Category: CBSE Class 8

NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 11
Chapter Name	Force and Pressure
Number of Questions Solved	10
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure

NCERT TEXTBOOK EXERCISES

Question 1.
Give two examples of each of situations in which you push or pull to change the state of motion of objects.
Answer.
(1) If a rubber ball or marble is placed on a very smooth surface and given a small push, it starts moving with some speed. If we keep an obstacle in the way of motion of the marble/ball, the marble/ball will stop moving at the obstacle. Here a push is given to the marble/ball at rest to change its state of rest to motion.

(2) If a child is placed on a hanging swing in the state of rest and the swing is pulled again and again by a rope, the swing will move to and fro with a speed. If the pull is bigger, the swing will move at a bigger distance. This is an example of a pull that changed the state of an object from the rest of the motion.

Question 2.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer.

1. If an inflated balloon is taken and pressed from two sides with a hand, its shape changed, i.e., the figure is disturbed. If the inflated balloon is pressed with more force, the balloon will burst.
2. If a plate of steel is beaten with a hammer, after four-five big blows the plate’s shape will change.

Question 3.
Fill in the blanks in the following statements:

1. To draw water from a well, we have to ……….. at the rope.
2. A charged body………….an uncharged body towards it.
3. To move a loaded trolley, we have to…………...it.
4. The north pole of a magnet…………….the north pole of another magnet.

Answer.

1. pull
2. attracts
3. pull/push
4. repels.

Question 4.
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms: muscular, contact, non-contact, gravity, friction, shape, attraction.

1. To stretch the bow, the archer applies a force that causes a change in its……..
   
2. The force applied by the archer to stretch the bow is an example of.………..force.
3. The type of force responsible for a change in the state of motion of the arrow is an example of a…………….force.
4. While the arrow moves towards its target, the forces acting on it are due to……….and that due to of air.

Answer.

1. shape
2. muscular
3. contact
4. gravity, friction.

Question 5.
In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.
(b) Taking out paste from a toothpaste tube.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.
Answer.

S. No.	Agent exerting the force	Object on which it acts	Form of effect
(a)	Fingers	Lemon as whole	Change in shape
(b)	Fingers	Tube as whole	Change in shape
(c)	Load	Spring	Change in shape
(d)	Athlete	Bar	High jump

Question 6.
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer.
The shape of the hot piece of iron changes. It flattens and becomes thinner than earlier. This is the effect of force due to hammering the piece of iron.

Question 7.
An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Answer.
Electrostatic force.

Question 8.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
Answer.
The forces that act on the bucket are as follows:

1. The pressure of water contained in it exerted on its wall and on the base of the bucket.
2. Force of gravity exerted by earth.
3. Muscular force by my hand.

The water is contained in a bucket and the pressure is exerted by water on the walls of the bucket, which is sufficient to take it as a force. This force is counterbalanced by the force exerted by the walls of the bucket on water. As the bucket (with water) is held in my hand, so I overcome the force of gravity of the earth.

Thus, it can be concluded that there is no net effect of forces acting on the bucket full of water. That is why these forces do not bring a change in its state of motion.

Question 9.
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
Answer.
The two forces that are acting on the rocket immediately after leaving the launching pad are:

1. Force of gravity of earth acting down-ward
2. The frictional force produced by air particles.

Question 10.
When we press the bulb of a dropper with its nozzle kept in water, the air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
(a) pressure of water
(b) the gravity of the earth
(c) the shape of a rubber bulb
(d) atmospheric pressure
Answer.
(a) the pressure of water.

We hope the NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 11 Force and Pressure, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 10
Chapter Name	Reaching the Age of Adolescence
Number of Questions Solved	9
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence

NCERT TEXTBOOK EXERCISES

Question 1.
What is the term used for chemical secretions of endocrine glands responsible for changes taking place in the body?
Answer.
The term used for secretions of endocrine glands is hormones, which are responsible for various changes taking place in the body.

Question 2.
Define adolescence.
Answer.
The period of life when the body undergoes changes, leading to reproductive maturity is called adolescence.

Question 3.
What is menstruation? Explain.
Answer.
When the uterus receives the egg and it is fertilized, pregnancy occurs. If fertilization does not occur, the released egg and the thickened lining of the uterus along with its blood vessels are shed off: This causes bleeding in women, which is called menstruation.

Question 4.
List changes in the body that take place at puberty.
Answer.
The onset of puberty brings about:

1. Growth of the reproductive organs which begin to function.
2. Hair grows at various places of the body. Breasts develop in girls and facial hair (mustache and beard) appear in boys.
3. The voice of the boys becomes hoarse as the voice box enlarges during adolescence.

Question 5.
Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer.

Column A	Column B
Name of endocrine glands (i)Testes (ii)Ovaries	Name of hormones Testosterone (male) Estrogen (female)
Pituitary glands (iii)Thyroid (iv) Adrenal glands (v) Pancreas	Sex hormones and brain hormones Thyroxine Adrenalin Insulin

Question 6.
What are sex hormones? Why are they named so? State their function.
Answer.
Hormones secreted by testes and ovaries are termed as sex-hormones.

