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Balbharti Maharashtra State Board Class 7 Science Solutions Chapter 12 The Muscular System and Digestive System in Human Beings Notes, Textbook Exercise Important Questions and Answers.

Std 7 Science Chapter 12 The Muscular System and Digestive System in Human Beings Question Answer Maharashtra Board

Class 7 Science Chapter 12 The Muscular System and Digestive System in Human Beings Question Answer Maharashtra Board

1. Fill in the blanks with the right word from the brackets:

Question a.
The process of digestion starts from the ………….. (stomach, mouth).
Answer:
mouth

Question b.
Eyelids have …………… muscles. (voluntary, involuntary)
Answer:
involuntary

Question c.
……………. is not a function of muscular system. (production of blood cell, performing movement)
Answer:
Production of blood cells

Question d.
Muscles of the heart are …………….. . (ordinary muscles, cardiac muscles)
Answer:
cardiac muscles

Question e.
Pushing forward the food that has been chewed is the function of the …………… . (stomach, oesophagus)
Answer:
Oesophagus.

2. Find a match for me.

Question a.

Column ‘A’	Column B’
1. Cardiac muscle	a. Always functions in pairs
2. Are brought about by muscle	b. We never feel tired
3. Pepsin	c. Uncontrolled and painful contraction of muscles
4. Cramps	d. Chewing movement of the jaw
5. Skeletal muscles	e. Enzymes of the gastric juice

3. Who is telling a lie?

Question a.

Organ	Statement
1. Tongue	a. My taste buds can tell only a sweet taste.
2. Liver	b. I am the largest gland in the body.
3. Large intestine	c. I am 7.5 metre long.
4. Appendix	d. Digestion is impossible without me
5. Lung	e. I play an important role in excretion.

Answer:

1. Lie. My taste buds can tell all tastes – sweet sour, bitter.
2. Truth.
3. Lie. It is 1.5 metre long.
4. Truth.
5. Lung → Lie. It plays important role in breathing.

4. Give reasons.

Question 1.
Food becomes acidic in the stomach.
Answer:

1. The gastric glands of stomach secrete gastric juice.
2. Food that has entered stomach is churned.
3. Three components of gastric juice namely hydrochloric acid, pepsin and mucus are mixed with food here and the food becomes acidic.

Question 2.
Cardiac muscles are said to be involuntary muscles.
Answer:

1. Cardiac muscles are found in the heart.
2. These muscles bring about the contraction and relaxation (beating) of the heart.
3. Their movement is involuntary.
4. Cardiac muscles cause our heart to relax and contract continuously at a rate of about 70 times per minute. They do not depend upon our will.
5. Beating is carried out in their own fixed manner.

So cardiac muscles are said to be involuntary muscles.

Question 3.
Intoxicating substances should not be consumed.
Answer:

1. Physical health is important for our organ system to function properly.
2. But harmful habits like smoking, chewing of tobacco, drinking alcohol affect our health adversely.
3. If we consume any tobacco products, the mouth, pharynx, alimentary canal, and other organs of the digestive system cannot function properly.
4. It causes problems like vomiting, nausea, and headache.
5. Tobacco particles stick to teeth, gums, and skin of the mouth cavity and slowly cause injury to those parts resulting in their dysfunction.
6. This causes swelling of the gums and pain when moving the jaws.
7. The pharynx and intestine become inflamed it progress into cancer leading to death.

Question 4.
Your muscles should be strong and efficient.
Answer:
Muscles are bundles of fibres that can contract and relax as required.

1. The action of muscles is necessary for all kinds of movements from the small movements of eyelid to those that demand great strength when chopping wood with an axe.
2. We use muscles for various movements like talking laughing, walking, jumping, throwing etc.
3. Therefore our muscles should be strong and efficient to do our day today work well and smooth functioning of life processes.

5. Answer the following. 

Question a.
How many types of muscles are there? Which are those types?
Answer:
Muscles are bundles of fibres that can contract and relax as required. There are three types of muscles.

• Skeletal muscles.
• Heart or cardiac muscles.
• Smooth muscles.

1. Skeletal muscles: (a) Skeletal muscles work with bones, the two ends of each of these muscles are attached to two different bones. (b) They are responsible for holding the bones of the skeleton together and giving shape to our body, (c) Skeletal muscles permits movement of t the body and maintain the posture of the body. (d) Skeletal muscle is voluntary e.g. muscles in our arms and legs are voluntary muscles, their action depends upon our will. That’s why they are called voluntary muscles.

2. Heart or cardiac muscles: (a) Heart or cardiac muscles bring about the contraction and relaxation (beating) of the heart. (b) Their movement is involuntary, (c) Cardiac muscles cause our heart to relax and contract continuously at a rate of about 70 times per minute, (d) Cardiac muscle is found in heart.

3. Smooth muscles: (a) These muscles are present in the internal organs other than the heart, e.g. muscles of the stomach, intestine, blood vessels, uterus etc. (b)Their movements are involuntary and slow, (c) They are not according to our will. (d) Various vital functions of our body such as digestion, respiration and movement of food material of which we remain quite unaware, are carried out by these special muscles.

Question b.
What causes the problem of acidity? What is its effect on the body?
Answer:

1. Stress is the main cause of acidity.
2. Hectic lifestyle and stress can lead to unhealthy or irregular meals, not good for digestion process, and this may cause acidity.
3. Other reasons are eating spicy food, drinking too much alcohol, missing meals, an empty stomach may lead to acidity.
4. Acidity leads to stomach upset, burning sensation in chest and stomach, constriction of blood vessels, weight gain, obesity, cardiovascular damage.

Question c.
Name the different types of teeth. What is the function of each type?
Answer:
There are four types of teeth, namely incisors, canines, pre-molars, and molars.
Each tooth is covered by a hard substance called enamel. Enamel is made up of calcium salt.
The process of digestion begins with the function of the teeth in the mouth.
1. Incisors: (a) These come in first 6-months of age. Incisors are the eight teeth in the front and centre four on top and four on bottom, (b) They are sharp and blade like for cutting food. e.g. for biting an apple, (c) We use them to take first bite of food.

2. Canines: (a) These are strong and pointed, sharpest of all for tearing food. e.g. to tear off a piece of tough meat, (b) They play important role in digestion of food, (c) They appear between 11 and 20 months of age.

3. Pre-molar: Pre molar share features of both canines and molars. (a) You can use them for grinding and chewing food. So that it becomes semi-liquid helping to gulp down the throat easily, (b) They are situated at each side of your mouth in deep settings, (c) They appear at the age of 10 years.

4. Molar: (a) These are broad and flat on top for crushing and grinding food. e.g. to grind up nutmeats. (b) Two teeth above and two teeth below, they appear at the age 11-13 years. (c) Molars are more prone to germ attack because of their remote location in our mouth.
So we should keep them clean.

6. Sketch and label a diagram of the digestive system and describe it in your own words.

Question a.
Sketch and label a diagram of the digestive system and describe it in your own words.
Answer:

1. Conversion of food into a soluble form and its absorption into the blood is called digestion.
2. The digestive system consists of the alimentary canal and digestive glands.
3. The total length of alimentary canal is about 9 metres.
4. Its main parts are the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
5. The salivary glands, liver, pancreas are the digestive glands connected to the alimentary canal.
6. Different organs of the digestive system perform the function of digestion.
7. There are different stages in the process of digestion of food.
8. The process of digestion begins with the function of the teeth in the mouth, food is chewed into small pieces.
9. There are four types of teeth, incisors, canines, pre-molars and molars.
10. Saliva in the mouth contains enzymes, ptyalin, or amylase. It converts starch into maltose.

a. Oesophagus:

1. It is a tube leading from the pharynx to the stomach,
2. It pushes the food towards the stomach.

b. Stomach:

1. The large sac like part of the alimentary canal is called the stomach.
2. Food that has entered is churned.
3. The gastric glands of stomach secrete gastric juice which contain hydrochloric acid, pepsin and mucus.
4. They mix with food and food becomes acidic.
5. Mainly proteins are digested in stomach.
6. Due to the churning and actions of gastric juice, food become a semi-solid slurry which is pushed into the small intestine.

c. Small intestine: (6m long)

1. Bile secreted by liver mixes with food in small intestine,
2. Most of the digestion and absorption of food takes place here.

d. Large intestine: (1.5m long) only water is absorbed in the large intestine. Undigested remain is thrown out of the body through the anus.

Project:

Question 1.
Make charts about maintaining good health.

Question 2.
Design a power point presentation about the digestive system and present it in the class.

Class 7 Science Chapter 12 The Muscular System and Digestive System in Human Beings Important Questions and Answers

Choose and write the correct word.

Question 1.
The structure that connects bones to the muscles is the ………………….. .
(a) ligament
(b) tendon
(c) fascicle
(d) skin
Answer:
(b) tendon

Question 2.
………………….. is not performed by muscles.
(a) Motion
(b) Excretion
(c) Maintenance of posture
(d) Heat production
Answer:
(d) Heat production

Question 3.
Approximately ………………….. skeletal muscles are there in the human body.
(a) 1000
(b) 600
(c) 100
(d) 60
Answer:
(b) 600

Question 4.
Most of the fat digestion occurs in ………………….. .
(a) rectum
(b) stomach
(c) small intestine
(d) large intestine
Answer:
(c) small intestine

Question 5.
Protein digestion is accomplished in ………………….. .
(a) stomach
(b) ileum
(c) rectum
(d) duodenum
Answer:
(b) ileum

Question 6.
The main function of the muscular system is ………………….. .
(a) excretion
(b) digestion
(c)movement
(d) contraction
Answer:
(c)movement

Question 7.
The largest muscle of our body is in the ………………….. .
(a) arm
(b) face
(c) thigh
(d) None
Answer:
(c) thigh

State whether True or False. Correct the false statement and rewrite:

Question 1.
Saliva is mixed with food in the mouth.
Answer:
True.

Question 2.
Gastric juice makes food alkaline.
Answer:
False. Gastric juice makes food acidic.

Question 3.
Pancreas is the largest gland in the body.
Answer:
False. Liver is the largest gland in the body.

Question 4.
Food becomes acidic in stomach.
Answer:
True

Question 5.
Cardiac muscles are said to be voluntary muscles.
Answer:
False. Cardiac muscles are involuntary.

Question 6.
Muscles contribute 60% of the weight of a healthy adult human body.
Answer:
False. Muscles contribute almost 40% of the weight of a healthy adult human body.

Question 7.
There are about 30 muscles in the human face.
Answer:
True

Question 8.
Muscles in our arms and legs have involuntary muscles.
Answer:
False. Muscles in our arm and legs are voluntary muscles.

Question 9.
Functions of organs like stomach, intestine, heart are carried out by voluntary muscles.
Answer:
False. Functions of these organs are carried out by involuntary muscles.

Question 10.
Smooth muscles are involuntary muscles.
Answer:
True.

Question 11.
The digestive function of the liver is to produce bile.
Answer:
True.

Question 12.
The muscular tissue has the ability to contract or shorten.
Answer:
True.

Find a match for me.

Question 1.

Column A’	Column B’
1. Salivary gland	a. Making food acidic
2. Liver	b. Regulation of sugar level
3. Pancreas	c. Digestion of carbohydrates
4. Stomach	d. Digestion of protein, fats, carbohydrate

Answer:

Column A’	Column B’
1. Salivary gland	c. Digestion of carbohydrates
2. Liver	d. Digestion of protein, fats, carbohydrate
3. Pancreas	b. Regulation of sugar level
4. Stomach	a. Making food acidic

Question 2.

Column ‘A’	Column B’
1. Saliva	a. Gastric juice
2. Juice in mouth	b. Bile
3. Juice produced by stomach	c. Ptyalin
4. Juice stored by gall bladder	d. Lubricates food

Answer:

Column ‘A’	Column B’
1. Saliva	d. Lubricates food
2. Juice in mouth	c. Ptyalin
3. Juice produced by stomach	a. Gastric juice
4. Juice stored by gall bladder	b. Bile

Question 4.

Column ‘A’	Column B’
1. Cardiac muscle	a. Inside of organs like stomach
2. Skeletal muscle	b. Found in heart
3. Smooth muscle	c. Attached to bones

Answer:

Column ‘A’	Column B’
1. Cardiac muscle	b. Found in heart
2. Skeletal muscle	c. Attached to bones
3. Smooth muscle	a. Inside of organs like stomach

Find the odd man out:

Question 1.
Stomach, esophagus, liver, small intestine, rectum
Answer:
Liver which is a gland and others are parts of digestive tract.

Question 2.
Saliva, bile, pancreatic juice, gastric juice chyme
Answer:
Chyme, it is a liquid food others are digestive juices.

Name the following:

Question 1.
Gastric juices in stomach
Answer:
Hydrochloric acid, Pepsin, Mucus.

Question 2.
Juices secreted by liver
Answer:
Bile.

Question 3.
Pancreatic juices.
Answer:
Trypsin, Lipase, Amylase.

Question 4.
Salivary gland secretion.
Answer:
Saliva

Question 5.
Enzyme present in saliva.
Answer:
Ptyalin or Amylase.

Question 6.
Types of muscles.
Answer:
Skeletal, Cardiac and Smooth muscles.

Question 7.
Study of muscles.
Answer:
Myology

Give scientific reason:

Question 1.
Skeletal muscles give shape to our body.
Answer:

1. Skeletal muscles are voluntary muscles. The two ends of each of these muscles are attached to two different bones.
2. Muscles of the arms and legs are skeletal muscles.
3. They are responsible for holding the bones of the skeleton together and giving shape to our body.

Question 2.
The process of digestion begins in the mouth.
Answer:

1. The process of digestion begins with the function of the teeth.
2. There are 4 types of teeth – incisors, canines, pre-molar, and molar.
3. They are responsible for grinding the food.
4. Saliva present in the mouth mixes with the food and makes it soft.
5. An enzyme present in saliva called ptyalin amylase converts starch into maltose. Thus, the process of digestion begins in the mouth.

Question 3.
Metabolic processes are impossible without enzymes.
Answer:

1. Enzymes are substances secreted’ in the body of an organism which bring about specific chemical reactions.
2. Enzymes are specific type of proteins. They are most active at normal body temperature.
3. Digestion enzymes of the digestive system bring about changes in the food material.
4. Food is digested with the help of enzymes and converted into more soluble and simple form.

Write short notes on:

Question 1.
Voluntary muscles
Answer:

1. Working with our hands, walking, eating are functions that depend upon our will.
2. Muscles used in these actions are called voluntary muscles, e.g. skeletal muscles are voluntary muscles.

Question 2.
Involuntary muscles
Answer:

1. Various processes like breathing, blood circulation, digestion are vital function, essential for life.
2. They do not depend upon our will.
3. The muscles of organs which carry out these involuntary functions are called involuntary muscles.
4. Functions of organs like the stomach, intestine, heart are carried out in their own fixed manner by involuntary muscles, e.g. cardiac muscle present in heart, smooth muscles in lining of stomach, small intestine, blood vessel, uterus.

Question 3.
Muscle and its types
Answer:
There are three types of muscles in body

1. Skeletal Muscles
2. Cardiac Muscles
3. Smooth Muscles

Question 4.
Digestive glands
Answer:
The salivary glands, liver and pancreas are the digestive glands connected to the alimentary canal.
1. Salivary glands: (a) Saliva is produced in the salivary glands in the mouth cavity, located in front of the ears, below the tongue, (b) It is carried to the mouth via ducts, (c) It is mixed with food during the process of chewing.

2. Saliva: contains an enzyme called Ptyalin or salivary amylase. Ptyalin convdrtfe starch into a sugar called maltose.

3. Liver: (a) The liver is the largest gland in the body, (b) Main function is storage of glucose, (c) The digestive juice secreted by the liver is bile, (d) Bile is carried into small intestine, it mixes with food and helps in digestion of fats.

4. Pancreas: The pancreas secretes the pancreatic juice that contains various enzymes

• Trypsin → converts proteins into amino acids.
• Lipase → converts fats into fatty acids, glycerol
• Amylase → converts complex carbohydrate into simple sugar

Question 5.
Enzymes
Answer:
Enzymes are substances secreted in the body an organism which bring about specific chemical reactions.

1. Metabolic processes are impossible without enzymes.
2. Digestive exzymes of the digestive system bring about changes in the find material.
3. They break down the food into simple form.
4. They are a type of protein.
5. Saliva contain pytalin which converts starch into maltose.
   • Trypsin: Convert proteins into amino acids.
   • Lipase: Convert fats into fatty acid.
   • Amylase: Converts complex carbohydrates into simple sugar.

Question 6.
Draw the structure of the different layers of the tooth.
Answer:

Differentiate between:

Question 1.
Voluntary and Involuntary muscles.
Answer:

Voluntary muscle	Involuntary muscle
1. Voluntary muscle means you can control it consciously.	1. Involuntary muscles are controlled by your subconscious. You have no control over them.
2. Skeletal muscles are voluntary muscles.	2. Cardiac muscles and smooth muscles are involuntary muscles.
3. Muscles in our arms and legs are voluntary muscles.	3. Muscles in heart, stomach, blood vessel, intestine are involuntary muscles.

Question 2.
Skeletal muscle and Cardiac muscle.
Answer:

Skeletal muscle	Cardiac muscle
1. Skeletal muscles are voluntary muscles.	1. Cardiac muscles are involuntary muscles.
2. Muscles in our arms and legs are voluntary muscles.	2. Muscles in heart, stomach, blood vessel, intestine are involuntary muscles.
3. They hold bones of the skeleton together and gives shapes to our body.	3. They bring about contraction and relaxation of heart.

Answer the following:

Question 1.
What is meant by organ system?
Answer:

1. There are different structural organizational levels in living organism.
2. Cells → tissues → organ → organ system → organism
3. Different organs together form one organ system.

Question 2.
How are the bones in our body joined to each other?
Answer:
Skeleted muscles join two bones with the help of tendons.

Can you tell?

Answer the following questions:

Question 1.
What is the mutual relationship between muscles and bones?
Answer:

1. Muscles are firmly attached to bones by means of tendons.
2. When muscles contract there is movement at the joint and there is pull on tendon which in turn pull on the bones to which they are attached.

Question 2.
Are the muscles of the different organs in our body identical?
Answer:
No, muscles of the different organs are not identical, some are voluntary, some are involuntary.

Question 3.
How do muscles perform their functions?
Answer:

1. Muscles in our body always work in groups.
2. When some muscles contract other muscles of the same group relax.
3. This is how muscles help in proper performance of the various functions of own body.

Answer the following questions:

Question 1.
Which parts of our body are made up only of muscles?
Answer:
Tongue, heart, stomach, liver, pancreas, intestines are made up of only muscles.

Question 2.
What would happen if the cardiac muscles do not move?
Answer:

1. Cardiac muscles cause our heart to relax and contract continuously at a rate of about 70 times per minute.
2. These muscles bring about the contraction and relaxation (beating) of the heart.
3. If the cardiac muscles do not move, heart will stop beating, and will not pump blood to other parts of the body and person will die.

Question 3.
Food enters the stomach and the stomach muscles do not move.
Answer:

1. Smooth muscles are present in the lining of stomach.
2. Their movement is responsible for churning of food.
3. If the muscles do not move, food will not be digested.

Question 4.
During digestion does all the food that we have eaten get converted into useful nutritive substances?
Answer:

1. During digestion not all the food is converted into useful nutritive substance, only whatever nutrients we obtain by digestion of food gets absorbed into the blood in small intestine.
2. Undigested remains of the food enters the large intestine and thrown out of the body through the anus.

