currents are also changed. Deposition of sludge makes the water polluted.

4. Due to soil erosion, surrounding the water bodies, the microbes, bacteria, protozoans and the worms and larvae of nematodes enter the water causing severe biological pollution. Many inorganic pollutants are also added to the water. The fungand bacteria present in the water make it non-potable. Such water spreads water-borne diseases.

Question d.
Suggest four preventive measures for air pollution.
Answer:
The following methods are adopted to control air pollution from the industries:

The source discharge is diluted by tall chimneys.
There are source correction methods like changing the raw material, equipment modification, process modification, etc.
Effective pollution controlling equipment like dust collectors, electrostatic precipitators, wet scrubbers, etc. should be used.
There should be ban and control over atomic tests and chemical weapons on the international level.

Question e.
Explain relation between greenhouse effect and global warming.
Answer:
Because of greenhouse effect, there is increase in the global temperature. The heat on the earth remains trapped due to envelope of greenhouse gases. The percentage of carbon dioxide and methane is constantly increasing and hence there is increase in the temperature too. Thus the greenhouse effect is directly related to the global warming.
Effects of this relation between greenhouse effect and global warming are as follows:

The polar ice caps and the glaciers at both the poles are melting due to increased temperature.
The oceans’ water is rising due to this melted ice. The sea level rise is causing coastal land submergence. The islands at various regions are threatened of drowning.
Many species of living organisms are already extinct due to global warming. The rest are also threatened.
Wild animals are showing weird migrations. Polar bear is endangered.
The increased temperature of the oceanic water is causing many changes in the tides and currents. This results into increased occurrence of cyclones, hurricanes and cloud bursting. The natural disasters are rising in last decade.
The agricultural production is decreasing. The regions with less rainfall are facing draughts.

Question f.
Construct two slogans each on air, water and soil pollution.
Answer:
Air pollution:

Be a part of the solution and not part of pollution.
Show your care, clean your air.

Water pollution:

Water, water everywhere, Not a drop to drink. The pollution is making all the water stink.
Save the fish and the little turtle. Don’t throw plastic or it will encircle.

Soil Pollution:

Don’t be mean, keep environment clean.
Let’s keep land clean, together only we can win.

7. Classify the following pollutants into natural and manmade categories.

Question
Classify the following pollutants into natural and manmade categories.
Sewage, dust, pollen grains, chemical fertilizers, vehicular smoke, algae, pesticides, waste of animals and birds.
Answer:

Man-made	Natural
1. Sewage	1. Dust (Natural)
2. Dust (Construction related)	2. Pollen grains
3. Chemical fertilizers	3. Algae
4. Vehicular smoke	4. Waste (Excreta) of animals and
5. Pesticides

Project:

Question 1.
Visit the water testing laboratory in your area and collect the information about tests for checking the purity of water.

Question 2.
Visit the square having heavy traffic in your area and report the pollution at different times of day and find out the duration of maximum pollution.

Class 8 Science Chapter 8 Pollution Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Natural pollutants are destroyed in due course of time by …………. .
Answer:
Natural pollutants are destroyed in due course of time by nature’s rule.

Question 2.
Air pollutants with ……….. cause colour change in paints, oil paintings, nylon, etc.
Answer:
Air pollutants with sulphur cause colour change in paints, oil paintings, nylon, etc.

Question 3.
Boards indicating the …………. are displayed in busy squares in metro cities.
Answer:
Boards indicating the air quality index are displayed in busy squares in metro cities.

Question 4.
Soil ………… decreases due to pollution.
Answer:
Soil fertility decreases due to pollution.

Question 5.
Problem of …………… pollution increases due to soil pollution.
Answer:
Problem of water pollution increases due to soil pollution.

State whether the following statements are True or False. Explain your statement:

Question 1.
Polluted water is responsible for diseases such as cholera, hepatitis, typhoid, skin diseases and diseases of the alimentary canal.
Answer:
True. (The water sources if they are contaminated with biological pollutants such as bacteria, viruses or protozoans, can cause variety of water-borne diseases.)

Question 2.
When water is mixed with natural or artificial unwanted material, the dissolved oxygen level of such water increases.
Answer:
False. (When water is mixed with natural or artificial unwanted material, the dissolved oxygen level of such water decreases. This causes harm to the resident animals. However when aquatic weeds and algae outgrow in number it causes rise in oxygen only during day time.)

Question 3.
Though any amount of pollutants are added to the soil, the toxic substances do not leach into water.
Answer:
False. (The toxic substances added to the soil can leach in the groundwater and cause water pollution.)

Identify the odd term:

Question 1.
Industrialization, Population explosion, Mining, Vehicular transport, Dust storms.
Answer:
Dust storms (All others are man-made causes environmental degradation.)

Question 2.
Poisoning, asthma, Silicosis, respiratory diseases.
Answer:
Silicosis (All others are effects of methane.)

Question 3.
Irritation of eyes, respiratory tract, excess mucus, mental weakness
Answer:
Mental weakness (All other are effects of sulphur dioxide.)

Question 4.
Volcanic eruption, Earthquake, Atomic explosion, Forest fires.
Answer:
Atomic explosion (All others are natural causes of air pollution.)

Question 5.
Uranium, Sulphur, Thorium, Plutonium.
Answer:
Sulphur (All others are elements which are used in the production of atomic energy.)

Consider the relation between the items in the first pair and write the correlation for second pair:

Question 1.
Industrialization: Sulphur compounds : :…………………. : Lead compounds
Answer:
Use of fuels/Transportation

Question 2.
City where smoke and soot caused it to be called black city : Petersburg : : Indian city where worst ever industrial accident has occurred : ……………….
Answer:
Bhopal

Question 3.
Arsenic and Cadmium : Inorganic water pollutants : : Weedicides and insecticides : ………….
Answer:
Organic water pollutants.

Write definitions:

Question 1.
Air pollution.
Answer:
Contamination of air by toxic gaseous and particulate pollutants in concentration which is harmful to human beings and his surroundings is called air pollution.

Question 2.
Water pollution.
Answer:
When toxic and unwanted substances enter, dissolve or remain suspended in the water bodies deteriorating the quality of water and affecting the aquatic ecosystem, then it is known as water pollution.

Question 3.
Soil pollution.
Answer:
Soil pollution is the phenomenon caused due to natural or man-made causes, which occurs when there are changes in its physical, biological and chemical properties of the soil leading to decreased fertility due to either natural or man-made reasons.

Distinguish between the following:

Question 1.
Degradable and Non-degradable pollutants:

Degradable pollutants	Non-degradable pollutants
1. Degradable pollutants can degrade on their own after some time.	1. non-degradable pollutants cannot degrade on their own.
2. Degradable pollutants are usually acted upon by microorganisms to reduce them to inorganic substances.	2. non-degradable pollutants are not acted upon by microorganisms and hence are not reduced to inorganic substances.
3. Degradable pollutants are not accumulated in nature.	3. non-degradable pollutants accumulate in nature and remain there for a long period of time.
4. Degradable pollutants emit foul odour when they are being decomposed.	4. non-degradable pollutants may not emit foul odour as they are not decomposed.
5. Vegetables and fruits, food refuse, organic matter, etc. form degradable pollutants.	5. Metals, plastic, glass, etc. form non-degradable pollutants.

Question 2.
Industrial waste and Domestic waste:

Industrial waste	Domestic waste
1. Most of the industrial waste contains non-degradable pollutants.	1. Most of the domestic waste contains bio-degradable pollutants.
2. Industrial wastes are produced during industrial and manufacturing processes.	2. Domestic wastes are produced in every home due to day to day activities.
3. Pollution monitoring and controlling bodies like MPCB keep a watch on the proportion of industrial wastes.	3. Pollution monitoring and controlling bodies like MPCB do not keep a watch on the proportion of domestic wastes. It is the individual responsibility of every citizen to reduce the amount of domestic waste that they produce.
4. Fly ash from thermal power plants, heavy metals, chemicals, etc. form the industrial wastes.	4. Garbage, domestic refuse, and discarded solid materials containing food waste, paper, cardboard, peels of fruits, vegetable matter, etc. form the domestic wastes.

Give scientific reasons:

Question 1.
Domestic sewage is harmful for all forms of life.
Answer:

Domestic sewage contains water
There are detergents and washing private vehicles. powders containing phosphate, which are used to soften the water.
These chemicals are harmful to aquatic animals.
They also contain disease. causing pathogenic bacteria and viruses.
Hence, domestic sewage is harmful for originating from kitchen, bathrooms, toilet, forms of

Question 2.
Use public transport instead of private vehicles.
Answer:

All the automobiles use fossil used to soften the water. fuels Burning of fossil fuels causes air pollution by gaseous pollutants as well as by particulates.
Toxic gases such as CO, CH₄, SO₂, etc. are emitted through automobile exhausts.
When each person uses private vehicles, the proportion of air pollution increases.
Instead, public transport helps to reduce air pollution it will also help to ease trafficams.
Therefore, as a role of citizen in pollution control, public transport should be used instead of private vehicles.

Question 3.
Due to agriculture, there can be a lot of air pollution.
Answer:

During agricultural practices, open field burning is done. Due to this burning there is emission of gases like SO₂, CO₂, CH₄, CO and oxides of nitrogen along with large amounts of particulate matter.
In agricultural practices, pesticides used emit toxic chemicals.
Industrial farms pollute air by emitting foul odour and airborne pollutants.
When manure is decomposed, there is production of greenhouse gases.

Question 4.
A hole has been observed in the ozone layer in the stratosphere near Antarctica.
Answer:

Ozone layer depletion is mainly caused due to the action of CFC (Chlorofluorocarbon) molecules in the air.
Due to various increased activities of humans, the magnitude of air pollution has been increasing in the last few decades.
CFC molecules were used as coolants in refrigerators, freezers and air conditioners.
They were also present in industrial solvents, dry cleaning agents and hospital sterilants, aerosols and foam. Due to such enhanced use, much of the CFCs were liberated in the last few years.
CFC molecules are decomposed by ultraviolet rays which release chlorine and fluorine molecules.
Chlorine and fluorine react with the ozone resulting in a hole in the ozone layer present in the stratosphere.

Therefore, a hole has been observed in the ozone layer in the stratosphere above Antarctica.

Answer the following.

Question 1.
What do you mean by ozone layer depletion? What are the causes of ozone layer depletion?
Answer:
1. The ozone layer is present at the top of the stratosphere. The stratosphere is the second layer of the atmosphere which is present 48 km above the earth’s surface.
2. Ozone layer is protective layer for living organisms of the earth, as it absorbs harmful UV rays from the sun. When this layer is reduced or destroyed, it is called ozone layer depletion.

3. Causes of the ozone layer depletion:

The main cause of ozone depletion are CFC molecules.
Chlorine atoms are present in chlorofluoro-carbons (CFC) molecules. They react with ozone and deplete it.
CFCs are used as coolants in refrigerators, freezers and air conditioners manufactured before 1995.
CFCs are also present in industrial solvents, dry cleaning agents and hospital sterilants (sterilizers), aerosols and foam. All the above materials release a lot of CFCs into the atmosphere.
CFC molecules are broken down by ultraviolet radiations which result in release of chlorine and fluorine, which further reduce the ozone layer.

Question 2.
What adverse effect does ozone depletion have?
Answer:

When the ozone layer is depleted, the ultraviolet radiations of the sun can reach the earth’s surface in greater proportion.
This results in damage to animal and plant life on the earth.
Ultraviolet rays cause skin cancer and cataract in human beings.
The ozone hole is seen in the stratosphere above Antarctica.

Question 3.
Describe the effects of air pollution on animals and plants.
Answer:
1. Effects of air pollution on animals:

Air pollutants affect breathing of the animals.
Particulate pollutants can cause problems to the wildlife.
Particulate matter containing heavy metals is accumulated in the bodies of animals. The accumulated heavy metals at high levels in the body tissues, can cause problems. ‘
Acid rain causes serious problems to animal life.

2. Effects of air pollution on plants:

Various parts of the plant show reduced growth after coming in contact with air pollutants.
The leaves show yellowing or chlorosis on exposure to air pollutants.

Question 4.
What are man-made reasons for water pollution?
Answer:
The effluents and other substances released by man into the surrounding water bodies together can be called man-made reasons for water pollution.
1. Domestic sewage: The excreta, urine and other domestic-use water is added to the water bodies in many cities and villages. In big metro-cities, the sewage is partially treated but these management practices are not enough.

2. Industrial effluent: Different industries and factories release effluents which may contain toxic and harmful components, such as various pigments, bleaching chemicals, leather pieces, fibres, mercury, lead, etc.

3. Oil pollution: Oil spillages are seen in the seas due to leakage of crude oil. The crude oil is hazardous as it contains cancer causing hydrocarbons.

4. Fertilizers and pesticides: These compounds when used in farm, may get washed off to nearby water body. The chemical fertilizer containing N, P, K cause water pollution. Pesticides such as endrin, chlorine, carbonate containing pesticides, etc. are mixed with water. They cause contamination of the aquatic animals.

5. The wrong behaviour of human beings causes water pollution. The addition of wastes, defecation near coasts, washing clothes, decomposing hemp and flax in water, disposal of ashes, floral offerings to god, dumping ashes all such activities result into water pollution.

6. The warm water released into the water body through thermal power plants cause thermal pollution.

Question 5.
What are the effects of water pollution on human beings?
Answer:
The water-borne diseases that are caused by different bacteria and viruses cause infections to human beings through contaminated water. Some bacterial and viral diseases are spread through epidemics. Cholera, hepatitis, enteritis, diarrhoea, typhoid are such diseases that can cause severe infections to man. Polluted water also cause skin diseases and deformities of bones, Some pollutants accumulated in vital organs cause their ailments. Liver, kidneys, brain, etc. are affected in this way. Person may develop hypertension too due to pollutants.

Question 6.
What are the effects of water pollution on the ecosystem?
Answer:
Biological effects:

Plants in the ecosystem show retarded growth, resulting into species loss.
Due to imbalance in the ecosystem, the food chain and food web is disturbed.
Pollutants cause mortality in fish and other aquatic animals.
Oil slick causes harmful impact on the marine birds.
Useful bacterial fauna in the water is lost.

Abiotic effects:

Pollutants cause changes in physical and chemical properties of water.
Salinity of the water changes.
Dissolved oxygen in the water is depleted, causing mortality of fishes.

Question 7.
Describe the effects of air pollution on the environment.
Answer:
Air pollution can cause the following serious effects on the environment:

Deforestation and fuel consumption bring about rise in CO₂ concentration.
Excess CO₂ in air causes rise in atmospheric temperature of the earth.
The increased temperature is called global warming.
The global warming results into melting of glaciers, subsequently causing rise in the sea level.
There is a change in the climate and pattern of rainfall. This may indirectly affect the agricultural production.

Question 8.
Describe the effects of soil pollution.
Answer:
Effect of soil pollution:

There are many pathogenic bacteria, viruses and parasitic intestinal worms in the sewage sludge. These are able to cause many diseases.
Soil and vegetable crops are contaminated by manure made from human and animal excreta containing pathogens. This can lead to various diseases.
There is loss of fertility and productivity of soil and land due to soil pollution.
Soil pollution leads to water pollution, when toxic chemicals leach into the groundwater. Similarly, when contaminated soil enters into streams or lakes, it also causes water pollution.
Radioactive materials and soil contaminants can travel through food chains. They move away from the soil into crops, livestock and human bodies.

Question 9.
How do biodegradable and non- biodegradable wastes cause land pollution?
Answer:

Biodegradable material is mainly present in the domestic waste.
It is in the form of food waste, peels of fruits, vegetables, etc.
Paper is also a main part of the domestic waste which is biodegradable.
Polythene bags, plastic waste and footwear, etc. are non-biodegradable waste from the domestic sources. All of these pollute the land.

Question 10.
How do you protect soil from being polluted?
Answer:

We should not throw domestic waste and industrial waste indiscriminately on the land, so that it contaminates soil.
Proper disposal of solid wastes and more importantly safe disposal of biomedical waste material should be practised.
Instead of throwing non-biodegradable materials on the land, they should be properly recycled and reused.
Biodegradable materials should be composted and converted into useful manure, rather than throwing them to cause pollution of the soil.
Excessive use of fertilizers and pesticides should be avoided so that the soil does not get contaminated.

Question 11.
What are the different laws to prevent pollution?
Answer:
The different laws to prevent pollution are as follows:

Water (Prevention and Control of Pollution) Act, 1974.
Air (Prevention and Control of Pollution) Act, 1981.
Environment (Protection) Act, 1986.
There are different laws and rules which have been made for the disposal of hazardous waste, biomedical waste, solid waste and prevention of noise pollution.

Question 12.
Who implements the laws related to pollution?
Answer:
The Central Pollution Control Board (CPCB) and Maharashtra Pollution Control Board (MPCB) check whether the organizations like factories, industrial estates, Municipalities, Zilla Parishads, Panchayat Samities and Gram Panchayats follow all the laws related to control of pollution.

Use your brain power!

Question 1.
Which types of pollutants are observed?
Answer:
Pollutants are of many varied types. They can be classified according to their sources, according to which ecosystem they are polluting, and according to their characteristics.

Question 2.
Whether the pollutants are degradable or non-degradable?
Answer:
Some pollutants are biodegradable while some are non-biodegradable. The pollutants that spread in the air are in the form of gases or particulate matter. Though they are non-degradable, they constantly make chemical reactions with each other.

The pollutants thrown in water and on land are of both the types. Pollutant like plastic is totally non-biodegradable. The biodegradable substances can be decomposed by various bacteria and fungand are converted back into elemental form. The pollutants added in S the water are also of two types. The heavy metals and colours are non-degradable.

Think about it:

Question 1.
If natural materials are pollutants, why do we not perceive their adverse effects during their use? When such materials are referred as pollutants?
Answer:
The natural pollutants are active only for a short duration. Due to natural reasons their activity is limited, and they are lost after a specific time. Their sources are not continuous and their spread too is not regular as in case of man-made pollutants which are emitted steadily.

Thus, we can avoid these substances. We also use them in limited quantity. Therefore, the natural substances, though may be polluting in nature, we are unable to perceive its toxicity. However, if we use them in abundance and create an imbalance, then its effect can be experienced as a great hazard.

Question 2.
What are the reasons other than those mentioned on the textbook page no. 55 mentioned responsible for air pollution?
Answer:
1. The automobile vehicles like two-wheelers and four-wheelers are increasing tremendously in numbers. This uncontrolled number of vehicles and their heavy traffic is causing air pollution to very high level in megacities.
2. Construction industries, demolition of the old buildings, digging the roads, are such activities which are adding to the particulate air pollution of the cities.
3. The bursting of firecrackers on the occasion of festivals and ceremonies, the spread of gulal during processions are also actions which result into unwanted air pollution.
4. Aeroplane traffic, rocket launching, industrial farming are the modern sources of air pollution.

Question 3.
Whether the vehicles with two- stroke engine cause more pollution than four stroke engine?
Answer:
Yes, they do. Scooters and motor cycles are more dominant source of air pollution as they emit soot and organic particles. In urban areas this proportion is high. These particles are toxic and they create heavy air pollution.

The two-wheelers have two-stroke engines. Such engines are far less efficient in burning the fuel that is used in the vehicles. The exhaust systems are also less effective at removing pollutants. On the contrary most of the four-wheelers have catalytic converters. Therefore, the exhaust fumes from scooters contain higher levels of the chemicals found in the fuel and oil they use.

The vehicles with two-stroke engine such as two wheelers emit significantly more primary organic aerosols and volatile organic compounds from incomplete burning of the fuel. They also produce significant secondary organic aerosols as gases released from the exhaust react with the air and microscopic particles of soot.

These pollutants increase the risk of heart and lung disease. Older two-stroke vehicles produced reactive oxygen molecules that are known to be potentially harmful for lung health. In recent times there is excessive use of two-wheelers which is deteriorating the air quality to great extent.

Question 4.
Give 5 examples of each of domestic waste, biological waste and agricultural waste and write in your own words about soil pollution due to those wastes.
Answer:
Domestic waste:

Empty containers of medicines, papers, bottles, etc.
Plastic
Glass pieces
Old utensils, clothes
Tins and cartons of used items, the discarded household items.

Biological waste:

Dead corpse of animals.
Urine and faeces
Peels of fruits, stalks of vegetables and fruits.
Food waste
Garlands and old bouquets.

Agricultural waste:

The stubs of crops after the grains are removed.
Cattle dung and urine
Some persistent amount of insecticides
Some amount of fertilizers
Empty containers, bags, cartons of insecticide, chemical fertilizers, seeds, gunny bags, etc.

Diagram based questions:

Question 1.
Given below is a diagram showing hazardous polluting event.
Explain what is this and what are its effects shown in the diagram.

Answer:
The above picture depicts the formation and effects of acid rain. The toxic gases such as SO2 , CO2 and NO2 are released through the chimneys of factories. These oxides are released in air. They get dissolved in the rainwater and reach back the earth’s surface in the form of acids. The plants, animals and houses are being damaged due to this acid rain.

Question 2.
Draw a well labelled diagram to show greenhouse effect.
Answer:

Activity based questions:

Question 1.
Discuss the issues like ‘dry waste-wet waste’ and ‘toilet in each home’ and write information in your own words.

MCQs based on practical:

Question 1.
Which fertilizers when used in excessive amounts cause soil pollution that spreads to neighbouring water bodies and cause water pollution too?
(a) Chemical
(b) Organic
(c) Artificial
(d) Compost
Answer:
(a) Chemical

Question 2.
What is the type of pollutants that are present in the industrial effluents that is released in the rivers and sea?
(a) Inorganic
(b) Organic
(c) Biological
(d) Biomedical
Answer:
(a) Inorganic

Question 3.
What grows in excess when eutrophication of the water bodies take place?
(a) Plants
(b) Algae
(c) Fishes
(d) Fungi
Answer:
(b) Algae

Question 4.
Which of the following is seen in the polluted water body?
(1) flowers used in pooja
(2) fruits
(3) fishes
(4) aquatic insects
(5) plastic bags
(6) turtles
(7) thick growth of algae
(8) light blue colour of water
(9) cattle wading in water
(10) broken idols
(a) (1) (3) (5) (6) (9) (10)
(b) (1) (2) (5) (7) (9) (10)
(c) (1) (3) (6) (8) (9) (10)
(d) (1) (2) (4) (7) (8) (9)
Answer:
(b) (1) (2) (5) (7) (9) (10)

Question 5.
Which is the easiest method to identify the polluted water?
(a) To taste the water
(b) To check the depth of water
(c) To observe colour and odour of the water
(d) To swim in the water
Answer:
(c) To observe colour and odour of the water

Formative Evaluation:

Question 1.
Which factors are responsible for pollution shown in the following pictures?

Question 2.
Compare the two neighbouring photographs.

8th Std Science Questions And Answers:

Man-made Materials Class 8 Science Chapter 17 Questions And Answers Maharashtra Board

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 17 Man-made Materials Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 17 Man-made Materials Question Answer Maharashtra Board

Class 8 Science Chapter 17 Man-made Materials Question Answer Maharashtra Board

1. Try to find it:

Question a.
Plastic shows …………. property, hence it can be moulded to any shape.
Answer:
Plastic shows plasticity property, hence it can be moulded to any shape.

Question b.
Motor cars are coated with ……… .
Answer:
Motor cars are coated with Teflon.

Question c.
Thermocol melts at ………… °C.
Answer:
Thermocol melts at more than 100 °C (it is about 240 °C).

Question d.
…………….. glass dissolves in water.
Answer:
Alkali silicate or water glass dissolves in water.

2. Who is my partner?

Question a.

Column ‘A’	Column ‘B’
1. Lead glass	a. Plates
2. Bakelite	b. Mattresses
3. Thermocol	c. Electric bulb
4. Optic glass	d. Electric switch
5. Polypropylene	e. Lens

Answer:

Column ‘A’	Column ‘B’
1. Lead glass	c. Electric bulb
2. Bakelite	d. Electric switch
3. Thermocol	a. Plates
4. Optic glass	e. Lens
5. Polypropylene	b. Mattresses

3. Answer the following.

Question a.
Thermocol is produced from which material?
Answer:
Thermocol is made from polystyrene which is also a complex thermoplastic substance.

Question b.
Write uses of PVC.
Answer:
PVC or Polyvinyl chloride is used for making bottles, raincoat, pipes, handbags, shoes, electric cable insulation, furniture, ropes, toys, etc.

Question c.
Write the natural or man-made raw material of the following items.
Mattress, beaker, bangle, chair, gunny bag, broom, knife, pen.
Answer:

Items	Natural raw material	Man-made raw materials
Mattress	Cotton, Coir (Jute fibres)	Polypropylene
Beaker	___	Glass (Silicate or borosilicate glass)
Bangle	Gold, silver, lac, copper	Plastic, Glass
Chair	Wood	Plastic (PVC)
Gunny bag	Jute, cotton	Plastic (PVC)
Broom	Plant fibres	Plastic fibres (PVC)
Knife	Metals such as iron	Plastic
Pen	Metals	Plastic

Question d.
Which are the main ingredients of glass?
Answer:
The main ingredients of glass are sand and silica.

Question e.
How the plastic is produced?
Answer:

Plastics are derived from natural materials such as natural gas, oil, coal, minerals and plants.
The first synthetic plastics were i derived from cellulose, a substance found in plants and trees. This cellulose was heated with chemicals and resulted in a plastic like material.
In modern times, the different raw materials are used for making plastics, but most plastics are made from the hydrocarbons present in the natural gas, oil and coal.
Plastics are simply chains of like molecules linked together. These chains are called polymers. Thus, many plastics begin with “poly,” such as polyethylene, polystyrene and polypropylene.
These polymers are made of carbon and hydrogen and sometimes oxygen, nitrogen, sulphur, chlorine, fluorine, phosphorous or silicon.
Plastic is produced in factories by suitable chemical reactions.

4. Distinguish between.

Question a.
Man-made material and natural material
Answer:

Man-made material	Natural material
1. The man-made materials are obtained from processes in scientific laboratory.	1. Natural materials are obtained from nature.
2. Man-made materials are subjected to rigorous processing to alter the material for serving the intended purpose.	2. Natural materials are subjected to less treatment and processing.
3. Man-made materials are typically much more durable having a very long lifespan.	3. Natural materials have shorter lifespan, because these materials were once alive and so gradually perish over time.
4. Maintaining man-made materials require less care and attention.	4. Maintaining natural materials requires lots of care and continuous attention.
5. Man-made materials can have a negative environmental impact because they are not sustainable. E.g. Glass, plastic, Thermocol, soil, metals, rubber.	5. Natural materials do not have a negative environmental impact because they can be degraded easily. E.g. Cotton, silk, wood.

Question b.
Thermoplastic and Thermosetting plastic:
Answer:

Thermoplastic	Thermosetting plastic
1. The plastic that can be moulded as per our wish is called thermoplastic.	1. The plastic in which a specific shape is given with the help of mould and this shape cannot be changed again on heating is called thermosetting plastic.
2. Thermoplastic substances can be recycled and reused. E.g. PVC – Polyvinyl chloride, PS – Polystyrene, PE – Polyethylene and PP – Polypropylene are types of thermoplastics.	2. Thermosetting plastic cannot be reused again. E.g. Bakelite, Melamine, Polyurethane and polyster are the types of thermosetting plastics.

5. Answer the following in your own words.

Question a.
Explain the effect of following materials on environment and human health.
1. Plastic
2. Glass.
3. Thermocol.
Answer:
1. Plastic:

Plastic is non-degradable substance. Hence if thrown in any ecosystem, it remains unchanged for many years.
It is one of the worst environmental pollutants as its disposal is a major problem.
If thrown in water bodies, it affects the aquatic animals. Many of turtles mistake it for algae and eat the plastic. Eventually such animals die due to choking.
In terrestrial environment, the grazing animals like cattle are affected due to plastic.
If burnt it emits very toxic gases.
In landfill sites, it remains unchanged for thousands of years.