• They are named so because they are secreted by the reproductive organs.

Functions of sex-hormones.

• These hormones are responsible for the secondary sexual characters of males and females.

Question 7.
Choose the correct option.
(a) Adolescents should be careful about what they eat, because
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.
Answer.
(ii) proper diet is needed for the rapid growth taking place in their body. Reproductive age in women starts when their

(b) Reproductive age in women starts when their
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.
Answer.
(i) menstruation starts.

(c) The right meal for adolescents consists of
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.
Answer.
(ii) Chapati, dal, vegetables.

Question 8.
Write notes on:

1. Adam’s apple.
2. Secondary sexual characters.
3. Sex determination in the unborn baby.

Answer.

1. At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple. This makes a boy’s voice hoarse.
2. In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, mustaches and beards. As these features help to distinguish the male from the female, they are called secondary sexual characters.
3. Sex Determination in the Unborn Baby: All human beings have 1 pair of sex chromosomes, as the names X and Y. A female has two X chromosomes,

while male has one X and one Y chromosome. When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote, that will have ‘XT would develop into a male child. Now you know that the sex chromosomes of the father determine the sex of a baby.

Question 9.
Word game: Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone
Down
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through the bloodstream
6. Voicebox
7. Term for changes at adolescence.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 9
Chapter Name	Reproduction in Animals
Number of Questions Solved	10
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals

NCERT TEXTBOOK EXERCISES

Question 1.
Explain the importance of reproduction in organisms.
Answer.
The production of new individuals from their parents is known as reproduction. Reproduction is very important as it ensures the continuation of a species. If the process of reproduction does not exist, the species would get vanished from the earth.

Question 2.
Describe the process of fertilisation in human beings.
Answer.
The first step in the process of reproduction is the fusion of a sperm and an ovum. Millions of sperms from the male are transferred into the female body. The sperms swim in the oviduct with the help of their tails to reach the egg. When they come in contact with the egg, one of the sperms may fuse with the egg.

Such fusion of the egg and the sperm is called fertilization. During fertilization, the nucleus of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote.

Question 3.
Choose the most appropriate answer:
(a) Internal fertilisation occurs
(i) in female body.
(ii) outside the female body.
(iii) in male body.
(iv) outside male body.
Answer.
(i) in female body.

(b) A tadpole develops into an adult frog by the process of
(i) fertilisation.
(ii) metamorphosis.
(iii) embedding.
(iv) budding.
Answer.
(ii) metamorphosis.

(c) The number of nuclei present in a zygote is
(i) none
(ii) one
(iii) two
(iv) four.
Answer.
(ii) one.

Question 4.
Indicate whether the following statements are True (T) or False (F):

1. Oviparous animals give birth to young ones. ( )
2. Each sperm is a single cell. ( )
3. External fertilisation takes place in frogs. ( )
4. A new human individual develops from a cell called gamete. ( )
5. Egg laid after fertilisation is made up of a single cell. ( )
6. Amoeba reproduces by budding. ( )
7. Fertilization is necessary even in asexual reproduction. ( )
8. Binary fission is a method of asexual reproduction. ( )
9. A zygote is formed as a result of fertilisation. ( )
10. An embryo is made up of a single cell. ( )

Answer.

1. False
2. True
3. True
4. False
5. True
6. False
7. False
8. True
9. True
10. False

Question 5.
Give two differences between a zygote and a foetus.
Answer.

Zygote	Foetus.
1.  It is single-celled.	1. It is multicellular.
2. Zygote is formed by the fusion of male and female gametes.	2. Foetus is formed by the repeated division of zygote and differentiation.

Question 6.
Define asexual reproduction. Describe two methods of asexual reproduction in animals. ‘
Answer.

The type of reproduction in which only a single parent is involved is called asexual reproduction.

Budding: The asexual reproduction in which an individual develops from buds, which is detached from a parent body is known as budding. For example, Hydra reproduces by this method. Many bulges are found in the parent body of hydra. These bulges called buds to develop into new individuals.

Budding fission: It is a type of asexual reproduction in which an animal reproduces by dividing into two individuals. This type of reproduction is observed in the microscopic organism, amoeba. The reproduction in Amoeba begins by a division of its nucleus into two nuclei. This is followed by a division of its body into two with each part receiving a nucleus. Finally, two amoebae are produced from a single Amoeba.

Question 7.
In which female reproductive organ does the embryo get embedded?
Answer.
The embryo gets embedded in the wall of the uterus (of the female) for further development.

Question 8
What is metamorphosis? Give examples.
Answer.
The drastic change that transforms a larva into an adult is called metamorphosis. Frog, SilkWorm, Honeybee, are some animals in which metamorphosis occurs.

Question 9.
Differentiate between internal fertilisation and external fertilisation.
Answer.

Fertilization	External fertilisation.
1.Takes place inside the body of the female.	1. Takes place outside the body of the female.
2. Female lays either fertilized eggs or a fully grown individual is born.	2. Female lays unfertilized eggs.