7th Std Science Questions And Answers:

• Cell Structure and Micro-organisms Class 7 Questions And Answers
• The Muscular System and Digestive System in Human Beings Class 7 Questions And Answers
• Changes – Physical and Chemical Class 7 Questions And Answers
• Elements, Compounds and Mixtures Class 7 Questions And Answers
• Materials We Use Class 7 Questions And Answers
• Natural Resources Class 7 Questions And Answers
• Effects of Light Class 7 Questions And Answers
• Sound: Production of Sound Class 7 Questions And Answers
• Properties of a Magnetic Field Class 7 Questions And Answers
• In the World of Stars Class 7 Questions And Answers

Balbharti Maharashtra State Board Class 6 Science Solutions Chapter 6 Substances in Daily Use Notes, Textbook Exercise Important Questions and Answers.

Std 6 Science Chapter 6 Substances in Daily Use Question Answer Maharashtra Board

Class 6 Science Chapter 6 Substances in Daily Use Question Answer Maharashtra Board

1. Fill in the blanks using proper works:

Question a.
Rubber made by vulcanization is a …………… material.
Answer:
hard

Question b.
Man-made materials are made by …………… natural materials.
Answer:
processing

Question c.
…………… thread was developed simultaneously in New York and London.
Answer:
Nylon

Question d.
Rayon is also known as …………… .
Answer:
synthetic silk

2. Answer the following questions. 

Question a.
Why did the need for man-made materials arise?
Answer:
The need for man-made materials arose due to the following reasons:

1. To meet the needs of an increasing population.
2. Human nature to try to make life more comfortable.
3. They can be made available in plenty at a low cost.
4. The reserve of natural substances is decreasing.

c

Question b.
Which are the natural materials obtained from plants and animals?
Answer:
Leather, jute, wool, cotton, silk are the natural substances obtained from plants and animals.

Question c.
What is vulcanization?
Answer:

1. Vulcanization is the process in which rubber is heated with sulphur for three to four hours.
2. Sulphur is mixed to give hardness to rubber.
3. The proportion of sulphur depends on the purpose for which the rubber is to be used.

Question d.
Which natural materials are used to obtain fibres?
Answer:
Cotton, wood pulp and various hydrocarbons obtained from mineral oils are used to obtain fibres.

3. What are we used for?

Question a.
What are we used for?
Answer:

1. Soil: It supports plant life and hence indirectly supports all living things. It is used for making clay pot, utensils, bricks etc.
2. Wood: It is used in paper industry. It is also used to make furniture.
3. Nylon: It is used to manufacture clothes, fishing nets, ropes, etc.
4. Paper. It is used in our textbooks, note books, currency notes, etc.
5. Rubber: It is used in the manufacture of erasers, tyres, rubber toys, rubber bands, etc.

4. How is paper manufactured? Write in your own words.

Question a.
How is paper manufactured? Write in your own words.
Answer:
Coniferous trees like pine trees are used to make paper.

1. The bark of the logs of these trees is first removed and the wood is broken into small pieces.
2. The mixture of these pieces with some chemicals is kept soaked for a long time to form pulp.
3. On completion of chemical process, fibrous substances from wood pulp are separated and some dyes are added.
4. The pulp is then passed through rollers, dried to form paper and finally wound on reels.

5. Give scientific reasons.

Question a.
We must use cotton clothes during summer.
Answer:

1. During summer we sweat more due to high temperature.
2. Cotton clothes absorb sweat.
3. Synthetic clothes are water repellent. They do not absorb sweat and we feel uncomfortable. Hence we must use cotton clothes in summer.

Question b.
We must observe economy in the use of materials.
Answer:

1. Due to excessive use of natural substances by human beings to fulfil their needs; they are getting depleted at a faster rate.
2. At the same time, it takes a very long time for these substances to get naturally formed again.
3. Hence, we must observe economy in the use of materials so that they are available for the future generation also.

Question c.
Saving paper is the need of the hour.
Answer:

1. Saving paper means saving trees as wood is used as the raw material to manufacture paper.
2. Trees are natural habitat for many Living things.
3. Trees help in increasing rainfall and water availability. Hence, saving paper helps in saving trees which in turn maintains balance in nature.

Question d.
Man-made materials have more demand.
Answer:

1. Man-made substances are waterproof, lightweight and easy for transportation.
   Substances in Daily Use
2. They are easier to use and can be made available in plenty at a low cost.
   Hence, there is more demand for man-made materials.

Question e.
Humus is a natural material.
Answer:

1. Humus is obtained from plant and animal wastes.
2. Micro-organisms act on these wastes and convert them into humus.
3. Hence, humus is a natural material.

6. Find out.

Question 1.
How is lac obtained from nature?
Answer:

1. Lac is a resinous substance secreted from the glands present in the skin of female lac insect.
2. Lac insects live on the Palash trees. In India lac is mainly produced in the states of Rajasthan and Bihar.

Question 2.
How are pearls obtained?
Answer:

1. Pearls are formed when a foreign particle such as a grain of sand or a small particle of rock accidentally enters the space between the mantle and shell of an oyster’s body.
2. Oysters cannot reject the particle, and as a defence mechanism its produces a shining coating called nacre on the particle layer by layer.
3. As the shiny layers get added, a pearl is formed.
4. Cultured pearls are artificially formed by inserting a bead in oyster shell and allowed to coat it with nacre over several years.

Activity:

Question 1.
Visit a rubber, paper or textile industry in your area and collect information about it.

Question 2.
Collect various samples of paper and note their uses.

Question 3.
Use blank pages from old note-books and make a new one.

Class 6 Science Chapter 6 Substances in Daily Use Important Questions and Answers

Fill in the blanks using proper works.

Question 1.
Natural rubber is obtained from …………… of trees.
Answer:
latex

Question 2.
Changes where the original constituent substances cannot be obtained again from the new substances are called …………… changes.
Answer:
irreversible

Question 3.
A paper factory in Maharashtra is situated at …………… .
Answer:
Ballarpur

Question 4.
Glass can be made from …………… and …………… .
Answer:
sand, calcium

Question 5.
Botanical name of rubber plant is …………… .
Answer:
Hevea brasiliensis

Question 6.
…………… obtained from mineral oils are used to make polymer chains.
Answer:
Hydrocarbons

Question 7.
The maximum production of rubber in India is in …………… .
Answer:
Kerala

Question 8.
…………… invented the process of vulcanisation.
Answer:
Charles Goodyear

Match the columns:

Question 1.

Column ‘A’	Column ‘B’
1. Jute	a. Animal origin
2. Air	b. Plant origin
3. Leather	c. Man-made
4. Cement	d. Abiotic

Answer:

Column ‘A’	Column ‘B’
1. Jute	b. Plant origin
2. Air	d. Abiotic
3. Leather	a. Animal origin
4. Cement	c. Man-made

State whether the following statements are ‘true’ or ‘false’.

Question 1.
We can find plastic in nature.
Answer:
False

Question 2.
Soap is a man-made substance.
Answer:
True

Question 3.
We should reuse available resources.
Answer:
True

Question 4.
Nylon clothes are good summer wear.
Answer:
False

Question 5.
Glass is a man-made substance.
Answer:
True

Question 6.
In irreversible changes original substances can be obtained again.
Answer:
False

Question 7.
Rayon is made up of cotton and wood pulp.
Answer:
True

Give two examples of each of the following:

Question 1.
Natural fibres
Answer:
cotton, silk

Question 2.
Synthetic fibres
Answer:
terylene, rayon

Question 3.
Biotic natural substances
Answer:
wool, jute

Question 4.
Abiotic natural substances
Answer:
air, water

Question 5.
Man-made substances.
Answer:
paper, glass

Classify the following substances in the table given below.
(iron, wood, brick, paper, terylene, stone, jute, air, silk, utensils, plastic, rayon, water, wool, dacron, lac, nylon, pearl)
Answer:

Natural Substances	Man-made Substances               Natural Fibres		Synthetic Fibres
iron, wood, stone, water, lac, pearl	brick, paper, utensils, plastic	jute, silk, wool	terylene, rayon, dacron, nylon

Define:

Question 1.
Natural substances.
Answer:
Substances available in nature are called natural substances.

Question 2.
Man-made substances.
Answer:
Man-made substances are new substances produced by processing naturally available resources.

Question 3.
Biotic substances.
Answer:
Natural substances obtained from living things are called biotic substances.

Question 4.
Abiotic substances.
Answer:
Natural substances that are not obtained from living things are called abiotic substances.

Question 5.
Plant-originated substance.
Answer:
A substance obtained from a plant is called a plant-originated substance.

Question 6.
Animal-originated substance.
Answer:
A substances obtained from an animal is called an animal-originated substance.

Question 7.
Hydrocarbons.
Answer:
Substances obtained from mineral oil are called hydrocarbons.

Answer the following in one or two sentences.

Question 1.
Why was Rayon named so?
Answer:
The threads of Rayon have shine and strength. They appeared to be shining bright like the sun’s rays. Hence, they were named ‘Rayon.

Question 2.
How are TV sets, refrigerators, etc. packed? Why?
Answer:
To pack TV sets, refrigerators, etc. big cartons and thermocol are used. These man-made substances are water resistant, light weight and easy for transportation.

Question 3.
Give the properties and uses of nylon.
Answer:
Nylon threads have a shine and are strong, transparent and water resistant. They are used to manufacture clothes, fishing nets, ropes, etc.

Question 4.
What is latex?
Answer:
Latex is a milky white natural substance produced in the stems of rubber trees.

Question 5.
Name the basic material used to obtain paper.
Answer:
Wood is the basic material used in the manufacture of paper.

Question 6.
What kind of paper is used for currency notes manufacturing?
Answer:
Flax fibre is used in the manufacture of currency notes.

Question 7.
Where was the process of making paper invented?
Answer:
The process of making paper was invented in China.

Answer in brief:

Question 1.
What are the advantages of synthetic fibre?
Answer:
Advantages of synthetic fibre are:

1. These fibres can be manufactured on a large scale.
2. They cost less.
3. They are strong and durable.
4. They can be used for a long time.
5. They are water repellent. They dyy easily.
6. They are light weight and comfortable to wear.
7. Clothes made from these threads are wrinkle free and scratch free.

Question 2.
Give the shortcomings of synthetic fibre.
Answer:

1. They are water repellent. Hence, they do not absorb sweat from the skin.
2. Continuous use of these clothes keeps the skin moist which may cause skin diseases.
3. Synthetic clothes are uncomfortable to wear especially in summer.
4. They catch fire easily.
5. If they catch fire, they stick to the skin and cause skin injuries.
6. These fibres are not decomposed by micro-organisms.

Question 3.
Write a short note on natural rubber.
Answer:

1. Rubber is a natural substance obtained by collecting the latex of certain trees.
2. The botanical name of this tree is ‘Hevea brasiliensis’
3. In India, the maximum production of rubber is in Kerala.

Question 4.
What are dacron, terylene and terene?
Answer:

1. Dacron, terelyne and terene are synthetic fibres prepared from hydrocarbons.
2. Various hydrocarbons obtained from mineral oil are used to make polymer chains.
3. A solution of such polymer is pressed through a strainer with fine holes.
4. The fibre formed after cooling are long and unbroken threads.
5. These threads have been named as dacron, terylene and terene.

Give scientific reasons:

Question 1.
Natural substances are depleting.
Answer:

1. Due to increase in population there is an increase in demand. To meet this demand, natural substances are used to a greater extent.
2. Due to human nature to make his life more comfortable, he learnt to use natural resources and also began to process them to make new substances. Hence natural substances are depleting at an alarming rate.

Can you tell?

Question 1.
Difference between leather, jute, wool, cotton and soil, water, metals.
Answer:

1. Leather, jute, wool are biotic natural substances.
2. Soil, water, metals are abiotic natural substances.

Question 2.
How are leather and wool different from jute and cotton?
Answer:
Leather and wool are obtained from animals while jute and cotton are obtained from plants.

Question 3.
Do you find plastic, nylon, brass or cement in nature?
Answer:
No, they are all man-made materials.

Question 4.
Can red chillies become green chillies again?
Answer:
No, the change from green chillies to red chillies is irreversible.

Question 5.
From which substances in nature can we get threads or fibre?
Answer:
Cotton plant, jute, silkworm.

Question 6.
What are clothes made from?
Answer:
Clothes are made from yarn obtained from fibre.

Classify the following substances according to their uses:
sand, soap, wool, window glass, bamboo, cotton, bricks, silk, leafy vegetables, cement, fruits, water, sugar.
Answer:

• For construction: Sand, window glass, bamboo, bricks, cement.
• As food: Leafy vegetables, fruits, water, sugar.
• At home: Soap for cleaning.
• For clothes: Wool, cotton, silk.

Make a list of objects, each of which can be made from several substances.
Answer:

Objects	Substances
Table	Wood, glass, plastic.
Toys	Wood, plastic, clay.
Utensils	Aluminium, wood, glass, ceramic, plastic.

Use your brain power!

Question 1.
Complete the table below, showing how substance of daily use are classified.

Answer:

1. Natural
2. Biotic
3. Cement
4. Animal Origin
5. Cotton

6th Std Science Questions And Answers:

• Natural Resources – Air, Water and Land Class 6 Questions And Answers
• The Living World  Class 6 Questions And Answers
• Diversity in Living Things and their Classification Class 6 Questions And Answers
• Disaster Management Class 6 Questions And Answers
• Substances in the Surroundings – Their States and Properties Class 6 Questions And Answers
• Substances in Daily Use Class 6 Questions And Answers
• Nutrition and Diet Class 6 Questions And Answers
• Our Skeletal System and the Skin Class 6 Questions And Answers
• Motion and Types of Motion
• Force and Types of Force Class 6 Questions And Answers

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 18 Ecosystems Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 18 Ecosystems Question Answer Maharashtra Board

Class 8 Science Chapter 18 Ecosystems Question Answer Maharashtra Board

1. Complete the following by using the correct option:

Question a.
Air, water, minerals, soil are ………….. factors of an ecosystem. (physical, organic, inorganic)
Answer:
Air, water, minerals, soil are physical factors of an ecosystem.

Question b.
River, ponds, ocean are …………. ecosystems, (land, aquatic, synthetic)
Answer:
River, ponds, ocean are aquatic ecosystems.

Question c.
Man is ………….. in an ecosystem. (producer, consumer, decomposer)
Answer:
Man is consumer in an ecosystem.

2. Match the following:

Question a.

Producer	Ecosystem
1. Cactus	a. Forest
2. Aquatic plants	b. Creek
3. Mangroves	c. Aquatic
4. Pine	d. Desert

Answer:

Producer	Ecosystem
1. Cactus	d. Desert
2. Aquatic plants	c. Aquatic
3. Mangroves	b. Creek
4. Pine	a. Forest

3. Give my information:

Question a.
Ecosystem.
Answer:
Ecosystem is the structure formed by the interrelationships between the living organisms and non-living components in their surrounding habitats. Living organisms are also called biotic factors while the non-living components are called abiotic factors. The abiotic and biotic factors have a reciprocal relationship with each other. The ecosystem has plants as producers, animals as consumers and microbes as decomposers.

The decomposers return the substances back to the nature by process of decomposition in which the organic complex molecules are reduced to their inorganic constituents. Thus the dead remains of plants and animals are once again recycled back to the nature in any healthy ecosystem.

Question b.
Biome.
Answer:
Biomes are a larger collection of small ecosystems which are similar in their structure. In a particular biome there are same climatic, abiotic factors and similar living organisms. Biomes are of two main types, land biomes and aquatic biomes. The land biomes exist only on land. Land biomes are of following subtypes based on the abiotic factors. E.g. Grasslands, evergreen forests, deserts, Tundra ecosystem, ecosystems in Taiga, tropical rainforests, etc. Aquatic biomes include freshwater ecosystem, marine ecosystem and brackish water ecosystem found in the creeks.

Question c.
Food web.
Answer:
The complex feeding relationships form a food web. In nature in any ecosystem, the food chains are not straight and linear. But these are quite complex. A prey is consumed by a predator but this predator can itself be a prey to some other predator. E.g. Frog is a predator for variety of insects but frog is preyed upon by snake and the snake can be eaten by a bird. The same bird can also feed on insects or frog. The interrelationships between different biotic components of any ecosystem thus form the complicated food web.

4. Give scientific reasons: 

Question a.
Plants in an ecosystem are called producers.
Answer:
are cut down causing deforestation. The wild animals lose their habitat. Many of them become extinct. There is great loss of flora and fauna due to construction of large dams. There is undue pressure on the land surface caused due to stored water column. This may cause earthquakes. The human settlements are removed as their houses and farms are immersed under water. In all the above ways large dams destroy the ecosystems.

Question b.
Large dams destroy ecosystems.
Answer:
When a large dam is constructed, the original landscape is changed. The trees are cut down causing deforestation. The wild animals lose their habitat. Many of them become extinct. There is great loss of flora and fauna due to construction of large dams. There is undue pressure on the land surface caused due to stored water column. This may cause earthquakes. The human settlements are removed as their houses and farms are immersed under water. In all the above ways large dams destroy the ecosystems.

Question c.
Rhinos were restored in Dudhwa forest.
Answer:
Long ago in last century, Dudhwa forest was the natural habitat of the one-horned Rhino. However, due to hunting and poaching, the Rhino became almost extinct. In order to restore it back the breeding in captivity was attempted and the young ones were released in the natural habitat. Saving the precious wildlife is important and hence these efforts were done.

5. Answer the following:

Question a.
What are the effects of increased population (of human beings) on ecosystems?
Answer:

1. Human population growth rate is very big as compared to other animals.
2. Moreover, they are apex consumers in an ecosystem. Just like any other organisms, ecosystems provide all the basic needs to humans, too.
3. However, man demands much more due to excessive population. The natural resources are utilized on the large scale only by man.
4. Changing lifestyles, consumerism, degradation of nature and pollution are certain aspects which are created only by human beings.
5. All these cause increased stress on the ecosystems. Large human population also produces large-scale solid wastes.

Question b.
How is urbanization responsible for destruction of ecosystems?
Answer:
When people do not get sufficient food and other amenities, they migrate to the cities. The cities provide employment for many people due to industries, factories and other facilities. Every day many people migrate to cities. This causes urbanization. Due to increased population in cities, there is more need for housing. This results in loss of agricultural lands, marshlands, wetlands, forests and grasslands, etc.

The natural ecosystems are lost in an attempt to have developmental work. Human interference causes changes in the ecosystems. When land usage is changed many naturally occurring species of plants and animals are exterminated. Animal- human conflicts are very common in newly established urban areas which are near the natural forests.

Question c.
What are the reasons for war?
Answer:
There are difference of opinions and competition over land, water, mineral resources, etc. among neighbouring countries. Moreover, there can be economic and political causes which lead to war among different countries. Many times the l religions and ethnicity are also caused for dispute. Due to international conflicts, the peace is disturbed and it results in war.

Question d.
Explain the interactions among the factors of an ecosystem.
Answer:

1. The abiotic factors such as air, water, soil, sunlight, temperature, humidity, etc. affect the biotic factors, i.e. the surviving plants, animals and microbes in the ecosystem.
2. The type of abiotic factors in an ecosystem determine the survival of biotic factors. The population of these biotic factors is also dependent on the quality of abiotic factors.
3. The proportion of abiotic factors in an ecosystem fluctuates as biotic factors use up or release particular abiotic factors.
4. Every biotic factor also interacts with its necessary abiotic factors as well as other biotic factors around it.

Question e.
Differentiate between evergreen forests and grasslands.
Answer:

Evergreen forests	Grasslands
1. About seven percent of the Earth’s surface is occupied by evergreen forests.	1. About 30 percent of the Earth’s surface is covered by grasslands.
2.  More than half of the earth’s terrestrial plants and animals are seen in evergreen forests.	2. Grazing animals are seen in grasslands.
3. Tropical evergreen forests are dense, multi-layered.	3. Grasslands consist of tall grass. There are wild grasses and there may be some trees.
4. These forests are found in the areas receiving more than 200 cm annual rainfall i.e. very heavy rainfall.	4. There is an average of 20 – 35 inches of rainfall a year in grasslands.
5. Tropical regions show evergreen forests.	5. Several parts of the world have grasslands.