2. Glass:

The glass production is carried out at high temperatures of about 1500 °C. This burning emits many hazardous gases like sulphur dioxide, nitrogen dioxide, carbon dioxide. These gases cause the greenhouse effect.
Moreover, glass being non-degradable, cause pollution.
If broken glass pieces or any waste glass material is disposed into aquatic environment, it affects animals and plants.
Similarly, glass pieces block the drainages.
The waste glass thrown anywhere cause injury to terrestrial fauna.

3. Thermocol:

Thermocol contains carcinogenic ingredients in the form of styrene. If there is prolonged contact with thermocol, there is a possibility of blood cancer like leukemia and lymphoma.
Thermocol is non-degradable. It cannot be degraded into harmless substances easily.
If it is burnt for destruction, it releases toxic gases in atmosphere.
The plates and cups used for food, water, tea, etc. are made up of thermocol. This may affect the health. Reheating the food kept in thermocol releases styrene. This styrene may dissolve in that food, causing health problems like cancer.

Question b.
Which measures will you arrange to minimize the environmental problems arising due to non-degradable plastic?
Answer:

The use of plastic should be minimum. Reducing the consumption, reusing the same plastic again and again, recycling the used plastic and making some new products from the used plastic are some of the measures that can be adopted.
There are attempts to use plastic in making roads. Therefore, plastic is bought with good price at some places.
Therefore, instead of disposing of it anywhere, it should be collected and sold in best possible way.
The better alternatives for plastic should be adopted.
The awareness programmes about misuse of plastic should be arranged so that common man can understand the dangers of using plastic.

6. Write short notes.

Question a.
Glass production:
Answer:
The general preparation of the glass is as follows:

Mixture of sand, soda, lime and small quantity of magnesium oxide is heated in furnace.
At 1700 °C sand or silicon dioxide melts.
To make the mixture melt at lesser temperature, pieces of discarded glasses are added to it.
This addition makes the mixture to melt at lesser temperature of 850 °C.
When all the ingredients of mixture are liquified, then again it is heated up to 1500 °C.
This heating is immediately followed by cooling.
The sudden cooling causes the mixture to become homogeneous, amorphous and transparent instead of crystalline.
For variety of glass types, different proportions of ingredients are used for heating.

Question b.
Optic glass:
Answer:

Optic glass or optical glass needs to be very clear and transparent as it is used in spectacles, lenses and other devices like microscopes.
Optic glasses are produced from the mixture of sand, soda, limestone, barium oxide and boron.

Question c.
Uses of plastic:
Answer:
Plastic, the man-made material is used in various forms in modern age. According to the type of plastic, its uses are different.

I. Thermoplastic materials are used for manufacturing following articles:

Polyvinyl chloride or PVC is used to make bottles, raincoat, pipes, handbags,: shoes, electric cable insulation, furniture, ropes, toys, etc.
Polystyrene is used in making thermo insulating parts of electric appliances like refrigerators, gears of machines, toys, protective coverings like covers of CD and DVD, etc.
Polyethylene (PE) plastics are used for making milk bags, packing bags, flexible garden pipes, etc.
Polypropylene (PP) is used in making parts of loudspeakers and vehicles, ropes, mattresses, laboratory appliances, etc.

II. Thermosetting plastic is used in the manufacturing of the following items:

Bakelite for making cabinets of radio, T.V., telephones, electric switches, toys, plastic handles of cookers, etc.
Melamine for making domestically useful items like cup – saucers, plates, tray, some spare parts of airplane engines, electric and sound insulating coverings, etc.
Polyurethane in making surfing boards, small boats, furniture, seats in vehicles, etc.
Polyester in fibreglass, toners of laser printers, textile industry, etc.

Can you tell?

Question 1.
Make a list of 20 different man-made materials present in your home, school and places around and discuss.
Answer:
Schoolbag, books, computer, table lamp, tube lights, benches, shoes, dress, pencil, pen, tiffin box, water bottle, raincoat, umbrella, medicine tablets, pen drive, chalk, duster, utensils, gas burner, biscuits.

Can you recall?

Question 1.
How many plastic carry bags are brought in your home in a day? What happens to those later on?
Answer:
Till May 2018 about one or two plastic bags were brought in our home every day. But now due to prohibition on plastic bags and other plastic items by the Government, the use of plastic has been drastically reduced. The bags brought at home caused lot of plastic pollution. Plastic is non-biodegradable, thus it always created problem of their disposal.

If dumped in a water body, it can be hazardous for aquatic animals. If thrown in the garbage, plastic articles find their way to landfilling areas. If thrown anyhow plastic may be consumed by stray animals. This causes toxic effects on them. If burnt they emit toxic gases.

Question 2.
How are the used up and thrown away carry bags, water bottles, milk bags recycled?
Answer:
The plastic waste is collected by the kabadiwala or sweepers. They sell these articles to the recycling units. In recycling units, the recycling of some of the plastic items is done. This leads to formation of plastic of low quality which may be used in making some newer plastic items.

Question 3.
Which material is wrapped around the items of glass or similar material during transport to prevent from breaking up?
Answer:
The plastic bubble wrap or thermocol is used to protect fragile items from the shocks and breaks during their transport.

Project:

Question 1.
Collect the information about the plastic used in production of utensils used in microwave oven.

Question 2.
Collect the information about the material used in production of denture. (A set of artificial teeth)

Class 8 Science Chapter 17 Man-made Materials Important Questions and Answers

Try to find it:

Question 1.
The plastic that can be moulded as per our wish is called …………… .
Answer:
The plastic that can be moulded as per our wish is called thermoplastic.

Question 2.
…………… is a type of plastic used for manufacturing artificial teeth.
Answer:
Polyacrylic is a type of plastic used for manufacturing artificial teeth.

Question 3.
Thermocol is a form of a complex material called ……………. .
Answer:
Thermocol is a form of a complex material called polystyrene.

Write whether the following statements are True or False: Rewrite the false statements after correcting:

Question 1.
Plastics are inorganic polymers that show plasticity.
Answer:
False. (Plastics are organic polymers that show plasticity.)

Question 2.
Polythene, PVC are thermosetting plastic materials.
Answer:
False. (Polythene, PVC are thermoplastic materials.)

Question 3.
Plastic is bad conductor of heat and electricity.
Answer:
True.

Question 4.
Surfing boards are made up of bakelite.
Answer:
False. (Surfing boards are made up of polyurethane.)

Question 5.
Being bad conductor of electricity, glass is used as insulator in electric appliances.
Answer:
True.

Match the columns:

Question 1.

Column A	Column B
1. Borosilicate glass	a. Oxide of specific metal.
2. Alkali silicate glass	b. Sand, soda, limestone, barium oxide and boron.
3. Lead glass	c. Sand and soda.
4. Optical glass	d. Sand, soda, limestone and lead oxide.
5. Coloured glass	e. Sand, soda, boric acid and aluminium oxide.

Answer:

Column A	Column B
1. Borosilicate glass	e. Sand, soda, boric acid and aluminium oxide.
2. Alkali silicate glass	c. Sand and soda.
3. Lead glass	d. Sand, soda, limestone and lead oxide.
4. Optical glass	b. Sand, soda, limestone, barium oxide and boron.
5. Coloured glass	a. Oxide of specific metal.

Find the odd one out:

Question 1.
Bakelite, Melamine, Polystyrene, Polyester.
Answer:
Polystyrene (All others are thermosetting plastic materials, polystyrene is thermoplastic.)

Question 2.
Polyvinyl chloride, Polystyrene, Polypropylene, Polyurethane.
Answer:
Polyurethane (All others are thermoplastic materials, polyurethane is thermosetting plastic.)

Question 3.
Vegetable peels, Cotton bolls, Wooden scraps, Plastic bag.
Answer:
Plastic bag (All others are degradable materials, plastic is non-degradable.)

Question 4.
Teflon, Polyacrylic, Fibreglass, Polyester.
Answer:
Fibreglass (All others are types of plastic.)

Considering the relationship in the first pair, complete the second pair:

Question 1.
Processed glass: Fen glass : : Alkali silicate glass : ………..
Answer:
Water glass

Question 2.
Ferrous oxide: Bluish green glass : : Copper oxide : ……..
Answer:
Red glass

Question 3.
Lens : Optical glass : : Laboratory glassware : ……….
Answer:
Silica glass

Question 4.
Light bulbs, Tubes: Lead glass : : Medicine storing : ………
Answer:
Borosilicate glass

Question 5.
Glass: Mixture of silica and silicate : : Thermocol : ………..
Answer:
Polystyrene.

Distinguish between:

Question 1.
Degradable and Non-degradable substances:
Answer:

Degradable substances	Non-degradable substances
1. The substances which can be naturally reduced into their inorganic constituents are called degradable substances.	1. The substances that cannot be degraded on their own into their inorganic constituents are called non-degradable substances.
2. Degradable substances are not accumulated in the nature.	2. Non-degradable substances remain accumulated in the nature for a long time.
3. Degradable substances emit foul odour when they are being decomposed.	3. Non-degradable substances may not emit foul odour as they are not degraded. But they make the place look dirty.
4. Usually microorganisms play a part in the degradation process, hence such substances are also called biodegradable. E.g. Vegetables, fruits, wood, cotton or wool fibres, etc.	4. Microorganisms cannot act on non-degradable substances and hence they are also called non-biodegradable substances. E.g. Plastic, thermocol, glass, metals, etc.

Write short notes:

Question 1.
Properties of plastic:
Answer:

Plastic is non-corrosive.
It is non-degradable as it does not decompose.
The factors such as humidity, heat, rain, etc. do not affect plastic.
Any coloured item can be manufactured from plastic.
Plastic shows property of plasticity. Thus it can be moulded into any shape that is needed.
Plastic is a bad conductor of heat and electricity.
Plastic is light-weight and thus preferred for carrying.

Question 2.
Properties of Glass:
Answer:
The glass becomes soft on heating and thus can be moulded into desired shape.

According to ingredients added at the time of preparation of glass, its density changes accordingly.
Glass is slow conductor of heat. If a cold glass is quickly heated, it cracks suddenly. Similarly, the warm glass if exposed to sudden cooling, it too cracks.
Glass is a bad conductor of electricity. Therefore, it is used as insulating material in electric appliances.
Glass is transparent, allowing most of light to pass through it. If there are chromium, vanadium or iron oxides in the glass, large amount of light is absorbed in glass.

Answer the following questions in one sentence only:

Question 1.
What is the use of plastic in healthcare sector?
Answer:
Saline bottles, pouches, blood bags, syringes and medicine bottles are made up of plastic, making plastic irreplaceable in the healthcare sector.

Question 2.
Which material is used in coating of vehicles? Why?
Answer:
Teflon is used for coating the vehicle as it protects the vehicles from scratches.

Question 3.
What is the use of polyacrylic type of plastic?
Answer:
Polyacrylic plastic used for manufacturing lenses and in the manufacture of artificial teeth.

Question 4.
What is 4R principle?
Answer:
The 4R principle is the way of behaviour that prevents or lessens the environmental pollution. The 4Rs are Reduce, Reuse, Recycle and Recover.

Question 5.
What are the eco-friendly options for a plastic bag?
Answer:
Jute bag, cloth bag and reusable bags of any natural materials are the eco-friendly options for the plastic bag.

Question 6.
How is Borosilicate glass produced?
Answer:
Borosilicate glass is produced by melting the mixture of sand, soda, boric acid and aluminium oxide.

Question 7.
When is large amount of light absorbed in the glass?
Answer:
If there are oxides of either chromium, vanadium or iron in the glass, large amount of light is absorbed in it.

Give scientific reasons:

Question 1.
It is harmful to eat food kept in thermocol.
Answer:
Thermocol is made up from polystyrene. It is carcinogenic (cancer causing) substance. When food kept in r thermocol containers is reheated, this , styrene dissolves in it. This may affect the r health of the person who consumes such food. It has been noted that there is a great possibility of blood cancer like leukaemia r and lymphoma if one remains in contact with thermocol for a longer time. Thus, it is harmful to eat food kept in thermocol.

Question 2.
Vessels used to cook food in the microwave oven are made up of plastic.
Answer:
The vessels made from metals cannot be used in the microwave oven. The microwaves cannot penetrate steel and so ‘ can only heat the contents through the open top. Some metals cause sparking with microwaves. Microwave energy is absorbed differently by different materials. Plastics of only certain kind are more suitable to be used in the microwave oven.

Answer the following:

Question 1.
What are the qualities of thermocol?
Answer:

Thermocol is modern man-made material made from polystyrene.
It can be transformed into liquid state when heated at more than 100 °C temperature. On cooling, it returns to the solid state.
Therefore, any desired shape can be given to it.
It acts as a good shock-absorber and hence used as a packing material to transport brittle material.
It is a bad insulator of heat and hence used for storing fish and other perishable articles in market.

Think about it:

Question 1.
Why are the plastic tanks used for storage of chemicals?
Answer:
Plastic is non-corrosive. It is comparatively non-reactive and it does not decompose. Moreover, the plastic containers are easier for handling. They are lighter and unbreakable. Hence the plastic tanks are used for storage of chemicals.

Question 2.
Why most of domestically useful items are replaced by plastic?
Answer:
Plastic is lighter and unbreakable. The handling thus becomes easier. It is non-corrosive, hence pickles, spices, etc. can be stored in plastic containers. It is cheaper as compared to the metal and glass articles. Thus, it becomes popular with general public. It is easier to wash and maintain the plastic articles. These are some of the reasons of making plastic a domestically useful material.

Collect information:

Question 1.
To prevent the degradation due to sunlight, some materials are stored in which type of bottles?
Answer:

The amber glass or brown coloured glass bottles are used to store the materials that may get degraded due to sunlight. This colour prevents the ultraviolet rays of the sun to enter the bottle and bring about chemical changes in the materials. Especially, for sensitive medicines, brown glass bottles are used.

Question 2.
Which type of glass is used in vehicles to avoid injuries in accidents?
Answer:
Front and rear doors have tempered glass. The windshield has laminated safety glass. Even if the accident takes place the glass pieces do not injure the passengers. Laminated safety glass combines two curved glass sheets and a plastic lamina between the two layers of the glass.

This glass is tough and protective. Tempered glass on the other hand is toughened glass which is processed by controlled thermal or chemical treatments. Upon breaking, the tempered glasses crumble into small granular chunks instead of splintering into sharp glass pieces. This prevents the injuries.

Sketch and label the diagram of glass manufacturing process:

Open-Ended Questions:

Question 1.
Classify and make a chart of the materials used in various items in house. Make additions to that chart with reference to various materials.

Answer:

Question 2.
Make list about use of thermocol in your daily life.
Answer:

Decorative items used at the time of festivals.
Packing materials.
Insulating boxes to keep food warm.
Insulating boxes to keep fish in iced condition to prevent decomposition.
Thermocol beads in the bean bags.

8th Std Science Questions And Answers:

Living World and Classification of Microbes Class 8 Science Chapter 1 Questions And Answers Maharashtra Board

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 1 Living World and Classification of Microbes Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 1 Living World and Classification of Microbes Question Answer Maharashtra Board

Class 8 Science Chapter 1 Living World and Classification of Microbes Question Answer Maharashtra Board

1. Use Whittaker method to classify bacteria, protozoa, fungi, algae, prokaryotic, eukaryotic, microbes.

Living World And Classification Of Microbes Exercises Question 1.
Use Whittaker method to classify bacteria, protozoa, fungi, algae, prokaryotic, eukaryotic, microbes.
Answer:

Bacteria: Kingdom Monera
Protozoa: Kingdom Protista
Fungi: Kingdom Fungi
Algae: If unicellular, Kingdom Protista. If multicellular, Kingdom Plantae
Prokaryotic: Kingdom Monera
Eukaryotic: Any kingdom other than Monera.
Microbes: Kingdom Monera or Protista.

2. Complete the five kingdom method of classification using-living organism, prokaryotes, eukaryotes, multicellular, unicellular, protista, animals, plants, fungi.

Living World And Classification Of MicrobesQuestion 1.
Complete the five kingdom method of classification using-living organism, prokaryotes, eukaryotes, multicellular, unicellular, protista, animals, plants, fungi.

Answer:

3. Find out my partner

Question 1.

Answer:

A	B
1. Fungi	Candida
2. Protozoa	Amoeba
3. Virus	Bacteriophage
4. Algae	Chlorella
5. Bacteria	Prokaryotic.

4. State whether the following statements are True or False. Explain your statement:

Question a.
Lactobacilli are harmful bacteria.
Answer:
False.
Explanation Lactobacilli are useful bacteria. They are used for curdling the milk. They are also used for preparing variety of milk products.

Question b.
Cell wall of fungi is made up of chitin.
Answer:
True.
Explanation The cell wall of the plants is made up of cellulose while the cell wall of fungi is made up of complex sugar called chitin. Inside the fungal cell wall there is cytoplasm which contains many nuclei.

Question d.
Organ of locomotion in amoeba is pseudopodia.
Answer:
True.
Explanation Amoeba is a protozoan, primitive organism which possesses pseudopodia as the organ for locomotion.

Question e.
Tomato wilt is a viral disease.
Answer:
True.
Explanation: Tomato wilt is a viral disease. These viruses are able to infect only plant cells.

5. Give answers

Question a.
State the merits of Whittaker’s method of classification.
Answer:
For the answer of Merits of Whittaker’s method refer to point I of answer given on this Digest’s page no. 11; under “Use your brain power!”

Question b.
Write the characteristics of viruses.
Answer:
1. Viruses are extremely minute of the size range of 10 nrn to 100 nm. They are on the borderline of living and non-living. They are 10 to 100 times smaller than bacteria and are visible only through the electron microscope.

2. Though they are not considered as living, they can make replica of their own.
3. They exist in the form of independent particles. They are long molecules of DNA or RNA which are covered by a protein coat.

4. Their survival is possible only inside the living plant or animal cells. When they infect the host cells, they produce their own proteins with the machinery of the host cell. These proteins form many replicas of the infecting virus.

5. This infection destroys the host cell and the virus replicas are released. These free replicas re-infect the other adjoining cells of the host.
6. Most of the viruses are pathogenic, they cause diseases in plants and animals.

Question c.
Explain the nutrition in fungi.
Answer:
Most of the fungi are saprophytic in their nutrition. They absorb the nourishment from dead and decaying matter. By taking the organic matter from dead bodies of plants and animals, fungi survive. In this process they degrade the organic matter completely.

Question d.
Which living organisms are included in the kingdom Monera?
Answer:

All the living organisms belonging to Kingdom Monera are unicellular.
The mode of nutrition in them is either autotrophic or heterotrophic.
All of them are prokaryotic and thus they do not have well-formed nucleus. The nuclear membrane and the cell organelles are absent in them.
Kingdom Monera consists of different types of bacteria and blue-green algae.

E.g. Bacteria Clostridium titani, Vibrio choleri, Treponema pallidum, Streptococcus pneumoniae, Legionella pneumoniae, Salmonella typhi, Staphylococcus aureus, Clostridium botulinum.

6. Who am I?

Question a.
I don’t have true nucleus, cell organelles or plasma membrane.
Answer:
Microbe from Monera

Question b.
I have nucleus and membrane bound cell organelles.
Answer:
Protozoan from Protista/I am any one of Eukaryote

Question c.
I live on decaying organic matter.
Answer:
Fungus

Question d.
I reproduce mainly by cell division. (*Binary fission)
Answer:
Bacteria and some Protozoa.

Question e.
I can produce my replica.
Answer:
Virus

Question f.
I am green, but don’t have organs.
Answer:
Algae

7. Draw neat and labelled diagrams.

Question a.
Different types of bacteria:
Answer:

Question b.
Paramoecium:
Answer:

Question c.
Bacteriophage
Answer:

8. Arrange the following in ascending order of size Bacteria, Fungi, Viruses, Algae.

Question a.
Arrange the following ¡n ascending order of size Bacteria, Fungi, Viruses, Algae.
Answer:
Viruses, Bacteria, Fungi, Algae.

Project:

Question 1.
Prepare a chart showing infectious bacteria and the diseases caused by them.

Question 2.
Visit a nearby pathology lab. Get the information about pathogenic microbes, methods to observe them, different microscopes from the technicians there.

Class 8 Science Chapter 1 Living World and Classification of Microbes Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
The process of dividing living organism into groups and subgroups is called …………… .
Answer:
Biological classification.

Question 2.
Organisms with cell wall but not able to perform photosynthesis are called …………… .
Answer:
Fungi.

Question 3.
Most of the fungi are …………… .
Answer:
saprotrophic.

Question 4.
Viruses can be seen only with …………… .
Answer:
electron microscope.

Question 5.
…………… viruses attack bacteria.
Answer:
Bacteriophage

Question 6.
In fungi the cell wall is made up of j tough and complex sugar called …………… .
Answer:
‘Chitin’.

State whether the following statements are True or False. Explain your statement:

Question 1.
Plasmodium causes dysentery.
Answer:
False.
Explanation Plasmodium causes malaria. Entamoeba histolytica causes amoebic dysentery or amoebiasis.

Find out my partner

Question 1.

Scientist	Pattern of classification
1. Carl Linnaeus	(a) 5 groups of living organisms
2. Haeckel	(b) 2 groups as Prokaryotes and Eukaryotes
3. Chatton	(c) 4 groups as Monera, Protista, Plants and Animals
4. Kopland	(d) 3 kingdoms – Protista, Plants and Animals.
5. Whittaker	(e) 2 kingdoms of living organisms

Answer:

Scientist	Pattern of classification
1. Carl Linnaeus	(e) 2 kingdoms of living organisms
2. Haeckel	(d) 3 kingdoms – Protista, Plants and Animals.
3. Chatton	(b) 2 groups as Prokaryotes and Eukaryotes
4. Kopland	(c) 4 groups as Monera, Protista, Plants and Animals
5. Whittaker	(a) 5 groups of living organisms

Question 2.

Living organism	Group
1. Clostridium titani	(a) Heterotrophic Protista
2. Paramoecium	(b) Fungi
3. Chlamydomonas	(c) Bacteria belonging to Monera
4. Baker’s yeast	(d) Algae
	(e) Virus

Answer:

Living organism	Group
1. Clostridium titani	(c) Bacteria belonging to Monera
2. Paramoecium	(a) Heterotrophic Protista
3. Chlamydomonas	(d) Algae
4. Baker’s yeast	((b) Fungi
	(e) Virus

Question 3.

Microbes	Size
1. Virus	(a) 1 μm to 10 μm
2. Algae	(b) 200 μm
3. Protozoa	(c) 10 μm to 100μm
4. Bacteria	(d) 10 nm to 100 nm

Answer:

Microbes	Size
1. Virus	(d) 10 nm to 100 nm
2. Algae	(c) 10 μm to 100 μm
3. Protozoa	(b) 200 μm
4. Bacteria	(a) 1 μm to 10 μm

Name the following/ Give examples

Question 1.
Three organs of locomotion in Protista
Answer:

Pseudopodia
Cilia
Flagella

Question 2.
Two autotrophic Protista
Answer:

Euglena
Volvox

Question 3.
Institute in India which is involved in research on viruses
Answer:
National Institute of Virology, Pune

Question 4.
Two methods of asexual reproduction in Fungi
Answer:

Binary fission
Budding

Question 5.
Two pathogenic protozoans and the diseases caused by them
Answer:

Entamoeba histolytica causes amoebiasis
Plasmodium vivax – causes malaria.

Answer the following questions in one sentence:

Question 1.
What are the types of living organisms according to their lifestyle?
Answer:
Producers, consumers and decomposers are the types of living organisms according to their lifestyle.

Question 2.
What are the characteristics of prokaryotic cells?
Answer:
Absence of nuclear membrane, well- formed nucleus and lack of cell organelles are the characteristics of the prokaryotic cells.

Question 3.
When do virus destroy the host cells?
Answer:
After synthesising their own proteins and creating numerous replica of their own type, then the virus destroys the host cells.

Give answers:

Question 1.
Which criteria were considered for classification method of Whittaker?
Answer:
The criteria considered for classification by Whittaker are as follows:
1. Complexity of cell structure: Whether the cells of the organisms are prokaryotic or eukaryotic.

2. Complexity of organisms Whether the organisms are unicellular or multicellular is considered.

3. Mode of nutrition Whether the organism is autotrophic and is performing photosynthesis on its own or it is heterotrophic is considered. Plants are autotrophic, fungi are saprotrophic while animals use food from plants or other animals and hence they are heterotrophic.

4. Lifestyle According to nutrition, every living organism is at certain trophic level. This is called lifestyle. Plants are producers, animals are consumers while fungi are decomposers.

5. Phylogenetic relationship When the evolution proceeded gradually, there was transition from prokaryotes to eukaryotes, unicellular to multicellular. In this order the different groups of living organisms were evolved. This is known as phylogenetic relationship.

Use your brain power!
(Textbook page 3)

Question 1.
Explain merits and demerits of Whittaker’s classification.
Answer:
I. Merits of Whittaker’s classification:

The classification system that Whittaker has adapted is totally based on scientific foundation.
Prokaryotes are placed separately in a different kingdom. The prokaryotic organisms are different from other organisms, thus placing them separately is justified.
All unicellular eukaryotic organisms are clubbed together in one kingdom named, Protista. This has helped to solve the placement of Euglena.
Euglena has chloroplasts like plants but as animals it has flagella and thus there was conflict about such species during previous classification systems. It was placed in protozoa previously.
Fungi are saprophytic and hence they are placed separately in a unique kingdom.
According to five kingdom classification, the cell structure, organization of cell, mode of nutrition, lifestyle and phylogenetic relationship are taken into consideration.
Therefore the system of 5 kingdom classification becomes most authentic system of biological classification.

II. Demerits of Whittaker’s method of classification:

1. Some organisms belonging to Monera and Protista have ability to perform photosynthesis. Thus they show mode of nutrition as autotrophic, while others are heterotrophic. Similarly some monerans have cell wall and some Protists also have cell wall. This becomes confusing during their placement.

2. In kingdom Protista, organisms show varied characteristics. In spite of this they are placed together.

3. In kingdoms, Plantae, Animalia and Fungi the organisms having primitive characters and were initial examples during evolution are not included. E.g. In Kingdom Animalia, amoeba is not included though it is said to be unicellular animal. This creates confusion.

4. Similarly if algae are unicellular, they are placed in kingdom Protista and if they are multicellular they are placed in kingdom Plantae. In reality, unicellular and multicellular algae both show much similarity. But due to Whittaker’s classification system they are placed away from each other.

5. Species of algae such as Chlorella, Chlamydomonas are not included in Kingdom Protista.

6. Viruses are not included in any of the kingdoms by Whittaker. Their classification has become a point of debate among the biologists.

Write short notes:

Question 1.
Characteristics of Fungi.
Answer:

The organisms which are placed in kingdom Fungi are multicellular, heterotrophic, non-green, and eukaryotic in nature.
Most of the fungi are saprophytic and they sustain on the dead and decaying organic matter.
The cell wall of the fungal cells is made up of chitin. Chitin is the tough and complex sugar.
Fungi have thread like body. The cytoplasm of the fungal cells contain many nuclei.
The reproduction in Fungi is either sexual or asexual. Asexual reproduction is by fission or by budding.
Examples Baker’s yeast, Candida, Mushroom, Aspergillus (Fungus on corn), Penicillium

Question 2.
Characteristics of Bacteria.
Answer:

Bacteria are microscopic, unicellular, prokaryotic organisms belonging to the kingdom Monera.
Some bacteria are solitary with independent existence. Some are colonial forms.
The bacterial cell lacks well-formed nucleus with nuclear membrane and cell organelles.
Reproduction is by binary fission.
In favourable conditions, bacteria duplicate with a great speed. Within 20 minutes they can double in number.
Bacteria may be round as in Cocci, elongated as in Bacillus, comma shaped as in Vibrio and spiral shaped as in Spirillum.