Question 10.
Across
1. The process of the fusion of the gametes.
6. The type of fertilisation in the hen.
7. The term used for bulges observed on the sides of the body of Hydra.
8. Eggs are produced here.
Down
2. Sperms are produced in these male reproductive organs.
3. Another term for in vitro fertilisation.
4. These animals lay eggs.
5. A type of fission in amoeba.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 8
Chapter Name	Cell Structure and Functions
Number of Questions Solved	10
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions

NCERT TEXTBOOK EXERCISES

Question 1.
Indicate whether the following statements are True (T) or False (F):
(a) Unicellular organisms have a one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has an irregular shape. (T/F)
Answer.
(a) True
(b) True
(c) False
(d) True.

Question 2.
Make a sketch of the human nerve cell. What function do nerve cells
perform?
Answer.

The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.

Question 3.
Write short notes on the following:

1. Cytoplasm
2. Nucleus of a cell.

Answer.

1. It is the jelly-like substance found between the nucleus and the cell membrane. It contains the nucleus and many small structures called organelles. Cytoplasm, along with nucleoplasm, forms the living substance of the cell, called the protoplasm.
2. It is an important component of the living cell. It is generally spherical and located in the center of the cell. The Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. The liquid substance of the nucleus is termed nucleoplasm. There is a smaller spherical body in the nucleus which is called the nucleolus. The Nucleus also contains thread-like structures called chromosomes. These carry genes and help in inheritance. The Nucleus acts as the control center of the activities of the cell.

With a microscope of higher magnification, we can see a smaller spherical, dense body in the nucleus. It is called the nucleolus. In addition, the nucleus contains thread-like structures called chromosomes. These carry genes and help in the inheritance or transfer of characters from the parents to the next generation. The chromosomes can be seen only when the cell divides. The nucleus, in addition to its role in inheritance, acts as the control centre of the activities of the cell.

Question 4.
Which part of the cell contains organelles?
Answer.
The Cytoplasm contains organelles of the cell.

Question 5.
Make sketches of animal and plant cells. State three differences between them.
Answer.

Plant cells	Animal cells
1.  The outermost covering is cell wall which is made of cellulose. 2.   Plastids (e.g., chloroplasts) are present. 3.   Large vacuoles are present.	1. The outermost covering is the plasma membrane which is living material. 2.  Plastids are absent. 3.     No or small vacuoles Eire present.

Question 6.
State the difference between eukaryotes and prokaryotes.
Answer.

Eukaryotes	Prokaryotes
1. Nucleus of the cell has a nuclear membrane.	1. Nucleus is not bounded by a membrane.
2. Possess membrane-bound organelles.	2. Membrane-bound organelles are absent.
3. Examples include all higher plants and animals.	3. Examples are bacteria and blue-green algae.

Question 7.
Where are chromosomes found in a cell? State their functions.
Answer.
Chromosomes are found in the nucleus of the cell. They carry genes and help in inheritance i.e., transfer of characters from the parents to the offspring.

Question 8.
‘Cells are the basic structural units of living organisms. Explain.
Answer.
All organisms are made up of cells. They have different designs, shapes and sizes in the living organism. All the life processes take place inside a cell. Many similar cells aggregate together to make tissue. So many tissues are organised to form organs and finally, many organs are organised to form a system. So we can say that cells are the basic units of living organisms.

Question 9.
Explain why chloroplasts are found only in plant cells?
Answer.
Chloroplasts contain chlorophyll which synthesizes food in plants by the process of photosynthesis. As photosynthesis does not occur in animals, it does not contain chloroplasts.

Question 10.
Complete the crossword with the help of clues given below:
Across
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.
Down
1. Green plastids.
2. Formed by a collection of tissues.
4. It separates the contents of the cell from the surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 7
Chapter Name	Conservation of Plants and Animals
Number of Questions Solved	11
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals

NCERT TEXTBOOK EXERCISES

Question 1.
Fill in the blanks:

1. A place where animals are protected in their natural habitat is called………….
2. Species found only in a particular area is known as…………
3. Migratory birds fly to faraway places because of…………… changes.

Answer.

1. wildlife sanctuary
2. endemic species
3. climatic.

Question 2.
Differentiate between the following:

1. Wildlife sanctuary and biosphere reserve
2. Zoo and wildlife sanctuary
3. Endangered and extinct species
4. Flora and fauna

Answer.

1. Wildlife Sanctuary: The area that is reserved in a forest for the protection and preservation of wild animals. It also provides suitable living conditions.
   Biosphere Reserve: The area that is meant for the conservation of biodiversity. It also helps to maintain the culture of that area. One biosphere reserve may also contain other protected areas in it.
2. Zoo: A place where animals are protected in an artificial habitat.
   Wildlife Sanctuary: The area, that is reserved in a forest for the protection and preservation of wild animals.
3. Endangered Species: The animal species whose numbers are diminishing to a level that they might face extinction.
   Extinct Species: The animal species, whose numbers are nil (zero), because of changes in their habitat and other calamities.
4. Flora: The plants that are found in a particular area are called flora. For example, Sal, teak, jamun etc.
   Fauna: The animals that are found in a particular area are called fauna. For example, Chinkara, cheeta, leopard etc.