6. Describe the following pictures:

Question a.
Describe the following pictures

Answer:
The picture no. 1 is showing desert ecosystem, while the picture no. 2 is showing a forest ecosystem where a wetland (a lake) is also shown. In desert ecosystem, the producers are green cactus and a palm tree. Since in desert there are scanty rains, the vegetation is very less. The soil is sandy soil. The consumers of the desert are also limited.

In the above picture camel is shown which is a primary consumer in the desert ecosystem. Camel is very well adapted for desert life. There is also the scarcity of water in desert and hence cactus shows xerophytic (suitable to survive in desert) adaptations.

In second picture, the forest ecosystem is shown because we can see elephant and tiger in the picture. Also, giant hornbill is sitting on the tree. This forest must be tropical evergreen forest. The rainfall is heavy in such areas and hence different types of wetlands can be seen in forests. Wetlands support variety of life. A separate aquatic ecosystem does exist here which is closely interconnected with the terrestrial ecosystems through food chains and food web.

The birds utilize the fish as their prey. The wild animals come to wetlands to quench their thirst. In this picture the plants, grass, etc. are producers, small fishes in the lake are primary consumers. They will be eaten by larger fishes which are secondary consumer in the aquatic ecosystem. The elephant is herbivorous animal and hence it is primary consumer. Snake is the secondary consumer while the birds of prey (eagle that is flying) and tiger are tertiary consumers.

Can you recall?

Question 1.
Which factors do you find in your surroundings?
Answer:
In our surroundings there are abiotic and biotic factors. The biotic factors are animals and plants in the surroundings. The invisible bacteria and fungi also have important role in the ecosystem as decomposers. Important abiotic factors are air, water, land, sunlight, etc.

Question 2.
Are these factors directly or indirectly related to you?
Answer:
We are directly or indirectly connected to every single factor in the surrounding in which we reside. For the requirement of food, we are dependent on plants and animals. For our survival we continuously need oxygen, water and other minerals, etc.

Classify:

Question 1.
Classify the following into living and non-living factors. Sunlight, Sunflower, Elephant, Lotus, Algae, Stone, Grass, Water, Ant, Soil, Cat, Fern, Air, Lion.
Answer:

Living Factors	Non-living Factors
Sunflower, Elephant, Lotus, Algae, Grass, Ant, Cat, Fern, Air, Lion.	Sunlight, Stone, Water, Soil, Air.

Can you tell?

Question 1.
What is the role of microbes in above interaction?
Answer:
Microbes play the role of decomposers in the above interactions.

Question 2.
How do producers obtain abiotic factors?
Answer:
Producers obtain solar energy from sunlight. The other nutrients are obtained from soil, water and air.

Question 3.
From where do the consumers get their food?
Answer:
Consumers get their food from producers and other consumers.

Project:

Question 1.
Visit an ecosystem nearby, List the biotic and abiotic factors in it. Show with pictures or sketches, how they are dependant on each other.

Question 2.
With the help of internet find out the loss of ecosystems due to wars or atomic explosions. Describe in your words.

Class 8 Science Chapter 18 Ecosystems Important Questions and Answers

Complete the following by using the correct option:

Question 1.
Biotic community is another name for ………. (ecology, ecosystem, population)
Answer:
Biotic community is another name Biotic for ecosystem.

Question 2.
Microbes in an ecosystem are ………… (producers, consumers, decomposers)
Answer:
Microbes in an ecosystem are decomposers.

Question 3.
Many types of ecosystems are found in ………… (oceans, deserts, biosphere)
Answer:
Many types of ecosystems are found in biosphere.

Question 4.
………….. is a type of grassland ecosystem. (Taiga, Tundra, Desert)
Answer:
Taiga is a type of grassland ecosystem.

Question 5.
Gir forest in Gujarat is the only habitat/shelter for the spectacular ………….. (Asiatic lion, Royal Bengal tiger, One-horned rhino)
Answer:
Gir forest in Gujarat is the only habitat shelter for the spectacular Asiatic lion.

Correct the following statements by changing one or two words:

Question 1.
Primary, secondary, tertiary consumers are the abiotic factors of the ecosystem.
Answer:
Primary, secondary, tertiary consumers are the biotic factors of the ecosystem.

Question 2.
Most of the ecosystems are simple.
Answer:
Most of the ecosystems are complex.

Question 3.
The word ecosystem was brought in the use by Ray Claffam.
Answer:
The word ecosystem was brought in the use by A.G. Tansle.

Question 4.
Specific ecosystem developed in a vast area is called a biosphere.
Answer:
Specific ecosystem developed in a vast area is called a biomes.

Question 5.
Longer summer and limited rain develop very tall plants in the grassland ecosystem.
Answer:
Longer summer and limited rain develop dwarf plants in the grassland ecosystem.

Question 6.
29 % of the earth surface is covered by water and only 71 % has land on it.
Answer:
71 % of the earth surface is covered by water and only 29 % has land on it.

Question 7.
Dams increase the water current in lower area.
Answer:
Dams lessen the water current in lower area.

Match the following:

Question 1.

Column ‘A’	Column ‘B’
1. The Great Himalayan National Park	a. Asiatic lion
2. Kaziranga	b. Tigers
3. Bharatpur	c. Aquatic birds
4. Ranthambore	d. One-horned Rhino
5. Gir forest	e. White panther

Answer:

Column ‘A’	Column ‘B’
1. The Great Himalayan National Park	e. White panther
2. Kaziranga	d. One-horned Rhino
3. Bharatpur	c. Aquatic birds
4. Ranthambore	b. Tigers
5. Gir forest	a. Asiatic lion

Find the odd one out:

Question 1.
Typha, Pistia, Eichhornia, Dipterocarpus
Answer:
Dipterocarpus. (All others are aquatic plants.)

Question 2.
Teak, Parthenium, Pine, Sandalwood
Answer:
Parthenium. (All others are forest trees.)

Question 3.
Giraffe, Zebra, Cheetah, Elephant
Answer:
Cheetah.. (All others are surviving grassland animals, Cheetah is a forest animal that is extinct from Asia.)

Question 4.
Hyena, Cow, Deer, Rabbit
Answer:
Hyena. (All others are primary consumers, Hyena is tertiary consumer.)

Question 5.
Fusarium, Leptocorsia, Aspergillus, Polycarpus
Answer:
Leptocorsia. (All others are decomposers, Leptocorsia is primary consumer.)

Taking into consideration the relationship in the first pair, complete the second pair :

Question 1.
Plants : Producers : : ……… : Consumers
Answer:
Animals

Question 2.
Secondary consumers : Jackals : : Tertiary consumer : ………..
Answer:
Kite/Lion/Hyena

Question 3.
Goat, sheep : Grassland ecosystem : : Tigers : …………..
Answer:
Forest ecosystem

Question 4.
Desert : Land biome : : Creek : …………….
Answer:
Aquatic biome

Question 5.
Limited rain : Grassland ecosystem : : ……….. : Tropical rainforests
Answer:
Excessive rain.

Answer in one sentence:

Question 1.
What is an ecosystem?
Answer:
The structure which is formed due to interactions between abiotic and biotic factors is called an ecosystem.

Question 2.
What is an ecological niche?
Answer:
The position of any living organism with reference to other living organisms and the role played by that organism is called ecological niche.

Question 3.
How are types of ecosystems formed?
Answer:
Types of ecosystems are formed according to size, place, climate, types of plants and animals that survive in that ecosystem.

Question 4.
Give examples of land biomes.
Answer:
Grasslands, evergreen forests, deserts, Tundra or polar ecosystem, ecosystems in Taiga, tropical rainforests, etc. are land biomes.

Question 5.
What are the reasons for tourism among the people?
Answer:
Tourism is mainly because people like to visit scenic places, undertake nature watch, wish to visit to sacred places and for entertainment purpose.

Question 6.
Why we should protect natural ecosystems?
Answer:
Natural ecosystems must be protected as they maintain balance in the biosphere.

Give my information Write short notes:

Question 1.
Dudhwa forest.
Answer:
Dudhwa forest is in Uttar Pradesh. About a century back, Dudhwa forest was the habitat for one-horned Rhino. However, due to hunting and poaching in 20th century, this animal became endangered. Thus to restore their populations, on 1st April 1984 rhino were introduced there again. Rhinos can were bred in captivity followed by releasing them back into natural ecosystem.

For this purpose at first the land was selected. This was 27 square km grassland and forest with continuous water supply through natural resources. Two observatories were established for making these efforts successful. Now Dudhwa is known for one¬horned Rhino population.

Question 2.
Aquatic ecosystems.
Answer:
Earth’s 71 % of surface is covered over by aquatic ecosystems. They are of three main types, viz. fresh water ecosystem, marine ecosystem and brackish water ecosystem. Rivers, lakes and ponds and streams are some of the fresh water ecosystem. Fresh water contains less salt and hence it is potable. Marine water has more salinity, i.e. its salt content is high. Brackish water ecosystem is present in the creeks. Here the saline and fresh water mix together. Hence salinity here is lesser than that of the marine water.

Give scientific reasons:

Question 1.
Microbes are called decomposers.
Answer:
Decomposition is the process in which the organic compounds are broken down to their inorganic constituents. The organic substances such as carbohydrates, proteins and lipids which are locked in the dead remains of plants and animals are converted into hydrogen, oxygen, calcium, iron, sodium, potassium, etc. by microbes. Therefore, microbes are called decomposers.

Use your brain power:

Question 1.
Which biotic factors get affected due to a dam?
Answer:
The biotic factors include plants, animals and humans. Lot of vegetation is submerged from the place where dam is constructed. The forests are wiped out. Large scale deforestation takes place in the proposed dam area. Wildlife is destroyed completely. The resident animals whose habitat are there either migrate away or are killed due to lack of their food and shelter. Many instances of animal-human conflicts arise when the wild animals drift to the neighbouring human settlements.

If human settlements are shifted, people are displaced. They lose their houses and agricultural land. Though compensation is given to them, there is great change for the people. Water current in lower area of the dam is reduced due to construction of dam-walls. Therefore, the original lotic (running 5 water) ecosystems that were present are destroyed after the construction of dam.

Question 2.
What will be the effects on biotic factors in the running water of river?
Answer:
The aquatic flora (plants) and fauna (animals) are well adapted to their habitats. The running water ecosystems are known as lotic ecosystems. The non-moving waters on the contrary create lentic ecosystems. Lotic ecosystems provide special adaptations to the plants and animals living therein. Plants are mostly in the form of freely floating algae and phytoplankton. Animals are well adapted for swimming in the currents of water. The fishes especially show a stream-lined body, fins for swimming, and gills to take up dissolved oxygen in the water. The other animals are also well adapted to the currents of water.

Think about it:

Question 1.
Can we call a tree an independent ecosystem?
Answer:
The huge tree can be an independent ecosystem. On one such tree there may be different habitats. Variety of insects thrive on huge tree by making their habitats in cracks and crevices on the tree. Many birds visit the tree to feed on such insects. There are many bird species that live in the hollow of the tree. Garden lizards, chameleons, snakes are the different reptiles seen associated with the tree ecosystem.

Squirrels, rabbits, bats are the mammals which take shelter in and around the trees, also inhabit a tree variety of fungi, lichens, mosses and epiphytic plants like orchids survive on the huge trees. Many food chains and complicated food webs are formed with the support of the tree. Thus one can say that a tree is an independent ecosystem.

Question 2.
Today Divija visited a hill. Honey: bees were hovering on flowers. One of them stung Divijia’s hand. Divija was hurt due to that sting and said with anger that all the honey-bees from the whole world must get destroyed. Afterwards, she thought what will happen if all honey-bees are destroyed? We will get honey, nothing more. What would be your explanation to Divija?
Answer:
Honey bees provide us with honey and bee-wax. Both of these are commercial products. But more than that the role played by honey bees in the pollination of flowers is very important. Due to their nectar collecting behaviour, they bring about pollination of the flowers.

Presence of honey bees is thus very essential for the agriculture and horticulture. Without honey bees, the growth of fruits and grains will not be possible, if pollination and subsequent fertilization does not take place in nature. This will create famine-like conditions. Therefore, honey bees’ position in the nature is very important.

Chart based questions:

Question 1.
Complete the following chart in context to a grassland.

Answer:

Question 2.
Write the information about various components of forest.

Answer:

Question 3.
Observe such ecosystems around you and complete the following chart.

Answer:

Question 4.
Complete the table.

Answer:

National Park/Sanctuary	State
1. Gir	Gujarat
2. Dachigam	Jammu-Kashmir
3. Ranthambore	Rajasthan
4. Dajipur	Maharashtra
5. Kaziranga	Assam
6. Sunderbans	Bengal
7. Melghat	Maharashtra
8. Periyar	Kerala

Question 5.
Complete the following chart:

Answer:

Diagram based questions:

Question 1.
Correct the following diagram:

Answer:

MCQs based on experiment:

Question 1.
Which one out of the following is not biotic factor?
(a) Humidity
(b) Rabbit
(c) Snake
(d) Bacteria
Answer:
(a) Humidity

Question 2.
Which climatic factor is causing migration of the birds in certain regions of the earth?
(a) Humidity and rainfall
(b) Ambient temperature
(c) Amount of carbon dioxide
(d) Amount of plant matter
Answer:
(b) Ambient temperature

Question 3.
Which abiotic factor mainly distinguishes marine water from the fresh water?
(a) Temperature
(b) Dissolved oxygen:
(c) Salinity
(d) Surface tension
Answer:
(c) Salinity

Question 4.
Why is creek water different from the river water?
(a) Creek water is more polluted than the river water.
(b) Creek water is less salty than the river water.
(c) Creek water is more saline than the river water.
(d) Creek water is less turbulent than the river water.
Answer:
(b) Creek water is less salty than the river water.

Question 5.
Which land biome shows presence of cacti plants more?
(a) Polar regions
(b) Grasslands
(c) Rainforest
(d) Desert
Answer:
(d) Desert

Projects:

Collect information

Question 1.
What are the possible threats to grasslands?
Answer:
Man tries to use grasslands for agricultural purpose. This transformation causes loss of natural ecosystem. Many animals from grasslands are killed by hunting and poaching. Though now Wildlife Act has protected these animals, many wildlife species are already extinct. There are chances of forest fires which is the greatest threat to grasslands. The global warming may also cause grasslands to become a desert.

Question 2.
Why did Asian Cheetah become extinct in last century?
Answer:
When British ruled India, Asian Cheetah was hunted to a great extent. The kings and British rulers did rampant hunting. The forest lands were also reduced due to encroachment by humans to build their settlements. Dams were constructed. Mega highways, bridges and roads caused loss of habitat for Asian Cheetah. Cheetah needs large thickly forested territory. This was lost due to all man-made activities. All these reasons made Asian Cheetah extinct in last century.

Question 3.
Observe Asian Cheetah on internet. Describe it.
Answer:
Cheetah is the fastest running feline animal on the earth. Though from Asian regions it is said to be extinct, in African grasslands, its occurrence is still there. But it is endangered animal. By 2016, the global cheetah population is estimated at approximately 7,100 individuals in the wild. Several African countries have taken steps to improve cheetah conservation measures.

Cheetah has a slender body, deep chest, spotted coat. Its head is small rounded and on the face there is black tear-like streaks. It has long thin legs and a long spotted tail. Cheetah in India were tamed during Moghul period for assisting in hunting. Stories about such episodes are commonly told. However, the last Cheetah in India was spotted in Bastar, M.P. in 1948.

8th Std Science Questions And Answers:

• Human Body and Organ System Class 8 Questions And Answers
• Introduction to Acid and Base Class 8 Questions And Answers
• Chemical Change and Chemical Bond Class 8 Questions And Answers
• Measurement and Effects of Heat Class 8 Questions And Answers
• Sound Class 8 Questions And Answers
• Reflection of Light Class 8 Questions And Answers
• Man-made Materials Class 8 Questions And Answers
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Balbharti Maharashtra State Board Class 7 Science Solutions Chapter 16 Natural Resources Notes, Textbook Exercise Important Questions and Answers.

Std 7 Science Chapter 16 Natural Resources Question Answer Maharashtra Board

Class 7 Science Chapter 16 Natural Resources Question Answer Maharashtra Board

1. Describe natural resources with reference to the following 3 types:

Question a.
Mineral resources
Answer:
Mineral wealth has an important place among natural resources. The rocks on the earth are mainly made of minerals. These minerals can be obtained by mining. Minerals that contain a high proportion of metals are ores, (i) Minerals are formed from the magma in the earth’s crust and the lava from the eruption of volcanoes when they cool and get transformed into crystals e.g. magnetite, mica, (ii) Minerals get transformed from one form into another due to large changes in temperature and pressure e.g. Diamond, Graphite, (iii) There are 3 types of minerals according to their properties Non-metal minerals: e.g. mica, sulphur, potash, diamond.

• Metals minerals: e.g. Iron, gold, silver, tin, bauxite, platinum.
• Energy minerals: e.g. Coal, mineral oil, natural gas, diamond, ruby, sapphire, jade are used as gems.

Some important minerals and ores are Iron ore, manganese, bauxite, copper and mica.

Question b.
Forest resources
Answer:

1. A forest is a natural habitat of plants, animals and microbes.
2. Forest perform certain specific protective and productive functions.
3. We get different types of wood and many medicinal plants from forests.
4. Forest wealth includes fire wood, trees like teak, mahogany, neem, acacia, subabhul, fibers, paper, rubber, gum, aromatic substances.
5. We get fragrant essential oils from lemon grass, vanilla, kewada, vetiver (khus) and eucalyptus.
6. Sandalwood and oil of eucalyptus are used for making soaps, cosmetics and incense sticks.
7. Also we get fruits, bulbs, roots, honey, sealing wax, dyes from forest.
8. Many medicinal plants adulsa, bel, neem, periwinkle, cinnamon, are used for treatment of various diseases such as cough cold, malaria, diarrhoea, cancer, fever and cold.
9. Wood is used as a source of energy for cooking purpose and for keeping warm.
10. For making furniture, tool handles, matches, bridges, boats etc.
11. Bamboos are used for matting, flooring, basket, ropes, rafts, cots etc.
12. Bamboos, wood are used in the manufacture of rayon, yams, artificial silk-fibers.

Question c.
Ocean resources
Answer:

1. Oceans occupy about 70% of a earth’s surface.
2. Energy can be obtained on a large scale from oceans.
3. Sea waves at high and low tide and ocean currents are being used for generation of power.
4. There are billions of tons of minerals dissolved in ocean water.
5. There are large reserves of tin, chromium, potassium, phosphates, copper, zinc, iron, lead, thorium, manganese, sulphur, uranium in the ocean and sea beds.
6. Also we get many types of gems, conches, shells and pearls from the sea.
7. There are large reserves of mineral oil and natural gas at the bottom of sea.
8. We get fishes, dried shrimp, shells, fungi, shark, cod fish and sea cucumber from the ocean.