Question 3.
Characteristics of Protozoa.
Answer:

Protozoa are unicellular, eukaryotic organisms belonging to kingdom, Protista.
They are microscopic of the size of about 200 pm.
They have different organs of locomotion such as pseudopodia, cilia and flagella.?
Reproduction is by asexual method, usually by binary fission. .
Protozoa are seen in varied habitats such as soil, fresh water and marine water.
Some protozoans are parasitic and cause various types of illness in hosts. E.g. Entamoeba histolytica is a species of amoeba that causes amoebiasis. Malaria is caused by Plasmodium vivax.
Protozoa show different modes of nutrition.

E.g. Euglena is autotrophic as it does photosynthesis with the help of 5 chloroplasts present in its body. Amoeba and Paramoecium are heterotrophic and free living seen in contaminated water.

Complete the paragraph using the words given in the brackets

[Monera, Euglena, autotrophic, cell organelles, chitin, nuclear, prokaryotic, viruses, replicas, saprotrophic, viral particles]

In Kingdom ……….. bacteria were included but not ………….. Viruses are on the border line of living and non-living. Do we really call them living? If they are making …………. of their own type, are they not considered as living? Throughout the world they spread hazardous epidemics. Antibiotics do not act on ………… However, bacteria can be controlled by antibiotics. All the living organisms belonging to Monera are with …………… cell. They do not have ………….. membrane and neither they have ……………… But a nice nucleus is seen in …………….., Euglena is ………… protist. The fungi with cell wall of …………….. are ………….. in their mode of nutrition.
Answer:
In Kingdom Monera bacteria were included but not viruses. Viruses are on the border line of living and non-living. Do we really call them living? If they are making replicas of their own type, are they not considered as living? Throughout the world they spread hazardous epidemics. Antibiotics do not act on viral particles. However, bacteria can be controlled by antibiotics. All the living organisms belonging to Monera are with prokaryotic cell. They do not have nuclear membrane and neither they have cell organelles. But a nice nucleus is seen in Euglena. Euglena is autotrophic protist. The fungi with cell wall of chitin are saprotrophic in their mode of nutrition.

Complete the chart:

Question 1.
Draw a chart showing different types of Microorganisms.
Answer:

Draw neat and labelled diagrams:

Question 1.
Fungi:
Answer:

Question 2.
Euglena:
Answer:

Question 3.
Amoeba:
Answer:

Question 4.
Correctly label the various organisms shown in the Kingdom Monera:

Answer:

Streptococcus pneumoniae
Clostridium titani
Vibrio choleri
Treponema pallidum
Staphylococcus aureus
Legionella pneumoniae
Salmonella typhi
Clostridium botulinum

Activity-based questions

1. Try this:
Activity Take a small drop of curd or buttermilk on a clean glass slide. Dilute it with a little water. Carefully keep a coverslip. Observe it under high power of compound microscope. What did you see?
Answer:
In the slide we can see Lactobacilli \ bacteria.

2. Try this:
Activity Prepare a temporary mount of one drop of pond water on a glass slide. Observe it under low power and high power microscope.
Answer:
The drop on the slide shows motile microscopic organisms which have irregular shape. They are amoeba.

3. Try this:
Activity Take a moist piece of bread or bhakri and keep it in a container with lid for 2-3 days. After 2-3 days a fine cotton thread like tuft is found growing on the surface of the bread. Prepare a temporary mount of few threads from this culture and observe it under the microscope.
Answer:
Upon observation of thread like structures the fungal hyphae ( fibre like body) are seen.

MCQs based on experiments:

Choose the appropriate alternative of the following:

Experiment 1: To observe lactobacilli in curd/buttermilk.

Question 1.
Which of the following bacterium is used to make curds from milk?
(a) Streptococcus
(b) Lactobacillus
(c) Staphylococcus
(d) Clostridium
Answer:
(b) Lactobacillus

Question 2.
In which kingdom is Lactobacillus included?
(a) Monera
(b) Protista
(c) Fungi
(d) Plantae
Answer:
(a) Monera

Question 3.
Which is the other organism that has been added in kingdom Monera in addition to bacteria?
(a) Virus
(b) Blue-green algae
(c) Fungi
(d) Protozoa
Answer:
(b) Blue-green algae

Experiment 2: To observe fungus on the bread

Question 1.
In which kingdom is fungus growing on the bread included?
(a) Fungi
(b) Protozoa
(c) Monera
(d) Protista
Answer:
(a) Fungi

Question 2.
What are dark coloured particles which are seen when the fungus is growing on the bread?
(a) Sporangiophore
(b) Rhizoids
(c) spores
d) Columella
Answer:
(c) spores

Question 3.
Why is there growth of fungus on all the stale food?
(a) Fungus has affinity for food.
(b) Fungus grows on decaying organic matter.
(c) As food is open, the fungus drops on it and starts growing.
(d) None of the alternative is correct.
Answer:
(b) Fungus grows on decaying organic matter.

8th Std Science Questions And Answers:

Chemical Change and Chemical Bond Class 8 Science Chapter 13 Questions And Answers Maharashtra Board

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 13 Chemical Change and Chemical Bond Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 13 Chemical Change and Chemical Bond Question Answer Maharashtra Board

Class 8 Science Chapter 13 Chemical Change and Chemical Bond Question Answer Maharashtra Board

1. Complete the statement by filling the gaps using appropriate term from the terms given in the brackets:
(slow, coloured, arrow, fast, smell, milky, physical, product, chemical, reactant, covalent, ionic, octet, duplet, exchange, sharing, equality sign)

Question a.
An ……….. is drawn in between the reactants and products while writing the equation for a chemical reaction.
Answer:
An arrow is drawn in between the reactants and products while writing the equation for a chemical reaction.

Question b.
Rusting of iron is a ……….. chemical change.
Answer:
Rusting of iron is a slow chemical change.

Question c.
The spoiling of food is a chemical change which is recognized from the generation of certain …………. due to it.
Answer:
The spoiling of food is a chemical change which is recognized from the generation of certain smell due to it.

Question d.
A colourless solution of calcium hydroxide in a test tube turns ………….. on blowing in it through a blow tube for some time.
Answer:
A colourless solution of calcium hydroxide in a test tube turns milky on blowing in it through a blow tube for some time.

Question e.
The white particles of baking soda disappear when put in lemon juice. This means that it is a ……….. change.
Answer:
The white particles of baking soda disappear when put in lemon juice. This means that it is a chemical change.

Question f.
Oxygen is a …………….. in respiration.
Answer:
Oxygen is a reactant in respiration.

Question g.
Sodium chloride is …………… compound while hydrogen chloride is compound.
Answer:
Sodium chloride is ionic compound while hydrogen chloride is covalent compound.

Question h.
Electron …………….. is complete in each hydrogen in a hydrogen molecule.
Answer:
Electron duplet is complete in each hydrogen in a hydrogen molecule.

Question i.
Chlorine (Cl₂) molecule is formed by ………….. of electrons between two chlorine atoms.
Answer:
Chlorine (Cl₂) molecule is formed by sharing of electrons between two chlorine atoms.

2. Explain by writing a word equation.

Question a.
Respiration is a chemical change.
Answer:
Respiration is a biological process, in this process air is inhaled, oxygen present in this inhaled air reacts with glucose present in the cells of the body forming carbon dioxide and water. Moreover, we cannot obtain glucose and oxygen from carbon dioxide and water. Hence, respiration is a chemical change.
Word equation:

Question b.
Hard water gets softened on mixing with a solution of washing soda.
Answer:
Hard water does not form lather with soap and is brackish to taste. This is because hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state. When a solution of washing soda is added to hard water, it forms a precipitate of calcium carbonate and magnesium carbonate, which is removed by filtration thus water is softened.
Word equation:

Question c.
Limestone powder disappears on adding to dilute hydrochloric acids.
Answer:
In the reaction of dil. HCl and limestone powder (CaCO₃), limestone disappears slowly and carbon dioxide (CO₂) liberates slowly.
Word equation:

Question d.
Bubbles are seen on adding lemon juice to baking soda.
Answer:
When baking soda is added to lemon juice a chemical change takes place in citric acid present in the lemon juice and carbon dioxide gas is formed. Word equation:

This is a neutralization reaction.

3. Match the pairs.

Question a.

Column I	Column II
1. Photosynthesis	a. Tendency to lose electrons
2. Water	b. Reactant in combustion process
3. Sodium chloride	c. Chemical change
4. Dissolution of salt in water	d. Covalent bond
5. Carbon	e. Ionic bond
6. Fluorine	f. Physical change
7. Magnesium	g. Tendency to form anion

Answer:

Column I	Column II
1. Photosynthesis	c. Chemical change
2. Water	d. Covalent bond
3. Sodium chloride	e. Ionic bond
4. Dissolution of salt in water	f. Physical change
5. Carbon	b. Reactant in combustion process
6. Fluorine	g. Tendency to form anion
7. Magnesium	a. Tendency to lose electrons

4. Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms.

Question a.
Sodium Chloride:

Answer:
1. Sodium has atomic number 11 and electronic configuration 2, 8, 1.
2. Sodium atom has 1 electron in its outermost shell.

3. It loses one electron from its outermost shell, i.e., M shell. Then its L shell becomes the outermost shell with a stable octet. The nucleus of sodium atom has 11 protons but the number of electrons in the atom has become 10. So, there is a net unit positive charge giving a sodium cation (Na⁺).

4. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.
5. Thus, the electron lost by sodium is taken up by chlorine.

6. When chlorine atom gains one electron, octet of chlorine is completed and its K, L, M shells have together 18 electrons and the nucleus has 17 protons. This leads to the formation of an ion (CP).

7. Thus, a chlorine atom accepts one electron from a sodium atom and consequently a chloride ion with one unit negative charge and a sodium ion with one unit positive charge are formed.

8. Sodium and chloride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of sodium chloride (NaCl) molecule.

Question b.
Potassium fluoride:
Answer:
1. Potassium has atomic number 19 and electronic configuration 2, 8, 8, 1.
2. Potassium atom has 1 electron in its outermost shell.

3. It loses one electron from its outermost shell, i.e. N shell. Then its M shell becomes the outermost shell with a stable octet. The nucleus of potassium atom has 19 protons but the number of electrons in the atom has become 18. So there is a net unit positive charge giving a potassium cation (K⁺).

4. On the other hand, fluorine has electronic configuration 2, 7. Fluorine has 7 electrons in the outermost shell and requires one electron to complete its octet.

5. Thus, the electron lost by potassium is taken up by chlorine.

6. When fluorine atom gains one electron, octet of fluorine is completed, its K and L shells have together 10 electrons and the nucleus has 9 protons. This leads to the formation of an ion (F^–).

7. Thus, a fluorine atom accepts one electron from a potassium atom and consequently a fluoride ion with one unit negative charge and a potassium ion with one unit positive charge are formed.

8. Potassium and fluoride ions, being oppositely charged, attract each other due to electrostatic force of attraction. An ionic bond is formed and this results in the formation of potassium fluoride (KF) molecule.

Question c.
Water:
Answer:

1. Hydrogen has atomic number 1 and electronic configuration 1.
2. Hydrogen has 1 electron in its K shell.

3. Oxygen has atomic 8 and electronic configuration 2, 6. There are 6 electrons in the valence shell of oxygen atom. It means that the electron octet in oxygen is short of two electrons and the valency of oxygen is two.

4. In the H₂O molecule, the oxygen atom complete its octet by sharing two electrons one each with two hydrogen atoms, thus, forming two covalent bonds. While this happens, the duplets of two hydrogen atoms are completed.

Question d.
Hydrogen chloride:
Answer:
1. Hydrogen has atomic number 1 and electronic configuration 1, that means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one.

2. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.

3. The two atoms, hydrogen and chlorine share one electron with each other. As a result, the electron duplet of hydrogen and octet of chlorine is complete and a covalent band is formed between them.

Can you recall?

Question a.
What are the methods of classification of changes?
Answer:
The methods of classification of changes: Physical change and chemical change.

Question b.
What is the difference between physical and chemical change?
Answer:

In physical change, the composition of substance does not change. No new substance is formed.
In chemical change, the composition of compounds change and new compounds are formed.

Question c.
Classify the following changes into physical and chemical change. Ripening of mango, melting of ice, boiling of water, dissolution of salt in water, Ripening of banana, fragrance on ripening fruit, darkening of a cut potato, bursting of an inflated balloon, sound of bursting fire cracker, foul smell from a portion of spoiled food.
Answer:

Physical change: Melting of ice, boiling of water, dissolution of salt in water.
Chemical change: Ripening of mango, ripening of banana, fragrance of ripening fruit, darkening of a cut potato, bursting of an inflated balloon, sound of bursting firecracker, foul smell from a spoiled food.

Project:

Question a.
Prepare a list of the chemical changes that occur in your house and surroundings and discuss these in the class.

Class 8 Science Chapter 13 Chemical Change and Chemical Bond Important Questions and Answers

Fill in the blanks:

Question 1.
……………. is a continuously occurring biological process.
Answer:
Respiration is a continuously occurring biological process.

Question 2.
The reaction between citric acid and sodium bicarbonate is a ……………. reaction.
Answer:
The reaction between citric acid and sodium bicarbonate is a neutralization reaction.

Question 3.
Combustion of fuel is a ………… and ……………. chemical change.
Answer:
Combustion of fuel is a fast and irreversible chemical change.

Question 4
Electronic configuration of sodium is …………….
Answer:
Electronic configuration of sodium is 2, 8, 1.

Question 5.
Electronic configuration of chlorine is …………….
Answer:
Electronic configuration of chlorine is 2, 8, 7.

Question 6.
A chemical bond formed by sharing of valence electrons of two atoms with each other is called a …………….
Answer:
A chemical bond formed by sharing of valence electrons of two atoms with each other is called a covalent bond.

Question 7.
Hard water contains the chloride and sulphate salts of ……………. and ……………. in dissolved state.
Answer:
Hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state.

Question 8.
Electronic configuration of fluorine is …………….
Answer:
Electronic configuration of fluorine is 2, 7.

Question 9.
Green plants perform ……………. in sunlight.
Answer:
Green plants perform photosynthesis in sunlight.

Question 10.
Melting of ice is a ……………. change.
Answer:
Melting of ice is a physical change.

Question 11.
The chloride ion has a ……………. charge.
Answer:
The chloride ion has a negative charge.

Question 12.
A covalent bond between two atoms is also represented by ……………. joining their symbols.
Answer:
A covalent bond between two atoms is also represented by dash joining their symbols.

Rewrite the following statements by selecting the correct options:

Question 1.
Sodium atoms and sodium ions ………….. .
(a) are chemically the same
(b) have the same number of protons
(c) have the same number of electrons
(d) form covalent bond
Answer:
(b) have the same number of protons

Question 2.
An ionic bond is formed when …………….. .
(a) two metallic elements react
(b) two nonmetallic elements react
(c) a metallic element reacts with a non-metallic element
(d) a pair of elements react
Answer:
(c) a metallic element reacts with a non-metallic element

Question 3.
…………….. tries to establish the duplet state in its outermost orbit by sharing electrons.
(a) Sodium
(b) Potassium
(c) Hydrogen
(d) Magnesium
Answer:
(c) Hydrogen

Question 4.
…………… is an electron donor.
(a) Helium
(b) Iodine
(c) Chlorine
(d) Magnesium
Answer:
(d) Magnesium

Question 5.
………………. combine to form an ionic compound.
(a) Hydrogen and chlorine
(b) Hydrogen and oxygen
(c) Potassium and chlorine
(d) Nitrogen and oxygen
Answer:
(c) Potassium and chlorine

Question 6.
……………. is an example of chemical change.
(a) Magnetism of iron
(b) Rusting of iron
(c) Heating of iron till it becomes red hot
(d) Dissolution of salt in water
Answer:
(b) Rusting of iron.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)

Question 1.
The preparation of cold drink soda- lemon is a physical change.
Answer:
False. [The preparation of cold drink soda-lemon is a chemical change.]

Question 2.
Hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state.
Answer:
True.

Question 3.
Combustion of fuel is a fast and irreversible man-made chemical change.
Answer:
True.

Question 4.
Photosynthesis reaction is a man-made chemical change.
Answer:
False. [Photosynthesis reaction is a natural chemical change.]

Question 5.
The atoms with incomplete electron octet/duplet form chemical bonds.
Answer:
True.

Question 6.
Electronic configuration of chlorine is 2, 8, 6.
Answer:
False. (Electronic configuration of chlorine is 2, 8, 7.)

Question 7.
One ionic bond is formed due to the electrical change +1 or -1 on an ion.
Answer:
True.

Question 8.
H₂O Molecule is an ionic compound.
Answer:
False. (H₂O molecule is a covalent compound.)

Question 9.
The bond between two chlorine atoms is a covalent band.
Answer:
True.

Question 10.
Arrow indicates the direction of the reaction.
Answer:
True.

Consider the correlation between the words of the first pair, match the third word/words with the most appropriate answer:

Question 1.
K : 2, 8, 8, 1 : : Mg : ………………
Answer:
2, 8, 2

Question 2.
MgCl₂ : Ionic bond : : CaO : ……………..
Answer:
Covalent bond

Question 3.
Photosynthesis : Natural chemical change : : Cold drink, soda lemon : ………
Answer:
Man-made chemical change

Question 4.
Respiration: Glucose + Oxygen : : Neutralization : ………….
Answer:
Acid + alkali.

Match the columns:

Question 1.

Column I	Column II
1. Respiration	a. Potassium and fluorine
2. Acid + Base	b. Glucose and oxygen
3. Photosynthesis	c. Carbon dioxide and water
4. Ionic bond	d. Salt and water

Answer:

Column I	Column II
1. Respiration	c. Carbon dioxide and water
2. Acid + Base	d. Salt and water
3. Photosynthesis	b. Glucose and oxygen
4. Ionic bond	a. Potassium and fluorine

Define the following:

Chemical change: In a chemical change, the chemical composition of the original matter changes and new substances having different properties and different chemical composition are formed.
Ionic bond: The chemical bond formed due to an electrostatic force of attraction between the oppositely charged cation and anion is called an ionic bond or an electrovalent bond.
Covalent bond: The chemical bond formed by sharing of valence electrons of two atoms with each other is called a covalent bond.

Answer the following questions in one sentence each:

Question 1.
Name the reactants in respiration.
Answer:
Glucose and oxygen are the reactants in respiration.

Question 2.
Name the products of respiration.
Answer:
Carbon dioxide and water are the products of respiration.

Question 3.
Name the reactants in photosynthesis.
Answer:
Carbon dioxide and water are the reactants in photosynthesis.

Question 4.
Name the products of photosynthesis.
Answer:
Glucose and oxygen are the products of photosynthesis.

Question 5.
Name the salts present in hard water.
Answer:
Salts present in hard water are calcium chloride, magnesium chloride, calcium sulphate and magnesium sulphate.

Question 6.
Give two examples of ionic compounds.
Answer:
Ionic compounds: Sodium chloride (NaCl), Potassium fluoride (KF).

Question 7.
Give two examples of covalent compounds.
Answer:
Covalent compounds: Hydrogen (H₂), Water (H₂O).

Question 8.
Name an acid used for cleaning Shahabad tile.
Answer:
An acid used for cleaning Shahabad tile is dilute hydrochloric acid (HCl).

Question 9.
Write a chemical equation for combustion of fuel.
Answer:
Chemical equation:
C + O₂ → CO₂

Question 10.
Write a chemical equation for photosynthesis.
Answer:
Chemical equation:

Answer the following questions:

1. Explain by writing a word equation.

Question 1.
Combustion of fuel is a fast and irreversible chemical change.
Answer:
Wood, coal, petrol or cooking gas are burnt for producing energy. Carbon is the common substance that burns in all these fuels. The product carbon dioxide is formed when carbon combines with oxygen in the air during the combustion process. We cannot obtain fuel from carbon dioxide by employing any other method. Properties of carbon dioxide are altogether different from those of fuel. Hence, this change is a irreversible chemical change.
Word equation:
Carbon + Oxygen → Carbon dioxide

Question 2.
Dilute hydrochloric acid is used for cleaning Shahabad tiles.
Answer:
The main constituent of Shahabad tile is calcium carbonate. During its cleaning with hydrochloric acid, the upper layer of the tile reacts with hydrochloric acid and three products are formed. One of them is calcium chloride, which being soluble in water, gets washed away with water. The second product is carbon dioxide, it mixes with air. The third product is water.
Word equation:

2. Write a chemical equation (unbalanced) for the following reactions:

Question 1.

Answer:
Chemical equation:
CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

Question 2.

Answer:
Chemical equation:
CaCO₃ + HCl → CaCl₂ + CO₂ + H₂O

Question 3.
Magnesium salts during the softening of hard water.

Answer:
Chemical equation:
MgCl₂ + Na2CO₃ → MgCOg + 2NaCl

3. Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms.

Question 1.
Hydrogen molecule:
Answer:
1. Hydrogen has atomic number 1 and electronic configuration 1. That means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one.

2. The two atoms of hydrogen are identical, they share their electrons with each other.
3. As a result, the electron duplet of both the hydrogen atoms is complete and a covalent band is formed between them.

4. There is one covalent bond between the component atoms H and Cl of the molecule HCl. Use this information to represent the formation of HCl molecules from H and Cl atoms diagrammatically.
(Use your brainpower)
Answer:
Hydrogen chloride:
1. Hydrogen has atomic number 1 and electronic configuration 1, that means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one.

2. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.

3. The two atoms, hydrogen and chlorine share one electron with each other. As a result, the electron duplet of hydrogen and octet of chlorine is complete and a covalent band is formed between them.

5. Show the formation of the following ionic compounds from the corresponding elements using two methods namely, numerical and diagrammatic representation of electronic configuration.
(a) K⁺ F^–, from 19K and 9F, (b) Ca²⁺ O^2- from ₂₀Ca and ₈O.
(Use your brainpower)
Answer:
(a) K⁺F^– from ₁₉K and ₉F
Potassium fluoride:
1. Potassium has atomic number 19 and electronic configuration 2, 8, 8, 1.
2. Potassium atom has 1 electron in its outermost shell.

4. On the other hand, fluorine has electronic configuration 2, 7. Fluorine has 7 electrons in the outermost shell and requires one electron to complete its octet.

7. Thus, a fluorine atom accepts one electron from a potassium atom and consequently a fluoride ion with one unit negative charge and a potassium ion with one unit positive charge are formed.

(b) Ca²⁺O^2- from ₂₀Ca and ₈O.

Distinguish between the following:

Question 1.
Physical change and Chemical change:
Answer:

Physical change	Chemical change
1. In this change, the composition of the substance does not change. No new substance is formed.	1. In this change, the composition of the compounds change and new compounds are formed.
2. In this case, physical properties such as state, colour, density, etc. are changed.	2. In this case, physical and chemical properties are entirely changed.
3. This change is temporary.	3. This change is permanent.
4. In this case, the original substance can be recovered by simple means or by merely reversing the process.	4. In this case, the original substance cannot be recovered by easy means or by reversing the process.

Question 2.
Ionic bond and Covalent bond:
Answer:

Ionic bond	Covalent bond
1. Ionic bond is formed due to the transfer of electrons from one atom to another.	1. Covalent bond is formed due to the sharing of electrons between two or more atoms.
2. Atoms of metals and nonmetals combine to form ionic bonds.	2. Atoms of nonmetals combine to form covalent bonds.
3. Molecules of the compounds formed due to ionic bond split up into ions in aqueous solution.	3. Molecules of the compounds formed due to covalent bond so not split up into ions in a solution.

Give scientific reasons:

Question 1.
Ionic compounds are formed due to the combination of metallic and nonmetallic atoms.
Answer:
Metallic atoms have a tendency to lose electrons from their outermost orbits to establish the octet state in their penultimate orbits. Conversely, nonmetallic atoms gain electrons to establish the octet state of their outermost orbits.

When a metallic atom and a nonmetallic atom come close together, the metallic atom loses electrons and gets c converted into positively charged ion, while the nonmetallic’ atom gets converted into negatively charged ions so formed, develop an ionic bond and this results in the formation of an ionic compound. Hence, ionic compounds are formed due to the combination of metallic and nonmetallic atoms.

Activity-based questions:

Activity 1:

Take the lemon juice in a clean glass. Take two drops of the lemon juice in a spoon and taste. Add a pinch of baking soda in the glass of lemon juice. Did you notice bubbling around the particles of soda? Did you hear a sound on taking your ear near the glass? Now again taste it. Did it taste as sour as it was in the beginning? (Above activity is to be done using clean apparatus and edible material. Then only it is possible to test the ’taste’, otherwise keep in mind that the testing of ‘taste’ cannot be done.)

Activity 2:
Take some freshly prepared lime water (solution of calcium hydroxide) in a test tube. Keep on blowing in it with a blow tube. What is seen after some time? Did the colourless lime water turn milky? After some more time you will find that a white insoluble solid settles at the bottom of the test tube. This is a precipitate of calcium carbonate. The turning lime water milky means that the blown gas mixed in it was carbon dioxide.

Write a chemical equation for the above word equation.
Chemical equation:
CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

8th Std Science Questions And Answers:

Maharashtra Board Class 8 Science Solutions Chapter 2 Health and Diseases

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 2 Health and Diseases Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 2 Health and Diseases

Class 8 Science Chapter 2 Health and Diseases Textbook Questions and Answers

1. Distinguish between- Infectious and non – infectious diseases.

Infectious diseases	Non-infectious diseases
1. The diseases which can be transmitted from one patient to other person are called infectious diseases.	1. The diseases which cannot be transmitted from one patient to other person, are called non-infectious diseases.
2. Contaminated air, water, food or carrier! vector animals or insects spread the infectious diseases.	2. Non-infectious diseases are not transmitted through any medium.
3. infectious diseases are acute diseases as they are suddenly caused due to infections from either bacteria, virus or protozoan. Thus, their symptoms are seen sooner.	3. Some non-infectious diseases are due to hereditary causes, some are a clue to failure in metabolism, some due to deficiency of the nutrients. Their symptoms are not seen suddenly but are developed gradually.
4. Antibiotics or antihelminth medicines are used to treat the infectious diseases. E.g. Tuberculosis, hepatitis, leprosy, cough and cold, etc.	4. Antibiotics cannot be used for treating non-infectious diseases. These diseases have a proper treatment. E.g. Diabetes, cancer, heart diseases, etc.Tuberculosis, hepatitis, leprosy, cough and cold, etc.

2. Identify the odd term.

Question a.
Malaria, hepatitis, elephantiasis, dengue.
Answer:
Hepatitis (All other diseases are caused by the carrier mosquito.)

Question b.
Plague, AIDS, Cholera, T.B.
Answer:
AIDS [All others are bacterial (caused by bacteria) diseases.]

3. Answer in one to two sentences.

Question a.
Which are various media of spreading the infectious diseases?
Answer:
Infectious diseases spread through contaminated air, water, food, vectors such as insects, animals and man.

Question b.
Give the names of five non-infectious diseases other than given in the lesson.
Answer:
Asthma, cataract, diseases of kidney such as kidney stones and renal failure, arthritis, Alzheimer which is a condition during old age, hypertension, migraine, etc.

Question c.
Which are the main reasons of diabetes and heart diseases?
Answer:
Improper lifestyle, wrong type of diet, lack of exercise, excessive mental stress and strain, imbalance in secretion of hormones, etc. are the main reasons for diabetes and heart diseases.

4. What can be achieved/can be prevented?

Question a.
Drinking boiled and filtered water.
Answer:

When water is boiled, all the disease causing pathogens present in it are killed.
Different diseases like cholera, enteritis, diarrhoea, dysentery, hepatitis, typhoid are caused by such water-borne pathogens.
If we boil the water we are protected against all such diseases.
If the i water is filtered we can avoid infections from nematode Dracunculus which causes Naru. By boiling and filtering water, even the epidemics by such infectious diseases can be controlled.

Question b.
Avoiding smoking and alcoholism.
Answer:
1. Smoking and alcoholism are two dangerous habits that cause addictions. Alcoholism causes disorders of liver.
2. The addict suffers from malnourishment.