Question 3.
Discuss the effects of deforestation on the following:

1. Wild animals
2. Environment
3. Villages (Rural areas)
4. Cities (Urban areas)
5. Earth
6. The next generation

Answer.

1. They won’t get their natural habitat and surroundings, as well as food. So either they will extinct or reach the verge of extinction or they will migrate to another forest. In course of their migration, they might be killed by humans.
2. Climatic changes disturb the environment. Global warming is caused due to accumulation of carbon dioxide. Because of deforestation and an increase in the temperature on earth, the water cycle will get disturbed and the reduced rainfall will cause droughts.
3. Villagers cannot grow food (crops) because of no rain as drought situations will prevail. Many poor villagers may die for want of food. The villagers will move to towns and cities. On one hand, villages will be completely deserted and on the other hand, the towns and cities will be overcrowded.
4. Cities flooded with drought-affected villagers will disturb the environment. Food-grains will either not available or if available, they will be costlier. People will also not get wood for making furniture and buildings.
5. Deforestation is a major cause, which leads to change in soil properties. Gradually the land will get converted into a desert. On the other hand, the snow of the mountains will melt due to global warming, and many coastal cities will be flooded causing disaster.
6. The next generation will either be extinct or if at all it exists, it will suffer from diseases and face life scarcity of food in life. So, the next generation will be ill, weak, and, consequently, face extinction.

Question 4.
What will happen if:

1. we go on cutting trees.
2. the habitat of an animal is disturbed.
3. the top layer of soil is exposed.

Answer.

1. If we go on cutting trees, then:
   • The survival of mankind will become a threat, because of the low oxygen concentration in the atmosphere.
   • We have to face high temperatures and increased pollution levels.
   • Natural calamities will disrupt our life.
   • The water cycle will be disturbed.
2. If the habitat of an animal is disturbed, then:
   • The animals will lose their natural habitat and ultimately will be at the periphery to become endangered.
   • The survival of animal will be difficult, because of the drought and the rise in temperature.
3. If the top layer of soil is exposed, then:
   • The exposed top layer loses all its nutrients, especially the hummus.
   • It leads to a decrease in the water holding capacity of the soil.
   • The vegetation will go off from the field, and desertification will be the result.

Question 5.
Answer in brief.

1. Why should we conserve biodiversity?
2. Protected forests are also not completely safe for wild animals. Why?
3. Some tribals depend on the jungle. How?
4. What are the causes and consequences of deforestation?
5. What is Red Data Book?
6. What do you understand by the term migration?

Answer.

1. Biodiversity refers to the variety in life existing on Earth, their interrelationships, and their relationship with the environment, so we should conserve as the food chain should not get disturbed, otherwise the whole ecosystem will be affected.
2. Protected forests are also not completely safe for wild animals, because poaching or capturing of the animal takes place in these areas. Wild animals are killed by poachers.
3. Tribes, usually the residents of the jungle, are dependent on the jungle for the fulfillment of their daily needs of life.
4. The causes and consequences of deforestation are:
   • It increases the temperature and pollution level on earth.
   • It decreases the level of oxygen in the atmosphere and groundwater level is also lowered.
   • The rainfall and the fertility of the soil will decrease.
   • The chances of natural calamities are more because of deforestation.
   • It changes the soil properties.
   • It affects the top layer of the soil, which exposes the lower hard and rocky layers.
5. The Red Data Book is the only source as a book, which keeps a record of all the endangered animals and plants.
6. The term migration means the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for some specific purposes like breeding or to overcome unfavourable conditions.

Question 6.
In order to meet the ever-increasing demand in factories and for shelter, trees are being continually cut. Is it justified to cut trees for such projects? Discuss and prepare a brief report.
Answer.
Of course, to meet the ever-increasing demand in factories and for shelter, trees are being continually cut, which is hot justified at all. If one tree is cut, at least five trees should be grown so that the reforestation process may remain continuous.

But, if trees are cut blindly and no trees are planted then the earth may face global warming, no rainfall, climatic change, soil erosion, and desertification, etc. So, cutting trees for any reason at all is not justified.

Question 7.
How can you contribute to the maintenance of the green wealth of your locality? Make a list of actions to be taken by you.
Answer.
For the contribution to maintain of green wealth in my locality, the different actions to be taken are:

1. not to allow anybody to cut any trees;
2. always try to plant saplings in the residing area;
3. never ever show the neglection to water the plants;
4. always trimming the plants from time to time for their better growth.

Question 8.
Explain how deforestation leads to reduced rainfall.
Answer.
Deforestation leads to the accumulation of CO₂ in the atmosphere which results in global warming as CO₂ traps the heat of the sunrays. The increase in temperature on earth will disturb the water cycle and reduce rainfall, causing drought in the region.

Question 9.
Find out about national parks in your state. Identify and show their location on the outline map of India.
Answer.
Do yourself.