2. Write answers to the following questions in your own words.

Question a.
What is meant by fossil fuel? What are their types?
Answer:

1. Fossil fuels (such as coal or natural gas) are formed in the earth from dead plants and animals, due to high pressure from above and the heat from the earth’s interior.
2. The dead plants, animals get transformed into fossil fuel.
3. There are three types of fossil fuels which can be used for energy production, Coal, oil and natural gas.

a. Coal:

1. Coal is a solid fossil fuel formed over millions of years by the decay of land vegetation,
2. Coal is a store house of carbon. Coal is found in mines,
3. It is like porous, hard, black rock.
4. It is burnt to obtain heat energy.
5. It is used as a fuel in thermal power plants and to run boilers and railway engines, for cooking and baking bricks.
6. Anthracite is the coal of the highest grade.
7. Producer gas and water gas are obtained from coal.

b. Mineral oil:

1. Mineral oil is the liquid fuel formed by the decomposition of organic substances buried underground,
2. The underground mineral oil is extracted through oil wells.
3. Mineral oil is found mainly in oil sands, shale, sandstone and limestone at a depth of about 1000 to 3000 metres.
4. Mineral oil is also known as petroleum or crude oil. It is greenish-brown in colour.
5. Petroleum is a mixture of many compounds mainly of the hydrocarbon type.
6. It also contains compounds of oxygen, nitrogen and sulphur.
7. Petroleum is extracted through oil wells and refined by fractional distillation to separate other components,
8. Aviation petrol, gasoline, diesel, kerosene, naphtha, lubricating oil, tar are all obtained from petroleum.
9. They are used as fuel and for production of dyes, pesticides, perfumes and artificial fibres.

c. Natural gas:

1. Natural gas is an important fossil fuel.
2. It is lighter than air. It is found with petroleum in underground oil wells and in some places as natural gas alone.
3. The main component of natural gas is methane (CH₄), ethane (C₂H₆), propane (C₃H₈) and butane (C₄H₁₀) are present in small proportions.
4. This gas is highly flammable.
5. This fuel can be carried over long distance by means of a gas pipeline.
6. In absence of pipeline, it is transformed under high pressure into compressed natural gas (CNG) and liquefied natural gas (LNG).

Question b.
Make a list of the components we obtain from mineral oil.
Answer:

1. Mineral oil is the liquid fuel. It is also known as petroleum or crude oil. Petroleum is refined by fractional distillation to separate other components.
2. Aviation petrol, gasoline, diesel, kerosene, naphtha, lubricating oil, tar are the components we obtain from mineral oil.

Question c.
What do we get from forest?
Answer:

1. A forest is a natural habitat of plants, animals and microbes. We get wood, firewood from trees like teak, mahogany, neem, subabhul.
2. Also we get fibers, paper, rubber, gum and aromatic substances.
3. We get many medicinal plants like Adulsa, Bel, Neem, Periwinkle, Cinnamon, Cinchona which are used for treatment of various diseases like cough, cold, diarrhea, fever, cancer, diarrhoea, nausea, malaria.
4. We get fragrant essential oils from lemon grass, vanilla, kewada, khus, eucalyptus.
5. In addition to this we get fruits, bulbs and roots, honey, sealing wax, catechu, dyes from forest.

Question d.
What are the items included in ocean resources? What are their uses?
Answer:

1. Tons of minerals are found in ocean water.
2. They are tin, chromium, phosphates, copper, zinc, iron, lead, manganese, sulphur, uranium etc.
3. We also get many types of gems, conches, shells and pearls from the sea.
4. Mineral oil and natural gas is found at the bottom of sea.

Bio-resources in oceans

• Fishes – like pomfret, seer fish as also shrimps
• prawns – they are sources of proteins and vitamins, therefore, mainly used as sea food
• Dried shrimp, Bombay duck powder – used as poultry feed and is a good manure.
• Shells – used for preparation of medicines, ornaments and decorative articles.
• Fungi – used for the production of antibiotics.
• shark and cod fish – used for producing edible oil rich in Vitamins A, D and E.
• Sea cucumbers – used as medicine for treating cancer and tumours.

Mineral resources from oceans

• Thorium – used in the production of atomic energy.
• Magnesium – used in the flash bulb of a camera.
• Potassium – the main ingredient in production of soap, glass, fertilizer.
• Sodium – used in the production of cloth and paper.
• Sulphate – used in making artificial silk.

Question e.
Why should we prevent the wastage of fuels used for vehicles?
Answer:

1. Vehicles are powered by gasoline or diesel petrol.
2. Nowadays compressed natural gas (CNG) is also used.
3. Aviation petrol, gasoline, diesel, we get from petroleum after fractional distillation.
4. Petroleum is a non-renewable source of energy.
5. It is getting depleted day by day and the demand for fuel has increased greatly due to the rapidly growing population.
6. But the reserves of petroleum (fossil fuel) are limited.
7. It is becoming difficult to meet the increased demand. So we should prevent the wastage of fuel.

Question f.
Why is the diversity of plants and animals in the forests declining?
Answer:

1. The major causes of biodiversity decline are land use changes, pollution, changes in atmosphere, CO₂ concentration, changes in the nitrogen cycle, acid rain, climate alteration and introduction of exotic species.
2. All this is due to population growth.
3. This is the main cause of the loss of biodiversity. More of wood for fuel is been used, more land is required for food production, livestock grazing etc.
4. Rainforest land is converted to industrial and residential usage, so natural habitat of birds, animals is destroyed.
5. Due to population growth most of wild land is converted to crop land. So no space for animals to live, their natural habitat is destroyed.

Question g.
Write the names of five minerals and the useful substances obtained from them.
Answer:
Some important minerals and ores are:

1. Iron ore: It is used for making farming implements, rails of railway tracks etc.
2. Manganese: Compounds of manganese are used in the preparation of medicines and for giving a pink tinge to glass. Manganese is also used in electrical appliances.
3. Bauxite: It contains 55% Aluminium. Therefore, it is used mainly in aeroplanes, transport vehicles and to make electric wire.
4. Copper: It is used to make electric wires as well as in radios, telephones, vehicles, and for making kitchen utensils and statues.
5. Mica: Mica has many uses such as in ayurvedic medicines, dyes, electric machines and equipment, wireless communication equipment, etc.

Question h.
Name the two important stages in the process of obtaining metals from ores.
Answer:
The two important stages in the process of obtaining metals from ores are extraction and purification.

3. What steps are taken for protection and conservation of natural resources?

Question a
What steps are taken for protection and conservation of natural resources?
Answer:

1. Protection and conservation of natural resources is necessary to protect the natural world. (CNRM) Community Natural Resource Management has been promoted in recent years for biological conservation.
2. The World Conservation Union has been formed. It is the world’s leading authority and democratic platform in conservation and sustainability.
3. Young trees should not be cut. More and more trees need to be grown.
4. The stringent restrictions/ laws/ Regulations regarding use of forests should be strictly followed. Awareness is being created through Mass media.

4. Complete the Flow Chart:

Question a.

Answer:

5. How does the economic condition of a nation depend on its natural resources?

Question a.
How does the economic condition of a nation depend on its natural resources?
Answer:
1. Natural resources are a necessary condition for economic growth.
2. Three circles enclosed within one another shows how both economy and society are subsets of our planetary ecological system.

3. Natural resource economics deals with the supply, demand and allocation of the Earth’s natural resources.
4. Economic growth is an increase in the value of goods and services produced in an economy.
5. The natural resources of a country depend on the climatic and environmental conditions.
6. Countries having plenty of natural resources enjoy good growth than countries with small amount of natural resources.
7. A country having skilled and educated work force with rich natural resources takes the economy on the growth path, because skilled and educated people can efficiently utilize or exploit natural resources, e.g. Saudi Arabia: their economic growth is high, because they have oil wells.
8. All countries import fuel or oil from them so Saudi Arabia is economically a rich country.

6. Which medicinal plants will you grow on your school premises and near your house? Why?

Question a.
Which medicinal plants will you grow on your school premises and near your house? Why?
Answer:
1. I will grow tulsi, neem, lemon grass, bel, adulsa, periwinkle, cinnamon, ashwagandha, shatavari, amla, hirda, behda.
2. These plants are used for treatment of various diseases.

• Tulsi → for cough and cold.
• Amla, hirda, behda → Help in digestion of food or any stomach related problems.
• Adulsa → for cough and cold
• Bel → for Diarrhoea
• Neem → Fever and cold
• Periwinkle → Cancer
• Cinnamon → Diarrhoea, nausea.
• Cinchona → Malaria.
• Ashwagandha → It can reduce blood sugar levels. It can reduce stress and anxiety, may reduce symptom of depression.
• Shatavari → has been used for centuries in Ayurveda to support the reproductive system.
• Amla → Excellent source of vitamin C. Amla juice is best tonic to keep you younger for long.
• Hirda → This fruit is commonly called Haritaki. It is used for treating arthritis, dental problems like caries, bleeding gums.
• Behda →(Beleric) is a rejuvenative and laxative, proves beneficial for hair, throat and eyes.
• Tulsi → Tulsi has germicidal, fungicidal, anti-bacterial anti-biotic properties, cures fever. Treats diabetes, protects the heart. Tulsi has anti-oxidant component Eugenol which keeps one’s blood pressure under control.

Project:

Question 1.
Collect conches and shells of various shapes and colours and make a decorative article.

Question 2.
Collect information about the mines of various minerals.

Class 7 Science Chapter 16 Natural Resources Important Questions and Answers

Fill in the blanks:

Question 1.
………….. is the major raw material for biogas.
Answer:
cow dung

Question 2.
Atomic energy is obtained by using ores of ………….. .
Answer:
Uranium

Question 3.
Biogas generation is mainly based on the principle of ………….. .
Answer:
Fermentation

Question 4.
Floods can be prevented by ………….. .
Answer:
Afforestation

Question 5.
Coal, petroleum, natural gas are ………….. resources.
Answer:
non-renewable

Question 6.
The total percent of land of world under forest cover is ………….. .
Answer:
30%

Question 7.
A naturally occurring substance ………….. .
Answer:
minerals

Question 8.
Minerals that contain a high proportion of metal are called ………….. .
Answer:
ore

Question 9.
Coal, mineral oil and natural gas are ………….. .
Answer:
fossil fuel

Question 10.
Deposits of common salt are also found in the earth. This salt is called ………….. .
Answer:
rock salt

Question 11.
………….. is the liquid fuel formed by the decomposition of organic substances.
Answer:
Mineral oil

Question 12.
The underground mineral oil is extracted through ………….. .
Answer:
oil wells

Question 13.
Mineral oil is also known as ………….. or ………….. .
Answer:
petroleum, crude oil

Question 14.
………….. are the preserved remains of dead organisms in rock.
Answer:
Fossil

Question 15.
Coal can be formed from ………….. .
Answer:
Fossils

Question 16.
Impurities of sand and soil in ore are called ………….. .
Answer:
Gangue

Question 17.
Coal mainly contains ………….. .
Answer:
carbon

Question 18.
Petroleum is formed from ………….. .
Answer:
organisms in sea

Question 19.
Separation of various fractions of petroleum is called ………….. .
Answer:
Refining

Question 20.
We can obtain minerals from rocks by ………….. .
Answer:
mining

Question 21.
………….. is the most important ore of aluminium
Answer:
Bauxite

Question 22.
………….. is the coal of the highest grade.
Answer:
Anthracite

Question 23.
Metals are obtained from their ore by ………….. and ………….. .
Answer:
extraction, purification

Question 24.
………….. is the largest oil and gas research and production company in India.
Answer:
ONGC

Question 25.
Natural gas is transformed under high pressure into ………….. and ………….. .
Answer:
LNG and CNG

Question 26.
The main component of Natural gas is ………….. .
Answer:
Methane

Question 27.
………….. and ………….. are used for adding fragrance in soaps and incense sticks.
Answer:
Sandalwood and oil of Encalyptus

Question 28.
………….. is a natural herbal medicine for cough and cold.
Answer:
Adulsa

Answer the following:

Question 1.
What is meant by natural resources?
Answer:

1. We get many substances from nature.
2. They satisfy a variety of our daily needs. Soil, stones, minerals, air, water, plants and animals on the earth are all various kinds of natural resources.

Question 2.
What are alternative fuels?
Answer:
Hydrogen, biofuels, methanol or wood alcohol, ethanol or green alcohol are some of the alternative fuels.

Question 3.
What is meant by fuels?
Answer:

1. Fuel is a substance that is used in day-to-day life and burned to generate energy.
2. Fuels such as coal, wood, oil, gas provide energy when burned.
3. Fuels are found in solid, liquid or gaseous state.

Question 4.
Which natural resources do we use as fuels?
Answer:
We use coal, mineral oil and natural gas as fuels.

Question 5.
What is meant by forests?
Answer:
An extensive area of land covered by a variety of plants is called a forest. A forest is a natural habitat of plants, animals and microbes.

Question 6.
What are the uses of forests?
OR
Write short note on forest and its uses.
Answer:

1. A forest is a natural habitat of plants, animals and microbes.
2. Forest help improve and maintain the quality of environment.
3. Forest helps in prevention of soil-erosion, help to control floods, protects wild life, maintains the balance of atmospheric gases.
4. We get many medicinal plants from forest which help in treatment of various diseases.
5. Examples Adulsa, Bel, Neem, periwinkle, amla tulsi, cinnamon.
6. We also get wood, firewood from trees like teak, mahogani, neem, sababhul. Wood is useful for making furniture, farming implements, in construction work.
7. Forest wealth includes fibres, paper, rubber, gum and aromatic substances.
8. We get fragrant essential oils from lemon grass, vanilla, kewada and eucalyptus.
9. They are used for making soaps, cosmetics and incense sticks. We get various fruits, bulbs, roots, honey, sealing wax, catechu dyes etc. from forest.

Question 7.
Are minerals to be found in seas and on the seabed as they are found inside the earth?
Answer:
Yes, there are very large reserves of tin chromium, phosphates, copper, zinc, iron, lead, manganese, sulphur, uranium etc. in the ocean and seabed.

Question 8.
How is mineral oil formed?
Answer:

1. Mineral oil is the liquid fuel formed by the decomposition of organic substances buried underground.
2. Millions of years ago, bodies of dead sea organisms sank to the bottom of the sea.
3. Layers of soil and sand collected on them.
4. Due to high pressure and temperature the remains of the dead organisms were transformed into mineral oil.
5. The underground mineral oil is extracted through oil wells.

Use your brain power!

Question 1.
Why are all minerals not ores?
Answer:

1. Minerals that contain a high proportion of metal are called ores.
2. Majority of the metals occur in the form of compounds called ores.
3. But all minerals are not ores.
4. Few metals like gold, silver, copper, platinum and bismuth occur in free state in nature. So all minerals are not ores.

Question 2.
What is meant by metal mineral and non¬metal mineral?
Answer:

1. Metal-minerals contain metallic elements in their chemical formula. So they are called metal-minerals, for example, iron, copper, gold, silver etc.
2. They contain metal in raw form.
3. Non-metallic minerals do not contain metal elements in their inorganic chemical formula Example, Clay, Diamond, Dolomite, Gypsum, Mica, Quartz.

Question 3.
Why is mineral oil called ‘liquid gold’?
Answer:
Because of its high price and value and its economic need, the mineral oil is called liquid gold. It’s reserve is less and demand is more.

Question 4.
Why is coal called black gold?
Answer:

1. Coal is a storehouse of carbon. Coal is used as a fuel, in thermal power plants as well as to run boilers and railway engines.
2. It is used as a fuel for cooking and for baking bricks in kilns on a large scale.
3. The gaseous fuels, producer gas and water gas are obtained from coal.
4. Coal as an energy resource, contributes greatly to industrial development.
5. As coal is black in colour and worth a lot of money just like gold, it is called black gold.

Question 5.
What would happen if underground mineral resources are exhausted?
Answer:

1. Coal, petroleum and other mineral are all non-renewable sources of energy.
2. The reserve is less and demand is more. They would get exhausted one day.
3. If such a situation occurs, we will not get electricity.
4. All our household and industries depend on electricity.
5. Transportation and household items, and food items would become very costly.
6. The survival of human life will be ver\ difficult.

Question 6.
Why is natural gas an eco-friendly fuel?
Answer:

1. Natural gas is an important source of energy which is eco-friendly because of its low carbon dioxide emission.
2. When burned it produces 45% less CO₂ than coal, 30% less than oil, and about 15% less than wood.
3. It does not produce carbon monoxide, sulphur dioxide or airborne particles, all of which are harmful to human and animal health.
4. It is referred as the clean energy source and is fuel for the present century as it does not ‘ pollute the atmosphere or contribute to global warming.

Question 7.
What useful things will we have to do without if rubber is no longer available?
Answer:

1. Rubber has played a largely hidden role in global environment history for more than 150 years.
2. In industries, rubber is needed to connect and protect all moving parts of machines.
3. Native people used rubber for rubber boots.
4. Household uses rubber in everything viz dish washing gloves, toys, jar seals, tyres in vehicles.
5. Welcome mat at the door, Boots, raincoats, mattress cushions, earplugs, hot water bottles, surgical tubing and gloves, in labs, birth control device.
6. In schools rubber bands, erasers, mouse pads, key board, rolling chair wheels. Head phone pads, rubber stamps are useful items used in schools and offices.

Question 8.
What are the adverse effects of clearing of forest or cutting down trees?
Answer:

1. Clearing of forest is also called Deforestation.
2. Removal or cutting down of trees has resulted in damage to habitat, biodiversity loss and aridity.
3. If has adverse impacts on concentration of atmospheric carbon dioxide. (Trees use up carbon dioxide from the atmosphere for the process of photosynthesis.)
4. Deforestation is a main contributor to global warming. Major cause of enhanced greenhouse effect. Deforestation cause carbon dioxide to linger in the atmosphere.
5. Deforestation reduced the content of water in the soil and ground water and atmospheric moisture, because trees extract ground water through the roots and release it into the atmosphere.
6. When a part of forest is removed the trees no longer transpire this water, resulting in much drier climate.
7. Due to deforestation soil erosion and flooding, landslide problems occur.
8. Deforestation results in decline in biodiversity, on a natural global scale is known to cause the extinction of many species.
9. Forest is habitat for wild life, and many medicinal plants. If forests are removed it will affect wild life and also we will not get medicinal plants.

Find out:

Question 1.
How did the various ages of the prehistoric period get their names on the basis of the uses of metals.
Answer:
1. The three-age system in history archaeology, and physical anthropology is a methodological concept adopted during the 19th century by which artifacts and events of late prehistory and early history could be ordered into a recognizable chronology.

2. Initially developed by C. J. Thomson, director of the Royal Museum of Nordic Antiquities, Copenhagen – as a means to classify the museum’s collection according to whether the artifacts were made of stone, bronze or iron.

3. Depending-upon the use of stone, bronze, iron, that period was known as stone age, bronze age, and iron age, respectively.

Answer the following:

Question 1.
Write down the difference between Metal minerals and Non-metallic minerals.
Answer:

Metal minerals	Non-metallic minerals
1. Metal minerals contain metal in raw form.	1. Non-metallic minerals do not contain metal.
2. These metals are generally associated with igenous rocks.	2. These metals are generally associated with sedimentary rocks.
3. They are usually hard and have shine of their own.	3. They are not usually hard, have no shine of their own.
4. e.g. Iron, copper tine, bauxite.	4. e.g. Salt, coal, mica, clay.

Question 2.
Write down the different types of coal.
Answer:
Peat, lignite (brown coal), bituminous coal and anthracite are various types of coal.
Anthracite is the coal of the highest grade.

Question 3.
Write down the characteristics of Compressed Natural Gas.
Answer:
Characteristics of CNG:

1. Catches fire easily.
2. No solid waste remains after combustion.
3. Carbon dioxide and water are formed in small quantities.
4. Other pollutants are not produced.
5. Can be transported easily.
6. Combustion can be controlled easily.

Observe the pictures and answer the question.

Question a.
What is the process shown in the given picture?
Answer:
The process shown is formation of mineral oil and natural gas.

Question b.
Explain the process.
Answer:

1. Mineral oil is the liquid fuel formed by the decomposition of organic substances buried underground.
2. Millions of years ago, bodies of dead sea organisms sank to the bottom of the sea.
3. Layers of soil and sand collected on them.
4. Due to high pressure and temperature the remains of the dead organisms were transformed into mineral oil.
5. The underground mineral oil is extracted through oil wells.

Question c.
What are the gaseous substances formed in the above process?
Answer:
Natural gas is also formed along with mineral oil. It contains methane, ethane, propane and butane gases.