3. His I mental and psychological conditions become abnormal. There is social and familial) impacts too due to alcoholistn.

4. Smoking is an invitation for cancer. In cigarettes/ bidis, there is hazardous nicotine. Nicotine is not only toxic but is also carcinogenic. Cancers of oral cavity, tongue, respiratory tract, lungs is very common among smokers. Therefore, addictions like smoking and alcoholism should always be avoided.

Question c.
Regular balanced diet and exercise.
Answer:
1. Regular and balanced diet results into perfect health. The disease fighting power or immunity of a person is increased due to healthy diet.
2. One can avoid of frequent infections and also mental well¬being is established.
3. Heart disease, diabetes, obesity, etc. can be avoided by not consuming high caloric junk food.
4. Exercise improves blood circulation. Many disorders which are caused by faulty lifestyle can be prevented by having regular balanced diet and exercise, thus one must always follow these for well-being.

Question d.
Proper checking of blood before blood donation.
Answer:
1. There are definite blood groups.
2. During blood transfusion, the donor’s and recipient’s blood should be well-matched with each other. Otherwise, blood gets clumped inside the body of recipient.
3. Through infected blood, the viruses such as those causing hepatitis B or AIDS are transmitted to other healthy persons. Thus, for prevention of transmission of such diseases, blood should be checked before blood donation.

5. Read the passage and answer the questions.

Master X’ is a 3-year-old child. He is living with his family in a slum. The public toilet is present near his house. His father is drunkard. His mother does not know the importance of balanced diet.

Question a.
Master ‘X’ can suffer from which different possible diseases in above conditions?
Answer:
Master ‘X’ stays in an area which is devoid of cleanliness. The public toilet is near his house. This indicates that he will have to fight against many infectious diseases. Because his father is a drunkard, there will always be a dearth of money in r the house. He may not be able to afford, enough and balanced food. Thus his diet must be deficient in vitamins and minerals.

Moreover, his mother is ignorant about the importance of health and a balanced diet. This must be causing Master ‘X’ malnourishment and loss of immunity. The financial conditions and the addition of the father must be causing stress in the house.

This will further add stress on Master ‘X’ resulting into susceptibility to infections. As it is due to the location the germs are around and thus they may be attacking Master ‘X’. He will on and off suffer from digestive disorders! such as typhoid, hepatitis, cholera, enteritis, etc.

Question b.
How will you help him and his family in this situation?
Answer:
Initially, we shall help Master ‘X’ to procure healthy and balanced diet having fruits, vegetables, milk, etc. His mother will be taught importance of the balanced diet. The surroundings should be clean and hygienic. Food should be covered, houseflies should not be allowed to contaminate the food. Germicidal floor cleaners and disinfectants should be used to keep off the houseflies and cockroaches. His father will be taken to de-addiction centres such as ‘Alcoholics Anonymous’. He will be persuaded to leave alcoholism.

Question c.
Which disease can occur to the i father of master ‘X’?
Answer:
Father of Master ‘X’ can develop diseases of liver and kidney.

6. Give the preventive measures of following diseases:

Question a.
Dengue:
Answer:
Dengue is transmitted through bite of mosquito of Aedes aegypti. DEN-1, 2 virus belonging to the type – flavivirus is the causative pathogen for Dengue. Wherever there is stagnant or accumulated water, there is possibility of mosquito breeding. Therefore, care is to be taken to drain of such water. Thus this is a very important preventive measure. Especially, in the man¬made containers and in clean water, the Aedes mosquito prefers to breed.

Therefore, such water storages should be either covered or should be decanted. Another way to keep off from dengue is to increase our immunity to fight against the virus. There is vaccine called CYD-TDV or Dengvaxia which is synthesised in 2017. But it is still not considered to be completely safe.

Question b.
Cancer:
Answer:
The most important preventive measure is to remain away from the carcinogenic substances. Tobacco, gutkha, cigarette, bidi, etc. are addictive things which are very bad for our health. The nicotine present in these cause cancers of oral cavity and of respiratory system. Radiations can also cause cancer.

We should not expose ourselves to hazardous radiations. Balanced and healthy diet, proper exercise and living stress free with mental balance are some of the preventive measures of the cancer. Only for few types of cancer like cervical cancer in women, vaccine has been developed.

Question c.
AIDS:
Answer:
When blood transfusion is done, the blood should be checked for the presence of HIV. The used syringes, needles, etc. should not be used without sterilization. Through blood and blood products and body fluids HIV finds its way into the body. Therefore, these precautions should be taken. Unsafe sexual contact is the most important mode of transmission of HIV. Thus one should never deal with such dangerous acts. Awareness about AIDS and HIV is the real preventive measure.

7. Explain the importance.

Question a.
Balanced diet.
Answer:
The diet that contains all the nutrients in the balanced proportion is called balanced diet. One can avoid malnutrition by taking balanced diet. The immunity increases due to balanced diet containing good proportion of vitamins and minerals. Some diseases can be avoided due to raised immunity. Wrong lifestyle and wrong diet can cause hypertension, diabetes or heart disease. To maintain our health and keep the body in equilibrium, we have to take balanced diet.

Question b.
Physical exercise/Yogasanas.
Answer:
By exercise and yoga, the blood circulation of body is improved. Body and joints remain flexible. Mental strain and stress is reduced. Insomnia (inability to fall asleep), arthritis, indigestion, and some other disorders can be avoided. The person who performs exercise, always remains away from the addictions. Yoga makes levels of hormones, enzymes, etc. in equilibrium. By keeping control over breathing through pranayama many respiratory and circulatory disorders can be prevented.

8. Make a list.

Question a.
Viral diseases.
Answer:
AIDS, Hepatitis, Influenza, Rabies, Polio.

Question b.
Bacterial diseases.
Answer:
Typhoid, Tuberculosis, Cholera, Leprosy.

Question c.
Diseases spread through insects.
Answer:
Malaria, Dengue, Elephantiasis.

Question d.
Hereditary diseases.
Answer:
Diabetes, Haemophilia, Muscular dystrophy, Colourblindness.

9. Write the information on modern diagnostics and treatments of cancer.

Question a.
Answer:
1. Following methods are used as diagnostic methods to detect the cancer. Techniques like CT scan, MRI scan, mammography, biopsy.
Treatment of the cancer is done by the following methods:

2. For treatment of cancer, some conventional methods are used. Along with these methods, chemotherapy, radiation therapy and surgery are commonly used to treat cancerous growth and tumours. New and modern techniques of robotic and laparoscopic surgery are also used for the treatment.

10. Enlist the names and composition of the medicines present at your home.

Question 1.
Prepare posters giving information about various diseases, public awareness and arrange exhibition in school.

Question 2.
Visit the public health center/clinic nearby and collect the information about vaccination.

Question 3.
Compose a street-play to increase public awareness about dengue, malaria, swine flu and present ¡tin the area nearby your school.

Project:

Question 1.
Prepare posters giving information about various diseases, public awareness and arrange exhibition in school.

Question 2.
Visit the public health center/clinic nearby and collect the information about vaccination.

Question 3.
Compose a street-play to increase public awareness about dengue, malaria, swine flu and present it in the area nearby your school.

Class 8 Science Chapter 2 Health and Diseases Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
For eradication of tuberculosis everybody should be vaccinated by …………. vaccine.
Answer:
For eradication of tuberculosis everybody j should be vaccinated by B.C.G vaccine.

Question 2.
Hepatitis B can be transmitted by ………….
Answer:
Hepatitis B can be transmitted by blood transfusion.

Question 3.
For treating diarrhoea/dysentery…………. is given to the patient.
Answer:
For treating diarrhoea/dysentery O.R.S. is given to the patient.

Question 4.
…………. virus is responsible for the infection of swine flu.
Answer:
Influenza A (H1N1) virus is responsible for the infection of swine flu.

Question 5.
…………. mosquito spreads dengue.
Answer:
Aedes aegypti mosquito spreads dengue.

Question 6.
Malaria is caused by female mosquito of …………. genus.
Answer:
Malaria is caused by female mosquito of Anopheles genus.

Question 7.
…………. test is performed on blood to diagnose AIDS.
Answer:
ELISA test is performed on blood to diagnose AIDS.

One word in the following sentences is wrong. Change it to make the sentences correct:

Question 1.
Culex mosquito is seen in clean water.
Answer:
Culex mosquito is seen in dirty water.

Question 2.
Transmission of swine flu is done by dogs and human beings.
Answer:
Transmission of swine flu is done by pigs and human beings.

Question 3.
Hydrophobia is the main symptom of typhoid.
Answer:
Hydrophobia is the main symptom of rabies.

Question 4.
The maximum number of patients of diabetes are found in America.
Answer:
The maximum number of patients of diabetes are found in India.

Question 5.
Generic medicines are also called branded medicines.
Answer:
Generic medicines are also called general medicines.

Question 6.
If the secretion of insulin is increased, then the diabetes is caused.
Answer:
If the secretion of insulin is decreased, then the diabetes is caused.

Question 7.
Virus causing rabies enter the brain through food.
Answer:
Virus causing rabies enter the brain through neurons.

Match the columns:

Question 1.

Bacterial diseases	Bacteria
1. Typhoid	(a) Mycobacterium tuberculi
2. Cholera	(b) Bacillus
3. Diarrhoea	(c) Vibrio choleri
4. Tuberculosis	(d) Salmonella typhi

Answer:

Bacterial diseases	Bacteria
1. Typhoid	(d) Salmonella typhi
2. Cholera	(c) Vibrio choleri
3. Diarrhoea	(b) Bacillus
4. Tuberculosis	(a) Mycobacterium tuberculin

Question 2.

Importance of the day	Date
1. World Diabetes Day	(a) 7th April
2. World Heart Day	(b) 14th June
3. World Blood Donation Day	(c) 29th September
4. World Health Day	(d) 14th November

Answer:

Importance of the day	Date
1. World Diabetes Day	(d) 14th November
2. World Heart Day	(c) 29th September
3. World Blood Donation Day	(b) 14th June
4. World Health Day	(a) 7th April

Identify the odd term:

Question 1.
Chemotherapy, Radiation therapy, Surgery, Pranayama
Answer:
Pranayama (All others are treatment for cancer.)

Question 2.
Chronic cough, Hoarse voice, Uncontrolled blood sugar level, Difficulty in swallowing.
Answer:
Uncontrolled blood sugar level (All others are symptoms of cancer of throat.)

Question 3.
Mantra, Vaccination, Black magic, Hatred.
Answer:
Vaccination (This is the only way for prevention of diseases. Rest of the others are blind faiths which are unscientific.)

Consider the relation between the items in the first pair and write the correlation for second pair:

1. Swine flu : Virus : :
Tuberculosis : : …………….
Answer:
Bacteria

2. Anopheles : Malaria :
Culex : …………………
Answer:
Elephantiasis

3. Housefly : Typhoid : : Dog : ………….
Answer:
Rabies

4. Decrease in blood platelets : :
Dengue : : Difficulty in breathing : ……………
Answer:
Swine flu

5. Cancer : Laparoscopic surgery : :
Heart disease :……………
Answer:
By-Pass surgery.

Distinguish between the following:

Question 1.
Typhoid and Tuberculosis :
Answer:

Typhoid	Tuberculosis
1. Typhoid is caused by bacteria (Salmonella) that is passed by contaminated food and water and is spread through house flies.	1. Tuberculosis is caused by bacteria (Mycobacterium) which pass through the spittle of the patient.
2. The infection of typhoid is through food or water via the mouth.	2. The infection of tuberculosis is through air via the nose.
3. Typhoid affects stomach and intestine.	3. Tuberculosis affects lungs and chest.
4. There is high fever for specific period in typhoid.	4. There is continuous low grade fever in tuberculosis.
5. There is stomachache and headache in typhoid.	5. There is chest pain in tuberculosis.
6. Vaccination for typhoid is given at the time of suspected epidemic.	6. BCG vaccination is given to all at a young age only.

What can be achieved/can be prevented?/Give reasons.

Question 1.
People suffering from communicable diseases should avoid going to public places.
Answer:

Communicable diseases spread when people share space with a diseased person.
If people suffering from l communicable diseases go to a public place, they would spread the disease causing germs in the air.
These germs can be transmitted to other healthy persons.
If the resistance power of the persons is less, they will fall sick by getting infected.
This may break into an epidemic. Therefore, people suffering from communicable diseases should avoid going to public places.

Question 2.
Pet animals should be given anti-rabies vaccine.
Answer:

We keep animals like cats and dogs at home as pets.
They may get infected with the virus of rabies.
If such an infected pet bites us, we may also get rabies.
Rabies is a lethal disease.
In order to protect the animals and to prevent rabies being transmitted, they should be given anti-rabies vaccine.

Question 3.
Tuberculosis is considered as the most communicable disease.
Answer:

Tuberculosis is caused due to bacterial infection.
It is an air-borne infection and spreads through the spittle of T.B. patient.
When personal and public hygiene is not followed, this disease spreads very rapidly.
It is estimated that every two minutes, one patient dies of T.B. in India. Tuberculosis, therefore, is considered as the most communicable disease.

Question 4.
ORS gives temporary relief to the patient of diarrhoea.
Answer:

In diarrhoea, due to loose motions the patient becomes dehydrated.
The eyes get sunken and the mouth becomes dry.
If immediate help is not given, the condition can become critical. The absorption function of the intestine is disturbed.
But by giving ORS, enough water, sugar and salt enter the body saving the life of the patient.
The sugar and salt in the ORS gets absorbed in the intestine and reduce the dehydration.
However, for eradication of infection, proper medical treatment is to be given, therefore, ORS gives only a temporary relief to the patient of diarrhoea.

Answer the following questions in one sentence:

Question 1.
Which virus causes dengue and how does it spread?
Answer:
Dengue is caused by DEN-1, 2 virus belonging to the type – flavivirus. Aedes aegypti type of mosquito spreads the disease by transferring this virus through its bite.

Question 2.
What are the reasons for spread of swine flu?
Answer:
Swine flu is caused by the virus influenza A (H1N1). Its carrier is pig. The contact with such pigs or infected persons can cause infection of swine flu. The infection spreads through sweat and through secretions of nose, throat and saliva of the diseased person.

Question 3.
What are the symptoms of swine flu?
Answer:
Symptoms of swine flu : Palpitations, difficulty in breathing, sore throat, body pain along with high fever.

Question 4.
In whom was HIV first reported?
Answer:
HIV was first reported in an African species of monkeys

Question 5.
What is a malignant tumour?
Answer:
Due to uncontrolled cell division
there is a formation of lump of cancerous cells. If this lump is without the covering, then it is called malignant tumour.

Question 6.
How is efficiency of the heart reduced?
Answer:
When the blood circulation for the heart muscles is obstructed, it does not receive enough oxygen and nutrients. Due to this condition heart has to exert more and gets stressed resulting into loss of efficiency.

Question 7.
What are the different types of treatment for heart diseases?
Answer:
Angioplasty, By-Pass surgery, open heart surgery, installation of stents, installation of pacemaker, heart transplant are some of the treatment for heart diseases.

Question 8.
What is Pradhan Mantri Jan Aushadhi Yojana? When was it started?
Answer:
Government of India started the Pradhan Mantri Jan Aushadhi Yojana on 1st July 2015. Under this scheme people who are not able to afford best quality medicines are given generic medicines of the same quality at much reduced price.

Question 9.
When can eye donation be done? What is the advantage of eye donation?
Answer:
Anybody can donate eyes posthumously. Due to eye donation, some blind person can regain the sight.

Explain the importance:

Question 1.
Generic medicines.
Answer:
Generic medicines are also called general medicines. They are affordable for the common citizens of India. These medicines are manufactured and distributed without any patent. They are similar in quality and composition as the branded i medicines. The proportion of compounds in these medicines and its formula of preparation is readily available. Thus the money spent on the research is reduced. Therefore, generic medicines are much cheaper than the expensive branded medicines.

Question 2.
Blood donation.
Answer:
Blood donation is said to be the greatest donation that one can give. Blood donation can save someone’s life. By one unit blood of a single donor, three different patients can be saved. From such blood red blood cells, white blood cells and blood i platelets can be separated and given to different patients who are in need with corresponding component. Blood cannot be manufactured artificially and hence blood donation is the only way to collect blood. One healthy person can donate blood four r times in a year, thus saving 12 patients.

Question 3.
First Aid for Heart Disease.
Answer:
A person who is suffering from cardiac problems can get a heart attack suddenly. In such case, the patient should be given immediate and appropriate treatment to save his or her life. First and foremost one should call 108 for cardiac ambulance. Then the patient’s pulse or heartbeats should be checked to know his/her condition. Check the consciousness of the patient. Then make the patient to lie on a hard surface in horizontal position.

Perform C.O.L.S. or, ‘Compression Only Life Support’ on the patient. During this procedure, a pressure is given in the centre of the thorax of a patient for at least 30 times at the rate of 100 to 120 r strokes per minute. This is a first aid for the r heart attack. Before the arrival of doctor or proper medical aid, the life of a patient is saved.

Answer the following questions:

Question 1.
Write a brief account about tuberculosis.
Answer:
Mycobacterium tuberculae is the bacteria which causes tuberculosis (TB) infection. This infectious and communicable disease passes through spittle of the patient. The sneezing and coughing of patient cause f droplet infections. With prolonged contact with the patient and using the objects of the patient there is greater chance of acquiring TB infection. Different body organs such as bones, uterus and lungs can be affected by tuberculosis.

The pulmonary TB i.e. TB of the lungs is more common. The symptoms of TB are prolonged cough, blood through spittle, decrease in the body weight and difficulty in breathing. B.C.G. vaccine can be given in young age for prevention of TB. The patient needs to be isolated if TB is detected. Regular antibiotics have to be taken. DOTS process of medication needs to be followed.

Question 2.
Write the symptoms of dengue.
Answer:
Symptoms of dengue are as follows:

High and severe fever.
Severe headache accompanied with vomiting.
Pain in the eye sockets as if someone is pushing the eyes out.
Rapid reduction in the number of blood platelets.
Internal haemorrhages in the body.

Question 3.
How is rabies caused? What are the important symptoms of the rabies?
Answer:
Rabies is a viral disease. The bite of a rabid animal (the animal who is already infected with rabies virus) transfers the virus in the human blood through the bite wound. Dog, rabbit, monkey and cat can be infected with rabies if they are not vaccinated. The virus of rabies enters the brain through neurons. If not treated in time, rabies can be fatal.

Symptoms of rabies: There is a fever which lasts for 2 to 12 weeks. The victim becomes hyper-excited. He /She shows exaggerations in behaviour. Hydrophobia is very unique symptom in which person is scared and phobic of water. The symptoms can be seen within 90 to 175 days after the animal-bite.
When the dog or any animal bites, before the symptoms are seen, the victim should immediately take anti-rabies vaccine. This vaccination can save a person.

Question 4.
What are the causes of cancer?
Answer:
The carcinogenic substances can cause cancer. Thus such substances should never be used. Tobacco, gutkha and other nicotine containing products can cause cancer. Smoking and alcoholism can also induce cancer development. Cancer is also hereditary disease which is said to be caused by oncogenes. The lack of high fibre food in the diet and junk food in great quantities can induce the cancer development in some part of the alimentary canal.

Question 5.
Write the symptoms of cancer.
Answer:

If part of the respiratory system is under the attack of cancer, it can cause, long term cough, hoarse voice, difficulty in swallowing or difficulty in breathing.
The wounds do not become cured and the scar too is incurable. Inflammations does not subside.
There is formation of tumour like lump in the breast of the females.
In all the types of cancer there is unexplained weight loss.

Question 6.
What are the preventive measures to avoid the cancer?
Answer:
Complete control over diet should be followed. It should be’ healthy and nutritive. Such diet protects one from the cancer. The modern treatment processes should be immediately carried out, if the cancer is detected. With time-lapse, the growth of the cancer keeps on increasing. Physical exercises should be regularly done. Tobacco consumption, smoking are some addictions that can induce cancer. These should never be tried.

Question 7.
What are the causes and symptoms of diabetes?
Answer:
Causes of diabetes: The pancreas in normal persons secrete hormone insulin which maintains the sugar level in the blood. When there is deficiency of insulin, the symptoms of diabetes develop due to uncontrolled blood sugar level. Hereditary causes also can develop diabetes.

Obesity, lack of physical exercise, mental stress can also lead to diabetes. Overconsumption of fried food and over-indulgence in eating sweetmeats increase the chances of diabetes.

Symptoms of diabetes: The person who develops diabetes has frequent urination and continuous thirst. The body weight also reduces rapidly. Sometimes it may rise suddenly. There is continuous feeling of fatigue.

Question 8.
What are the causes of heart diseases?
Answer:
Addictions such as smoking, alcoholism and junk food lead to heart disease. Diabetes, hypertension, obesity are responsible for developing heart disease. Lack of physical exercise, no physical work, continuous sedentary mode are some causes which reduce the efficiency of the working of heart. Mental strain and stress, anger, frustration, anxiety are some psychological reasons that can lead to heart problems

Question 9.
What happens when medicines are missed?
Answer:
When medicines are taken without the consultation of doctor, there are certain problems. When the medicines and drugs are taken without any cause or symptom, then it is a misuse. Overdose of pain killers produce side effects. Some of these cause damage to nervous system, excretory system and liver. Overdose of antibiotics develops nausea, stomachache, loose motions and rash, white patches on tongue, etc.

Questions based on charts/tables:

Question 1.
Complete the table: Prepare similar table of information as the table given on page 7 about various disease like enteritis, malaria, plague and leprosy.
Answer:

Question 2.
Draw a flow diagram to show treatment for heart diseases.
Answer:

Activity-based questions:

Question 1.
Enlist the names and composition of the medicines present at your home.
Answer:
Students are expected to write this answer based on the medicines in their own homes.

Question 2.
Observe and discuss :

Answer:
Observe the following pictures and write description in the boxes.

Open-Ended Questions:

Question 1.
Poor people do not afford the costly medicines. Is there any alternative for this? Which one?

Answer:
Some medicines are very costly. The poor people cannot afford such expensive medicines. In such cases, some social organizations may give some help to these patients. Some trusts like Tata trust can also offer help to the needy for the treatment.

Some hospitals have social workers who help the needy for raising the funds for poor patients. Another way is to use generic medicines.

These medicines are at par in quality with the branded medicines but they are quite less in the price. They are available in the generic medicine shops. One can also take benefit of Pradhan Mantri Jan Aushadhi Yojana.

Question 2.
What measures will you take to stop the breeding of mosquitoes?
Answer:
We have to take care that there is no water stagnated in and around the house. The garden plants and pots in the house should be checked for the mosquito larvae and eggs if any. If water is not receding and remaining accumulated, then the spraying of insecticides should be done with the help of elders. With the help of elders in the house, the complaint can be lodged in the Malaria eradication department in the nearby Municipality or Gram Panachyat office.

If the water is in ponds, we can release guppy fishes to eradicate the mosquito larvae. The fish feed on the larvae and automatically control the mosquito population.

Question 3.
Our behaviour with HIV infected person must be normal or should not be normal? What is your opinion? Write it with correct explanation.
Answer:
Our behaviour with HIV infected person must be normal. There are no chances of acquiring AIDS by having normal behaviour with the HIV positive person. HIV can pass only through body fluids and blood from HIV infected person to the other normal person. Similarly, the needles or syringes used by HIV infected person can cause the infection of HIV to the other person.

Such ways of contamination should always be avoided. The sexual contact or the blood transfusion with HIV positive person should always be avoided. But the normal behaviour such as hand-shake, eating together, studying in the same class will not matter at all in the transmission of AIDS.

Force and Pressure Class 8 Science Chapter 3 Questions And Answers Maharashtra Board

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 3 Force and Pressure Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 3 Force and Pressure Question Answer Maharashtra Board

Class 8 Science Chapter 3 Force and Pressure Question Answer Maharashtra Board

1. Write proper word In the blank space:

Question a.
The SI unit of force is the ………..
(dyne, newton, joule)
Answer:
The SI unit of force is the newton.

Question b.
The air pressure on our body is equal to the …………. pressure.
(atmospheric, sea bottom, space)
Answer:
The air pressure on our body is equal to the atmospheric pressure.

Question c.
For a given object, the buoyant force in liquids of different ………… is ………….. .
(the same, density, different, area)
Answer:
For a given object, the buoyant force in liquids of different density is the same.

Question d.
The SI unit of pressure is ………………
(N/m³, N/m², kg/m², Pa/m²)
Answer:
The SI unit of pressure is N/m².

2. Make a match.

Question a.

Group ‘A’	Group ‘B’
1. Fluid	a. Higher pressure
2. Blunt knife	b. Atmospheric pressure
3. Sharp needle	c. Specific gravity
4. Relative density	d. Lower pressure
5. Hectopascal	e. Same pressure in all directions

Answer:

Group ‘A’	Group ‘B’
1. Fluid	e. Same pressure in all directions
2. Blunt knife	d. Lower pressure
3. Sharp needle	a. Higher pressure
4. Relative density	c. Specific gravity
5. Hectopascal	b. Atmospheric pressure

3. Answer the following questions in brief.

Question a.
A plastic cube is released in water. Will it sink or come to the surface of water?
Answer:
It will come to the surface of water.
[Note: This is because its density is less than that of water. When it floats, the unbalanced force acting on it is zero.]

Question b.
Why do the load carrying heavy vehicles have large number of wheels?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. Load carrying heavy vehicles have large number of wheels so that the load (weight, force) is distributed over large surface area of the wheels in contact with the road. Hence, the pressure decreases and the tyres do not burst.

Try this :
Pressure of a liquid:

Activity 1:
Take a plastic bottle. Take a 10 cm long piece of a glass tube on which a rubber balloon can be fitted. Warm up one end of the glass tube and gently push it into the bottle at about balloon inflates. What is observed? The pressure of water acts on the side of the bottle as well.

[Note: Here, the area of cross section of the tube remains the same. As the level of the water in the bottle rises, the mass of the water increases resulting in increase in the weight. As the applied force increases, the pressure increases. Therefore, the balloon increases in size.]

Activity 2:
Take a plastic bottle. Pierce it with a thick needle (or with a hot nail) at the points 1, 2, 3 as shown in the Fig. Fill water in the bottle up to full height. A shown in the figure, water jets will be seen emerging and projecting out. The water jet emerging from the hole at the top will fall closest to the bottle. The jet from the lowest hole falls farthest from the bottle.

Also, jets coming out from the two holes at the same level fall at the same distance from the bottle. What is understood from this? At any one level, the liquid pressure is the same. Also, the pressure increases as the depth of the liquid increases.

Question c.
How much pressure do we carry on our heads? Why don’t we feel it?
Answer:
The air pressure at the sea level is about 101 × 10³ Pa. This is the pressure that we carry on our heads. The cavities in our body are filled with air, and arteries and veins are filled with blood. Their pressure balances the pressure due to the atmosphere. Hence, we don’t feel the atmospheric pressure.

4. Why does it happen?

Question a.
Why does it happen? A ship dips to a larger depth in freshwater as compared to marine water.
Answer:
The buoyant force acting on a body is proportional to the density of the fluid in which the body is immersed. The density of freshwater is less than that of marine water. Hence, the buoyant force on a body in freshwater is less than that in marine water. Therefore, a ship dips to a larger depth in freshwater as compared to marine water.

Question b.
Why does it happen? Fruits can easily he cut with a sharp knife.
Answer:

It is easy to cut vegetables. fruits with a sharp knife. A blunt knife does not work here.
The force exerted perpendicularly on a unit area is called ‘pressure’
Presently we are considering only the force acting on an area in a direction perpendicular to it.

Question c.
Why does it happen? The wall of a dam is broad at its base.
Answer:
1. The pressure at a point in a liquid is proportional to the height of the liquid column above it. Hence, the pressure of water in a dam is much greater at the bottom of the dam than at the top.
2. To withstand this high pressure, the wall of a dam is made stronger and thicker (broad) at the base than at the top.