Question 10.
Why should the paper be saved? Prepare a list of ways by which you can save paper.
Answer.
Manufacturing paper needs trees. By cutting trees, deforestation is caused which disturbs the balance in nature. If the paper is saved or recycled, many trees can be saved. Paper can be saved by recycling. Paper can be recycled.5-7 times and can be used. If everyone who uses paper, could save at least one sheet of paper in a day, we can save many trees in a year.

We should save and reuse the used paper and recycle it. By following these steps we can save not only the trees but also the energy and water needed for manufacturing paper.

Question 11.
Complete the word puzzle:
Down
1. Species on the verge of extinction.
2. A book carrying information about endangered species.
5. Consequence of deforestation.
Across
1. Species which have vanished.
3. Species found only in a particular habitat.
4. Variety of plants, animals, and microorganisms found in an area.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 6
Chapter Name	Combustion and Flame
Number of Questions Solved	13
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame

NCERT TEXTBOOK EXERCISES

Question 1.
List conditions under which combustion can take place.
Answer.
Conditions under which combustion can take place are as follows :

1. The presence of air (oxygen).
2. The ignition temperature should be reached.
3. A source of inflammable substance.

Question 2.
Fill in the blanks:

1. Burning of wood and coal causes………….of air.
2. A liquid fuel, used in homes is…………..
3. Fuel must be heated to its………… before it starts burning.
4. Fire produced by oil cannot be controlled by……………..

Answer.

1. pollution
2. Kerosene
3. ignition temperature
4. water.

Question 3.
Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer.
CNG is a clean fuel. It produces harmful products in a very small amount. That is why pollution in our cities has reduced.

Question 4.
Compare LPG and wood as fuels.
Answer.

LPG	Wood
1. No residue after burning.	1. Leaves a lot of ash on burning.
2. It can be easily stored in cylinders for convenient transportation.	2. Cannot be transported easily like LPG.
3. Burns easily.	3. Catches fire with more difficulty.
4. Low ignition temperature.	4. High ignition temperature.
5. No smoke on burning.	5. Burns with smoke.

Question 5.
Give reasons:

1. Water is not used to control fires involving electrical equipment.
2. LPG is a better domestic fuel than wood.
3. Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Answer.

1. Water is not used to control fires produced by .electrical equipment because water is a conductor of electricity and may cause electrocution or electric shock.
2. LPG is a substance which is readily available. It is cheaper and bums easily in the air at a moderate rate. It produces a large amount of heat and does not leave behind any undesirable substance.
3. Paper catches fire easily, but when it is wrapped around an aluminium pipe and heat is supplied then in the presence of aluminium pipe, the ignition temperature of the paper does not reach, because heat given to it is passed to the aluminium pipe which lowers the temperature of the paper. That is why the paper does not catch fire.

Question 6.
Make a labelled diagram of a candle flame.
Answer.

Fig. 6.1. Different zones of a candle flame

Question 7.
Name the unit in which the calorific value of a fuel is expressed.
Answer.
The calorific value of a fuel is expressed in kilojoules per kg (kJ/kg).

Question 8.
Explain how CO₂ is able to control fires.
Answer.
CO₂, being heavier than oxygen, covers the fire like blanket and also brings down the temperature of fuel. Since the contact between the fuel and oxygen is cut off, the fire comes under control.

Question 9.
It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer.
Green leaves contain a lot of water. So, when we try to burn green leaves, water present in the leaves cools the combustible materials (leaves), so that their temperature is brought below their ignition temperature. This prevents the burning of green leaves.

On the other hand, dry leaves do not contain any water. So when a burning process starts, their temperature is raised drastically above their ignition temperature and the leaves catch fire easily.

Question 10.
Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer.
A goldsmith uses the outermost zone of a flame for melting gold and silver because it is the hottest zone of the flame (temperature ≈ 800°C) and is non-luminous in nature.

Question 11.
In an experiment, 4.5 kg of fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.
Answer.
The calorific value of the fuel:
Calorific value = heat produced/amount of fuel = 1,80,000 kJ/4.5 kg = 40,000 kJ/kg

Question 12.
Can the process of rusting be called combustion? Discuss.
Answer.
Yes, the process of rusting can be called combustion, in fact, slow combustion because rusting also takes place in the air (O₂) in the presence of humidity.

Question 13.
Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Answer.
The water of Ramesh’s beaker will get heated in a shorter time because the outermost part of the flame is the hottest.

We hope the NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame, drop a comment below and we will get back to you at the earliest

NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 18
Chapter Name	Pollution of Air and Water
Number of Questions Solved	11
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water

NCERT TEXTBOOK EXERCISES

Question 1.
What are the different ways in which water gets contaminated?
Answer.
Water gets contaminated due to the addition of substances harmful to health. Sewage, agricultural chemicals, and industrial waste are some of the major contaminants of water.