Question d.
When the products of the process is refined, what other components are produced?
Answer:
When mineral oil is refined by fractional distillation products produced are petrol, diesel, kerosene, naphtha lubricating oil, tar, etc.

7th Std Science Questions And Answers:

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• Changes – Physical and Chemical Class 7 Questions And Answers
• Elements, Compounds and Mixtures Class 7 Questions And Answers
• Materials We Use Class 7 Questions And Answers
• Natural Resources Class 7 Questions And Answers
• Effects of Light Class 7 Questions And Answers
• Sound: Production of Sound Class 7 Questions And Answers
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• In the World of Stars Class 7 Questions And Answers

Balbharti Maharashtra State Board Class 7 Science Solutions Chapter 20 In the World of Stars Notes, Textbook Exercise Important Questions and Answers.

Std 7 Science Chapter 20 In the World of Stars Question Answer Maharashtra Board

Class 7 Science Chapter 20 In the World of Stars Question Answer Maharashtra Board

1. Write the proper words in the blanks:
(meridian, horizon, twelve, nine, apparent, celestial, ecliptic)

Question a.
When seen from a great distance, the sky seems to be touching the ground along a circle. This circle is called the …………… .
Answer:
horizon

Question b.
The ………….. is used while defining the zodiac sign.
Answer:
meridian

Question c.
Classified according to seasons, one season will have ………… nakshatras.
Answer:
nine

Question d.
The rising of the sun in the east and its setting in the west is the ………. motion of the sun.
Answer:
apparent

2. A star rises at 8 pm. tonight. At what time will it rise after a month? Why?

Question a.
A star rises at 8 pm. tonight. At what time will it rise after a month? Why?
Answer:

1. Str s rise and set 4 minutes earlier every day. If star rises at 8 pm tonight, it will rise at 7:56 pm tomorrow.
2. It will rise at 5:24 pm after a month.
3. The sun and the moon are seen to move from the west to the east against the background of stars.
4. The sun moves through one degree every day and the moon through 12 to 13 degrees.
5. This happens due to the motion of the earth around the sun and the moon around the earth which affects the duration of the stars and shortens its time period.

3. What is meant by “The sun enters a nakshatra?” It is said that in the rainy season the sun enters the mrug nakshatra. What does it mean?

Question a.
What is meant by “The sun enters a nakshatra?” It is said that in the rainy season the sun enters the mrug nakshatra. What does it mean?
Answer:

1. When we look at the sun we see not only the sun but also constellation behind the sun.
2. The constellation cannot be seen in bright sunlight but it is indeed present behind the sun.
3. As the earth changes its position, a different constellation or zodiac sign or raashi appears behind the sun.
4. This is what we express when we say that the sun enters a particular zodiac sign or raashi.
5. In rainy season due to the perceived motion of the sun, it enters mrug nakshatra and that is how it is expressed.

4. Answer the following questions. 

Question a.
What is a constellation?
Answer:
A group of stars occupying a small portion of the celestial sphere is called a constellation.

Question b.
What points should be considered before a skywatch?
Answer:

1. The place for sky watching should be away from the city and as far as possible it should be new moon night.
2. Binoculars or telescopes should be used for skywatch.
3. Identifying the pole star in the north makes the skywatch easier. Hence the pole star should be used as a reference point for skywatch.
4. As the stars in the west set early, sky watching should begin with stars in the west.
5. (a) On a sky map, the north and south are towards the bottom and top of the map respectively, (b) This is because the sky map is to be held overhead in such a way that the direction we face is at the bottom side.

Question c.
It is wrong to say that the planets, stars and nakshatras affect human life. Why?
Answer:

1. Science has proved that the constituents of the solar system e.g. planets, satellites and comets as also distant stars and constellations do not have any influence on human life.
2. Man has stepped on the moon and will conquer Mars in the 21st century.
3. Hence, in this age of science, holding on to beliefs which have been proved wrong by numerous scientific tests, is an unnecessary waste of time and energy.
4. It is important to consider all these issues with a scientific frame of mind.

5. Write a paragraph on the birth and life cycle of stars using following figure.

Question a.
Write a paragraph on the birth and life cycle of stars using following figure.
Answer:
Stars are born out of nebulae. Nebulae are clouds made up mainly of hydrogen gas and dust particles which are attracted towards one another by the force of gravity, (i) As a result of pressure, the internal temperature increases and the cloud becomes dense and spherical in shape, (ii) From the diagram, life cycle of two stars can be explained.

(a) Ordinary star: (i) The ordinary star forms a Red giant star at the later stage of its evolution when it runs out of hydrogen gas at its core. (ii) At the end stage of its life it forms a white dwarf. Stars like the sun become white dwarf when its nuclear fuel is totally exhausted. (iii) It is 1% in diameter of its original size.

(b) Massive Star: (i) Massive star forms Red super giant star at the end of its life cycle, (ii) They are also called super red giants with a relatively cool outer surface, (iii) Supernova is the explosive death of the star of the end of its life with the brightness of 100 million stars in a short amount of time, (iv) A neutron star is the dense core of the supernova. (v) It is the smallest and the densest star known to exist with a 10 km radius, (vi) Neutron stars sometimes end as a black hole, (vii) Black holes are not seen from telescopes and are identified by their intense gravitational pull where even light cannot escape.

Project:

Question a.
Visit a planetarium, collect information and present it in your school on Science day.

Class 7 Science Chapter 20 In the World of Stars Important Questions and Answers

Fill in the blanks:

Question 1.
The different group of stars is known as ………….. .
Answer:
constellation

Question 2.
The pole star is ………….. .
Answer:
North star

Question 3.
The moon moves around the earth in about ………….. days.
Answer:
27 days

Question 4.
The celestial objects are ………….. .
Answer:
The stars

Question 5.
The star that lies close to the aris of rotation of the earth ………….. .
Answer:
Pole star

Question 6.
The definite elliptical path in which a planet revolves around the sun is called ………….. .
Answer:
Orbit

Question 7.
Our earth as well as the sun belongs to the galaxy which has a spiral shape called ………….. .
Answer:
milky way

Question 8.
………….. is made up of five bright stars which are distributed along the figure of the letter M.
Answer:
Sharmishtha

Question 9.
The pole star has ……………. on one-side and ……………… on the other.
Answer:
Saptarashi, Sharmishtha

Question 10.
The continuous empty space between the planets and stars in the sky is called ………….. .
Answer:
space

Name the following:

Question 1.
The brightest star in the nakshatra.
Answer:
Yogatara

Question 2.
The stars forming a group that has a recognizable shape.
Answer:
Constellation

Question 3.
Millions of stars and planets present in the sky forming a group.
Answer:
Milky way

Question 4.
The clouds from which stars are bom.
Answer:
Nebulae

Question 5.
Saptarshi constellation in English.
Answer:
Great Bear

Question 6.
The festival celebrated when sun enters Makar raashi.
Answer:
Makara Sankranti

Question 7.
The brightest star in the Orion constellation.
Answer:
Sirius

State whether the following statements are True or False. Correct the false statements:

Question 1.
The hydrogen gas and dust particles in a nebulae are attracted towards each other by gravity.
Answer:
True

Question 2.
While standing on the ground, the celestial sphere exactly below our feet is called the Zenith.
Answer:
False. The point on the celestial sphere exactly above our head is called the Zenith

Question 3.
The circle describing the apparent motion of the earth around the sun is called the ecliptic.
Answer:
False. Ecliptic is the apparent motion of sun around the earth

Question 4.
Vrushchik or Scorpio is a constellation with 10 to 12 stars.
Answer:
True

Question 5.
Makar raashi is also known as Capricorn zodiac sign.
Answer:
True

Match the following:

Question a.

Column ‘A’	Column ‘B’
1. Saptarshi	a. Divided into 88 constellations
2. Mmg nakshatra.	b. In the north direction.
3. Orion	c. Group of 7 bright stars (kite)
4. Vrushchik	d. Made up of 5 bright stars (M)
5. Pole star	e. 7 – 8 stars.
6. Celestial sphere	f. Group of 10 -12 stars

Answer:

Column ‘A’	Column ‘B’
1. Saptarshi	c. Group of 7 bright stars (kite)
2. Mmg nakshatra.	d. Made up of 5 bright stars (M)
3. Orion	e. 7 – 8 stars.
4. Vrushchik	a. Divided into 88 constellations
5. Pole star	b. In the north direction.
6. Celestial sphere	f. Group of 10 -12 stars

Answer in one line:

Question 1.
In which direction stars move in the sky except polar star?
Answer:
When seen from earth, stars appear to move from east to west.

Question 2.
What activity does IUCAA carry out?
Answer:
IUCAA which is present in PUNE carries out fundamental research in astronomy.

Question 3.
Define constellation.
Answer: A group of stars occupying a small portion of the celestial sphere is called constellation.

Question 4.
What is Nakshatra?
Answer:
The moon completes one revolution around the earth in approximately 27 days. The portion celestial sphere traversed by the moon in one day is called a nakshatra.

Question 5.
What is yogatara?
Answer:
A nakshatra is known from the brightest star that it contains. The brightest star is called the yogatara.

Define the following:

Question 1.
Horizon
Answer:
Far away the sky seems to be touching the ground. The line at which they meet is caled horizon.

Question 2.
Zenith
Answer:
While standing on the ground the point on the celestial sphere exactly above our head is called the Zenith.

Question 3.
Nadir
Answer:
While standing on the ground the point on the celestial sphere exactly below our feet is called the nadir.

Question 4.
Meridian
Answer:
The great circle which passes through both the celestial poles and the observer’s zenith and nadir is called a meridian.

Question 5.
Celestial equator
Answer:
If we uniformly expand earth’s equator in all directions indefinitely, it will penetrate the celestial sphere along a circle. This circle is known as the celestial equator.

Question 6.
Ecliptic
Answer:
The earth moves around the sun, but seen from the earth, the sun appears to move along a circle on the celestial sphere. This circle describing the apparent motion of the sun around the ‘ earth is called the ecliptic.

Question 7.
Zodiac sign
Answer:
The ecliptic has been imagined to divided into 12 equal parts. Each part subtends 30 degrees at the centre of the celestial sphere. Each of these part is called a raashi or zodiac sign.

Question 8.
Mrug Nakshatra or Orion
Answer:
It has 7 – 8 starts of which four are at the comers of quadrangle. The line passing through the three middle stars of the constellation when extended meets a very bright star. This is Vyadh or Sirius.

Find out.

Answer the following questions

Question 1.
Using a Marathi calendar collect information about 27 nakshatras, and divide them into the following 3 categories.
(i) Monsoon Nakshatra (ii) Winter Nakshatra (iii) Summer Nakshatra
Answer:
27 nakshtras: Ashwini, Bharani, Krittika, Rohini, Mrigashirasha, Ardra, Punarvasu, Pushya, Ashlesha, Magha, PurvaPhalguni, Uttara Phalguni, Hasta, Chitra, Swati, Vishakha, Anuradha, Jyeshtha, Mula, Purva Ashadha, Uttara Ashadha, Abhijit, Shravana, Dhanishtha, Shatabhishta, Purva Bhadrapada, Uttara Bhadrapada, Revati

Monsoon Season	Winter Season	Summer Season
Ashwini Karthe	Krittika	Visakha
Bharani Karthe	Rohini	Anuradha
Arudra Karthe	Mrigashirsha	Jyeshtha
Pushyani	Ardra	Mula

Aslesha	Punarvasu	Purva Ashadha
Magha		Uttara Ashadha
Purva Phalguni		Shravana
Uttara Phalguni
Chitra
Hasta

Question 2.
Write the difference between constellations Saptarshi and Mrug nakshatra
Answer:

Saptarshi	Mrug nakshatra
1. It is made up of five bright stars which are distributed along the figure of the letter M.	1. It is made up of seven-eight stars of which four are at the corners of a quadrangle.
2. Pole star is the brightest star in the constellation.	2. Sirius is the brigh jveutr0n Starie constellation.
3. It is on the meridian in the month of April and in the month of October.	3. It is on the meridian in the month of February and in June.
4. In English, it is called the Great Bear.	4. In English, it is called Orion.

Question 3.
Draw sketches to show the relative position of prominent stars in Ursa major and Orion.
Answer:
a. Ursa major (Saptarshi) appears like a big dipper, (or kite shape). There are 3 bright stars in the handle and 4 stars in the bowl of the dipper. (It can be seen during April in summer in northern skies).

(b) Orion appears like a hunter. Three bright stars appear in the belt, 5 bright stars are arranged in the form of a quadrilateral. (It is visible during winter in the northern skies)

Question 4.
Why is the pole star important for sky watch?
Answer:

1. Identifying the Pole Star in the north makes the sky watch easier. Hence the pole star should be used as a reference point for skywatch.
2. If we extend one side of the quadrangle of Saptarshi, it reaches the Pole Star.
   The pole star has Saptarshi on one side and Sharmishtha on the other.

Question 5.
What is the relation between the pole star and the constellations Saptarshi and Sharmishtha?
Answer:

1. Saptarshi is in the shape of a quandrangle with a tail made up 3 stars resembling a kite. If we extend one side of the quadrangle it reaches the Pole Star.
2. The constellations of Saptarshi and Sharmishtha are useful in locating the Pole Star.
3. The perpendicular bisector of the line joining the third and fourth stars in Sharmishtha goes towards the Pole star.
4. The Pole Star has Saptarshi on one side and Sharmishtha on the other.

Use your brain power!

Answer the following questions.

Question 1.
One Zodiac Sign = ………….. nakshatras
Answer:
27 nakshatras. Each nakshatra is divided in padas or charan. Every nakshatra has 4 padas. These 27 nakshatra complete the entire circle of 360° of zodiac.
The zodiac comprises of 360°.

Question 2.
Is sun the only star present in our Milky Way galaxy?
Answer:
No. Sun is not the only star present in the Milky Way. There are lakhs of stars in the Milky Way, some of them being many times bigger than our sun. Some of them have their own planetary systems with a great diversity in colour, brightness, as well as size.

7th Std Science Questions And Answers:

• Cell Structure and Micro-organisms Class 7 Questions And Answers
• The Muscular System and Digestive System in Human Beings Class 7 Questions And Answers
• Changes – Physical and Chemical Class 7 Questions And Answers
• Elements, Compounds and Mixtures Class 7 Questions And Answers
• Materials We Use Class 7 Questions And Answers
• Natural Resources Class 7 Questions And Answers
• Effects of Light Class 7 Questions And Answers
• Sound: Production of Sound Class 7 Questions And Answers
• Properties of a Magnetic Field Class 7 Questions And Answers
• In the World of Stars Class 7 Questions And Answers

Balbharti Maharashtra State Board Class 7 Science Solutions Chapter 8 Static Electricity Notes, Textbook Exercise Important Questions and Answers.

Std 7 Science Chapter 8 Static Electricity Question Answer Maharashtra Board

Class 7 Science Chapter 8 Static Electricity Question Answer Maharashtra Board

1. Choose the correct option and fill in the blanks.
(always repulsion, always attraction, displacement of negative charge, displacement of positive charge, atom, molecule, steel, copper, plastic, inflated balloon, charged object, gold)

Question a.
There is ………….. between like charges.
Answer:
always repulsion

Question b.
…………. is responsible for generation of electric charge in an object.
Answer:
displacement of negative charge

Question c.
A lightning conductor is made of a ……………… strip.
Answer:
copper

Question d.
……………… does not get electrically charged easily by rubbing.
Answer:
Steel

Question e.
There is …………………. when opposite electric charges come near each other.
Answer:
always attraction

Question f.
A ……………… canbe detected with an electroscope.
Answer:
charged object

2. Explain why it is not safe to go out with an umbrella when there is heavy raine lightning or thunder.

Question a.
Explain why it is not safe to go out with an umbrella when there is heavy raine lightning or thunder.
Answer:
Large amount of charges get built up in the clouds in rainy and stormy weather.

1. Sometimes these charges are transferred to the earth in the form of a bolt of lightning.
2. Wire of umbrella is made up of metal and cloth is made up of synthetic material.
3. If lightning strikes, then umbrella catches it and there are chances of fire and it would be dangerous.
4. So it is not safe to go out with an umbrella when there is heavy rain.

3. Answer in your own words.

Question a.
How will you protect yourself from lightning?
Answer:

1. To protect from the lightning, we have to put lightning conductor on high rise buildings,
2. we should not stand under a tree in rainy and stormy weather.
3. We should not go out with an umbrella in heavy rain, lightning or thunder.

Question b.
How are charges generated?
Answer:

1. Friction causes a charge to develop, because on rubbing, some negative particles are transferred from one substance to the other and the later develops a negative charge.
2. The substance from which particles are removed lose negative charge and hence, it develops a positive charge.

Question c.
In the lightning conductor, what provision is made for spreading the electricity into the ground?
Answer:

1. The lightning conductor, consists of a long i copper strip with one end forked. This end is ‘ at the highest part of the building.
2. The other end of the strip is connected to a plate of cast iron.
3. A pit is dug in the ground, coal and salt are filled into the pit and the iron plate is placed upright in the pit.
4. There is also a provision for pouring water into it.
5. This helps to spread the electric charge quickly into the ground.

Question d.
Why do farmers stick an iron staff into the ground while working in the field in rainy conditions?
Answer:

1. Large amount of charges get built up in the clouds in rainy and stormy weather.
2. Sometimes these charges are transferred to the earth in the form of a bolt of lightning.
3. Due to iron staff, the charges will be conducted to the earth through iron metal and spread quickly into the ground.
4. This way farmers are saved from lighting strike.

Question e.
Why is lightning not seen every day during the rainy season?
Answer:

1. When air and clouds rub against each other in the sky the upper part of some clouds becomes positively charged and the lower side become negatively charged.
2. When this negative charge at the bottom of the cloud becomes much larger than the charge on the ground, it starts flowing towards the ground in stages, but this doesn’t happen every day. So lightning is not seen every day during the rainy season.

4. What are the characteristics of a static electric charge?

Question a.
What are the characteristics of a static electric charge?
Answer:
Following are the characteristics of a static electric charge.

1. The electric charge generated by friction is called frictional electricity. This charge is produced only at the place of friction, hence it is called static electricity.
2. It remains on the object for a short duration.
3. The charges of static electricity are absorbed in moist air.
4. An electrically charged object attracts another object which has no electric charge.
5. Like charges repel each other.
6. Unlike charges attract each other.
7. Repulsion is the sure test of the existence of a static charge.

5. What is the damage caused by lightning? How will you ereate awareness to prevent it?

Question a.
What is the damage caused by lightning? How will you ereate awareness to prevent it?
Answer:
Due to lightning great damage can occur.

1. It may cause fire.
2. Person on whom lightning strikes may die also.
3. It causes more temperature than sun.

Awareness to prevent it:

1. Guide the people to install lightning conductor on tall buildings.
2. Do not stand on open ground, below a tree, or on a high location during the thunder storms.
3. Do not use plugged in electrical appliances.
4. Do not stand near an electric pole, telephone pole or a tower.
5. Stay in pucca house made of brick and cement.
6. Stand on only wood, a plastic sheet or sack of jute.

Project:

Question a.
Make an electroscope yourself by using a thin aluminium foil and check which substances become electrically charged.