Question d.
Why does it happen? If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.
Answer:
1. When passengers sit or stand in a stationary bus, they are in a state of rest. When the bus suddenly speeds up, the lower (parts of their body in contact with the bus acquire the speed of the bus.
2. The upper parts of their body, however, continue to be in the state of rest due to inertia. Hence, they are thrown in the backward direction.

5. Complete the following tables.

Question a.

Answer:
Using the formula,
density = mass/volume:

Mass (Kg)	Volume (m³)	Density (Kg/m³)
350	175	2
760	190	4

Question b.

Answer:
Using the formula, relative density = density of a metal/density of water:

Density of Metal (Kg/m³)	Density of water (Kg/m³)	Relative Density
5 × 10³	10³	5
8.5 × 10³	10³	4

Question c.

Answer:
Using the formula, pressure = weight/area:

Weight (N)	Area (m²)	Pressure (N.m^-2)
800	0.04	20000
1500	500	3

6. The density of a metal is 10.8 × 10³ kg/m³. Find the relative density of the metal.

Question a.
The density of a metal is 10.8 × 10³ kg/m³. Find the relative density of the metal.
Solution:
Data: Density of the metal = 10.8 × 10³ kg/m³
density of water = 10³ kg/m³
relative density of the metal = ?

The relative density of the metal = 10.8.

7. The volume of an object is 20 cm³ and the mass is 50 g. The density of water is 1 gm^-3. Will the object float on water or sink in water?

Question a.
The volume of an object is 20 cm³ and the mass is 50 g. The density of water is 1 gm^-3. Will the object float on water or sink in water?
Solution :

It is greater than the density of water.
Hence, the object will sink in water.

8. The volume of a plastic-covered sealed box is 350 cm³ and the box has a mass 500 g. Will the box float on water or sink in water? What will be the mass of water displaced by the box?

Question a.
The volume of a plastic-covered sealed box is 350 cm³ and the box has a mass 500 g. Will the box float on water or sink in water? What will be the mass of water displaced by the box?
Solution:

It is greater than that of water.
Hence, the box will sink in water.
The volume of water displaced by the box (V) = the volume of the box = 350 cm³

∴ The mass of water displaced by the box = 1 g.cm^-3× 350 cm³ = 350 g.

Project:

Question a.
Video record all the experiments (Try it) in this chapter with the help of mobile phone and send to others.

Class 8 Science Chapter 3 Force and Pressure Additional Important Questions and Answers

1. Rewrite the sentences after filling the blanks

Question 1.
The tendency of an object to remain in its existing state is called its …………. .
Answer:
The tendency of an object to remain in its existing state is called its inertia.

Question 2.
Pressure = ……………
Answer:

Question 3.
1 bar = ……………….. N/m².
Answer:
1 bar = 10⁵ N/m².

Question 4.
1 atmosphere = ………….. Pa.
Answer:
1 atmosphere = 101 × 10³ Pa.

Question 5.
The SI unit of density is …………. .
Answer:
The SI unit of density is kg/m³

Write proper word In the blank space:

Question 1.
According to Archimedes’ principle, the magnitude of the force of buoyancy acting on a body is …………. .
(Vρg, Vρ/g, Vρm, mρg)
Answer:
According to Archimedes’ principle, the magnitude of the force of buoyancy acting on a body is Vρg.

Question 2.
The pascal is the unit of ……………. .
(velocity, pressure, mass, force)
Answer:
The pascal is the unit of pressure.

Question 3.
Keeping the surface area constant, if the applied force is doubled, the pressure …………….. .
(becomes double, remains the same, becomes four times, becomes half)
Answer:
Keeping the surface area constant, if the applied force is doubled, the pressure becomes double.

State whether the following statements are True or False:

Question 1.
The density of water is 1000 g/cm³.
Answer:
False. [The density of water is 1000 kg/m³ (or 1 g/cm³)]

Question 2.
Force and weight have the same units.
Answer:
True.

Question 3.
Atmospheric pressure at sea level is about 10⁶ dynes/cm².
Answer:
True.

Question 4.
The buoyant force due to a liquid is proportional to the acceleration due to gravity.
Answer:
True.

Question 5.
Atmospheric pressure increases with altitude.
Answer:
False. (Atmospheric pressure decreases with altitude.)

Question 6.
Pressure due to a given force is directly proportional to the area on which the force acts.
Answer:
False. (Pressure due to a given force is inversely proportional to the area on which the force acts.)

Question 7.
When a body is completely immersed in a liquid, the buoyant force acting on it due to the liquid is proportional to the volume of the liquid displaced by the body.
Answer:
True.

Question 8.
The density of a material is useful to determine its purity.
Answer:
True.

Question 9.
One tends to slip over a banana peel on the street and one can slip due to mud are events that occur due to reduced friction.
Answer:
True.

Question 10.
Frictional force is electromagnetic in origin.
Answer:
True.

Identify the odd term:

Question 1.
Density, Pressure exerted by a gas, Mass, Force.
Answer:
Force. (Force is a vector quantity; other quantities are scalar quantities.)

Question 2.
Lactometer, Hydrometer, Voltmeter, Submarine.
Answer:
Voltmeter. (Its working is not based on Archimedes’ principle. The working of a lactometer, hydrometer and submarine is based on Archimedes’ principle.)

Rewrite the following table in such a way that Column 2 and Column 3 will match with Column 1:

Question 1.

Column 1	Column 2	Column 3
1. Pressure	Mass/volume	Specific gravity
2. Density	Force/area	Decreases with increase in height above the sea level
3. Atmospheric pressure	No unit	Useful to determine the purity of a substance
4. Relative density	The pascal	Decreases with increase in area

Answer:

Column 1	Column 2	Column 3
1. Pressure	Force/area	Decreases with increase in area
2. Density	Mass/volume	Useful to determine the purity of a substance
3. Atmospheric pressure	The pascal	Decreases with increase in height above the sea level
4. Relative density	No unit	Specific gravity

Answer the following questions in one sentence:

Question 1.
Which of the following has more inertia? A ₹ 10 coin and a ₹ 1 coin.
Answer:
A ₹ 10 coin has more inertia than a ₹ 1 coin.

Question 2.
Name the physical quantity expressed in pascal.
Answer:
Pressure is expressed in pascal.

Question 3.
State the SI unit of pressure.
Answer:
The SI unit of pressure is N/m², also called the pascal.

Question 4.
Name the property of a liquid due to which it exerts an upward force on an object immersed in it.
Answer:
Buoyancy is the property of a liquid due to which it exerts an upward force on an object immersed in it.

Question 5.
Name the principle used in designing ships and submarines.
Answer:
Archimedes’ principle is used in designing ships and submarines.

Question 6.
What is specific gravity?
Answer:
The specific gravity of a substance is another name used for relative density, i. e., the ratio of the density of the substance to the density of water.

Question 7.
State any one factor on which the pressure exerted by a liquid at a point inside the liquid depends.
Answer:
The pressure exerted by a liquid at a point inside the liquid depends on the density of the liquid.

Question 8.
State any one factor on which the buoyant force due to a liquid depends.
Answer:
The buoyant force due to a liquid depends on the density of the liquid.

Question 9.
Name the device used to determine the purity of a sample of milk.
Answer:
The lactometer is used to determine the purity of a sample of milk.

Question 10.
Name the device used to determine the density of a liquid.
Answer:
The hydrometer is used to determine the density of a liquid.

Question 11.
Name two instruments whose working is based on Archimedes’ principle.
Answer:
Working of the lactometer and hydrometer is based on Archimedes’ principle.

Answer the following questions:

Question 1.
Give three examples to show that a force acts on two bodies through an interaction between them.
Answer:

Consider a car at rest on a level (plane) road. If it is pushed from behind, it moves in the forward direction.
Iron nails get attracted to the poles of a magnet and stick to the magnet.
The moon revolves around the earth.

Question 2.
What is a contact force? Give one example.
Answer:
A force that acts through a direct contact of two objects or via one more object, is called a contact force.
Example: If a ball at rest on the ground is kicked, it starts moving.

Question 3.
What is a non contact force? Give one example.
Answer:
A force that acts between two objects even if the two objects are not in contact, is called a non contact force.
Example: The earth revolves around the Sun.

Use your brainpower!
Make a list of some more examples in which contact and non contact forces are applied. Write the types of force.
Answer:
1. Some examples in which contact forces are applied:

to cut an apple with a knife (muscular force, frictional force)
to lift a ball lying on the ground (muscular force, frictional force)

2. Some examples in which non contact forces are applied:

the motion of the earth around the Sun (gravitational force)
the motion of an electron around the nucleus of an atom (mainly the electric force).

Question 4.
In the following examples, state whether the force is a contact force or non contact force:

a reluctant dog is being pulled by his master
a boy playing football is kicking the ball away
when iron nails are brought near a magnet, they are attracted to the poles of the magnet and stick to the magnet
a coconut is falling from the coconut tree
when a comb is rubbed against hair, small pieces of paper kept on a table get attracted to the comb
when brakes are applied to a moving bicycle, it stops after some time

Answer:

contact force
contact force
non contact force
non contact force
non contact force
contact force.

Question 5.
Give one example in which frictional force is useful.
Answer:
While walking, we push the ground behind with our feet. In the absence of friction between the ground and the lower surface of our feet, we will slip and will not be able to walk.
[Note: Frictional force is electromagnetic in origin.]

Try this:
Take two plastic bottles with rectangular shape. Close their openings by fitting the lids tightly. Keep two small bar magnets on them and fix them neatly using a sticking tape.

Fill a big plastic tray with water and leave the two bottles floating with magnets at the top. Take one bottle near the other. If the north pole of the magnet is near the south pole of the other magnet, the bottles will head towards each other, because unlike poles attract each other.

Observe what will happen when the directions of the bottles are changed. We can observe change in the motion of the bottles without any direct contact. This means that there exists a non contact force between the two magnets.

Observation: When the directions of the bottles are changed, if the north pole of one magnet is near the north pole of the other magnet (or the south pole of one magnet is near the south pole of the other magnet), the bottles will move away from each other because like poles repel each other.

Use your brain power!

Question.
You have learnt about static electricity in the previous standard. Electrostatic force is a non contact force. To verify this, which experiment will you perform?
Answer:

Do not switch on the fan in the room. Keep very small pieces of paper on the table. Rub a plastic comb against hair and bring it near the bits of paper. You will find that the bits of paper are attracted by the comb. The comb, on rubbing acquires electrostatic charge. It induces opposite charges on the bits of paper. Hence, the bits of paper are attracted by the comb.

Try this:
Balanced forces and unbalanced force:

Take a cardboard box, tie thick string to its two sides and keep it on a smooth table as shown in Fig. Take the strings on both sides of the table. Tie weighing pans to the two ends. Keep equal masses in both the pans. The box does not move on the table.

If more mass is kept in one of the pans than in the other, the box starts moving in the direction of that pan. Equal gravitational force acts on both the pans when equal masses are kept in them. This means balanced forces act on the box, with effective force equal to zero as these are acting in opposite directions.

On the contrary, if more mass is kept in one pan than in the other, the box starts moving in the direction of the pan with more mass. When unequal forces are applied to the box on the two sides, an unbalanced force acts on the box resulting in imparting motion to the box.

Children playing tug of war pull the rope in their respective directions. If the pull of the force is equal on the two sides, the rope does not move. If the force is more on one side, the rope moves in that direction. This means that initially, the two forces are balanced; the rope moves in the direction of higher force when the forces become unbalanced.

Let us see one more example. When a big grain storage container is required to slide on the ground, it becomes easier if two persons push it rather than one person. When the force is applied by both in the same direction, the movement is easy. You may have experienced this. What do we understand from this example?

If several forces are applied on an object in the same direction, a force equal to their addition acts on that object.
If two forces are applied on one object in directions opposite to each other, a force equal to their difference acts on the object.
A force is expressed in magnitude and direction.

Force is a vector quantity. If more than one force are acting on a body, then the effect on the body is due to the net force. When a force is applied on a stationary object it moves, its speed and direction change. Similarly, a force is required to stop an object in motion.

An object can change its shape due to force. While kneading a dough made from flour, the dough changes its shape when a force is applied. A potter applies a force in a specific direction while shaping the pot. Rubber, when stretched, expands. There are many such examples. ,

Question 6.
What are balanced forces?
Answer:
If a body is acted upon by two forces, equal in magnitude, opposite in direction and having the same line of action, the forces are called balanced forces. Here, the net force acting on the body is zero.

Question 7.
What is an unbalanced force?
Answer:
If two or more forces act on a body such that their resultant is not zero, the resultant is an unbalanced force.
[Note: Unbalanced force acting on a body = mass of the body × acceleration of the body.]

Question 8.
Explain: Force has magnitude as well as direction. OR Force is a vector quantity.
Answer:
The effect of force applied to a body depends upon how much force we supply, i.e., the magnitude of the force, and the direction in which the force is applied. Consider a ball at rest on the ground. When ; we push it, it starts rolling. The greater the applied force, the greater is the speed acquired by the ball.

Consider a body moving in a straight line, If we apply a force in the direction of motion of the body, the speed of the body increases. On the contrary, if we apply a force in the direction opposite to that of motion of the body, the speed of the body decreases. These ( examples show that force has magnitude as well as direction, i.e., force is a vector quantity.

Question 9.
Explain the term balanced forces.
Answer:
Consider a rigid body acted upon by two forces, equal in magnitude, opposite in . direction and having the same line of action. These forces are called balanced forces as their net effect on the body is zero.
Example: A glass slab kept on a table is acted upon by two balanced forces: (i) the weight of the slab acting downward and (ii) the upward force on the slab due to the table. Their net effect on the slab being zero, the slab remains at rest.

Question 10.
Explain the term unbalanced force.
Answer:
A single force acting on a body is an unbalanced force. It produces acceleration in the body. If two or more forces act on a body such that their resultant is not zero, the resultant is an unbalanced force responsible for accelerating the body.
Example: When a ball lying on the ground is hit with a bat, the ball is set in motion by the applied force.

Question 11.
What will happen if the force is removed completely when an object acquires a certain speed?
Answer:
If the force is removed completely when an object acquires a certain speed, the object will move with the velocity it has at the instant the force is removed.

For example, a body moving with constant speed along a circular path in a horizontal plane will fly tangentially in the sense of motion if the centripetal force (the force directed towards the centre of the circle) is removed completely.

Always remember:

The tendency of an object to remain in its existing state is called its inertia.
This is why an object in stationary state remains in the same state and an object in motion remain in the state of motion in the absence of an external force.

Types of inertia:

1. Inertia of the state of rest: An object in the state of rest cannot change its state of rest due to its inherent property. This property is called the inertia of the state of rest.

2. Inertia of motion: The inherent property of an object due to which its state of motion cannot change, is called its inertia of motion. For example, a revolving’ electric fan continues to revolve even after it is switched off, passengers sitting in the running bus get aerk in the forward direction if the bus suddenly stops.

3. Directional inertia: The inherent property of an object due to which the object cannot change the direction of its motion, is called directional inertia. For example, if a vehicle in motion along a straight line suddenly turns, the passengers sitting in it are thrown opposite to the direction of turning.

Try this:
Activity 1:
Take a postcard and keep it on a glass. Keep a 5 Rupee coin on it. Now skilfully push the card. The coin straight away falls in the glass. Have you ever done this?
Answer:
Yes. (Explanation: The postcard moves forward due to the applied force and then falls due to the earth’s gravitational force. In the absence of adequate frictional force between the coin and the postcard, the coin does not move forward with the postcard, but straightaway falls in the glass due to the earth’s gravitational force.)

Activity 2: Hang a half a kg mass from a stand, with a string 1. Tie another string 2 to the mass and keep it hanging. Now pull the string 2 with a jerk. The string 2 breaks but the mass does not fall. Heavy mass does not move. Now pull the string 2 slowly. The string 1 breaks and the mass fall down. This is because of the tension developed in the string 2 due to the mass.

(Explanation: (1) As no force acts on the mass, it remains at rest due to inertia. (2) The transmission of force results in the tension in the string 1. As the string 1 cannot withstand it, it breaks and the mass falls down.)

Question 12.
What are the three types of inertia?
Answer:
Types of inertia:

inertia of rest
inertia of motion
inertia of direction.

Question 13.
What is inertia of rest ? Give two examples of inertia of rest.
Answer:
The inherent property of a body by virtue of which it cannot change its state of rest is called the inertia of rest.
Examples:

When we dust a carpet, the carpet moves but the dust particles in it remain at rest due to inertia and hence get separated from the carpet. Hence, the carpet becomes clean.
When a bus starts suddenly, the passengers experience a backwarderk due to inertia.

Question 14.
What is inertia of motion? Give two examples of inertia of motion.
Answer:
The inherent property of a body by virtue of which it cannot change its state of motion is called the inertia of motion.
Examples:

When a fan is switched off, its blades continue to rotate for some time. Due to internal friction and friction with air, the blades of the fan stop rotating after some time.
Passengers in a bus experience a forwarderk when the bus stops suddenly due to application of brakes.

Question 15.
What is inertia of direction? Give two examples of inertia of direction.
Answer:
The inherent property of a body by virtue of which it cannot change its direction of motion is called the inertia of direction.
Examples:

While sharpening a knife, sparks fly off tangentially in the sense of motion from the grinding stone.
When a vehicle moves, the mud particles sticking to its wheels fly off tangentially in the sense of motion. Hence, mudguards are fitted to vehicles.

Question 16.
Why do we fall sideways when we are sitting in a bus and it takes a sharp turn?
Answer:
When we sit in a bus and the bus is in motion, we are in a state of motion in the same direction. When the bus takes a sharp turn, our body tends to maintain the state of motion in the straight line due to inertia. The portion of our body in firm contact with the seat acquires the motion along the curved path, but the upper portion of our body, tends to move in the initial direction of motion. Hence, we fall sideways.

Question 17.
What happens when you shake a wet piece of cloth? Explain your observation.
Answer:

When we shake a wet piece of cloth, water droplets come out.
Initially, the wet piece of cloth is at rest. When the cloth is shaken, it is accelerated, but the water droplets in it, due to inertia, tend to maintain the state of rest. Hence, the droplets come out.

Question 18.
If brakes are suddenly applied to a moving car, the passengers in the car are pushed in the forward direction. Explain why.
Answer:
1. The passengers in a moving car have the same velocity as that of the car. When brakes are suddenly applied to the car, it stops suddenly and the lower parts of the passengers’ bodies in contact with the seats, come to rest.

2. The upper parts of their bodies, however, continue to be in a state of motion due to inertia. Hence, the passengers are pushed in the forward direction.

Question 19.
A person alighting from a moving train is likely to fall in the direction of motion of the train. Explain why.
Answer:

A person in a moving train has the same velocity as that of the train. After alighting from the moving train his feet come to rest on the platform.
However, due to inertia, the upper part of his body continues to be in a state of motion in the direction of motion of the train. Hence, he is likely to fall in the direction of motion of the train.

Try this:

Activity 3: Take some sharp pointed nails and push them into a wooden plank by hammering on their heads. Now take? a nail and hold it with its head on the plank and hammer it down from the pointed end. When pressing the drawing pins into a drawing board, they get into the board easily. By applying a force using the thumb one can push the pins into the boards. On the contrary, while pressing ordinary pins into the board with a thumb, the thumb may get hurt.

What does this simple experiment tell?
The nail easily penetrates into wood from its pointed end. From this you will notice that when a force is applied on the head of the nail, it is easy to hammer it into the plank.
Explanation: The less the area of the surface on which the force is applied, the greater is the effect of the force.

Question 20.
Define pressure.
Answer:
The force exerted perpendicularly on a unit area is called pressure.

Use your brain power!

Question 1.
It is easy to cut vegetables, fruits with a sharp knife. A blunt knife does not work here. Why does this happen?
Answer:
The effect of a given force varies l inversely as the area of the surface on ( which the force is applied. The less the surface area, the greater is the effect of the force. The cutting edge of a sharp ’ knife has less cross sectional area relative to that of a blunt knife. Hence, it is easy to cut vegetables, fruits with a sharp knife, rather than with a blunt knife. For a given force, pressure is inversely proportional to the area of the surface on which the force acts.

Question 21.
State the formula for pressure, Hence, determine the unit of pressure.
Answer:

The SI unit of force is the newton (N) and that of area is m². Therefore, the SI unit of pressure is N/m². It is called the pascal (Pa). 1 Pa = 1 N/m².
[Note: The unit pascal is named in honour of Blaise Pascal (1623-62), French mathematician, physicist and philosopher.]

Question 22.
State the CGS unit of pressure. State the relation betweeen the SI and CGS units of pressure.
Answer:
The CGS unit of pressure is the dyne/cm².
IN = 105 dynes, 1m² = (102 cm)² = 104 cm² 1 Pa = 1 N/m² = 105 dynes/104 cm² = 10 dynes/cm².

Question 23.
State the factors on which pressure depends.
Answer:
Pressure depends on the applied force and the area of the surface on which the force is applied.

Question 24.
Explain with a suitable example that pressure varies inversely as the area of the surface on which the force is applied, if the force remains constant.
Answer:
The tip of a pointed nail has an extremely small area, while that of a blunt nail has a comparatively large area. A given force creates a large pressure on the pointed nail and it can be easily hammered into the wood, while a very less pressure is created on the blunt nail and it cannot be easily hammered into the wood.

This shows that pressure varies inversely as the area of the surface on which the force is applied, if the force remains constant. If the same force is applied to surfaces having different areas, the pressure is more on the surface having a smaller area.

[Note: The bottom surface of a camel’s feet is broad. Hence, the camel’s weight acts on a large surface area. This reduces the pressure on the sand. Hence, the camel’s feet do not penetrate deep into the sand. Therefore, it becomes easier for the camel to walk on sand.]

Question 25.
With neat diagrams, describe an experiment to show that pressure increases if the surface area is decreased, keeping the applied force the same.
Answer:
Take a brick measuring 20 cm x 10 cm x 5 cm. Take some clay in a glass trough. Add water to it and knead it into a soft dough. Place the brick on the dough with one of its faces measuring 20 cm x 10 cm in contact with the dough. Observe how deep the brick penetrates into the dough.

Clean the brick and place it on the dough with one of its faces measuring 10 cm x 5 cm in contact with the dough. Observe how deep the brick penetrates into the dough. You will find that the brick penetrates deeper in this case than that in the first case.

In the first case, the weight of the brick acts on a surface area of 200 cm².
In the second case, the weight of the brick acts on a surface area of 50 cm².
This shows that pressure increases if the surface area is decreased, keeping the applied force the same.

Question 26.
State the unit for pressure used in atmospheric science. How is it related to the unit pascal?
Answer:
In atmospheric science, the unit used for pressure is the bar. 1 bar = 10 Pa (pascal).

Try this:

Question 1.
Do the activity as depicted in Figure What is seen?
Answer:
In Fig.(a), the plank is horizontal. In Fig.(b), four books are placed side by side on the plank. The plank bends slightly due to the pressure produced by the weight of the books.

In Fig.(c), the four books are placed one above the other in the middle of the plank. Here the area of the surface of the plank on which the force acts is reduced by a factor of four relative to the earlier case. Hence, the plank bends considerably.
[Note: This shows that for a given force, pressure varies inversely as the area of the surface on which the force acts.]

Use your brainpower!

Question 1.
You must have seen a vegetable vendor carrying a basket on her head. She keeps a twisted piece of cloth on the head, below the basket. How does it help?
Answer:
Keeping a twisted piece of cloth on the head increases the area of the surface on which the weight of the basket containing vegetables acts. Hence, the pressure produced by the force (weight) is reduced and it becomes easier to carry the basket.

Question 2.
We cannot stand at one place for a long time. How then can we sleep on a place for 8 and odd hours?
Answer:
When we stand, our weight acts on relatively small surface area, resulting in increased tension on the muscles of our legs. Hence, we cannot stand at one place for a long time. When we sleep, our weight acts on relatively large surface area, resulting in comparatively reduced tension. Therefore, we can sleep on a place for 8 and odd hours.

Question 3.
For skiing on ice, why are long flat skis used?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. The skis used to slide over snow are long and flat so that the area is increased and hence the pressure is decreased. This makes it easier to slide over snow.

Question 27.
Why do the blades of a pair of scissors have sharp edges?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The less the surface! area, the greater is the pressure produced, The blades of a pair of scissors have sharp edges so that the area is decreased and hence the pressure is increased. This makes cutting • an object such as cloth easier.
[Note: Answers to questions such as why is the blade of an axe sharp? or why is the blade of a saw sharp? can be written on the basis of the answer given above.]

Question 28.
Why does a needle have s sharp point?
Answer:
The pressure produced by a given force depends on the areas of the surface on which the force acts. The less the surface area, the greater is the pressure produced. A needle has a sharp point so that the area is decreased and hence the pressure is increased. This makes the action of piercing easier.

Question 29.
Why do school bags have broad shoulder straps?
Answer:
The pressure produced by a given force depends on the area of the surface on which the force acts. The greater the surface area, the less is the pressure produced. School bags have broad shoulder straps so that the weight of the bag is distributed over a large surface area thereby decreasing the pressure on the shoulders of the student carrying the bag.

Question 30.
How will the pressure change if the area is doubled keeping the force the same?
Answer:
If the area is doubled, keeping the force the same, the pressure will become half the initial pressure.

Question 31.
How will the pressure change if the force is doubled, keeping the area the same?
Answer:
If the force is doubled, keeping the area the same, the pressure will become double the initial pressure.

Question 32.
State the characteristics of the pressure due to a liquid (or a fluid in general).
OR
Write a short note on the pressure due to a liquid (a fluid in general).
Answer:
Characteristics of the pressure due to a liquid (or a fluid):

The pressure at a point in a liquid (or a fluid) is due to the weight of the liquid (fluid) column above that point.
It acts on all sides of the container.
At a given depth it is the same in all directions.
It is independent of the size and shape of the container.
It is proportional to the height of the liquid (fluid) column above the given point.
It is proportional to the density of the liquid (fluid).
It is proportional to the acceleration due to gravity at the given place.

[Note: The pressure exerted by a liquid (or gas or fluid) at a depth h below the free surface of the liquid = hpg, where p is the density of the liquid (or gas or fluid) and g is the acceleration due to gravity.]

Question 33.
Give two examples to show that air exerts equal pressure in all directions.
Answer:

When air is filled in a balloon, it acquires its characteristic shape such as round or oval.
When a bicycle tube is filled with air, it acquires its characteristic (tube-like) shape throughout. This shows that air exerts equal pressure in all directions.

Question 34.
Whatisafluid?Givetwoeamples.
Answer:
A fluid is a substance which can flow.
Examples:

Water (liquid)
Air (gas)

[Note: Liquids and gases together are called fluids. Gases have very low viscosity compared to liquids. A liquid with low viscosity flows easily. A liquid with high viscosity does not flow easily.]

Question 35.
Take two rubber balloons. Fill one with water and blow air into the other. Now prick both balloons with a pin. What do you observe?
Answer:
Water and air both come out of the balloons. Air escapes quickly compared to water and produces a loud sound.

Question 36.
State the characteristics of pressure exerted by a fluid.
OR
Write a short note on pressure exerted by a fluid.
Answer:
Characteristics of pressure exerted by a fluid:

A fluid due to its weight, exerts pressure on the base as well as the walls of the container that holds it.
A fluid exerts pressure on a body immersed in it.
The pressure exerted on any confined mass of fluid is transmitted undiminished in all directions.

[Note: The pressure exerted by a fluid is a scalar quantity.]

Question 37.
Take an empty can. Pour small quantity of water in it. Boil this water for a few minutes until the steam has driven out most of the air. Now close the can with the stopper tightly. Allow it to cool by pouring cold water over it. What do you observe?
Answer:
The can gets gradually crushed.
[Note: The steam inside the can condenses to form water as the can cools. Therefore, the pressure inside the can becomes much less than the external pressure of the air. Hence, the can gets crushed.]