Question 2.
At an individual level, how can you help to reduce air pollution?
Answer.
At the individual level we can do the following things to reduce air pollution:

1. Use CNG and unleaded petrol instead of ordinary petrol and diesel.
2. Use public transport as far as possible.
3. Generate awareness about air pollution among the members of our family and friends.
4. We can plant trees and nurture the ones already present in the neighborhood.

Question 3.
Clear, transparent water is always fit for drinking. Comment.
Answer.
No, water which looks clean may still have disease-carrying microorganisms and dissolved impurities. Hence, it is not always fit for drinking, so it is essential to purify water before drinking, say for example by boiling process.

Question 4.
You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.
Answer.
Following are some of the measures that would help our town to ensure the supply of clear water to all its residents:

1. Make the supply system leakproof as a lot of drinking water is being wasted through the leakages.
2. Proper cleaning of the water tank from time to time.
3. Chlorine tablets should be made available.
4. The water supply pipes should not come in contact with the sewage pipes.

Question 5.
Explain the differences between pure air and polluted air.
Answer.
Pure air is free from any pollutant, has no smell, is soothing, and not irritating to the eyes. Whereas polluted air gives a filthy smell and people cannot breathe in ut. If people inhale such (impure or polluted) air, they may suffer from various breathing, heart, and lung problems. Even sometimes people die inhaling polluted air.

Question 6.
Explain circumstances leading to acid rain. How does acid rain affect us?
Answer.
Pollutants like sulphur dioxide and nitrogen dioxide react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. These come down with the rain, making the rain acidic. This is called acid rain.
Acid rain affects us in many ways, e.g.

1. Acid rain removes basic nutrients such as calcium from the soil.
2. Acid rain increases the corrosion of metals.
3. Acid rain damages buildings and sculptural materials.
4. The low pH of add rainwater changes the rate of metabolism of some organisms.
5. Add rain causes damage to freshwater life, e.g., decrease in fish population of lakes.
6. Add mists cause direct damage to the leaves of plants.

Question 7.
Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen
Answer.
(d) Nitrogen

Question 8.
Describe the ‘Green House Effect’ in your own words.
Answer.
The sun’s rays when fall on the earth’s surface, warm it. Some of the sun’s rays are absorbed by the earth’s surface and left out rays are reflected back into space. Some of these rays are trapped by gases like C0₂, methane, etc. in the atmosphere, and these are not allowed to go out of the earth’s atmosphere.

These trapped rays begin to warm the earth’s surface. This causes heating of the earth’s atmosphere. This effect is named the Greenhouse effect because this is exactly like the greenhouse effect in a nursery.

Question 9.
Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer.
Today, global warming has appeared as one of the most severe threats to humankind. On one hand, carbon dioxide is added to the atmosphere due to human activities, by the other, as forest areas are also decreasing.

Question 10.
Describe the threat to the beauty of the Taj Mahal.
Answer.
Over the past 2 decades, India’s most famous tourist attraction, the Taj Mahal located at Agra, has become a matter of great concern. Experts have warned that air pollution is discolouring its white marble. So it is not only living organisms that get affected by polluted air but also the non-living things like buildings, monuments, and statues that are going to be affected.

The industries located in and around Agra like rubber processing, automobiles, chemicals and especially, the Mathura Oil Refinery have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. These come down with the rain, making the rain acidic. This is called acid rain. Acid rain has resulted in corrosion of the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particle emitted by the Mathura oil refinery, has contributed to the yellowing of the marble.

The Supreme Court has taken several steps to save the Taj Mahal. It has issued orders for the industries to either switch to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas) or to move to faraway places. Moreover, the automobiles should switch over to unleaded petrol in the Taj Mahal Zone.

Question 11.
Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer.
Chemicals used as fertilizers in agriculture dissolve in water and are washed away into water bodies from the field. The excessive quantities of chemicals like nitrates and phosphates which are present in fertilisers act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. They use up a lot of oxygen. This results in a decrease in the oxygen level which is harmful to the survival of other organisms.

We hope the NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 5
Chapter Name	Coal and Petroleum
Number of Questions Solved	9
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum

NCERT TEXTBOOK EXERCISES

Question 1.
What are the advantages of using CNG and LPG as fuels?
Answer.
The advantages of using CNG and LPG as fuels are as follows:

1. These are clean fuels.
2. These are low-cost fuels.
3. These are available easily.
4. These can be used directly for burning in homes and factories where it can be supplied through pipes.

Question 2.
Name the petroleum product used for surfacing roads.
Answer.
A petroleum product ‘Bitumen’ is used for surfacing of roads.

Question 3.
Describe how coal is formed from dead vegetation. What is this process called?
Answer.
About 300 million years ago, the earth was having dense forests in low-lying wetland areas. Due to earthquakes and volcanic eruptions, these forests got buried under the soil. As more soil deposited over them, they were compressed.

The temperature also raised as they sank deeper and deeper. Due to high temperature and lack of oxygen, dead plants inside the earth got slowly converted to coal. As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonization.

Question 4.
Fill in the blanks:
(a) Fossil fuels are.…….,…………. and………..
(b) Process of separation of different constituents from petroleum is called………………
(c) Least polluting fuel for a vehicle is……………
Answer.
(a) coal, petroleum, natural gas
(b) refining
(c) CNG.