Class 7 Science Chapter 8 Static Electricity Important Questions and Answers

1. Choose the correct option and fill in the blanks.
(always repulsion, always attraction, displacement of negative charge, displacement of positive charge, atom, molecule, steel, copper, plastic, inflated balloon, charged object, gold)

Question 1.
named the electric charges as positive charge and negative charge.
Answer:
Benjamin Franklin

Question 2.
Each atom contains a stationary charge and moving charges.
Answer:
positive, negative

Question 3.
Each atom is electrically
Answer:
neutral

Question 4.
Amber is called in the Greek language.
Answer:
electron

Question 5.
The charges of electricity are absorbed in moist air.
Answer:
static

Question 6.
Electrically charged objects uncharged objects.
Answer:
attract

Question 7.
is used as a test for identifying an electrically charged object.
Answer:
Repulsion

Question 8.
The property of amber to attract things was named electricity by in 1646 AD.
Answer:
Thomas Brown

Question 9.
The electric charge generated by stays only as long as the charged object is near to it.
Answer:
induction

Question 10.
A simple device is used to detect the electric charge on an object.
Answer:
gold leaf electroscope

Question 11.
Lightning is a form of
Answer:
electric charge

Question 12.
The gas protects us from the harmful ultra violet rays coming from the sun.
Answer:
ozone

Question 13.
The is a device used for protection from a lightning strike.
Answer:
lightning conductor

Question 14.
Due to the energy of the lightning, the oxygen in the air is converted into
Answer:
ozone

2. Match the columns:

Question a.

Column ‘A’	Column ‘B’
1. Like charges	a. gold leaf electroscope
2. Unlike charges	b. lightning conductor
3. Copper strip	c. attraction
4. Gold leaves.	d. repulsion

Answer:

Column ‘A’	Column ‘B’
1. Like charges	d. repulsion
2. Unlike charges	c. attraction
3. Copper strip	b. lightning conductor
4. Gold leaves.	a. gold leaf electroscope

Say whether true or false, correct and rewrite the false statement:

Question 1.
Charges cannot be transferred from one body to another.
Answer:
False. Charges can be transferred from one body to another

Question 2.
The word ‘electricity.’ came from the word ‘Elektron’.
Answer:
True

Question 3.
When an inflated balloon is rubbed on silk, it develops a charge.
Answer:
True

Question 4.
An ebonite rod rubbed on woollen cloth develops a positive charge.
Answer:
False. An ebonite rod rubbed on woollen cloth develops a negative charge

Question 5.
A glass rod rubbed on woollen cloth develops a negative charge.
Answer:
False. A glass rod rubbed on woollen cloth develops a positive charge

Question 6.
If the leaves of the electroscope spread only a little, the charge on them is less.
Answer:
True

Question 7.
An atom may have either a positive or a negative charge.
Answer:
False. An atom does not have any charge

Question 8.
When two substances are rubbed on each other, like charges are developed on each.
Answer:
False. When two substances are rubbed on each other unlike charges are developed on each

Question 9.
High rise buildings have lightning conductors.
Answer:
True

Question 10.
It is dangerous to stand under a tree in rainy and stormy weather.
Answer:
True

Give scientific reasons:

Question 1.
Ordinarily, an atom does not have any charge.
Answer:

1. Every atom contains smaller particles with either positive or negative charge.
2. As the number of positively and negatively charged particles in an atom is equal, they neutralize each other.
3. As a result the atom has no charge.

Question 2.
Charge cannot be developed on a copper rod.
Answer:
Charge cannot be developed on a copper rod because only certain pairs of substances give rise to electric charge, on rubbing.

Question 3.
High rise buildings have lightning conductors.
Answer:

1. High rise buildings are prone to lightning strikes during the monsoon.
2. When lightning strikes, a tremendous electric charge is transferred to the earth, which may damage the tall buildings.
3. To prevent this, high rise buildings have a forked metal rod, called a lightning conductor fitted on the top of the building.
4. The lower end of this rod is buried inside the earth.
5. If lightening strikes, the electric charge passes through this conductor and goes in to the earth. In this way the building is saved from damage.

Question 4.
It is dangerous to stand under a tree in rainy and stormy weather.
Answer:

1. Large amount of charges get built up in the clouds in rainy and storming weather.
2. Sometimes these charges are transferred to the earth in the form of a bolt of lightning.
3. Generally lightning strikes tall buildings and trees. If lightning strikes a tree then either the tree may fall or it may catch fire.
4. In both cases this would be dangerous for anyone standing under the tree, hence it is dangerous to stand under a tree in rainy and stormy weather.

Question 5.
Repulsion is a test used for identifying an electrically charged object.
Answer:

1. When a charged object is brought near a neutral object, it gets attracted when two oppositely charged objects are brought close, they get attracted. Therefore, attraction is not a test.
2. But when two like charges are brought close only then repulsion takes place.
3. Therefore, repulsion is the sure test for identifying an electrically charged object.

Question 6.
Mustard seeds when shaken vigorously in a glass bottle stick to the sides of the bottle.
Answer:
When seeds are shaken they get electrically charged and therefore they stick to the neutral walls of the glass.

Answer the following:

Question 1.
Why is the charge developed due to friction called static electric charge?
Answer:
The charge developed due to friction is called 1 static electric charge because the charge remains still on the object.

Question 2.
Why does the charge developed by induction disappear quickly?
Answer:
The charge developed by induction disappears quickly because it is very weak.

Question 3.
Why do the leaves of a gold leaf electroscope fly apart when a charged body touches its disc?
Answer:
The leaves of a gold leaf electroscope fly apart when a charged body touches its disc because like charges develop on both the leaves and hence they repel each other.

Draw a neat labelled diagram of Gold leaf electroscope and describe it.

Answer:

1. This is a simple device to detect the electric charge on object.
2. It consists of a copper rod which has a metal disc at the upper end and two thin gold leaves at the other.
3. The rod is placed in a bottle so that the disc is above the bottle.
4. When an uncharged object is taken near the disc, the leaves remain closed.
5. When a charged object is taken near the disc, both the leaves are charged by the same electric charge, and repel each other.
6. When we touch the disc with our hand, the leaves collapse because the charge in the leaves goes into the earth through our body, and the leaves get discharged.

Use your brainpower:

Question 1.
Do all the objects get charged by rubbing?
Answer:
No. Only certain pairs of substances get charged on rubbing.

Question 2.
Why does a charged balloon stick to a wall?
Answer:
A charged balloon stick to a wall because there is always attraction between a charged object and an uncharged object.

Question 3.
Can we use leaves of some other metal instead of gold, in the electroscope? Which properties must that metal have?
Answer:
We can use other metals than gold in gold leaf electroscope.

1. Only thing is that metal should be malleable and good conductor of electricity.
2. But the best is gold only because we can make extremely thin leaves of gold so even very small charge also can be detected.

Question 4.
What kind of damage is caused by a lightning strike?
Answer:
Due to lightning strike, great damage can occur. It may cause forest fire and burn down things. Person on whom lightning strikes may die. It causes more temperature than sun.

Question 5.
What measures will you take to prevent the damage caused by lightning?
Answer:
Following measures can be taken to prevent the damage caused by lightning:

1. Always put lightning conductor on tall buildings.
2. Do not stand on open ground, below a tree or near the electric or telephone pole during rain/ thunder storms.
3. Do not lean on wired fences.
4. Do not use plugged in electrical appliances.
5. Do not swim during thunder storms.
6. Stay in a pucca house with lightning conductor fitted on it.

Question 6.
Why is the upper end of the lighting conductor pointed?
Answer:

1. The pointed end makes it possible to increase the electric field near the point. The electric field set up at pointed end is high.
2. If the discharge of cloud occurs it would be easily passed through the lightening conductor to the ground and damage to the building is averted.

Question 7.
Why is coal and salt added to the pit in the ground?
Answer:
Coal and salt is filled in the pit and also there is a provision for pouring water into it. This helps to spread electric charge quickly into ground and prevent damage.

Observe the given diagram and answer the questions given.

Question a.
Name the phenomenon happening in the diagram and define it
Answer:
Phenomenon happening is static electricity.
When certain objects are rubbed against each other, they produce an electric charge on their surface at the place of friction. This is due to electrons which remain for a short time. This is called static electricity.

Question b.
What do you observe in “b” and “c” part of the diagram?
Answer:
In ‘b’, we observe attraction between the charged balloon and the uncharged aluminium ball. In ‘c’, we observe that the charge has been transferred to the aluminium ball and due to the same (like) charge, repulsion is observed.

7th Std Science Questions And Answers:

• The Living World: Adaptations and Classification Class 7 Questions And Answers
• Plants: Structure and Function Class 7 Questions And Answers
• Properties of Natural Resources Class 7 Questions And Answers
• Nutrition in Living Organisms Class 7 Questions And Answers
• Food Safety Class 7 Questions And Answers
• Measurement of Physical Quantities Class 7 Questions And Answers
• Motion, Force and Work Class 7 Questions And Answers
• Static Electricity Class 7 Questions And Answers
• Heat Class 7 Questions And Answers
• Disaster Management Class 7 Questions And Answers

Balbharti Maharashtra State Board Class 6 Science Solutions Chapter 10 Force and Types of Force Notes, Textbook Exercise Important Questions and Answers.

Std 6 Science Chapter 10 Force and Types of Force Question Answer Maharashtra Board

Class 6 Science Chapter 10 Force and Types of Force Question Answer Maharashtra Board

1. Choose the term and fill in the blanks:

Question a.
……….. has to be applied to change the ……….. of a ……….. object.
(moving, direction, force)
Answer:
force, direction, moving

Question b.
When an elephant drags a wooden log over the land, the forces that are applied on the log are …………., ………. and …………. .
(muscular force, mechanical force, gravitational force, frictional force)
Answer:
muscular force, gravitationalforce, frictionalforce.

Question c.
A ball was set rolling on a large table. If its …….. has to be changed, a ……….. will have to be applied on it.
(force, motion, gravitation)
Answer:
motion, force

Question d.
The force of friction always acts ……….. the motion.
(along, against)
Answer:
against

2. Match the following:

Question a.

Column ‘A’	Column ‘B’
1. An ox pulling a cart	a. Magnetic force
2. Lifting heavy iron object with a crane	b. Electrostatic force
3. Weighing with a spring balance	c. Muscular force
4. Applying brakes to a bicycle.	d. Gravitational force
5. Picking up pieces of paper with a plastic scale.	e. Frictional force

Answer:

Column ‘A’	Column ‘B’
1. An ox pulling a cart	c. Muscular force
2. Lifting heavy iron object with a crane	a. Magnetic force
3. Weighing with a spring balance	d. Gravitational force
4. Applying brakes to a bicycle.	e. Frictional force
5. Picking up pieces of paper with a plastic scale.	b. Electrostatic force

3. One or more forces are acting in the following examples. Name them.

Question a.
An object falling from a tall building …………. .
Answer:
Gravitational force

Question b.
An aeroplane flying in the sky. …………. .
Answer:
Mechanical force

Question c.
Sqeezing sugarcane juice with a squeezer. …………. .
Answer:
Muscular or mechanical force

Question d.
Winnowing foodgrain …………. .
Answer:
Muscular force, gravitational force

4. Explain in your own words giving one example each.
Muscular force, gravitational force, mechanical force, electrostatic force, the force of friction and magnetic force.

Question a.
Muscular force:
Answer:
The force applied with the help of muscles is called muscular force.
e.g. When a bullock pulls the load of a cart with sugarcane, he uses the force of his muscles that is muscular force.

Question b.
Gravitational force:
Answer:
The force applied by the earth to pull the objects towards itself is called gravitational force.
e.g. When a fruit falls from a tree, it is the gravitational force of the earth that pulls the fruit.

Question c.
Mechanical force:
Answer:
The force applied by means of a machine is called mechanical force. Some machines run by muscular force while some use electricity or fuel.
e.g.Washing machine, electric pump uses electricity to work.

Question d.
Electrostatic force:
Answer:
Static electricity is produced on materials like rubber, plastic and ebonite due to friction. The force exerted by such electrically charged materials is called electrostatic force, e.g. When a plastic comb is rubbed against the dry hair, comb develops electrostatic charge.

Question e.
The force of friction:
Answer:
When two surfaces rub against each other, a force of friction is produced. This force always acts against direction of motion, e.g. A ball rolling over a flat surface stops at certain distance due to friction between the ball and the surface.

Question f.
Magnetic force:
Answer:
The force exerted by a magnet is called magnetic force.
e.g. In a pin holder, the magnet attracts the pins.

5. Why?

Question a
Machines are oiled from time to time.
Answer:
To reduce the friction between the parts of machines, they are oiled. This will help efficient working of machines.

Question b.
An object thrown upwards comes down after reaching a point.
Answer:
An object is pulled by the gravitational force of the earth. Hence an object thrown upwards comes down after reaching at certain point.

Question c.
Powder is sprinkled on a carrom board.
Answer:
When powder is sprinkled on a carrom board, friction between the coin and the board decreases so that the coin can be pocketed easily.

Question d.
The ramp at a railway station has a rough surface.
Answer:
The rough surface of the ramp increases the friction between feet and the surface. This helps us to walk on the ramp without skidding or falling.

6. In what way are we different? 

Question a.
Muscular force and Mechanical force
Answer:

Muscular force		Mechanical force
1. The force applied with the help of muscles is called muscular force. e.g. A boy kicking a football.		1. The force applied by means of machine is called mechanical force. e.g. An electric pump works on electricity.
2. It is created by our muscles.		2. It is created by electricity or fuel or muscular force

Question b.
A force of friction and Gravitational force
Answer:

Force of friction		Gravitational force
1. When two surfaces rub against each other, the force of friction comes into force.		1. The force applied by the earth to pull an object towards itself, is called a gravitational force.
2. It comes to act between two surfaces.		2. It exists between two objects or an object and the earth.

7. Write answers to the following questions in your own words. 

Question a.
What are the things that can be done by applying force?
Answer:
By applying force:

1. we can set an object in motion.
2. we can stop a moving object.
3. we can change the speed or direction or both of a moving object.
4. we can change the shape of an object.

Question b.
What is meant by weight?
Answer:

1. The gravitational force acting on an object is called its weight.
2. Greater force must be applied to lift a greater weight.

Question c.
Which machines run on muscular force?
Answer:
The machines that run on muscular force are:

1. Bicycle
2. Hand cart
3. Boat
4. Cycle rickshaw
5. Stretching of a spring
6. Ball pen
7. Vegetable chopper
8. Sharpener
9. Pulley
10. Fruit peeler

8. Solve the following crossword puzzle.

Question a.
Solve the following crossword puzzle.

Down:
1. ………. force is applied to push a scooter that has failed.
2. ………. force can be used to pick up scattered pins.

Across:
3. A ………. pulls iron nails towards itself.
4. ……….. force is used when farm is ploughed with a tractor.
5. It is due to the force of ………… that raindrops fall to the ground.
Answer:

Activity:

Question 1.

Collect more information about the various forces that are used in our day-to-day life.

Question 2.
Make a list of such actions where many forces are applied simultaneously.

Class 6 Science Chapter 10 Force and Types of Force Important Questions and Answers

Choose the term and fill in the blanks:

Question 1.
When powder is sprinkled on a carrom board, friction ……….. .
(increases, decreases)
Answer:
decreases

Question 2.
Electrostatic force is due to …………. .
(gravitation, friction)
Answer:
friction

Question 3.
Fruits fall on the ground due to ………… force.
(mechanical, gravitational)
Answer:
gravitational

Question 4.
Friction between two rough surfaces is …………. than between two smooth surfaces.
(greater, lesser)
Answer:
greater

Question 5.
The sound created by a stone dropped in a bucket of water from 100 cm height is ………… than that dropped from 20 cm height.
(milder, louder)
Answer:
louder

Question 6.
A scooter has stopped in the middle of the road as the petrol tank has become empty. So Raju has to use …………. force to take it to petrol pump.
(mechanical, muscular)
Answer:
muscular

One or more forces are acting in the following examples. Name them.

Question 1.
Srikant is playing basketball
Answer:
Muscular force

Question 2.
Raju rubs a peacock feather between pages of his notebook
Answer:
Electrostatic force

Question 3.
When you rub the palm of your hands, you feel the heat on the palms
Answer:
Frictional force

Question 4.
A blacksmith uses a hammer to beat the hot piece of iron
Answer:
Muscular force

Question 5.
A cricketer hits the ball, but it stops just before the boundary line
Answer:
Frictional force

Question 6.
We can walk on the road without falling down.
Answer:
Frictional force

Give scientific reasons:

Question 1.
Magnet is used to lift heavy iron bar.
Answer:
A magnet attracts the iron bar. As a result it is easier to lift the heavy iron bar using magnetic force.

Question 2.
An inflated balloon when rubbed against a silk cloth, pulls the hair on our skin.
Answer:
When an inflated balloon is rubbed against a silk cloth, it develops electrostatic force due to friction. This force pulls the hair on our skin.

Question 3.
We are likely to slip when we walk on a oily or wet floor.
Answer:
Wet or oily floor reduces the friction between our feet and surface. Hence we are likely to slip on wet or oily floor.

Distinguish between:

Question 1.
Force of friction and Electrostatic force
Answer:

Force of friction	Electrostatic force
1. It exists between any two surfaces in contact.	1. It develops where certain objects are rubbed  against certain material.
2. No electric charge is developed, sometimes heat is developed. e.g. A brake is applied on a bicycle.	2. Electric charge is developed. e.g. Thermocol rubbed against silk cloth.

Answer the following:

Question 1.
Why do planets revolve round the sun in definite orbits?
Answer:

1. The gravitational force operates between the sun and the planets in the solar system.
2. Hence, they revolve round the sun in definite orbits.

Question 2.
Which forces are acting upon an aeroplane taking off into the sky?
Answer:
Aeroplane uses mechanical force, Pilot exerts muscular force. Frictional force between aeroplane and air, gravitational force due to weight of an aeroplane.

Question 3.
What happens to the iron nail when the magnet is taken away from it?
Answer:

1. As we take the magnet away from the iron nail, it does not attract the iron nail as magnetic force decreases.
2. Magnet is unable to exert force if the nail is not placed in the range of the magnetic field.

Question 4.
When brakes are applied while riding a bicycle, it stops after running a distance. Why?
Answer:

1. When brakes are applied while riding a bicycle, frictional force comes to act between the tyres of the bicycle and the surface.
2. This force opposes the tendency of the bicycle to stop.
3. Hence, the bicycle has to overcome this force before it stops.

Can you tell?

Question 1.
What happens when you hold the two ends of a spring and pull them apart?
Answer:
Its shape changes due to the force exerted by pull.

Question 2.
What happens when a blacksmith hammers a red hot piece of iron?
Answer:
Shape of iron piece changes.

Observe and discuss:

Observe the figures given and name the force needed for the motion.

Question 1.
Boat with boatman.

Answer:
Muscular force

Question 2.
Bullock cart.

Answer:
Muscular force

Question 3.
A tractor.

Answer:
Mechanical force

Question 4.
Sewing machine.

Answer:
Mechanical force

Question 5.
Fruit falling from tree.

Answer:
Gravitational force

Question 6.
A man carrying heavy sac.

Answer:
Gravitational force

Question 7.
A pin holder.

Answer:
Magnetic force

Question 8.
A ramp.

Answer:
Gravitational force

Question 9.
Carrom board.

Answer:
Frictional force

Question 10.
Mixer grinder.

Answer:
Mechanical force

6th Std Science Questions And Answers:

• Natural Resources – Air, Water and Land Class 6 Questions And Answers
• The Living World  Class 6 Questions And Answers
• Diversity in Living Things and their Classification Class 6 Questions And Answers
• Disaster Management Class 6 Questions And Answers
• Substances in the Surroundings – Their States and Properties Class 6 Questions And Answers
• Substances in Daily Use Class 6 Questions And Answers
• Nutrition and Diet Class 6 Questions And Answers
• Our Skeletal System and the Skin Class 6 Questions And Answers
• Motion and Types of Motion
• Force and Types of Force Class 6 Questions And Answers

Balbharti Maharashtra State Board Class 6 Science Solutions Chapter 5 Substances in the Surroundings – Their States and Properties Notes, Textbook Exercise Important Questions and Answers.

Std 6 Science Chapter 5 Substances in the Surroundings – Their States and Properties Question Answer Maharashtra Board

Class 6 Science Chapter 5 Substances in the Surroundings – Their States and Properties Question Answer Maharashtra Board

1. In the paragraph below write ‘solid’, ‘liquid’ or ‘gas’ in each of the blank (brackets) depending on the substance referred to just before.