Question 38.
Put a folded newspaper on a plastic bag. Blow air into the bag. What do you observe?
Answer:
The plastic bag inflates as air is blown into it. This raises the folded news¬paper put on the bag.

Question 39.
What is meant by atmospheric pressure?
Answer:
The earth is surrounded by air from all sides. This layer of air is called the atmosphere. Its density is high up to about 16 km from the earth’s surface. Beyond that, up to about 400 km, its density is very low. Air, due to its weight, exerts pressure on the surface of the earth.

The pressure exerted by air or the atmosphere surrounding the earth is known as the atmospheric pressure. It is the ratio of the weight of the air to the area of the surface of the earth. It decreases with altitude as the density of air decreases with altitude and also the weight of the air column above a given place.
[Note: At sea level the atmospheric pressure is about 105 Pa. We do not feel it because the pressure of blood and other fluids in our body balances it.]

Question 40.
State the relation between 1 atmosphere and the pascal.
Answer:
1 atmosphere = (about) 101 × 10³ Pa (pascal)
[Note: The air pressure at the sea level is (about) 1 atmosphere.
1 atmosphere = 101325 Pa.
1 bar = 10³ mbar (millibar)
1 mbar w 10³ Pa (hectopascal)
Atmospheric pressure is expressed in mbar or hectopascal (hPa).]

Use your brain power!

Question 1.
At the sea level the atmospheric pressure 101 × 10³ Pa is acting on a table top of size 1 m². Under such a heavy pressure, why doesn’t the table top crumble down?
Answer:
The air below the table top exerts pressure 101 × 10³ Pa on it in the upward direction. Hence, the table top doesn’t crumble down.

Question 41.
Think – Why?
Question i.
Some people feel their ears popping at the top of a mountain.
Answer:
Atmospheric pressure decreases with altitude. At the top of a mountain, it becomes less than the internal pressure in the ear. Hence, some people feel their ears popping at the top of a mountain.

Question ii.
Some people feel breathless as they climb higher and higher on a mountain.
Answer:
Atmospheric pressure decreases with altitude. Hence, some people feel breathless as they climb higher and higher on a mountain.

Question iii.
We can enjoy a cold-drink or fruit juice with the help of a straw but can we imagine drinking a cold-drink or fruit juice on the moon using a straw?
Answer:
When we suck air in the straw, the pressure of the air in the straw becomes less than that of the outside air on the cold drink or fruit juice in the bottle (or the glass). Hence, the cold drink or fruit juice rises in the straw and enters our mouth. We can then drink it. There is no atmosphere on the moon. Hence, it is not possible to enjoy a cold drink or fruituice on the moon by using a straw.

Question iv.
People are often advised not to carry fountain pens while travelling by air.
Answer:
The ink in a fountain pen (filled at sea level at atmosphere pressure) may come out through its mouth while travelling by air if the outside pressure becomes less than the pressure in the ink holder of the pen. This can spoil the clothes/purse/bag. Hence, people are often advised not to carry fountain pens while travelling by air.

Question 42.
Why do some people have earache when they travel by an aeroplane?
Answer:
When an aeroplane descends at a high speed, there is an increase in air pressure. This increases the pressure on the ear drum. Hence, some people have earache when they travel by an aeroplane.

Question 43.
Explain why a person may bleed from the nose when at a great height above the sea level.
Answer:
The pressure exerted by the blood in blood capillaries is slightly more than the atmospheric pressure and acts in a direction opposite to that of the atmospheric pressure. Atmospheric pressure decreases with height and at a great height above the sea level, it is very low.

As a result, there arises a difference in the internal and external pressures on the walls of the cells and blood capillaries. If the difference is large, it may cause the cell wall and the blood capillaries to burst. Thus, the capillaries in the nose (and ear) may burst causing bleeding.

Question 44.
When a rubber sucker is pressed onto a flat glass surface, it sticks tightly on the surface. Why? You need a large force to separate it from the surface. Why?
Answer:
When a rubber sucker is pressed onto a flat glass surface, practically all the air between the surfaces of the sucker and the glass is pushed out. The air pressure there becomes much less than the atmospheric pressure. Hence, the sucker sticks to the glass due to the external atmospheric pressure. The atmospheric pressure is about 105 Pa. It is very large. Hence, to work against it to separate the sucker from the glass, a large force is needed.

Question 45.
Describe a simple experiment to demonstrate atmospheric pressure.
Answer:
Fill a glass completely with water (to its brim) and cover it with a flat and stiff card paper (or a piece of glass). Holding your palm on the card, turn the glass upside down and take the palm away from the card.

You will find that the water does not spill. The atmospheric pressure on the card (acting upward) is greater than the pressure of the water in the glass (acting downward). Hence, the water in the glass does not spill.

Question 46.
Explain the working of an ink dropper.
[Application]
Answer:
An ink dropper consists of a tube of glass or plastic, with one end tapering to a narrow opening and the other end fitted with a small rubber bulb. When the narrow open end is dipped into the ink and the rubber bulb is pressed, some air in the tube escapes through the open end. This reduces the air pressure inside the dropper.

On releasing the bulb, the atmospheric pressure on the ink pushes the ink into the dropper. The dropper is then taken out and its open end is held over the open barrel of the pen. The bulb is then pressed so that the ink in the dropper enters the pen.
[Note: The medicine dropper works in the same manner.]

Question 47.
Why is the opening of a dropper very narrow?
Answer:
The pressure produced by a given force is inversely proportional to the area of the surface on which the force acts. The opening of a dropper is very narrow. Hence, its area of cross-section is very small. As a result, even if the dropper has a small amount of ink it, its pressure can equal the atmospheric pressure. As the opening is narrow, it is easier to transfer the ink to the pen. The possibility of ink spilling is very low.

Question 48.
What is the characteristic of the cap of eye drop bottles?
Answer:
The cap of an eye drop bottle is fitted with a dropper.

Question 49.
Explain the working of a syringe
used by children when they play with coloured water. [Application]
Answer:
As shown in the figure, a syringe used by children when they play with coloured water consists of a cylinder made of plastic or metal fitted with a piston. One end of the cylinder is in the form of a narrow

tube. The snugly fitting piston can slide in , and out smoothly. The rod connected to the i piston passes through a hole in the centre of the lid and has a handle at the other end. When the tip of the narrow tube is dipped in coloured water (or any other liquid) and the piston is pushed towards the tip, up to the bottom, most of the air in the cylinder escapes through the tube, reducing the pressure.

When the piston is moved up, the coloured water rises in the part of the cylinder below the piston due to the atmospheric pressure. Finally, the inner pressure equals the atmospheric pressure and no more coloured water enters in or comes out.

To spray the coloured water, the tube is taken out and the piston is moved towards the opening of the tube. As the inner pressure is now greater than the atmospheric pressure, the coloured water gushes out of the narrow opening of the tube.

Question 50.
How does the doctor’s syringe work?
Answer:
As shown in the figure, a syringe used by children when they play with coloured water consists of a cylinder made of plastic or metal fitted with a piston. One end of the cylinder is in the form of a narrow

tube. The snugly fitting piston can slide in , and out smoothly. The rod connected to the i piston passes through a hole in the centre of the lid and has a handle at the other end.

When the tip of the narrow tube is dipped in coloured water (or any other liquid) and the piston is pushed towards the tip, up to the bottom, most of the air in the cylinder escapes through the tube, reducing the pressure. When the piston is moved up, the coloured water rises in the part of the cylinder below the piston due to the atmospheric pressure.

Finally, the inner pressure equals the atmospheric pressure and no more coloured water enters in or comes out. To spray the coloured water, the tube is taken out and the piston is moved towards the opening of the tube. As the inner pressure is now greater than the atmospheric pressure, the coloured water gushes out of the narrow opening of the tube.

The tip of a syringe is fitted with a very fine and hollow needle. The required quantity of medicine can be taken in the syringe with the help of the piston. The medicine can then be injected into the body of a patient using the needle and the piston.

Question 51.
Explain the origin of pressure due to a gas enclosed in a container.
Answer:
Molecules of a gas are in a state of continuous random motion. These molecules possess energy due to motion. When the molecules collide with a wall of the container, they rebound. A large number of molecules collide with the wall every second. Hence, a significant force is exerted on the wall. Pressure is the force per unit surface area. Thus, a pressure is exerted by the gas on a wall of the container.

Try this:

Buoyant force:
Take a plastic bottle and fix the lid tightly. Now place it in wafer and see. It will float on water. Try and push it into the water. Even when pushed, it continues to float. This experiment can also be done with a plastic hollow ball. Now fill the bottle with water to the fullest capacity and close the lid, and release in water. The bottle will float inside the water. Why does this happen?

The empty plastic bottle floats on the surface of water. On the contrary, the bottle full of water floats inside water but does not go to the bottom. The weight of the empty bottle is negligible as compared with the weight of the water inside.

Such a bottle with water neither floats on the surface, nor does it go to the bottom. This means the force due to gravity acting downwards (fg), must have been balanced by an opposing force in the upward direction (fb) on the bottle filled with water. This force must have originated from the water surrounding the bottle. The upward force acting on the object in water or other fluid or gas is called buoyant force (fg).

Question 52.
Define buoyant force.
Answer:
The upward force acting on the object in water or other fluid or gas is called the buoyant force.

Question 53.
State the factors on which the buoyant force depends.
Answer:
The buoyant force depends upon the volume of the object immersed in the fluid (V), the density of the fluid (ρ1) and the acceleration due to gravity (g) at that place.
[Note: Magnitude of the buoyant force = Vρ1 g.]

Use your brain power!

Question.
While pulling a bucket from a well, the bucket full of water immersed fully in water appears to weigh less than when it has been pulled out of water. Why?
Answer:
1. When a bucket full of water is immersed in water, the net force acting on the bucket = weight of the bucket full of water-the buoyant force exerted by the water on the bucket. The buoyant force due to a fluid is proportional to the density of the fluid.

2. The density of water is much greater than that of air. Therefore, the buoyant force acting on a bucket full of water while it is in water is much greater than that when it is out of water, i.e., in air. Hence, it appears to weigh less, while it is in water than when it has been pulled out of water.

Try this:

Question 1.
Take a piece of thin aluminum sheet and dip it in water in a bucket. What do you observe?
Answer:
It sinks in the water.

Question 2.
Now shape the same piece of aluminium into a small boat and place it on the surface of water. It floats, isn’t it?
Answer:
Yes, the boat floats on the surface of water.

Question 54.
A lemon sinks in a glass filled with water but it floats when we stir in two spoons of salt in the water. Explain why.
Answer:
When salt is dissolved in water, the density of the water increases. The buoyant force is proportional to the density of the liquid. Hence, when the lemon is immersed in the water containing salt, the magnitude
of the buoyant force acting on the lemon becomes greater than the magnitude of the weight of the lemon. Therefore, it floats in water.

Do you know?

How is it decided that an object left in a liquid will get sink in the liquid, will float on the surface, or will float inside the liquid?
1. The object floats if the buoyant force is larger than its weight.
2. The object sinks if the buoyant force is smaller than its weight.
3. The object floats inside the liquid if the buoyant force is equal to its weight. Which forces are unbalanced in the above cases?
Answer:
Unbalanced force:
1. Magnitude of the unbalanced force acting on the object = magnitude of the buoyant force on the object-magnitude of the weight of the object. The direction of the unbalanced force is the direction of the buoyant force.

2. Magnitude of the unbalanced force on the object = magnitude of the weight of the object – magnitude of the buoyant force on the object. The direction of the unbalanced force is the direction of the weight of the object.

3. Here, the unbalanced force is zero.

Try this:

Take a long rubberband and cut it at one point. At one of its ends tie a clean washed stone or a 50 g weight as shown in Figure
Now hold the other end of the rubberband and make a mark there. Keep the stone hanging in air and measure the length of the rubberband from the stone to the mark made earlier.

Now take water in a pot and hold the rubberband at such a height that the stone sinks in it. Again measure the length of the rubberband up to the mark. What is observed? This length is shorter than the earlier length. While dipping the stone in water, length of the stretched rubber gets slowly reduced and is minimum when it sinks completely. What could be the reason for a shorter length of the rubberband in water?

When the stone is sunk in water, a buoyant force acts on it in the upward direction. The weight of the stone acts downwards. Therefore, the force which acts on it in the downward direction is effectively reduced.
(This decreases the downard force on the rubberband. Hence, its length decreases.)

Question 55.
State Archimedes’ principle.
Answer:
Archimedes’ principle: When an object is partially or fully immersed in a fluid, a force of buoyancy acts on it in the upward direction. This force is equal to the weight of the fluid displaced by the object.
[Note: The two forces mentioned here are equal in magnitude and opposite in direction.]

Question 56.
Using Archimedes’ principle, determine the magnitude of the buoyant force.
Answer:
Let m = mass of the body (object) immersed in the fluid, V = volume of the body, ρ = density of the body, ρ1 = density of the fluid, g = magnitude of the acceleration due to gravity. Suppose that the body is completely immersed in the fluid. Then the volume of the fluid displaced by the body = V. According to Archimedes’ principle, magnitude of the buoyant force = magnitude of the weight of the fluid displaced by the body = mass of the displaced fluid × g = volume of the displaced fluid × density of the fluid × g
(as density = mass/volume)

If the body is partially immersed in the fluid, the volume of the fluid displaced by the immersed part of the body = xV ; here 0 < x < 1.
In this case, the magnitude of the buoyant force

Question 57.
Using the formula for the magnitude of the buoyant force, state under what conditions the body will
1. sink in the fluid
2. float in the fluid
3. remain in equilibrium anywhere within the fluid.
Answer:
Magnitude of the buoyant force on the body = mg \(\left(\frac{\rho_{1}}{\rho}\right)\)
= magnitude of the weight of the body × \(\left(\frac{\rho_{1}}{\rho}\right)\)
1. If the density of the fluid (ρ1) is less than the density of the body (ρ), the magnitude of the buoyant force on the body will be less than the magnitude of the weight of the body. Therefore, the body will sink in the fluid.|

2. If the density of the fluid is greater than that of the body, the magnitude of the buoyant force on the body will be greater than that of the weight of the body. Therefore, the body will float in the fluid.

3. If the density of the fluid is equal to that of the body, the magnitude of the buoyant force on the body will be equal to that of the weight of the body. Therefore, the body will remain in equilibrium anywhere within the fluid.

Use your brain power!

Question.
Explain the observations in the earlier experiments according to the Archimedes’ principle.
Answer:
The increase in the length of the rubberband (y) is proportional to the downward force (f) acting on it.
1. When the stone tied to the rubberband is hanging in air, the magnitude of the buoyant force exerted by air on the stone is negligible compared to that of the weight of the stone. Hence, ignoring it, we have f = fg = mg, where m is the mass of the stone and g is the acceleration due to gravity.

2. When the stone is immersed partially in water, f = fg – fb, where fb is the magnitude of the buoyant force exerted by water on the stone.
Now, fg = Vρg and fb = xVρwg, where V = volume of the stone, ρ = density of the stone, xV= volume of the water displaced by the part of the stone immersed in water = volume of the part of the stone immersed in water (x < 1) and ρ = density of water.

This shows that as the stone is gradually lowered in water, x goes on increasing and hence/goes on decreasing. Therefore, elongation (y) of the rubberband goes on decreasing, i.e., the length of the rubberband goes on decreasing.

3. When the stone is completely immersed in water, x becomes maximum, equal to 1. Here, f = fg \(\left(1-\frac{\rho_{\mathrm{W}}}{\rho}\right)\). This is the minimum value of. Here, the elongation of the rubberband is minimum, i.e., the length of the rubberband is minimum.

Question 58.
State the applications of Archimedes’ principle.
Answer:
Archimedes’ principle is used in the construction of ships and submarines. The working of the lactometer and hydrometer is based on Archimedes’ principle.
[Note: The hydrometer is used to determine the density or relative density of a liquid.]

Question 59.
If a spring balance is used to weigh a body, will the weight of the body be the same in vacuum and air? Explain why.
Answer:
When a body is suspended in air, the buoyant force acts on the body. Hence, the magnitude of the net downward force on 1 the body = the magnitude of the weight of the body – the magnitude of the buoyant force on the body. Hence, when a spring balance is used to weigh a body, the weight of the body in air is less than that in vacuum.

Question 60.
What is density of a substance? I Obtain its SI unit.
Answer:
The density of a substance is the ratio of its mass to volume.
The SI unit of density = \(\frac{\text { the SI unit of mass }}{\text { the SI unit of volume }}\) = kg/m³
[Note: Density is useful in determining the purity of a substance. The CGS unit of density is g/cm³.
1 kg/m³ = 10³g/(100 cm)³ = 10^-3g/cm³
∴ 1g/cm³ = 1000 kg/m³]

Question 61.
What is relative density of a substance?
Answer:
The relative density of a substance is the ratio of its density to the density of water.
[Note: Relative density is also called specific gravity. It is a ratio of two equal (same) physical quantities. Hence, it has no unit.]

Question 62.
A piece of wood floats both in water and kerosine. In which liquid does it sink more during floating? Why?
Answer:
The piece of wood sinks more in kerosine than in water during floating. The density of kerosine is less than that of water. The buoyant force on a body is proportional to the density of the liquid in which the body is immersed. When a body floats, the magnitude of the buoyant force acting on the body is equal to that of the weight of the body.

Hence, the volume of the liquid displaced by a floating body is inversely proportional to the density of the liquid. As a result, when a piece of wood floats in kerosine, it displaces greater volume of kerosine compared to the volume of water displaced when the piece of wood floats in water. Hence, it sinks more in kerosine than in water.
[Note: When a body floats in a liquid fb = fg
∴ Vρ1g = Vbρbg
∴ The volume of the liquid displaced by the body is V = Vb \(\frac{\rho_{\mathrm{W}}}{\rho_{1}}\), where Vb is the volume of the body, ρb is the density of the material of the body and ρ1 is the density of the liquid. Thus, V ∝ 1 /ρ1]

Question 63.
State whether the body will float or sink in a liquid if the density of the body is 1. greater than that of the liquid 2. less than that of the liquid 3. equal to that of the liquid.
Answer:

The body will sink in the liquid if the density of the body is greater than that of the liquid.
The body will float in the liquid if the density of the body is less than that of the liquid.
The body will float inside the liquid if the density of the body is equal to that of the liquid.

Question 64.
If the relative density of a body is greater than 1, will it float in water?
Answer:
If the relative density of a body is greater than 1, it will not float in water.
[Note: The relative density of a pin is much greater than 1. But when kept gently on the surface of water, it floats. This is due to the surface tension of water.]

Question 65.
A glass of water has an ice cube floating in water. The water level must touches the rim of the glass. Will the water overflow when the ice melts? Give the reason.
Answer:
The water will not overflow when the ice melts. The water level will remain the same. Ice floats on water because its density is less than that of water. When ice melts, the volume of the water formed is less than the volume of the ice which has melted.

When ice in water melts, this difference equals the volume of the water formed when the part of ice above the surface of water melts. Therefore, the water level remains the same. Hence, there is no overflow of water when the ice melts.

Question 66.
A plastic ball is released underwater. State whether it will sink or come up to the surface of water. Give the reason.
Answer:
A plastic ball released under water will come up to the surface of water. The density of water is greater than that of plastic. Hence, when a plastic ball is under water, the magnitude of the buoyant force exerted by water on the ball is greater than the magnitude of the weight of the ball.

Therefore, the ball will start moving upward. As it comes up with part of the ball above the water surface, the volume of the water displaced by the ball becomes less and hence at a certain stage, the buoyant force and the weight balance each other. Then the ball continues to remain in that state, as the net force on the ball becomes zero.
[Note: Initially, the ball moves slightly up and down near the water surface. The force due to friction with water, opposing the motion of the ball, finally makes the ball steady.]

Write short notes:

Question 1.
Buoyant force.
Answer:
1. When a body is immersed partially or completely in a liquid, the liquid exerts forces on all sides of the body. This force is perpendicular to the surface of the body and equals the product of pressure and area at that point.

2. The resultant of all these forces acts upward. It is called the upthrust or buoyant force.

3. The buoyant force is proportional to (i) the volume of the liquid displaced by the body (ii) the density of the liquid (iii) the acceleration due to gravity. Its magnitude equals the magnitude of the weight of the liquid displaced by the body.

Question 2.
Applications of Archimedes’ principle.
Answer:
1. The working of a lactometer, a device used to determine the purity of a sample of milk, and a hydrometer, a device used to determine the density of a liquid, is based on Archimedes’ principle. The extent to which a lactometer floats (or sinks) depends on the density (and hence purity) of the milk. The same thing is true for a hydrometer. The greater the density of a liquid, the less is the extent to which a body sinks in it.

2. Archimedes’ principle is used in design of ships and submarines. A submarine is provided with large tanks at the front and the back. Its weight can be increased by filling the tanks with sea water or air from compressed air reservoirs. The weight can be decreased by pumping out water from the tanks by forcing compressed air in them. By controlling the weight, it can be made to sink or rise to the surface as desired.

3. The density of a body that floats or sinks in water or kerosine can be determined by. Archimedes’ principle.
4. The density of kerosine can be determined by Archimedes’ principle, using a body of material that is not affected by water and kerosine.

Give scientific reasons:

Question 1.
The tiles are placed over a slushy patch of ground to help cross It.
Answer:

Tiles have greater area than the area of our feet.
The weight of the person crossing the slushy patch is exerted over a large area of the tiles.
Therefore, there is a decrease in the pressure and hence the tiles do not sink much in the slushy patch of ground. This helps to cross the slushy patch of ground.

[Note: If there were no tiles, the feet will come in direct contact with the slushy ground. The area of the feet being less, the weight of the person will act over a smaller area. Therefore. there will be more pressure and hence the feet will sink into the slushy ground.]

Question 2.
Drawing pins have flattened heads.
Answer:

The head of a drawing pin is flattened and the other end is pointed.
When enough force is applied to the head of the pin, the pressure due to the force on the pointed end increases tremendously and the pin can be easily inserted in the drawing board.
When we press the flattened end, the force applied spreads over a larger area. This reduces the pressure of the reaction force acting on the thumb. Hence, the thumb is not injured.
If the head of the pin is sharp, then the pressure due to the force would be more and hence the pressure of the reaction force would also be more and the sharp end would prick the thumb causing injury.

Question 3.
An iron nail sinks in water but a ship made from iron floats on water.
Answer:
1. An iron nail sinks in water because its density is more than that of water.
2. A ship made from iron, due to the particular shape given to it, displaces a large amount of water so that the buoyant force acting on the ship due to water balances the weight of the ship. Hence, the ship floats on water.

Question 4.
A piece of iron sinks in water but floats on mercury.
Answer:
The density of iron is more than that of water but less than that of mercury. Hence, a piece of iron sinks in water but floats on mercury.

Question 5.
A sheet of metal that sinks in water can float if shaped like a pan.
Answer:

A sheet of metal sinks in water because its density is more than that of water.
If the sheet is shaped like a pan, it can displace a large amount of water such that the buoyant force on the pan due to water balances the weight of the pan. Hence, it can float on water.

Solve the following examples:

Problem 1.
(i) Calculate the pressure exerted by the wooden block when it is kept in the vertical position.
Given: The length of the wooden block is 80 cm, the breadth is 50 cm, the thickness is 20 cm and the weight is 500 N
(ii) Also calculate the pressure when the wooden block is kept in the horizontal position with its surface 80 cm × 50 cm touching the floor.

Solution:
Data: F = W = 500 N, l = 80 cm = 0.8 m, b = 50 cm = 0.5 m. h = 20 cm = 0.2 m
(i) A = bh = 0.5 m × 0.2 m = 0.1 m²

The pressure exerted in the vertical position of the block = 5000 N/m² or 5000 Pa.

(ii) A = lb = 0.8 m × 0.5 m = 0.4 m²

The pressure exerted in the horizontal position of the block = 1250 N/m² or 1250 Pa.

Problem 2.
Measure the length, breadth, height and mass of a rectangular tiffin box. Find the weight of the box and calculate the pressure in two different positions as in Ex. (1) above.
Solution:
Let l = 0.25 m, 6 = 0.1 m, h = 0.05 m, F = W= 0.5 N
(i) A = bh = 0.1 m × 0.05 m = 0.005 m²

(ii) A = lb = 0.25 m × 0.1 m = 0.025 m²

Problem 3.
A force of 1000 N is applied over an area 50 cm × 20 cm. Find the corresponding pressure.
Solution:
Data: F = 1000 N,
A = 50 cm × 20 cm = 0.5 m × 0.2 m = 0.1 m², pressure = ?

The pressure = 10 N/m².

Problem 4.
A metal block has thmensions 10 cm × 5 cm × 2 cm and the density of the metal is 8 × 10³ kg/m³. It is kept on a table with the face 10 cm × 5 cm in contact with the table. Find the force and pressure exerted by the block on the table. (g = 9.8 m/s²)
Solution :
Data : 1 = 10 cm, b = 5 cm,
h = 2 cm, p= 8 × 10 kg/m3, g = 9.8 m/s²,
A = lb = 10cm × 5cm = 50cm² = 50 × 104m²
= 5 × 10^-5m², force =?, pressure = ?
Volume of the block = lbh =
10 cm × 5 cm × 2 cm= 100 cm³
= 100 × 10^-6 m³ = 1 × 10^-4m³
Mass of the block = volume × density
(∵ density = mass/volume)
∴Mass of the block,
m = 1 × 10^-4 m³× 8 × 10³ kg/m³ = 0.8 kg
Weight of the block = mg = 0.8 kg × 9.8 m/s² = 7.84 N
∴ The force exerted by the block on the table = 7.84 N.
force 7.84 N

= 1.568 × 10³ N/m² or 1.568 × 10³ Pa
The pressure exerted by the block on the table = 1.568 × 10 N/m2 or 1.568 × 10³ Pa.

Problem 5.
A body of volume loo cm³ is immersed completely in water. Find the weight of the water displaced by the body. 1g = 9.8 m/s². p (water) = kg/m³]
Solution :
Data: V = 100 cm³ = 100 × 10^-6 m³
= 1 × 10 m³, p(water) = 10 kg/m³
g = 9.8 m/s², weight of the displaced water ?
Density = \(\frac{\text { mass }}{\text { volume }}\)
∴ Mass = volume × density
Volume of the water displaced by the body = l × 10^-4 m³
∴Mass of the water displaced,
m = l × 10^-4 m³ × 10 kg/m³ = 0.1 kg
∴Weight of the water displaced
= mg = 0.1 kg × 9.8 m/s² = 0.98 N.
The weight of the water displaced by the body = 0.98 N.

Problem 6.
A body of mass 200 g and volume 50 cm³ is put in a bucket containing water. Will it float or sink ?
[ρ(water) = 1 g/cm³]
Solution:
Data: m = 200 g, V= 50 cm³,
ρ (water) = 1 g/cm³Density(ρ) = \(\frac{\text { mass }}{\text { volume }}\)
∴ ρ (body) = \(\frac{200}{50 \mathrm{~cm}^{3}}\)
It is greater than the density of water.
Hence, the body will sink in water.

Problem 7.
A body of mass 200 g and volume 400 cm³ is put in a bucket containing water. Will it float or sink?
[ρ (water)=1 g/cm³]
Solution:
Proceed as above.
ρ (body) = \(\frac{200 \mathrm{~g}}{400 \mathrm{~cm}^{3}}\) = 0.5 g/cm³
It is less than the density of water.
∴ The body will float in water.