Question 5.
Tick True/False against the following statements:
(a) Fossil fuels can be made in the laboratory.   (T/F)
(b) CNG is more polluting fuel than petrol.   (T/F)
(c) Coke is almost pure form of carbon.  (T/F)
(d) Coal tar is a mixture of various substances.   (T/F)
(e) Kerosene is not a fossil fuel.  (T/F)
Answer.
(a) False
(b) False
(c) True
(d) True
(e) False.

Question 6.
Explain why fossil fuels are exhaustible natural resources.
Answer.
Fossil fuels are present in nature in limited quantity and are being exhausted abundantly by us. That is why fossil fuels are called exhaustible natural resources.

Question 7.
Describe characteristics and uses of coke.
Answer.
Coke is a tough, porous, and black substance. It is an almost a pure form of carbon. “Coke is obtained by heating soft coal in the absence or little supply of air”.
It is used in the manufacture of steel and in the extraction of many metals.

Question 8.
Explain the process of the formation of petroleum.
Answer.
Petroleum is formed from organisms living in the sea. When these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, they were transformed into petroleum and natural gas under the absence of air and the presence of high temperature and pressure.

Question 9.
The following table shows the total power shortage in India from 1991-1997.
Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis.
Answer.

S. No.	Year	Shortage (%)
1	1991	7.9
2	1992	7.8
3	1993	8.3
4	1994	7.4
5	1995	7.1
6	1996	9.2
7	1997	11.5

We hope the NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum, drop a comment below and we will get back to you at the earliest

NCERT Solutions for Class 8 Science Chapter 17 Stars and the Solar System are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 17 Stars and the Solar System.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 17
Chapter Name	Stars and the Solar System
Number of Questions Solved	16
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 17 Stars and the Solar System

NCERT TEXTBOOK EXERCISES

Choose the correct answer in Questions 1-3:

Question 1.
Which of the following is NOT a member of the solar system?
(a) An asteroid
(b) A satellite
(c) A constellation
(d) A comet
Answer.
(c) A constellation.

Question 2.
Which of the following is NOT a planet of the Sun?
(a) Sirius
(b) Mercury
(c) Saturn
(d) Earth
Answer.
(a) Sirius.

Question 3.
Phases of the moon occur because:
(a ) we can see only that part of the moon which reflects light towards us.
(b) our distance from the moon keeps changing.
(c) the shadow of the Earth covers only a part of the moon’s surface.
(d) the thickness of the moon’s atmosphere is not constant.
Answer.
(a) we can see only that part of the moon which reflects light towards us.

Question 4.
Fill in the blanks:

1. The planet which is farthest from the Sun is………….
2. The planet which appears reddish in colour is…………
3. A group of stars that appear to form a pattern in the sky is known as a……………
4. A celestial body that revolves around a planet is known as…………
5. Shooting stars are actually not…………..
6. Asteroids are found between the orbits of and.…………

Answer.

1. Neptune
2. Mars
3. constellation
4. satellite
5. meteors
6. Mars, Jupiter.

Question 5.
Mark the following statements as True (T) or False (F):

1. Pole star is a member of the solar system.   (   )
2. Mercury is the smallest planet in the solar system. (   )
3. Uranus is the farthest planet in the solar system.   (   )
4. INSAT is an artificial satellite.   (   )
5. There are nine planets in the solar system.    (   )
6. Constellation Orion can be seen only with a telescope.   (   )

Answer.

1. False
2. True
3. False
4. True
5. False
6. False

Question 6.
Match items in column A with one or more items in column B.

Answer.

Question 7.
In which part of the sky can you find Venus if it is visible as an evening star?
Answer.
Venus appears in the western sky just after sunset.

Question 8.
Name the largest planet of the solar system.
Answer.
Jupiter (Brihaspati).

Question 9.
What is a constellation? Name any two constellations.
Answer.
A group of stars that has a recognizable shape is called a constellation. Ursa Major and Orion are two examples of constellations.

Question 10.
Draw sketches to show the relative positions of prominent stars in:
(a) Ursa Major and (b) Orion.
Answer.

Question 11.
Name two objects other than planets which are members of the solar system.
Answer.
Satellites and asteroids are the objects that too, are members of the Solar system.

Question 12.
Explain how you can locate the Pole Star with the help of Ursa Major.
Answer.
Pole stars can be located with the help of the two stars at the end of Ursa Major. Imagine a straight line passing through these stars as shown in Fig. 17.2. Extend this imaginary line towards the north direction. (About five times the distance between the two stars). This line will lead to a star which is not too bright. This is the Pole Star.

Question 13.
Do all the stars in the sky move? Explain.
Answer.
No, no star moves in the sky. They appear to move from east to west because the Earth rotates from west to east about its axis.

Question 14.
Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light-years away from the Earth?
Answer.
The distance between stars is so large that it cannot be expressed in terms of a kilometer. That is why very large distances, are expressed in another unit known as light year. One light-year is the distance traveled by light in one year. If the distance of a star is eight light-years, it means that this distance is the distance traveled by light in eight years.