Question a.
On a bright sunny day, Riya and Gargi are playing with a ball (…..) in the park. Gargi feels thirsty. So, Riya brings tender coconut water (…..) for her. At the same time, a strong breeze (…..) starts blowing and it also begins to rain (…..). They run back into the house (…..), change their clothes (…..) and then their mother gives them a cup (…..) of hot milk (…..) to drink.
Answer:
solid, liquid, gas, liquid, solid, solid, solid, liquid.

2. Discuss.

Question a.
Riya pours some water from her bottle into another bottle. Does it change the shape of the water?
Answer:
Yes, the shape of water changes as water is in liquid state. Liquids do not have a shape of its own. They take the shape of the container.

Question b.
Halima picks up a small stone from the ground and puts it in the water in a dish. Does the shape of the stone change?
Answer:
No, the shape of the stone does not change. Stone is a solid, hence retains its shape.

3. Write the properties of these substances.
(water, glass, chalk, iron ball, sugar, salt, flour, coal, soil, pen, ink, soap)

Question a.
Write the properties of these substances.
(water, glass, chalk, iron ball, sugar, salt, flour, coal, soil, pen, ink, soap)
Answer:
Properties of substances:

Substance	State	Properties
1. Water	Liquid	Fluidity, density, solubility, transparency, thermal conductivity.
2. Glass	Solid	Brittleness, hardness, density, transparency.
3. Chalk	Solid	Brittleness, density.
4. Iron ball	Solid	Hardness, density, malleability, ductility, electrical ductility, conductivity, thermal conductivity, luster, sonority.
5. Sugar	Solid	Brittleness, density, solubility.
6. Salt	Solid	Brittleness, density, solubility.
7. Flour	Solid	Density, solubility.
8. Coal	Solid	Brittleness, density, thermal conductivity.
9. Soil	Solid	Brittleness, density.
10. Pen	Solid	Hardness, density.
11. Ink	Liquid	Fluidity, density, solubility.
12. Soap	Solid	Brittleness, hardness, density, solubility.

4. What is sublimation? Write the names of everyday substances that sublimate.

Question a.
What is sublimation? Write the names of everyday substances that sublimate.
Answer:

1. The change of a solid substance directly into a gas or vapour without first changing into liquid is called sublimation.
2. Substances that sublimate: Camphor, napthalene balls, ammonium chloride, iodine.

5. What is made from? Why? 
a. A sickle to cut sugarcane.
b. The sheets used for roofing.
c. A screwdriver
d. A pair of tongs.
e. Electric cables.
f. Ornaments.
g. Pots and pans.

Question a.
A sickle to cut sugarcane.
Answer:
A sickle is made of iron. An iron sickle is hard and malleable. When sharpened it will be able to cut the hard sugarcane.

Question b.
The sheets used for roofing:
Answer:

1. The sheets used for roofing are made of plastic, aluminium.
2. Plastic is hard, hence, protects against weather conditions.
3. Plastic is transparent, hence, sunlight can pass through it.
4. Aluminium is hard, light weight and durable, hence, protects against all weather conditions.
5. Malleable hence formed into thin sheets.

Question c.
A screwdriver:
Answer:

1. A screwdriver is made up of iron, steel, aluminium.
2. A screwdriver possesses property of hardness hence, it easily pierces a screw in piece of wood, wall, metals etc.

Question d.
A pair of tongs:
Answer:

1. A pair of tongs are made up of iron, steel aluminium etc. Tongs are used to lift hot, boiling utensils or vessels.
2. Tongs are hard, ductile and malleable.
3. Hence, have strong grip to hold utensils.
4. Rubbers fitted on the ends will protect from thermal conduction, from bums.

Question e.
Electric cables:
Answer:

1. Electric cables are metal wires (thin) wound in plastic.
2. Metal wires possess the property of hardness, ductility, electrical conductivity.
3. Plastic /rubber covering possesses the property of hardness, elasticity and are bad conductors of heat and electricity.

Question f.
Ornaments:
Answer:

1. They are made up of metals like gold and silver.
2. They possess the property of hardness, ductility, malleability, lustre.

Question g.
Pots and pans: Answer:

1. They are used to cook food, hence metals like aluminium, steel are used.
2. They possess the property of hardness, ductility, malleability, thermal conductivity, electrical conductivity, (microwave ovens)

6. What will happen if ….? And why?

Question a.
Nails are made of plastic
Answer:
If nails are made of plastic, they will not be able to pierce through other substances on being pushed or forced by a hammer. Plastic lacks the property of hardness.

Question b.
A bell is made of wood.
Answer:

1. If a bell is made of wood it will never make a ringing sound. A wooden bell does not have the property of being sonorous.
2. Sonority is the property of metals to produce a ringing sound.

Question c.
Rubber is not fitted on a pair of tongs.
Answer:

1. Rubber is a bad conductor of heat and electricity. It will not allow heat to pass to the hands/handle of the tongs, thus protecting us.
2. Pair of tongs are made up of metals which conduct heat and electricity. They have file property of thermal conduction and electrical conduction.
3. If rubber is not fitted on a pair of tongs, we will not be able to lift hot objects with it.

Question d.
A knife is made of wood.
Answer:
Wood does not have the property of malleability. Therefore, the edge of wooden knife will be blunt. Hence, we will not be able to cut anything with it.

Question e.
An axe is made of rubber.
Answer:

1. If an axe is made of rubber, it will not be used to cut wood or tree.
2. Rubber does not have the property of hardness that is required to push through to cut it.

7. Who am I?

Question a.
I’m found in a thermometer, I measure your temperature.
Answer:
Mercury

Question b.
I make things hot or cold.
Answer:
Heat

Question c.
I have no shape whatsoever!
Answer:
Liquid, gases

Question d.
I dissolve in water, but not in kerosene.
Answer:
Salt

8. Why does this happen? 

Question a.
Coconut oil thickens in winter.
Answer:
Coconut oil is in liquid state. In winter the surrounding temperature / atmospheric temperature starts decreasing. Coconut oil starts cooling or losing heat, it changes to solid state.
Thus coconut oil thickens in winter.

Question b.
Kerosene left open in a dish disappears.
Answer:
When kerosene is left open in a dish, it is exposed to surrounding temperature. As the temperature is more, kerosene starts continuously evaporating and finally disappears.

Question c.
The fragrance of incense sticks lighted in one corner of a room spreads to the other corner.
Answer:
The fragrance of incense sticks is given out in the form of scented vapours. As vapours are in gaseous state, the gas molecules spread out in the room. The molecules of gas move very fast and there are no forces to stop them from going apart. Therefore the fragrance of incense sticks lighted in one corner of room spreads to the other corner.

Question d.
What you see in the picture.

Answer:
The mass of plastic ball is less than an apple. This difference is because of their densities. Since an apple has greater density, it will sink to the bottom on other hand the plastic ball has lesser density, it will float over water surface.

Activity: 

Question 1.
Find out how the big statues of wax are made.

Question 2.
Visit a jeweller’s shop and find out how ornaments are made.

Class 6 Science Chapter 5 Substances in the Surroundings – Their States and Properties Important Questions and Answers

Fill in the blanks:

Question 1.
The state of a substance changes if it is …………… or …………… .
Answer:
heated, cooled

Question 2.
Every substance in our surroundings is found in either the ……………, …………… or gaseous state.
Answer:
solid, liquid

Question 3.
On …………… heat, the substance changes from solid to liquid and liquid to gas.
Answer:
gaining

Question 4.
When the substance cools, or …………… heat, it changes from gaseous to liquid and liquid to solid state.
Answer:
loses

Question 5.
A …………… amount of heat must be gained or lost before the state of a substance can change.
Answer:
specific

Question 6.
When a substance gets heat, it becomes …………… and then …………… .
Answer:
warm, hot

Question 7.
If the substance is very hot, we could get …………… .
Answer:
scalded

Question 8.
A thermometer is used to measure …………… .
Answer:
temperature

Question 9.
…………… is the unit of measuring temperature.
Answer:
Degree Celsius (°C)

Question 10.
Nowadays, …………… thermometers are frequently used.
Answer:
digital

Question 11.
Solids have a shape of its …………… .
Answer:
own

Question 12.
Solids have a …………… volume.
Answer:
definite

Question 13.
Liquids take the shape of the …………… .
Answer:
container

Question 14.
Liquids have a …………… volume.
Answer:
specific

Question 15.
Air occupies all the available …………… .
Answer:
space

Question 16.
Evaporation occurs from the …………… of the water.
Answer:
surface

Question 17.
At sea-level, pure water boils at …………… .
Answer:
100°C

Question 18.
Condensation of steam takes place at …………… .
Answer:
100°C

Question 19.
The temperature of a substance can fall below …………… .
Answer:
0°C

Question 20.
Ice melts at …………… .
Answer:
0°C

Question 21.
Each substance has a specific boiling point which is also its …………… point.
Answer:
condensation

Question 22.
Each substance has a specific melting point which is the same as its …………… point.
Answer:
freezing

Question 23.
Candles are made by melting …………… wax.
Answer:
paraffin

Question 24.
Solid carbon-dioxide is …………… .
Answer:
dry ice

Question 25.
Liquid …………… is used in animal husbandry.
Answer:
nitrogen

Question 26.
Sand is melted to make …………… .
Answer:
glass

Question 27.
Iron is melted to make …………… .
Answer:
tools

Question 28.
Substances can be identified by studying their …………… .
Answer:
properties

Question 29.
Substances that break into small particles are said to be …………… .
Answer:
brittle

Question 30.
The …………… of any liquid is determined by how easily it flows.
Answer:
fluidity

Question 31.
Between substances of the same volume, the ones with greater density are …………… than those of lesser density.
Answer:
heavier

Question 32.
The property of a substance of getting …………… is called its solubility.
Answer:
dissolved

Question 33.
Minerals from the earth’s crust are …………… to obtain metals.
Answer:
processed

Question 34.
Metals can be converted into …………… by hammering.
Answer:
sheets

Question 35.
Metals can be stretched and drawn into …………… .
Answer:
wires

Question 36.
All metals are …………… of electricity to a greater or lesser extent.
Answer:
conductors

Question 37.
Every metal has a …………… colour by which it can be identified.
Answer:
specific

Question 38.
Metals produce …………… sound.
Answer:
ringing

Question 39.
Metals form a …………… group of substances.
Answer:
separate

Question 40.
Heat is the cause of the change of the state of …………… .
Answer:
substances

Match the columns:

Question 1.

Column ‘A’	Column ‘B’
1. Boiling water	a. > 35° C
2. Body temperature	b. 0° C
3. Freezing water	c. < 5° C
4. Air (summer afternoon)	d. < 15° C
5. Inside a fridge	e. < -18° C
6. Air (winter night)	f. 100° C
7. Inside the freezer	g. 37°C

Answer:

Column ‘A’	Column ‘B’
1. Boiling water	f. 100° C
2. Body temperature	g. 37°C
3. Freezing water	b. 0° C
4. Air (summer afternoon)	a. > 35° C
5. Inside a fridge	c. < 5° C
6. Air (winter night)	d. < 15° C
7. Inside the freezer	e. < -18° C

Answer in one sentence:

Question 1.
What is change of state of substances?
Answer:
When a substance changes from one state to another, the process is called change of state of the substance.

Question 2.
When does state of substance change?
Answer:
State of substance changes when it is heated or cooled.

Question 3.
In which state do substances exist in our surroundings?
Answer:
The substances exist in solid, liquid and gaseous form in our surroundings.

Question 4.
What happens when a substance gains heat?
Answer:
When a substance gains heat, it changes its state i.e. from solid to liquid and liquid to gas.

Question 5.
What happens when a substance loses heat?
Answer:
When a substance loses heat, it changes its state from gaseous to liquid and liquid to solid state.

Question 6.
How do we tell how hot or cold a substance is?
Answer:
The temperature on the thermometer will tell us how hot or cold a substance is.

Question 7.
What is the unit of measuring temperature.
Answer:
Degrees Celsius (°C) is the unit of measuring temperature.

Question 8.
What is the boiling point of water?
Answer:
The boiling point of water is 100° C.

Question 9.
What is condensation?
Answer:
When vapour cools, it is converted into liquid again. This process is condensation.

Question 10.
At what temperature condensation of steam takes place?
Answer:
Condensation of steam takes place at 100° C.

Question 11.
What is the freezing point of water?
Answer:
0° C is the freezing point of water.

Question 12.
What is the temperature of air in the freezer of a refrigerator?
Answer:
-18° C is the temperature of air in the freezer of a refrigerator.

Question 13.
At what temperature ice melts?
Answer:
Ice melts at 0° C.

Question 14.
How are candles made?
Answer:
Candles are made by melting paraffin wax.

Question 15.
What is the use of solid carbon-dioxide?
Answer:
Solid carbon-dioxide (dry ice) is used to make ice cream and to keep it frozen.

Question 16.
What is the use of liquid nitrogen?
Answer:
Liquid nitrogen is used in animal husbandry.

Question 17.
What is sublimation?
Answer:
The change of a solid substance directly into gas or vapour without changing into a liquid is called sublimation.

Question 18.
Define brittleness / What is brittleness?
Answer:
Some substances break into small pieces or particles. Such substances are said to be brittle. This property of substances is called brittleness.

Question 19.
Define hardness / What is hardness?
Answer:
The hardness of a substance is determined by how much resistance it offers to the substances being pushed through it.

Question 20.
Define elasticity / What is elasticity?
Answer:
Some substances change their shape when a force is applied on them but return to their original shape and size when the force is removed. This property is called elasticity.

Question 21.
Define fluidity / What is fluidity?
Answer:
Liquids flow downward on a sloping surface. This property is called fluidity.

Question 22.
How is fluidity of any liquid determined?
Answer:
Fluidity of any liquid is determined by how easily it flows.

Question 23.
Define density / What is density?
Answer:
The mass of different substances having the same volume can be different. This difference is because of the difference in their densities. Between substances of the same volume, the ones with greater density are heavier than those of lesser density.

Question 24.
Define solubility / What is solubility?
Answer:
The property of a substance of getting dissolved is called its solubility.

Question 25.
Define transparency / What is transparency?
Answer:
When we can look through a substance and see things on the other side, then that substance is said to be transparent. This property of the substances is called transparency.

Question 26.
List some transparent substances.
Answer:
Glass, air, clean water and some types of plastic are transparent substances.

Question 27.
What are metals?
Answer:
Metals are substances like copper, gold, iron, aluminium. They are found in the form of minerals deep inside the earth. Minerals from the earth’s crust are processed to obtain metals.

Question 28.
Define malleability. / What is malleability?
Answer:
Metals can be converted into sheets by hammering. This property of metals is called malleability.

Question 29.
Define ductility. / What is ductility?
Answer:
Metals can be stretched and drawn into thin wires. This property of metals is called ductility

Question 30.
Name some ductile metals.
Answer:
Metals like silver, gold, platinum can be drawn into fine wires.

Question 31.
Define electrical conductivity. / What is electrical conduction?
Answer:
Electricity flows through metals. All metals are conductors of electricity to a greater or lesser extent.

Question 32.
Define thermal conductivity. / What is thermal conductivity?
Answer:
Metals allow heat to flow through them. This property is called thermal conductivity

Question 33.
What is lustre?
Answer:
The typical shine or characteristic colour by which metal can be identified is called lustre.

Question 34.
What is sonority of metals? / Define sonority.
Answer;
Metals produce a ringing sound. This property is called the sonority of metals.

Give scientific reasons for following:

Question 1.
Metals are used to make musical instruments.
Answer:
Metals possess the property of being sonorous, i.e. produce a ringing sound. Hence, they are used to make musical instruments.

Question 2.
Ornaments are made up of metals.
Answer:
Metals have the property of being malleable, ductile, lustrous. Hence, ornaments are made up of metals.

Question 3.
Why should we not put our hand or finger in the water to judge the hotness of water?
Answer:
We should never put our hand or finger in the water to judge how hot it is because that is not an accurate measure. Besides if the substance is very hot, we could get scalded.

Can you tell?

Question 1.
Why are electric boards fitted on the wall made of plastic or wood?
Answer:
Plastic or wood are bad conductors of heat and electricity. Electric boards are made up of plastic or wood. So that while touching we will not get electric shock.

Question 2.
The handle of cooker is made of plastic. Why?
Answer:
Cooker is made of metal. When food is cooked in it, it gets heated and the whole of its body becomes hot due to thermal conductivity. Hence with the plastic handle we can easily lift the hot cooker as plastic is a bad conductor of heat.

Question 3.
Use your brain power!
On opening a box of camphor, its smell spreads all around. Why does this happen?
Answer:

1. Camphor is a sublimate substance.
2. When a box of camphor is opened it changes its state from solid to gas or vapour state.
3. This change takes due to the process of sublimation where camphor absorbs heat from surrounding to change from solid to gaseous state.
4. Camphor particles in gaseous state start spreading all around.
5. Hence on opening a box of camphor its smell spreads all around.

Question 4.
Identify the objects shown in fig. 5.14. From which substances are they made? What are these substances called as a group?
Answer:
In fig 5.14, the metallic bars are shown, these bars are made up of shiny solid. These substances are called metals.

Question 5.
Name the solid, liquid and gaseous states of water.
Answer:

• Solid- Ice
• Liquid – water
• Gas – water vapour.

Question 6.
Read this list of substances:
spirit, camphor, petrol, ghee, coconut oil, naphthalene balls, ammonium chloride (navsagar).

Question a.
Which one freezes in winter?
Answer:
Coconut oil, ghee.

Question b.
Which liquids have you seen change into a vapour?
Answer:
Spirit, petrol.

Question c.
Which solid directly changes into gaseous state?
Answer:
Camphor, naphthalene balls, ammonium chloride.

Question 7.
The chart given below shows the boiling point and freezing point of some substances. State whether these substances are solid, liquid or gaseous at room temperature.

Substance	Freezing Point	Boiling Point
Candle	60 °C	350 °C
Plastic	> 250 °C	954 °C
Iron	1535 °C	2862 °C

Answer:
Candle, plastic and iron are in solid state at room temperature.

Distinguish between solids, liquids and gases.
Answer:

Solids	Liquid                                                  Gases
e.g.: A piece of iron	e.g.: Water, spirit, oil	e.g.: Air
Has a shape of its own, Retains shape, no matter how it is kept.	Does not have a shape of its own. Takes the shape of the container.	Does not have a shape of its own. Occupies all the available space.
Has a definite volume. Solids like sugar, sand when poured on a flat surface, form a heap.	It has a specific volume. Occupies definite portion of a container. Spreads on a flat surface on pouring. Flows downwards along a slope. Takes the shape of the surface.	Does not have a definite volume. On changing the pressure on a gas in a closed container, its volume also changes.

Distinguish between Boiling and Melting.
Answer:

Boiling	Melting
1. When heat is supplied to liquids, they boil.	1. When heat is supplied to solids, they melt.
2. Boiling leads liquids to vapour/gaseous state.	2. Melting leads solids to liquid state.
3. The temparature at which liquid starts boiling continuously is called boiling point.	3. The temperature at which solid turns to liquid completely is called melting point.

Answer the following briefly:

Question 1.
List properties of solids
Answer:

1. Solids have its own shape i.e. Retains shape, no matter how it is kept.
2. Solids have definite volume.
3. e.g. Sand when poured on a flat surface form a heap.

Question 2.
List properties of liquids.
Answer:

1. Liquid does not have a shape of its own. Takes the shape of the container.
2. A liquid has a specific volume i.e. occupies definite portion of a container.
3. Liquids: e.g. water, milk, kerosene.

Question 3.
List properties of gases.
Answer:

1. Gases does not have a shape of its own.
2. Occupies all the available space.
3. Does not have a definite volume.
4. e.g. Air.