Problem 8.
The mass of a tile is 500 g. If the density of the tile is 2.5 g/cm³, what will be the weight of the tile when it is completely immersed in water?
(g = 9.8 m/s², ρ(water) = 1000 kg/m³)
Solut10n:
Data: m = 500, g = 0.5 kg, ρ
(tile) = 2.5 g/cm³ = 2500 kg/m³, g = 9.8 m/s²,
ρ (water) = 1000 kg/m³, weight of the tile when completely immersed in water (also called the apparent weight) = ?
ρ = \(\frac{m}{V}\)

∴ Volume of water displaced by the tile
= 2 × 10^-4 m³
∴ Mass of water displaced by the tile
m’ = ρ (water) V = 1000 kg/m³ × 2 × 10^-4 m³
= 0.2kg
∴ Magnitude of the weight of this water
= mg = 0.2 kg × 9.8 m/s² = 1.96 N
∴ Buoyant force exerted on the tile = 1.96 N
Magnitude of the weight of the tile =
mg = 0.5 kg × 9.8 m/s² = 4.9 N
∴ Weight of the tile when completely immersed in water (apparent weight) = weight of the tile in air-buoyant force on the tile
= 4.9 N – 1.96 N = 2.94 N(downward)

Examples For Practice:

[g = 9.8 m/s², ρ (water) = 10³ kg/m³ = 1 g/cm³]

Question 1.
Calculate the relative density of a metal having density 7.5 g/cm³.
Answer:
7.5

Question 2.
Find the density of steel if its relative density is 8 and the density of water is 10 kg/m³.
Answer:
8 × 10³ g/cm³

Question 3.
A body has mass 200 g and volume 100 cm³. Find its density and relative density.
Answer:
2 g/cm³, 2

Question 4.
If the relative density of a material is 2.5, find its density.
Answer:
2.5 × kg/m³ or 2.5 g/cm³

Question 5.
A force of 100 N is applied on an area 40 cm × 25cm. Find the corresponding pressure.
Answer:
10³ N/m²

Question 6.
If the pressure exerted on an area 10 cm × 10 cm is 1000 dynes/cm², find the applied force.
Answer:
10⁵ dynes

Question 7.
A metal block of mass 10 kg is kept on a table. If the contact surface area Is 100 cm², find the pressure on the table.
Answer:
9.8 × 10³ N/m² or 9.8 × 10³ Pa

Question 8.
A body of volu.me 50 cm³ is immersed completely in water. Find the weight of the water displaced by the body.
Answer:
0.49 N

Question 9.
A block of mass 100 g and volume 20 cm³ is put in a bucket filled with water. Will it float or sink?
Answer:
The body will sink in water.

Question 10.
Will a block of mass 100g and volume 400 cm³ float or sink in water?
Answer:
The block will float in water.

Question 11.
The volume of a cube is 125 cm³ and its mass is 250 g. It is put in a tub containing water. Will it float or sink?
Answer:
It will sink in water.

8th Std Science Questions And Answers:

Cell and Cell Organelles Class 8 Science Chapter 10 Questions And Answers Maharashtra Board

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 10 Cell and Cell Organelles Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 10 Cell and Cell Organelles Question Answer Maharashtra Board

Class 8 Science Chapter 10 Cell and Cell Organelles Question Answer Maharashtra Board

1. Who am I?

Question a.
I am ATP producing factory.
Answer:
Mitochondria

Question b.
I am single-layered but maintain cellular osmotic pressure.
Answer:
Vacuole

Question c.
I support the cell, but I am not cell wall. I have a body resembling net.
Answer:
Endoplasmic reticulum

Question d.
I am chemical factory of the cell.
Answer:
Chloroplasts in case of plant cells can be called chemical factory as they synthesise carbohydrates. Ribosomes also synthesise proteins, so those can also be called chemical factory. Golgi complex is secretory in function, hence it can be also called factory. Mitochondria though mainly referred to as powerhouse of the cell, it is also mentioned as chemical factory by some authors.

Question e.
Leaves are green because of me.
Answer:
Chloroplast.

2. What would have happened? If……….

Question a.
RBCs had mitochondria.
Answer:
Mitochondria continuously carry out oxidation and form energy inside the cell. They produce energy-rich compound, ATP. In this process, they utilize carbohydrates, fats and proteins present in the cell. If RBCs has mitochondria, they would have used oxygen for this purpose than carrying it to all the cells of the body. The cells would not have obtained oxygen.

Question b.
There had been no difference between mitochondria and plastids.
Answer:
Mitochondria carry out oxidation of carbohydrates, fats, etc. with the help of enzymes. Plastids are synthesising carbohydrates with the help of solar energy and chlorophyll. Both the cell organelles have their own sets of different enzymes as per their role. If there would have been no difference between mitochondria and plastids, the specific functions would not have been taken place.

Question c.
Genes had been absent on the chromosomes.
Answer:
Genes are functional segments on the chromosomes which are responsible for transmitting the hereditary information.

Question d.
Plasma membrane had not been selectively permeable.
Answer:
Selectively permeable membrane allows some substances to enter the cell, while prevents other unwanted or harmful substances. If plasma membrane would not have been selectively permeable, there would be no control over entry and exit of any substances. The process of osmosis would also be erroneous in such case.

Question e.
Plants lacked anthocyanin.
Answer:
If plants lacked anthocyanin, no part of the plant would display purple or blue colour. Anthocyanin attracts the insects for pollination and seed dispersal. These processes will be affected due to lack of anthocyanin. These pigments are also said to be protective in nature for the plant. This protection will not be given to the plant in absence of anthocyanin.

3. Who is odd man among us? Give reason.

Question a.
Nucleolus, mitochondria, plastids, endoplasmic reticulum
Answer:
Nucleolus. (All the others are cell organelles but nucleolus is not a cell organelle present in cytoplasm.)

Question b.
DNA, Ribosomes, Chlorophyll
Answer:
Chlorophyll. (DNA and Ribosomes are present in plant as well as in animal cells. Chlorophyll is present only in plant cells.)

4. Give functions.

Question a.
Plasma membrane.

Answer:

Plasma membrane acts as a selectively permeable membrane. It allows entry of those useful substances which are needed for the cell. It does not allow entry of the harmful and unwanted substances.
Plasma membrane keeps the homeostasis in the cell. The cell is kept in steady state even if the external environment changes.
Plasma membrane is responsible for processes of endocytosis and exocytosis.
The processes of diffusion and osmosis are possible only due to plasma membrane.
In animal cells, plasma membrane is the outermost protective covering of the cell.

Question b.
Cytoplasm.
Answer:

All the cell organelles are spread in the cytoplasm of a cell.
The cytoplasm is the medium for many cellular chemical reactions.
The cytosol which is the part of cytoplasm other than cell organelles stores many vital substances like amino acids, glucose, vitamins, etc.
Cytosol also helps in the cellular movements.

Question c.
Lysosome.

Answer:

Lysosome helps in the destruction of attacking viruses and bacteria and thereby help in the immune response.
Lysosomes act as demolition squads. They destroy worn-out cellular organelles and organic debris. This process is called autolysis which All Pagesmeans self-destruction.
They are also called suicide bags as in a worn out, damaged or old cell, lysosomes automatically burst. The lytic enzymes present in the lysosome digest their own cells.
Lysosomes can digest stored proteins, fats during starvation.

Question d.
Vacuole.

Answer:

Vacuoles maintain the osmotic pressure of the cell.
Various metabolic byproducts and end products such as glycogen, proteins, water, etc. are stored in the lysosome.
In food vacuole of amoeba, the food is temporarily stored till digestion. In other animal cells, vacuoles can store waste products and food.
Vacuoles of plant cells can provide turgidity and rigidity as it contains good amount of cell sap.

Question e.
Nucleus.

Answer:

Nucleus is the controlling centre for the entire cell.
It controls all metabolic activities of the cell.
The cell division is possible due to the nucleus.
The chromosomes present in the nucleus carry the genes. These genes are responsible for the transmission of hereditary characters from parental generation to the next generations.

5. Who gives me the colour? (Select the correct option).

Question a.

Column ‘A’	Column ‘B’
1. Red tomato	a. Chlorophyll
2. Green leaf	b. Carotene
3. Carrot	c. Anthocyanin
4. Violet	d. Lycopene

Answer:

Column ‘A’	Column ‘B’
1. Red tomato	d. Lycopene
2. Green leaf	a. Chlorophyll
3. Carrot	b. Carotene
4. Violet	c. Anthocyanin

Project:

Question 1.
Prepare model of a cell using different ecofriendly materials.

Question 2.
Study osmosis using parchment paper or a similar membrane.

Question 3.
Form a friends’ group in your class. Give each one role of a cell organelle. Present a skit accordingly.

Class 8 Science Chapter 10 Cell and Cell Organelles Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Cell wall is mainly composed of carbohydrates like ……….. and …………. .
Answer:
Cell wall is mainly composed of carbohydrates like cellulose and pectin.

Question 2.
Plasma membrane is said to be a ……………. …………….. membrane as it allows some substances to enter the cell, while prevents other substances.
Answer:
Plasma membrane is said to be a selectively permeable membrane as it allows some substances to enter the cell, while prevents other substances.

Question 3.
Homeostasis is maintained in the cell by ………….. .
Answer:
Homeostasis is maintained in the cell by plasma membrane.

Question 4.
An …………… is a specialized subunit having specific function within the cell.
Answer:
An organelle is a specialized subunit having specific function within the cell.

Question 5.
……………. has ribosome granules on its outer surface.
Answer:
Rough ER has ribosome granules on its outer surface.

Question 6.
During starvation, ………………… digest stored proteins, fats.
Answer:
During starvation, lysosomes digest stored proteins, fats.

Question 7.
……………….. is the secretory organ of the cell.
Answer:
Golgi complex is the secretory organ of the cell.

Question 8.
……………. compound ATP is produced in the mitochondria.
Answer:
Energy-rich compound ATP is produced in the mitochondria.

Given below are incorrect statements. Rewrite them after correcting them:

Question 1.
In mitochondria, the inner membrane is porous and the outer membrane is deeply folded.
Answer:
In mitochondria, the outer membrane is porous and the inner membrane is deeply folded.

Question 2.
Vacuole is bound by double membrane.
Answer:
Vacuole is bound by single membrane.

Question 3.
If fruit pieces are kept in thick saturated sugar solution, the water from fruit pieces enter the sugar solution resulting into their swelling.
Answer:
If fruit pieces are kept in a thick saturated sugar solution, the water from fruit pieces enter the sugar solution resulting into their shrinking.

Question 4.
Raisins kept in water shrink after an hour.
Answer:
Raisins kept in water swell after an hour.

Question 5.
Lysosome produces vacuoles and secretory vesicles.
Answer:
Golgi complex produces vacuoles and secretory vesicles.

Who gives me the colour? (Select the correct option)

Question 1.

Column ‘A’	Column ‘B’
1. Nucleus	a. Pipelines of the cell
2. Endoplasmic reticulum	b. Powerhouse of the cell
3. Golgi complex	c. Suicidal bags
4. Mitochondria	d. Packing department
5. Lysosomes	e. Controlling centre

Answer:

Column ‘A’	Column ‘B’
1. Nucleus	e. Controlling centre
2. Endoplasmic reticulum	a. Pipelines of the cell
3. Golgi complex	d. Packing department
4. Mitochondria	b. Powerhouse of the cell
5. Lysosomes	c. Suicidal bags

Find the odd one out by giving suitable reasons:

Question 1.
Demolition squads, Suicide Bags, Immune system, Powerhouse of the cell.
Answer:
A powerhouse of the cell. (All the others are descriptions of the lysosomes.)

Question 2.
Lignin, Suberin, Cutin, Iodine
Answer:
Iodine. (All the others are polymers present in the cell wall.)

Question 3.
Nucleolus, Genes, Chromosomes, Ribosomes
Answer:
Ribosomes. (All the others are inclusions in the nucleus.)

Write definitions/Give meanings:

1. Homeostasis: The tendency of the cell to keep the cellular environment constant in spite of changes in the outer: environment is called homeostasis.

2. Endocytosis: To take in the food or any other substance from outer environment into the cell is called endocytosis.

3. Exocytosis: To give out the unwanted substances from the cell to the outer « environment is called exocytosis.

4. Diffusion: The movement of the molecules from region of higher concentration to the region of lower concentration is called diffusion.

5. Osmosis: The movement of solute from low concentration to high concentration and the movement of solvent from high concentration to the region of low concentration across semipermeable membrane is called osmosis.

6. Plasmolysis: When the cell is kept ?! in hypertonic medium, the water exits through the process of exosmosis causing shrinkage of the cytoplasm, this is known as plasmolysis.

7. Isotonic solution: When the concentration of the cell and that of the medium in which the cell is kept is same, then such solution is called isotonic solution.

8. Hypotonic solution: When the concentration of the water in the cell is less than that of the concentration of the water in the surrounding medium in which the cell is kept, then such solution is called hypotonic solution.

9. Hypertonic solution: When the concentration of the water in the cell is more than that of the concentration of water in the surrounding medium then such solution is called hypertonic solution.

Distinguish between the following:

Question 1.
Prokaryotic and eukaryotic cell:
Answer:

Prokaryotic cell	Eukaryotic cell
1. Nucleoid is present instead of a well-formed nucleus.	1. Nucleus is well-formed with nuclear membrane, chromatin network and nucleolus.
2. Chromosome number is always one.	2. Chromosome number is more than one and is specific for every species.
3. Membrane-bound cell organelles are absent.	3. There are membrane-bound cell organelles.
4. The size of the cell is 1 to 10 micrometre. Example: Bacteria	4. The size of the cell is 5 to 100 micrometre. Example: All highly evolved unicellular and multicellular plants and animals.

Question 2.
Plant cell and animal cell
Answer:

Plant cell	Animal cell
1. The cell wall is the outermost covering on the cell. The plant cells have both cell wall and the cell membrane	1. The cell membrane or plasma membrane is the outermost covering of the cell. The animal cells do not have cell wall
2. The vacuoles are large and centrally placed.	2. The vacuoles are small and uniformly distributed in the cytoplasm.
3. There are plastids in the plant cells. The chloroplasts have chlorophyll.	3. The plastids are absent in the animal cells.
4. The lysosomes are absent in the plant cells.	4. Lysosomes are present in the animal cells. They contain digestive enzymes.
5. The cytoplasm is thin and pushed to the periphery due to central vacuole.	5. The cytoplasm is dense and granular. It is uniformly spread throughout the cell.

Answer the following questions in one sentence:

Question 1.
What are the components of plasma membrane?
Answer:
In plasma membrane, protein molecules are embedded in two layers of phospholipids.

Question 2.
Which part of the cell maintains the homeostasis?
Answer:
Plasma membrane of the cell maintains the homeostasis.

Question 3.
What are genes?
Answer:
Genes are the functional segments on the chromosomes that carry hereditary i information from the parental generation to the offspring.

Question 4.
What is meant by rough ER?
Answer:
The endoplasmic reticulum that has ribosomes on its outer membrane is called rough ER.

Question 5.
Write the examples of plant pigments.
Answer:
Chlorophyll, Carotene, Xanthophyll, Anthocyanin, Betalains and Lycopene are some of the plant pigments.

Question 6.
What are the inclusions in the stroma of chloroplasts?
Answer:
Enzymes, DNA, ribosomes and carbohydrates that are necessary for photosynthesis are present in the stroma of the chloroplasts.

Question 7.
Which staining technique was developed by Camilio Golgi? Where was this technique used?
Answer:
Camilio Golgi developed the staining technique called ‘Black reaction’ which was used in the study of nervous system.

Question 8.
What type of work is done by National Centre for Cell Science?
Answer:
National Centre for Cell Science – NCCS is involved in research in cytology and research about cancer treatment and it also provides services for National Animal cell repository.

Question 9.
Ripe tomatoes appear red.
Answer:
When green tomatoes become ripe they lose chlorophyll and develop red pigment in them called lycopene. Therefore, ripe tomatoes appear red.

Give scientific reasons:

Question 1.
Raisins swell after keeping in plain water.
Answer:
When raisins are placed in plain water, there is action of endosmosis. The outer skin of raisins acts like selectively permeable membrane. Since the concentration of water inside the raisin is lesser than the concentration of water in the outer medium, water enters in the raisin. This causes raisins to swell after keeping them in plain water.

Question 2.
The fruit pieces kept in sugar syrup show shrinking.
Answer:
There is more concentration of water in the fruit pieces as compared to the concentration of water in the sugar syrup. Therefore, water is lost out by exosmosis. The membranes of the fruit pieces act as selectively permeable membranes. Thus the process of plasmolysis occurs resulting into shrinking of the fruit pieces.

Question 3.
The nucleus of the sieve tubes of the plant phloem is lost.
Answer:
The sieve tubes of the plant phloem conduct the food in plants. To make this transport easier, the nucleus of the sieve tubes of the plant phloem is lost,

Question 4.
Plant cells have less mitochondria than those of animal cells.
Answer:
Mitochondria are the cell organelles which are called powerhouse of the cell. They produce energy in the form of ATP. Animals are motile and need more energy for walking, running and moving. Plants are stationary. They do not need energy to greater extent. Therefore, they have lesser number of mitochondria.

Question 5.
Vacuoles do not have any typical size or shape.
Answer:
Vacuoles change their shape and size as per the need of the cell. Thus they do not have any fixed shape or size.

Question 6.
Ripe tomatoes appear red.
Answer:
When green tomatoes become ripe they lose chlorophyll and develop red pigment in them called lycopene. Therefore, ripe tomatoes appear red.

Give functions:

Question 1.
Endoplasmic reticulum.

Answer:

Endoplasmic reticulum or ER is the supporting framework of the cell.
The ribosomes attached to the membrane of the ER synthesize proteins. These proteins are conducted by ER.
The detoxification process is done by ER. The toxins that enter the cell through food, air and water are removed out by making them water soluble.

Question 2.
Golgi complex.

Answer:

Different secretions are prepared in the Golgi complex. Hence it is called the secretory organ of the cell.
The secretions are modified and sorted out as per their functions. They are further packed.
The enzymes, mucus, proteins, pigments, etc. are sorted and then dispatched to various target regions like plasma membrane, lysosome, etc.
Golgi complex also produces vacuoles and secretory vesicles.
Formation of cell wall, plasma membrane and lysosomes is aided by Golgi complex.

Question 3.
Plastids.
Answer:

Chloroplasts contain chlorophyll. They carry out the process of photosynthesis. They convert solar energy to chemical energy in the form of food.
Chromoplasts with different pigments can impart different colours to flowers and fruits.
Leucoplasts are responsible for the synthesis and storage of food like starch, oils and proteins.

Answer the following questions:

Question 1.
How does endosmosis and exosmosis occur in the cell?
Answer:

When the water concentration inside the cell is less as compared to the medium in which it is present, then the endosmosis takes place. This makes the water to enter inside the cell.
When water concentration inside the cell is more than the water concentration in the medium in which it is present, then the water comes out of the cell. This is called exosmosis.
Since the cell membrane acts as a semipermeable membrane, the processes of endosmosis and exosmosis takes place in the cell.

Question 2.
What is cytoplasm? What are the constituents of cytoplasm?
Answer:

The jelly like material present between the cell membrane and nucleus is called cytoplasm.
Cytoplasm without cell organelles is called cytosol.
All the cell organelles are spread in the cytoplasm.
Cytosol stores many vital constituents such as amino acids, glucose, vitamins, etc.
The cytoplasm of animal cells is dense and granular while that of plant cells is thin and peripheral. It is pushed to sides due to large central vacuole.

Question 3.
Describe the structure of the nucleus in the cell.

Answer:

Nucleus is the most important part of the eukaryotic cell.
Inside the nucleus there is round darkly stained nucleolus.
The nucleus is covered over by double membrane which is porous.
The nuclear pores allow the transport of different substances in and out of the nucleus to cytoplasm.
Inside the nucleus is the chromatin network which contains chromosomes. Chromatin fibres are thin which condense to form chromosomes. The chromosomes become clear and distinct at the time of cell division.
In every cell there are specific number of chromosomes. Chromosomes contain genes which are bearers of hereditary characters.

Question 4.
Why is endoplasmic reticulum compared with the pipelines?
Answer:

The endoplasmic reticulum works as pipelines to carry different substances in the cell.
It is a net like structure consisting of interconnected small tubes and sheets filled with fluid.
On the inner side the E.R. is connected to nucleus while at the outer side it is in contact with plasma membrane. Therefore, it works like a pipeline.

Question 5.
Write an account of the different structures seen in Golgi complex.
Answer:

Golgi complex is made up of 5-8 hollow and flat sacs called cisternae.
These are placed parallel to each other and are filled with different enzymes.
Golgi complex has two faces called forming face and maturation face.
The proteins packed in vesicles and coming from ER reach Golgi complex through cytoplasm.
They fuse with the formation face of the Golgi membranes for emptying their contents in the cisternae.
When these contents pass through the cisternae, they are chemically modified with the help of enzymes and are again packed in the vesicles.
These vesicles come out of Golgi ‘ complex at the maturation face.

Question 6.
How is energy produced in the mitochondria? How the structures of mitochondria help in this process?
Answer:

Around every mitochondrion there is a double membrane.
The outer membrane of these is porous while the inner membrane is deeply folded.
These folds or ‘cristae’ enclose the matrix filled with proteinaceous gel containing ribosomes, phosphate granules and DNA. Protein synthesis takes place in this matrix.
Mitochondria carry out oxidation of carbohydrates and fats in the cell. This produces energy in the form of ATP, s i.e. Adenosine Tri Phosphate

Question 7.
What is the benefit of foldings of inner membrane in mitochondria?

Answer:
The structure of the inner mitochondrial membrane is extensively folded and compartmentalized. The numerous imaginations of the membrane are called cristae. This folded inner membrane increases the area which is about 5 times more than that the outer membrane due to cristae. Cristae membranes have small round protein complexes known as Fx particles. In these particles the process of energy production goes on.

Research:

Question 1.
Keep 4 – 5 raisins in water and observe after an hour. Afterward, keep the same raisins in sugar solution and observe after an hour. Note down the observations and discuss in the classroom.
Answer:
When raisins are kept in water its outer skin acts as a semi-permeable membrane. The water content inside the raisin is lesser as compared to the water content in the outside medium. Therefore the water enters in the raisins due to process of endosmosis. Thus if raisins kept in plain water are observed after one hour, they are seen to be swollen.

On the other hand, if raisins are kept in sugar solution, they show plasmolysis and they shrink. The sugar solution acts as hypertonic medium. Water content in the raisin is higher than that present in the sugary solution. Thus water exists from raisins and its content thus shrinks.

Question 2.
Wooden doors fit very tightly in rainy season. Why does it happen?
Answer:
During rainy season there is more humidity in air. The doors get soaked in rain water. Though wood is non-living, it has the ability to absorb water. As the moisture is more in the surrounding area, it enters the wood. This is a type of endosmosis. It causes the doors to swell. The swollen doors then fit very tightly.

Diagram based questions:

Question 1.
Structure of the cell:

Answer:

(iii) Complete the chart:

Answer:

Component	Animal cell	Plant cell
Cell membrane	Present	Present
Cell wall	Absent	Present
Lysosomes	Present	Absent
Plastids	Absent	Present
Endoplasmic reticulum	Present	Present
Vocuole	Present	Present
Golgi complex	Present	Present
Mitochondria	Present	Present

Question 2.
Sketch the diagrams to show how osmosis occurs in plant cell if kept separately in isotonic, hypotonic and hypertonic medium.
Answer:

Question 3.
Sketch the diagrams to show how osmosis occurs in animal cell if kept separately in isotonic, hypotonic and hypertonic medium
Answer:

Activity-based questions:

Question 1.
Experiment Activity – Take a drop of water on a clean glass slide. Using an ice-cream spoon, gently scrap the inner surface of your cheek. With a needle, transfer a little material from spoon to the water drop on the slide and spread it evenly. Put a drop of methylene blue stain on the smear. Put a cover slip and observe under microscope. Did you observe the cells with blue nucleus?
Answer:
Students should do this activity at school laboratory. There are squamous epithelial cells in the inner side of the cheek. When stained with methylene blue the nucleus takes up dark stain and can be seen clearly.

Question 2.
Experiment Activity – Take out a thin peel of Rheo or Croton leaf and observe the chromoplasts under the compound microscope.
Answer:
Students are expected to do the observations in the school laboratory.

Question 3.
Can you recall? Observe the cells of onion peel under the microscope. Have you seen the fully turgid, rectangular cells of onion peelings?

Answer:
Students are expected to do the observations in the school laboratory.

8th Std Science Questions And Answers:

Life Cycle of Stars Class 8 Science Chapter 19 Questions And Answers Maharashtra Board

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 19 Life Cycle of Stars Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 19 Life Cycle of Stars Question Answer Maharashtra Board

Class 8 Science Chapter 19 Life Cycle of Stars Question Answer Maharashtra Board

1. Search and you will find:

Question a.
Our galaxy is called ………… .
Answer:
Our galaxy is called the Milky Way and Mandakini.

Question b.
For measuring large distances, ………… is used as a unit.
Answer:
For measuring large distances, the light year is used as a unit.

Question c.
The speed of light is …………. km/s.
Answer:
The speed of light is 300000 km/s.

Question d.
There are about ………… stars in our galaxy.
Answer:
There are about 100 billion stars in our galaxy.

Question e.
The end stage of the Sun will be …………. .
Answer:
The end stage of the Sun will be a white dwarf.

Question f.
Stars are born out of ………… clouds.
Answer:
Stars are born out of interstellar clouds.

Question g.
Milky way is a ………. galaxy.
Answer:
Milky way is a spiral galaxy.

Question h.
Stars are gigantic spheres of ………… gas.
Answer:
Stars are gigantic spheres of hot gas.

Question i.
The masses of other stars are measured relative to the mass of the …………. .
Answer:
The masses of other stars are measured relative to the mass of the Sun.

Question j.
Light takes ……………. to reach us from the Sun while it takes …….. to reach us from the moon.
Answer:
Light takes about 8 minutes to reach us from the Sun while it takes about 1 second to reach us from the moon.

Question k.
The larger the mass of a star, the faster is its ……….. .
Answer:
The larger the mass of a star, the faster is its evolution.

Question l.
The number of fuels used in the life of a star depends on its …………. .
Answer:
The number of fuels used in the life of a star depends on its mass.

2. Who is telling lies?

Question a.
Light year is used to measure time.
Answer:
False. (Light year is used to measure distance.)

Question b.
End stage of a star depends on its initial mass.
Answer:
True.

Question c.
A star ends its life as a neutron star when the pressure of its electrons balances its gravity.
Answer:
False. (A star ends its life as a neutron star when the pressure of its neutrons balances its gravity.)

Question d.
Only light can emit from the black hole.
Answer:
False. (Not even light can be emitted by a black hole.)

Question e.
The Sun will pass through the supergiant stage during its evolution.
Answer:
False. (The Sun will pass through the red giant stage during its evolution.)

Question f.
The Sun will end its life as a white dwarf.
Answer:
True.

3. Answer the following question:

Question a.
How do stars form?
Answer:
There are huge clouds of gas and dust in the empty spaces between the stars in a galaxy. These clouds are called interstellar clouds. The size of an interstellar cloud is about a few light years.

When an interstellar cloud starts contracting due to some disturbance, its density and temperature increase. This results in formation of a dense sphere of hot gas and nuclear energy generation starts at the centre of the star. Therefore, the gas sphere becomes self-luminous. Thus a star is formed, i.e., a star is born.
A huge interstellar cloud can produce thousands of stars at a time.

Question b.
Why do stars evolve?
Answer:
Although stars appear stable for quite a long period of time, their properties do change, though very slowly. A change in the properties of a star, leading to its passing through different stages, is called evolution of the star. Burning of the fuel at the centre of the star and a gradual decrease in its amount is the main reason of evolution of a star.

Question c.
What are the three end stages of stars?
Answer:

Stars having initial mass less than 8 times the mass of the Sun ultimately become white dwarfs.
Stars having initial mass between i 8 and 25 times the mass of the Sun ultimately become neutron stars.
Stars having initial mass larger than 25 times the mass of the Sun ultimately turn into black holes.

Question d.
Why was the name black hole given?
Answer:
When a star having initial mass larger than 25 times the mass of the Sun reaches its end stage, its gravitational force and density increase exponentially. All nearby objects get attracted towards the star and nothing can come out of it, not even light. All incident light is absorbed by the star. We can probably see a very minute black hole at its place. Hence, the name is given as black hole.