Question 4.
Explain with example how liquids take the shape of the surface.
Answer:
Liquids have a specific volume. They occupy definite portion of a container. Liquids spreads on a flat surface on pouring. Liquids flow downwards along a slope.

Question 5.
Explain Ebullition.
Answer:

1. As the water gets heated, its temperature increases and it evaporates at a faster and faster rate.
2. When water kept on a stove attains a particular temperature or level of heat, then evaporation takes place in all parts of the body of water.
3. Then we see water bubbles rising at a faster and faster rate to the surface and steam mixing in the air.
4. This is called boiling of water or Ebullition.

Question 6.
Explain: Boiling point and condensation point of water are one and the same.
Answer:
Water boils at 100°C. i.e. boiling point of water is 100°C. Condensation of steam also takes place at 100° C. Thus boiling point and condensation point of water are one and the same.

Question 7.
Explain freezing point of water.
Answer:

1. Water kept in a fridge or on ice becomes cooler and cooler i.e. its temperature falls.
2. At a certain temperature water does not cool further but starts freezing and forms ice.
3. The temperature at which this happens is called the freezing point of water. (0° C)

Question 8.
Explain: Freezing point and melting point of water are same.
Answer:

1. The temperature at which water does not get any cooler but starts freezing and forming ice is 0° C.
2. When ice gets heat, it starts melting or changes into liquid state at 0° C.
3. Thus, freezing point and melting point of water are one and the same.

Question 9.
List various uses of changes in physical state.
Answer:

1. Candles are made by melting paraffin wax.
2. Solid carbon-dioxide (dry ice) is used to make ice-cream and to keep it frozen.
3. Liquid nitrogen is used in animal husbandry.
4. Sand (silica) is melted to make glass.
5. Metals like gold and silver are melted to make ornaments.
6. Iron is melted to make tools.

Question 10.
List the properties of substances:
Answer:
The properties of substances are

1. Brittleness
2. Hardness
3. Elasticity
4. Fluidity
5. Density
6. Solubility
7. Transparency

Question 11.
List properties of metals:
Answer:
The properties of metals are

1. Malleability
2. Ductility
3. Electrical conductivity
4. Thermal conductivity
5. Lustre
6. Sonority

Question 12.
How can we change the volume of a gas?
Answer:
On changing the pressure on a gas in a closed container we can change its volume.

Can you tell?

Question 1.
Does water change into vapour the moment we place the vessel on a stove? Does water kept in fridge change at once into ice?
Answer:
No, it doesn’t. Water slowly changes from one state to another.

Question 2.
How do we tell how hot or cold a substance is?
Answer:
A thermometer is used to measure the temperature of the subatance which tell us hot or cold it is.

Question 3.
How will you identify the following

Question i.
A glass: Is it made of plastic, steel or glass?
Answer:
Glass is made of glass as it is transparent.

Question ii.
A rod: Iron or aluminium.
Answer:
A rod is made of iron as it is heavy.

Question iii.
A door: Wooden or glass?
Answer:
A door is wooden as it is opaque.

Question iv.
A white powder: Salt or chalk powder?
Answer:
If powder dissloves in water it is salt and if it does not dissolves in water it is chalk.

6th Std Science Questions And Answers:

• Natural Resources – Air, Water and Land Class 6 Questions And Answers
• The Living World  Class 6 Questions And Answers
• Diversity in Living Things and their Classification Class 6 Questions And Answers
• Disaster Management Class 6 Questions And Answers
• Substances in the Surroundings – Their States and Properties Class 6 Questions And Answers
• Substances in Daily Use Class 6 Questions And Answers
• Nutrition and Diet Class 6 Questions And Answers
• Our Skeletal System and the Skin Class 6 Questions And Answers
• Motion and Types of Motion
• Force and Types of Force Class 6 Questions And Answers

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 15 Sound Notes, Textbook Exercise Important Questions and Answers.

Std 8 Science Chapter 15 Sound Question Answer Maharashtra Board

Class 8 Science Chapter 15 Sound Question Answer Maharashtra Board

1. Fill in the blank with appropriate word:

Question a.
The region in a sound wave, with higher pressure and density is called ………….. and that with low pressure and density is called ……….. .
Answer:
The region in a sound wave, with higher pressure and density is called compression and that with low pressure and density is called rarefaction.

Question b.
Medium is …………… for generation of sound.
Answer:
Medium is needed (or necessary) for generation of sound.

Question c.
The total number of compressions and rarefactions produced per second in a sound wave is 1000. The frequency of the sound wave is ………… .
Answer:
The total number of compressions and rarefactions produced per second in a sound wave is 1000. The frequency of the sound wave is 500 Hz.
[Note: Total number: 100. ∴ 500 compressions and 500 rarefactions are produced per second.]

Question d.
Different sound notes have different ………………. .
Answer:
Different sound notes have different frequencies.

Question e.
In a loudspeaker, …………… energy is converted into ………….. energy.
Answer:
In a loudspeaker, mechanical energy is converted into sound energy.

2. Give scientific reasons:

Question a.
It is essential to change the tension in the vocal cords, as we produce different sound notes from our larynx.
Answer:
Different sound notes correspond to different frequencies. The frequency of sound depends on the tension in the vocal cords. Hence, it is essential to change the tension in the vocal cords, as we produce different sound notes our larynx.

Question b.
Astronauts on the moon cannot hear each other directly.
Answer:
Two astronauts on the moon talking to each other directly, will be unable to listen to each other, even if they are very close to each other. The moon does not have atmosphere. Since there is no medium which is necessary for generation and propagation of sound, between the astronauts, direct sound propagation between them is not possible. Therefore, the astronauts use some technology like the one used in our cell-phones to communicate with each other. The waves used in cell-phone do not need any medium for propagation.

Question c.
As the sound wave propagates from one place to the other in air, the air itself is not required to move from one place to the other.
Answer:
Propagation of sound through air occurs due to energy transfer by vibrating air molecules in one region to those in the adjacent region away from the source. The molecules simply vibrate about their mean positions. Hence, the air itself is not required to move from one place to the other.

3. How are different sound notes generated in musical instruments like guitar, which uses strings for sound generation, and flute, which uses blown air for sound generation?

Question a.
How are different sound notes generated in musical instruments like guitar, which uses strings for sound generation, and flute, which uses blown air for sound generation?
Answer:
1. Guitar: It is a string based, flat- backed instrument. It has usually six strings, the strings are plucked or strummed with the fingers or a small piece of plastic, wood, etc. It has a flat sounding board with a circular sound hole in the centre. Also it has a fretted fingerboard. Its frequency range is more than three octaves. The frequency of vibration of the string is changed by changing the tension in the string or changing the vibrating length of the string. As the tension is increased, the frequency increases. As the vibrating length is increased, the frequency decreases. This is how different sound notes are generated.
[Note: The acoustic guitar has hollow body and six or twelve strings while the electric guitar usually has solid body and six strings. The electric bass guitar has four strings.]

2. Flute: It is a wind instrument where air is blown against the edge or rim of the blowing hole. The frequency of the sound produced depends upon the length of the vibrating air column in the tube. The greater the length of the vibrating air column, the less is the frequency of the sound produced. This is how different sound notes are produced. The flute has six or seven or eight holes to generate sounds of different frequencies. Different notes can be generated also by changing the way of air-blowing.

4. How is sound produced in the human larynx and a loudspeaker?

Question a.
How is sound produced in the human larynx and a loudspeaker?
Answer:
1. Sound production in the human larynx:
In the humans, sound is produced in the voice box called the larynx. It is located at the upper end of the windpipe. Two vocal cords (chords) are stretched across it with a narrow slit between them for the passage of air (Fig. 15.5). When the lungs force air through the slit, the cords start vibrating.

The frequency of the sound produced depends upon the length and thickness of the cords, and the tension in the chords. The frequency increases with the increase in tension and the more the length or the thickness of the cord, the less is the frequency. Muscles attached to the cords can make the cords tight (more tension) or loose (less tension).

2. Sound produced in a loudspeaker:
Figure shows the internal construction of a loudspeaker. Here, a coil is wound around a permanent magnet. The conical screen of the loudspeaker is attached to the coil.

When a current is passed through the coil, a magnetic field is produced. Its interaction with the permanent magnet results in the back and forth motion of the coil. The frequency and the amplitude of the motion of the coil depends on the variation in the current through the coil.

As the coil moves, the conical screen also moves back and forth. The vibrations of the screen produce sound waves in air. Very loud sound can be produced by changing the current.
[Note: If you gently touch the vibrating screen, you can feel the vibrations.]

5. Explain the experiment, with0 a neat diagram, to prove the following:
‘Sound needs a material medium for propagation.’

Question a.
Explain the experiment, with0 a neat diagram, to prove the following:
‘Sound needs a material medium for propagation.’
Answer:

Figure shows part of the set up used in this experiment. What is not shown is the electric circuit in which the electric bell is connected. A vacuum tight bell jar contains an electric bell connected to a power supply through the lid of the jar. The jar is placed on a smooth horizontal surface such as that of glass.

Initially the vacuum pump is off and the jar contains air. The circuit containing the bell is completed using the key or the switch so that the bell starts ringing. This can be heard outside the jar.

Then the vacuum pump is switched on so that it starts removing the air from the jar. We find that the level of ringing sound heard goes on decreasing as the quantity of air in the jar becomes less and less.

When the pump is operated for a sufficiently long time interval, the quantity of air in the jar becomes so less that the level of ringing sound becomes very low; sound is hardly audible. But we can see the striker in the bell hitting the gong. By extrapolation, we conclude that sound generation and propagation needs a medium.

6. Match the following:

Question a.

Answer:

Column I	Column II
Human larynx	Vibrations in vocal cords
Loudspeaker	Vibrations of screen
Jaltarang	Vibrations in air column
Tuning fork	Vibrations of metal arms
Sitar	Vibrations in strings

Can you recall?

Question a.
How is sound produced?
Answer:
Sound is produced by the vibrations of an object such as a stretched membrane or a string under tension.

Project:

Question 1.
Take two plastic glasses and tie a thread between them to make a toy phone. Does the voice of your friend reach you through the thread? Take metal wire instead of the thread and also change the length of the thread wire and repeat the activity. Discuss with your friends and teacher about your conclusions.

Question 2.
Take a plastic or tin can or a plastic glass. Remove its bottom. Stretch a piece of rubber balloon across one end and fix it with a rubber band. Put a few grains of say ragi or bajra on the stretched rubber. Now ask your friend to shout ‘Hoorrey ……… Hoorrey ………… ‘ from the open end of the glass. Observe the dancing of the grains up and down. Discuss the reason behind this.

Class 8 Science Chapter 15 Sound Important Questions and Answers

Select the correct option and write the completed statements:

Question 1.
Sound waves cannot travel through a ………… .
(a) solid
(b) liquid
(c) gas
(d) vacuum
Answer:
Sound waves cannot travel through a vacuum.

Question 2.
If the frequency of a sound wave is 512 Hz, the number of rarefactions produced per second is ……………… .
(a) 256
(b) 512
(c) 1024
(d) 128
Answer:
If the frequency of a sound wave is 512 Hz, the number of rarefactions produced per second is 512.

Question 3.
In the experiment to show that a medium is necessary for propagation of sound, as the quantity of air inside the bell jar decreases, the level of ringing sound heard outside ……………… .
(a) increases
(b) decreases
(c) fluctuates randomly
(d) changes at regular intervals
Answer:
In the experiment to show that a medium is necessary for propagation of , sound, as the quantity of air inside the bell jar decreases, the level of ringing sound heard outside decreases.

Find the odd one out and give the reason:

Question 1.
Sound waves, Waves on the surface of water, Waves on a stretched string, Light waves
Answer:
Light waves. Light waves can travel in a vacuum. Other waves need a medium for propagation.

Question 2.
Sitar, Violin, Guitar, Flute.
Answer:
Flute. It is not a string based instrument. Others are string based instruments.

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

Question 1.
If the vibrating length of a stretched string is kept constant and the tension in the string is increased, the frequency of the sound produced increases.
Answer:
True.

Question 2.
In Jaltarang, the frequency of sound produced is independent of the height of the air column inside the glass cup.
Answer:
False. (In Jaltarang, the frequency of sound produced depends on the height of the air column inside the glass cup; the more the height of the air column, the less is the frequency of the sound produced.)

Answer the following questions in one sentence each:

Question 1.
What is sound?
Answer:
Sound is a form of energy which produces sensation of hearing in our ears.

Question 2.
What is vibration?
Answer:
Vibration is a rapid, to and from periodic motion of an object about its mean position.

Question 3.
What is compression?
Answer:
As a sound wave travels through air, the region in which air is at high pressure and high density is called compression.

Question 4.
What is rarefaction?
Answer:
As a sound wave travels through air, the region in which air is at low pressure and low density is called rarefaction.

Question 5.
What is the relation between the frequency of vibration and the vibrating length (or height) of the air column?
Answer:
The greater the vibrating length (or height) of the air column, the less is the frequency of vibration of the column.

Question 6.
For a particular string (given material and radius), what are the factors on which its frequency of vibration depends?
Answer:
For a particular string (given material and radius), the frequency of vibration of the string depends upon its vibrating length and the tension in the string.
[Note: in the above case, frequency is proportional to the square root of the tension and inversely proportional to the length.]

Question 7.
Name an instrument in which a stretched skin is used to produce musical sound.
Answer:
Tabla.

Answer the following questions:

Question 1.
Explain the production and propagation of sound in air.
Answer:
Let us consider production of sound by using a tuning fork. A tuning fork is made of a metal. It has a stem and two prongs (Fig). Figure (a) shows the state of air in the absence of propagation sound through it. Equally spaced vertical lines show that the average distance between the air molecules is the same everywhere. It means average pressure and average density in the regions A, B and C are the same.

Suppose the tuning fork is held vertical, its stem is fixed in a stand (not shown in the figure) and its prongs are struck lightly using a light hammer with a piece of rubber at the top. The prongs then start vibrating.
Figure (b) shows what happens when the prongs move away from each other. The air outside the prongs is compressed (layers in the region A). The pressure and density increase in this region.

Figure (c) shows what happens when the prongs move close to each other. The air molecules near the prongs move away from each other resulting in lower pressure and lower density.

This region is called rarefaction. Meanwhile, the compression produced earlier moves forward, i.e., away from the prongs because the air molecules in this region transfer their energy to the air molecules in the region B producing a compression there. The periodic formation of compression and rarefaction results in propagation of sound waves away from the prongs.

Eventually, these sound waves reach our ears, the ear-drum vibrates, and we get a sense of hearing a sound as the specific signals reach the brain.

Use your brain power:

Question a.
If sound waves are generated in air, what moves away from the source? Is it the air itself or the state of compression and rarefaction created in the air?
Answer:
If sound waves are generated in air, the state of compression and rarefaction created in the air moves away from the source.
[Note: The air does not move away from the source because air is elastic and the force due to the tuning fork varies periodically with time.]

Question 2.
Explain the term frequency of a sound wave.
Answer:
Sound travels in the form of waves. A wave consists of cycles of alternate compression and rarefaction. The number of cycles produced in the air (or any other medium) per second is called the frequency of the sound wave. It is expressed in hertz (Hz). 1 hertz = 1 cycle per second or 1 vibration per second or 1 oscillation per second.

[Note: The SI unit of frequency, the hertz, is named in honour of Heinrich Hertz (1857-94), German physicist.]

Question 3.
State the factors on which the frequency of a tuning fork depends.
Answer:
The frequency of a tuning fork depends on the dimensions of the prongs, i.e., length and thickness, and the material used for making the fork.

Try this:

Question a.
Take 6 – 7 glass cups. Arrange them in a line and fill them with water with gradually increasing water level from one end to other. Take a pencil and strike the cups sequentially. The sound generated by each cup will be different. Why is it so?
Use of ICT:
Download videos of Jaltarang from youtube and send them to your friends by email.

Answer:
When a cup is struck, waves are set up in the air column above the water level in the cup. The frequency of the generated wave depends on the height of the air column inside the glass cup. Since the water level in each glass is different, the height of the air column in each glass is also different. Therefore, the frequency of sound generated by each glass cup will also be different. So, the sound generated is different.

Question b.
An ‘app’ for measurement of sound frequency may be available on cellphones. With the help of your teacher, use the app to measure the frequency of the sound generated from each glass cup. Do you observe any relation between the frequency of generated sound and the height of the air column in the glass cup?
Answer:
Yes. The greater the height of the air column in the glass cup, the less is the frequency of the sound produced.

Question c.
This is your simple ‘Jaltarang’! Can this experiment be performed with stainless steel pots of different size?
Answer:
Do it. See what happens as the stainless steel pot itself starts vibrating producing a sound. Also see how this sound is damped by water.

Do you know?

Question a.
What are the frequencies of musical notes ‘sa’, ’re’, ‘ga’, ‘ma’, ‘pa’, ‘dha’, ‘ni’ in the ‘madhya saptak’?
Answer:

[Note: The diatonic scale:


Such a simple fraction is pleasing to the ear and is called a musical interval. Frequency ratios 2 : 1, 3 : 2, 4 : 3 are examples of musical interval.

Observe and discuss:

Question 1.
Identify the instruments and discuss sound production in them. [Students should see these musical instruments.]

Answer:

1. Sitar
2. Shehnai
3. Flute
4. Tabla
5. Santoor
6. Bugle
7. Mandoline or Mandolin
8. Saxophone.

Question i.
Sitar, Santoor and Mandoline or mandoline (String instruments):
Answer:
Vibrating strings produce the sound. The greater the tension in the string, the higher is the frequency of the sound. The greater the vibrating length and the diameter of the string, the lower is the frequency of the sound.

Question ii.
Flute, Saxophone and Shehnai (Wind instruments):
Answer:
Vibrating air column produces the sound. The greater the length of the column, the lower is the frequency of the sound.

Question iii.
Tabla (Percussion instrument):
Answer:
Vibrating skin produces the sound. The greater the tension in the skin, the higher is the frequency of the sound. The greater the thickness of the skin, the lower is the frequency of the sound.

Try this:
‘Apps’ for generation of different sound notes (sound note generator app) may be available on cellphones. With the help of your teacher, using such an app, generate sound notes listed in the table.

Vocal cords are 20 cm in length in male, about 15 cm in female and even smaller in children. Therefore the voice of male, female and children are different.
[Note: Vocal cords are 20 mm in length in male, about 15 mm in female and even smaller in children. Reference NCERT textbook Std. VIII, published in 2017.]

Question 1.
Produce a sound ‘bho … bho …’ just like a dog-barking and ‘meow … meow…’ just like a mewing cat. Carefully notice the tension on the vocal cords, when you produce these sounds. Do you feel that the tension on the vocal cords changes when you produce these two different sounds?
Answer:
Yes.

Question 2.
An ‘app’ may be available on cell-phones to measure the loudness of sound in decibel. With the help of your teacher, use the app to measure the sound level of a sound from a loudspeaker at some public place. Measure the sound level at different distances from the loudspeaker. Do you observe some relation between the distance from the loudspeaker and the sound level?
Answer:
Yes. As the distance increases, the sound level decreases.

Always remember:

We should take care that others are not disturbed when we study sound and its production. Sound pollution is a major cause affecting the environment and social health. Hence we should find ways to avoid sound pollution.

8th Std Science Questions And Answers:

• Human Body and Organ System Class 8 Questions And Answers
• Introduction to Acid and Base Class 8 Questions And Answers
• Chemical Change and Chemical Bond Class 8 Questions And Answers
• Measurement and Effects of Heat Class 8 Questions And Answers
• Sound Class 8 Questions And Answers
• Reflection of Light Class 8 Questions And Answers
• Man-made Materials Class 8 Questions And Answers
• Ecosystems Class 8 Questions And Answers
• Life Cycle of Stars Class 8 Questions And Answers