Question e.
Which types of stars end their life as a neutron star?
Answer:
Stars having initial mass between 8 and 25 times the mass of the Sun end up as neutron stars. When these stars pass through ( the supergiant stage, their size increases to 1000 times. Huge explosion that occurs in the last stage of these stars is very powerful and very high energy is given off. After the huge explosion, called the supernova explosion, their central portion contracts in size to about 10 km. In this stage, such stars are completely made up of neutrons and hence are called neutron stars.

4. A. If you are the Sun, write about your properties in your own words.
B. Describe white dwarfs.

Question A.
If you are the Sun, write about your properties in your own words.
Answer:

If you are the Sun, write about your properties in your own words.
Answer:
There are billions of stars in the galaxy called the Milky Way and Mandakini. I am one of the small stars called the Sun. I have my own family called the solar system. There are planets, satellites, asteroids, comets and meteors in my family. My mass is 2 × 1030 kg which is about 3.3 lakh times that of the earth. With a radius of 695700 km, my size is about 100 times that of the earth. My surface temperature is about 5800 K while it is 1.5 × 107 K at the centre.

72 % of my mass consists of hydrogen while 26 % consists of helium. Rest 2 % is made up of elements heavier than helium. I am about 4.5 billion years old and the scientists on the earth have concluded that not much change has taken place in my properties during this period. According to the scientists, in the end stage of my life, I will turn into a red giant star. Thereafter, I will first explode and then contract to become as small as the earth. I will appear small as well as white and hence, I will be called a white dwarf. This will be my last stage for ever.

Question B.
Describe white dwarfs.
Answer:
Depending on the initial mass, stars can reach one of the three end stages. White dwarf is one such stage of stars having initial mass less than 8 times the mass of the Sun. These stars undergo huge expansion and their radius increases by a factor of 100 to 200. These stars appear reddish because of their large size and lower temperature. Hence, these stars are also called red giant stars.

At the end of their evolution, these stars explode, their outer gas envelope is thrown outward and the inner part contracts to the size of the earth. However, the density in the star becomes very high. In this stage, the pressure due to electrons becomes independent of temperature and sufficient to balance the gravitational force for ever.

In this stage, such stars look white and due to their small size they are called white dwarfs.

Can you recall?

Question 1.
What is a galaxy?
Answer:
A system of billions of stars, their planetary systems and interstellar clouds of gas and dust held together by gravitational attraction is called a galaxy.

Question 2.
What are the different constituents of our solar system?
Answer:
The different constituents of our solar system are as follows :

Sun as a star.
Eight planets, namely, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune; of which Mercury, Venus, Earth and Mars are made up of rocks and minerals, while Jupiter, Saturn, Uranus and Neptune are made up of gases.
Natural satellites of some planets revolving around the respective planets.
Asteroids located between Mars and Jupiter.
Comets made up of ice, dust and gases.
Meteors and meteoroids.

Question 3.
What are the major differences between a star and a planet?
Answer:

Nuclear/atomic explosions regularly take place at the centre of stars. This causes the discharge of heat and light. Hence, stars shine. Planets do not discharge any light. They are visible due to the light reflected by them.
Stars are very big in size and massive relative to planets.
Stars twinkle, planets do not.
Stars are made up of hydrogen, helium and other light elements.
Planets are made up of solid, liquid or gaseous substances or a combination thereof.

Question 4.
What is a satellite?
Answer:
An astronomical object orbiting a planet is called a satellite.

Question 5.
Which is the star nearest to us?
Answer:
The star nearest to us is the Sun.

Project:

Question 1.
Use your imagination and make models of the Milky Way and the solar system.
Answer:
N.B. Students can make these models and display the same in science exhibition. You can use sand, scrap material, stones, pebbles, marbles, pieces of glass, beads, etc.

Question 2.
Write the effects: If the Sun disappears ………..
Answer:
N.B. You can write the effects with the help of the following points:

No sunrise, no sunset, no beauty of morning and evening wee hours.
In the absence of the gravitational force due to the Sun, the earth will drift away in the galaxy.
Darkness, no source of energy, end of life on the earth.
Moon will be invisible.
The temperature of the earth will fall below the freezing point of water. All oceans will also freeze.
Even the atmosphere will freeze and fall on the earth. This will cause more cosmic rays to reach the earth.

Class 8 Science Chapter 19 Life Cycle of Stars Important Questions and Answers

Match the columns:

Question 1.

Column ‘A’	Column ‘B’
1. Gravitational force	a. Alpha Centauri
2. The star nearest to us other than the Sun	b. 2 × 10³⁰ kg
3. Mass of the Sun	c. 10 ³⁰ g
	d. towards the centre of a star or a planet

Answer:

Column ‘A’	Column ‘B’
1. Gravitational force	d. towards the centre of a star or a planet
2. The star nearest to us other than the Sun	a. Alpha Centauri
3. Mass of the Sun	b. 2 × 10³⁰ kg

Question 2.
Mass of the star:

Column ‘A’	Column ‘B’
1. < 8 M_Sun	a. Proton star
2. between 8 and 25 times M_Sun	b. Black hole
3. > 25 M_Sun	c. Neutron star
	d. White dwarf

Answer:
Mass of the star:

Column ‘A’	Column ‘B’
1. < 8 M_Sun	d. White dwarf
2. between 8 and 25 times M_Sun	c. Neutron star
3. > 25 M_Sun	b. Black hole

Answer the following questions in one sentence each:

Question 1.
Name the star nearest to the earth.
Answer:
The Sun.

Question 2.
Other than the Sun, which is the star nearest to the earth?
Answer:
Alpha Centauri.

Question 3.
What would be the last stage of the Sun?
Answer:
The last stage of the Sun would be white dwarf.

Question 4.
Name two forces that act on any star.
Answer:
Gravitational force and the force due to the pressure of hot gas are the two forces that act on any star.

Question 5.
What is a black hole?
Answer:
A black hole is the end stage of a quite big star, where due to the extremely high gravitational force, nothing, not even light, comes out.

Answer the following questions:

Question 1.
How is stability of stars maintained?
Answer:
Properties of a star remain unchanged for quite a long time. The gravitational force and the force due to the pressure of the hot gas act together on a star. The gravitational force acts towards the centre of the star and tries to bring the gas particles close together. Hot gas shows the tendency to spread and its force acts away from the centre of the star. This force tries to disperse the gas particles. A balance between the gravitational force and the force due to the hot gas keeps the star stable.

However, if the magnitude of any one force is more than that of the other force, the star either contracts or expands depending upon which force dominates.

Question 2.
Why is the Sun called an ordinary star?
Answer:
The star nearest to the earth is the Sun. Hence, it appears quite big and bright. There are billions of stars in our galaxy called the Milky Way and Mandakini which are greater or lower in mass, size and temperature than the Sun. Hence, the Sun is called an ordinary star.

Do you know?

When the Sun will become a red giant, its diameter will increase so much that it will swallow Mercury and Venus. It is possible that the earth will also be absorbed by the Sun. It will take about 4-5 billion years for the Sun to reach this state.

Question 3.
Describe various stages of evolution of star.
Answer:
Though the properties of a star remain unchanged for quite a long time, this situation is never static. A star passes through different stages. This process is called the evolution of a star.
Important stages of the evolution of a star are as follows:

1. Initial stage of stability: The gravitational force and the force due to the pressure of the hot gas act together on a star. The gravitational force acts towards the centre of the star and tries to bring the gas particles close together. Hot gas shows the tendency to spread and its force acts away from the centre of the star.

This force tries to disperse the gas particles. A balance between the gravitational force and the force due to the hot gases keeps the star stable, as long as the energy generation continues at the centre of the star.

2. Burning of the fuel: As a star continuously emits energy, its energy constantly decreases. When the fuel at the centre of the star is exhausted, the energy generation stops and the temperature of the star starts decreasing. Decreasing temperature causes the gas pressure to decrease and the balance between the gravitational force and the force due to the gas pressure is no more maintained.

As the magnitude of the gravitational force is now more than that of the force due to the gas pressure, the star starts contracting. This causes another fuel to start burning, e.g. on exhausting hydrogen, helium starts undergoing fusion. Availability of multiple fuels depends on the mass of the star.

The higher the mass of the star, the more is the number of fuels used. The star either contracts or expands during the course of using these fuels. This may cause the imbalance between the gravitational force and the force due to the hot gas.

3. Total exhaustion of the fuel: When all fuels are exhausted, the energy generation in the star finally stops completely and the temperature of the star starts decreasing. The balance between the gravitational force and the force due to the gas pressure can no more be maintained. The evolution of the star ends and the star proceeds to its end stage.

4. End stage of a star: Once the fuel in the star is totally exhausted, the energy generation in the star stops and subsequently the gas pressure decreases, the star starts contracting and its density starts increasing. When the density becomes very high, some new types of pressures are generated which are independent of the temperature of the gas.

In such a case, the pressure remains stable despite low temperature and absence of any energy generation and thus the star remains stable for ever. This stage is the end stage of the star. Depending on the initial mass, stars can reach one of the three end stages.

Stars having initial mass less than 8 times the mass of the Sun ultimately become white dwarfs.
Stars having initial mass between 8 and 25 times the mass of the Sun ultimately become neutron stars.
Stars having initial mass larger than 25 times the mass of the Sun ultimately turn into black holes.

Write short notes on the following:

Question 1.
End stages of stars having initial mass less than 8 times the mass of the Sun.
Answer:
These stars undergo huge expansion and their radius increases by a factor of 100 to 200 during their various stages of evolution. These stars appear reddish due to their lower temperature. Hence, they are called red giant stars.

At the end of evolution, these stars explode, their outer gas envelope is thrown out and the inner part contracts roughly to the size of the earth. Hence, the density of the star becomes very high. In this stage, the pressure due to electrons becomes independent of temperature and sufficient to balance the gravitational force for ever. Such stars look white and due to their small size they are called white dwarfs.

Question 2.
End stage of the stars having mass between 8 and 25 times the mass of the Sun.
Answer:
These stars pass through the red giant stage and later super giant stage, during which their size may increase to 1000 times. The huge explosion, called the supernova explosion, occurs in the last stage of the evolution. It is very powerful and very high energy is given off in this case.

As a result, the stars are visible even during the day. Later their central portion contracts to about 10 km. In this stage, the stars are completely made up of neutrons and are called neutron stars. The pressure of these neutrons is independent of temperature and sufficient enough to balance the gravitational force for ever.

Question 3.
End stages of stars having mass larger than 25 times the mass of the Sun.
Answer:
After the supernova explosion, no pressure can balance the gravitational force. Hence these stars contract continuously and their gravitational force and density increase exponentially. All nearby objects get attracted towards these stars and not even light can come out of them. Light falling on these stars is completely absorbed by the star. We cannot see these stars. A very minute black hole is formed at the place of such a star. This is the end stage of these stars.

8th Std Science Questions And Answers:

Reflection of Light Class 8 Science Chapter 16 Questions And Answers Maharashtra Board

January 4, 2025January 3, 2025 by Bhagya

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 16 Reflection of Light Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 16 Reflection of Light Question Answer Maharashtra Board

Class 8 Science Chapter 16 Reflection of Light Question Answer Maharashtra Board

1. Fill in the blanks:

Question i.
The perpendicular to the mirror at the point of incidence is called …………. .
Answer:
The perpendicular to the mirror at the point of incidence is called the normal.

Question ii.
The reflection of light from a wooden surface is ……….. reflection.
Answer:
The reflection of light from a wooden surface is irregular reflection.

Question iii.
The working of a kaleidoscope is based on the properties of …………… .
Answer:
The working of a kaleidoscope is based on the properties of reflection of light.

2. Draw a figure describing the following: The reflecting surfaces of two mirrors make an angle of 90° with each other. If a ray incident on one mirror has an angle of incidence of 30°, i draw the ray reflected from the second mirror. What will be its angle of reflection?

Question a.
Draw a figure describing the following: The reflecting surfaces of two mirrors make an angle of 90° with each other. If a ray incident on one mirror has an angle of incidence of 30°, draw the ray reflected from the second mirror. What will be its angle of reflection?
Answer:
For the ray C, the angle of reflection = 60°.

3. How will you explain the statement ‘We cannot see the objects in a dark room’?

Question a.
How will you explain the statement ‘We cannot see the objects in a dark room’?
Answer:
In a room that is completely dark, no light falls on objects. Hence, no light enters our eyes. Hence, there is no sensation of vision, i.e., we cannot see the objects.

4. Explain the difference between regular and irregular reflection of light.

Question a.
Explain the difference between regular and irregular reflection of light.
Answer:
For regular reflection of light, the angles of incidence as well as the angles of reflection are the same for all parallel rays of light incident on the plane and smooth surface. Hence, the reflected rays are also parallel to one another.

For irregular reflection of light, the angles of incidence for parallel rays of light incident on the rough surface are not equal, and hence the angles of reflection are also not equal. Here, the reflected rays are not parallel to one another and spread over a large surface.

5. Draw a figure showing the following:
(a) Incident ray, (b) Normal, (c) Angle of incidence, (d) Angle of reflection, (e) Point of incidence, (f) Reflected ray.

Question a.
Draw a figure showing the following:
(a) Incident ray
(b) Normal
(c) Angle of incidence
(d) Angle of reflection
(e) Point of incidence
(f) Reflected ray.
Answer:

6. Study the following incident.

Swara and Yash were looking in a water-filled vessel. They could see their images clearly in the still water. At that instant, Yash threw a stone in the water. Now their images were blurred. Swara could not understand the reason for the blurring of the images.
Explain the reason for blurring of the images to Swara by answering the following questions:

Question i.
Is there a relation between the reflection of light and the blurring of the images?
Answer:
Yes.

Question ii.
Which types of reflection of light can you notice from this?
Answer:
Regular reflection of light when light is incident on the still water and irregular reflection of light when light is incident on the water as ripples are produced on its surface when a stone is thrown in the water.
Still water behaves as a plane and smooth surface while oscillating water behaves as a rough surface.

Question iii.
Are the laws of reflection followed in these types of reflection?
Answer:
Yes.

7. Solve the following examples.

Question a.
If the angle between the plane mirror and the incident ray is 40°, what are the angles of incidence and reflection?
Solution:
The angle between the plane mirror and the incident ray is 40°. Therefore, the angle of incidence (i) = the angle made by the incident ray with the normal to the plane mirror = 90° – 40° = 50°. The angle of reflection, r – i – 50°.

Question b.
If the angle between the mirror and reflected ray is 23°, what is the angle of incidence of the incident ray?
Solution:
The angle between the mirror and the reflected ray is 23°. Therefore, the angle of reflection (r) = the angle made by the reflected ray with the normal to the plane mirror = 90° – 23° = 67°.
∴ The angle of incidence, i = r = 67°.

Project:

Question a.
Apollo astronauts who stepped on the moon have kept some large mirrors there. Collect information about how the distance to the moon is measured using these.

Class 8 Science Chapter 16 Reflection of Light Important Questions and Answers

Rewrite the following statements by selecting the correct option:

Question 1.
If the angle made by the incident ray with the surface of a plane mirror is 30°, the angle of reflection must be …….. .
(a) 30°
(b) 90°
(c) 60°
(d) 15°
Answer:
If the angle made by the incident ray with the surface of a plane mirror is 30°, the angle of reflection must be 60°.

Question 2.
If the angle of incidence is 40°, the angle made by the reflected ray with the surface of the plane mirror must be ……. .
(a) 40°
(b) 50°
(c) 20°
(d) 80°
Answer:
If the angle of incidence is 40°, the angle made by the reflected ray with the surface of the plane mirror must be 50°.

Question 3.
If the angle of incidence is 20°, the angle made by the reflected ray with the normal to the surface must be ……… .
(a) 20°
(b) 70°
(c) 10°
(d) 40°
Answer:
If the angle of incidence is 20°, the angle made by the reflected ray with the normal to the surface must be 20°.

Question 4.
In a kaleidoscope, the mirrors are inclined to each other at ……. .
(a) 60°
(b) 30°
(c) 45°
(d) 90°
Answer:
In a kaleidoscope, the mirrors are inclined to each other at 60°.

Question 5.
In a periscope, the mirrors are ………….. .
(a) parallel to each other
(b) at right angles to each other
(c) inclined at 45° to each other
(d) inclined at 60° to each other
Answer:
In a periscope, the mirrors are parallel to each other.

Find the odd one out and give the reason:

Question 1.
Plane mirror, Plywood, Wood, Rough tile.
Answer:
Plane mirror. In this case, regular reflection of light takes place. In other cases, reflection of light is irregular.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)

Question 1.
The sense of vision is the most important among our five senses.
Answer:
True.

Question 2.
In a periscope, the angle between the incident ray and the normal to the mirror is 30°.
Answer:
False. (In a periscope, the angle between the incident ray and the normal to the mirror is 45°.)

Answer the following questions in one sentence each:

Question 1.
What is an incident ray?
OR
Define incident ray.
Answer:
A ray of light falling on a surface is called an incident ray.

Question 2.
What is the point of incidence?
OR
Define point of incidence.
Answer:
The point at which the incident ray strikes the surface is called the point of incidence.
[Note: It is also the point of reflection.]

Question 3.
What is the normal?
OR
Define normal.
Answer:
The perpendicular to a surface at the point of incidence is called the normal.

Question 4.
What is the reflected ray?
OR
Define reflected ray.
Answer:
The ray of light that leaves the surface at the point of reflection (the same as the point of incidence) is called the reflected ray.

Question 5.
What is the angle of incidence?
OR
Define angle of incidence.
Answer:
The angle between the incident ray and the normal is called the angle of incidence.

Question 6.
What is the angle of reflection?
OR
Define angle of reflection.
Answer:
The angle between the reflected ray and the normal is called the angle of reflection.

Try this:

Switch off the light in your room at night for some time and then turn it on again.

Question 1.
Could you see the objects in the room clearly when the light was switched off?
Ans.
No.

Question 2.
What did you feel when it was turned on again?
Answer:
We could see the objects clearly. From the above activity you can notice that there is some connection between the sense of vision and light. When we switch off the light at night, the objects in the room cannot be seen and they can be seen as before when the light is switched on again. Thus, we can see objects when the light coming from these objects enters our eyes.

Answer the following questions:

Question 1.
What is reflection of light?
Answer:
When light rays fall on an object, their direction changes and they turn back. This is called the reflection of light.

Try this:

Material:
Torch light, mirror, a stand for hanging the mirror, black paper, comb, white paper, drawing board.
Activity :
1. Fit a white paper tightly over a table or drawing board.
2. Leaving out some portion in the middle of the comb, cover the rest with black paper so that light can only pass through the open central portion.
3. Hold the comb perpendicular to the white paper and throw torch light on its central portion.
4. Adjust the comb and torch so as to get light rays on the white paper. Now keep a mirror in the path of this ray of light as shown in the figure.
5. What do you observe?

Answer:
Light rays which fall on the mirror get reflected and travel in a different direction.

Question 2.
State the laws of reflection of light.
Answer:

The angle of reflection is equal to the angle of incidence.
The incident ray, the reflected ray and the normal lie in the same plane.
The incident ray and the reflected ray are on the opposite sides of the normal.

Try this:

Verification of the laws of reflection of light.
Equipment: Mirror, drawing board, pins, white paper, protractor, scale, pencil.
Activity:

Fit a white paper on the drawing board tightly as possible.
On the paper draw a line PQ indicating the position of the mirror.
Draw a perpendicular ON to PQ at point O.
Draw a ray AO making an angle of 30° with ON.
Fix two pins S and R along AO.
Fix the mirror to a stand and place it along PQ perpendicular to the drawing board.
Fix pins at T and U along the line joining the bottom of the reflected images of the pins at S and R.
Remove the mirror and join the points T and U and extend it up to O.
Measure ZTON.
Repeat steps 4 to 9 for angle of incidence equal to 45° and 60° and write down the angles in the following table.

What relation do you find between the angle of incidence and the angle of reflection? If you have done the experiment carefully, you will find that the angle of incidence is equal to the angle of reflection in all three cases. This verifies the laws of reflection.

Question a.
What will happen when a light ray is incident perpendicular to the mirror?
Answer:

Here,
r = i = 90°.
Hence the light ray, on reflection, will retrace the path.

Question 3.
Figures (a) and (b) show three parallel rays, shown in grey, incident on smooth and rough surfaces. The reflected rays drawn using laws of reflection are shown in red.
1. Rays reflected from which surface are parallel to one another?
2. What conclusion can you draw from the figure?
Answer:
1. Rays reflected from the smooth surface are parallel to one another.

2.When the reflecting surface is plane and smooth, the angles of incidence (i) as well as of reflection (r) are the same for all parallel rays incident on the surface. If i₁, i₂, i₃, … are the angles of incidence for incident parallel rays, and r₁, r₂, r₃, …, are the corresponding angles of reflection, then, i₁ = i₂ = i₃ = ……. = r₁ = r₂ = r₃ = ….. This is called regular reflection. Here, the reflected rays are parallel to one another. If the reflecting surface is rough and parallel rays are incident on it, then the angles of incidence are not equal and hence the angles of reflection are also not equal. Here, i₁ ≠ i₂ ≠ i₃ … and r₁ ≠ r₂ ≠ r₃ …, but r₁ = i₁, r₂ = i₂, r₃ = i₃ … as laws of reflection are obeyed. This is called irregular reflection. [Fig.(b)]. Here, the reflected rays are not parallel to one another and spread over a large surface.

Question 4.
What is regular reflection of light?
Answer:
The reflection of light from a plane and smooth surface is called regular reflection of light.

Question 5.
What is irregular reflection of light?
Answer:
The reflection of light from a rough surface is called irregular reflection of light.

Always remember:

Laws of reflection are followed in both and regular and irregular reflection.
The reflection of light in irregular reflection has not been obtained because the laws of reflection are not followed. They are obtained because the surface is rough (irregular).
In irregular reflection, the angles of incidence at different points are different. But at any one point, the angles of incidence and reflection are equal, i.e. i₁ = r₁, i₂ = r₂ …..

Can you recall?

Reflection of reflected light :

Question 1.
How do you see if the barber m a saloon has cut the hair on your neck properly or not?
Answer:
In a saloon, there are mirrors in your front and at back. The image of the back of your head is formed in the mirror at the back. The image of this image is formed in the mirror in front of you. Thus you can see how the hair at the backside of your head is cut.

Question 2.
What type of image do we see in a mirror? What happens to the left and right sides?
Answer:
The image in a plane mirror is upright (erect) and of the same size as the object, but the left and right sides are interchanged. Our right hand appears to be the left hand in the image and the left hand appears to be the right hand in the image. (This is called lateral inversion.)

Question 3.
How do we see the image of the moon in water?
Answer:
The moon is not self luminous. The sunlight falling on the surface of the moon is reflected. This reflected light is again reflected by water to give us the image of the moon.

Try this:

Kaleidoscope:

Activity:

Take three rectangular mirrors of the same size.
Using sticking tape, stick the mirrors together making a triangle with the reflecting surface facing inwards (see Fig.).
Take a white paper of triangular shape and fix it with a tape at one end of the mirrors closing that end.
Insert 4 – 5 coloured glass pieces in the hollow of the mirrors.
Close the other end also with a paper and make a hole in it.
Look through the hole towards light. You will see innumerable images of the glass pieces. These are formed due to reflections by the three mirrors.

You can see different designs in the kaleidoscope. The speciality of a kaleidoscope is that the designs do not easily repeat themselves. Every time the design is different. People making wall papers which are used to decorate walls and cloth designers use a kaleidoscope for making new designs.

Periscope:
Activity:

Take a cardboard box. Make slits in the top and bottom sides of the box and place two mirrors so that they make an angle of 45° with the sides of the box and are parallel to each other. Fix them with a sticking tape.
Make two windows of 1 inch each near the two mirrors. Now see through the bottom window.
Make note of what you see.

From the bottom window, one can see what is in front of the top window. This device is called a periscope. This is used in submarines to see objects above the surface of water. It is also used to observe and keep a watch on the objects or persons on the ground from an underground bunker. The kaleidoscope and periscope both use the properties of reflection of light.

[Note: In a periscope, the angle of incidence is 45° and the two plane mirrors are parallel to each other. Hence, the emergent ray is parallel to the incident ray.]

Example questions for practice:

Question 1.
If the angle between the plane mirror and the incident ray is 20°, what is the angle between the reflected ray
and the plane mirror?
Answer:
20°.

Question 2.
See Fig. In terms of O, what are the angles (i) AON (ii) BON (iii) AOB (iv) BOQ?

Answer:
(i) 90° – θ (ii) 90° – θ (iii) 180° – 2θ

8th Std Science Questions And Answers:

Practice Set 1.1 Class 8 Answers Chapter 1 Rational and Irrational Numbers Maharashtra Board

December 7, 2024December 6, 2024 by Prasanna

Balbharti Maharashtra State Board Class 8 Maths Solutions covers the Practice Set 1.1 8th Std Maths Answers Solutions Chapter 1 Rational and Irrational Numbers.

Rational and Irrational Numbers Class 8 Maths Chapter 1 Practice Set 1.1 Solutions Maharashtra Board

Std 8 Maths Practice Set 1.1 Chapter 1 Solutions Answers

Question 1.
Show the following numbers on a number line. Draw a separate number line for each example.
i. \(\frac{3}{2}, \frac{5}{2},-\frac{3}{2}\)
ii. \(\frac{7}{5}, \frac{-2}{5}, \frac{-4}{5}\)
iii. \(\frac{-5}{8}, \frac{11}{8}\)
iv. \(\frac{13}{10}, \frac{-17}{10}\)
Solution:
i. \(\frac{3}{2}, \frac{5}{2},-\frac{3}{2}\)
Maharashtra Board Class 8 Maths Solutions Chapter 1 Rational and Irrational Numbers Practice Set 1.1 1
Here, the denominator of each fraction is 2.
∴ Each unit will be divided into 2 equal parts.

ii. \(\frac{7}{5}, \frac{-2}{5}, \frac{-4}{5}\)
Maharashtra Board Class 8 Maths Solutions Chapter 1 Rational and Irrational Numbers Practice Set 1.1 2
Here, the denominator of each fraction is 5.
∴ Each unit will be divided into 5 equal parts.

iii. \(\frac{-5}{8}, \frac{11}{8}\)
Maharashtra Board Class 8 Maths Solutions Chapter 1 Rational and Irrational Numbers Practice Set 1.1 3
Here, the denominator of each fraction is 8.
∴ Each unit will be divided into 8 equal parts.

iv. \(\frac{13}{10}, \frac{-17}{10}\)
Maharashtra Board Class 8 Maths Solutions Chapter 1 Rational and Irrational Numbers Practice Set 1.1 4
Here, the denominator of each fraction is 10.
∴ Each unit will be divided into 10 equal parts.

Question 2.
Observe the number line and answer the questions.
Maharashtra Board Class 8 Maths Solutions Chapter 1 Rational and Irrational Numbers Practice Set 1.1 5
i. Which number is indicated by point B?
ii. Which point indicates the number \(1\frac { 3 }{ 4 }\) ?
iii. State whether the statement, ‘the point D denotes the number \(\frac { 5 }{ 2 }\) is true or false.
Solution:
Here, each emit is divided into 4 equal parts.
i. Point B is marked on the 10th equal part on the left side of O.
∴ The number indicated by point B is \(\frac { -10 }{ 4 }\).

ii.
Maharashtra Board Class 8 Maths Solutions Chapter 1 Rational and Irrational Numbers Practice Set 1.1 6
Point C is marked on the 7th equal part on the right side of O.
∴ The number \(1\frac { 3 }{ 4 }\) is indicated by point C.

iii. True
Point D is marked on the 10th equal part on the right side of O.
∴ D denotes the number \(\frac{10}{4}=\frac{5 \times 2}{2 \times 2}=\frac{5}{2}\)

Std 8 Maths Digest