Question 15.
The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accommodate?
Answer.

Question 16.
Boojho made the following sketch (See Fig. 17.29 of NCERT) of the solar system.
Is the sketch correct? If not, correct it.
Answer.
It is not correct. Figure 17.3 is a correct sketch of the solar system.

We hope the NCERT Solutions for Class 8 Science Chapter 17 Stars and the Solar System help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 17 Stars and the Solar System, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 16 Light are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 16 Light.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 16
Chapter Name	Light
Number of Questions Solved	17
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 16 Light

NCERT TEXTBOOK EXERCISES

Question 1.
Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.
Answer.
We cannot see objects in the darkroom. But, we can see objects outside the room, in case there is light outside the room. It is so because to see an object, we need light which gets reflected from the object and enters our eyes.

Question 2.
Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
Answer.

Regular reflection	Diffused reflection
1. Occurs from shiny and smooth surfaces. 2. Reflected rays are parallel to each other.	1. Occurs from unpolished and rough surfaces. 2. Reflected rays are not parallel to each other.

No, diffused reflection does not mean, failure of the laws of reflection. It is due to irregularities in the reflecting surface, like that of cardboard.

Question 3.
Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.

1. Polished wooden table
2. Chalk powder
3. Cardboard surface
4. Marble floor with water spread over it
5. Mirror
6. Piece of paper

Answer.

1. Polished Wooden Table: Regular reflection will take place. This is because a polished wooden table will have a plane surface.
2. Chalk Powder: Diffused reflection because the surface of the chalk powder is not smooth.
3. Cardboard Surface: Diffused reflection since cardboard has a rough surface,
4. Marble Floor with Water Spread Over it: Regular reflection as it will act as a plane surface.
5. Mirror: Regular reflection because the mirror has a shiny surface which is even.
6. Piece of Paper: Diffused reflection because the surface of the paper is rough.

Question 4.
State the laws of reflection.
Answer.
The laws of reflection are as follows:

1. The angle of reflection is equal to the angle of incidence.
2. The incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane.

Question 5.
Describe an activity to show that the incident ray, the reflected ray, and the normal at the point of incidence lie in the same plane.
Answer.

Question 6.
Fill in the blanks in the following:

1. A person 1 m in front of a plane mirror seems to be…….. m away from his image.
2. If you touch your………..ear with your right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with
3. The size of the pupil becomes………………..when you see in dim light.
4. Night birds have…………..cones than rods in their eyes.

Answer.

1. 2
2. left, left hand
3. large
4. lesser (fewer).

Choose the correct option in Questions 7 and 8.

Question 7.
The angle of incidence is equal to the angle of reflection:
(a) Always
(b) Sometimes
(c) Under special conditions
(d) Never
Answer.
(a) Always.

Question 8.
The image formed by a plane mirror is
(a) virtual, behind the mirror and enlarged,
(b) virtual, behind the mirror and of the same size as the object.
(c) real at the surface of the mirror and enlarged.
(d) real, behind the mirror and of the same size as the object.
Answer.
(b) Virtual, behind the mirror and of the same size as the object.

Question 9.
Describe the construction of a kaleidoscope.
Answer.
A kaleidoscope is an optical instrument used to see a number of beautiful patterns. It is made up of a circular cardboard tube or tube of thick chart paper in which rectangular mirror strips are joined together to form a prism. At one end of the tube, touching these mirrors, a circular plane glass plate is fixed and several, small pieces of colored glass (broken pieces of colored bangles) are placed upon it. This end is closed by a ground glass plate and beautiful patterns are seen through the other end of the kaleidoscope.

Question 10.
Draw a labelled sketch of the human eye.
Answer.

Question 11.
Gurmit wanted to perform, activity 16.8 (NCERT) using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advice?
Answer.
Laser rays can cause a permanent defect in the eye. Thus, his friend will lose her eyesight if a laser torch is directed over her eyes.

Question 12.
Explain how you can take care of your eyes.
Answer.
The following measures should be taken to keep our eyes healthy and free from any defect:

1. We should not look at the sun or a powerful light source directly.
2. We should not try to see in too little or too much light. It is bad for the eyes. Insufficient light causes eye strain and headaches.
3. Too much light, like that of the sun, or powerful lamps, can injure the retina, which is very delicate.
4. If advised, suitable spectacles should be used.
5. We should wash our eyes frequently with clean water.
6. We should always read from a normal distance for distinct vision and not by bringing the book too close or keeping it too far.
7. We should never rub our eyes if any small particle of dust goes into the eyes. Instead, eyes should be washed with clean water and if the condition does not improve, a doctor should be consulted.
8. If food is deficient in some components, the eye may also suffer. Lack of vitamin A in our diet is responsible for many eye troubles. Most common amongst thorns is night blindness. Therefore, to get rid of this, we must include in our diet components that have vitamin A.

Question 13.
What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
Answer.

Question 14.
How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?
Answer.
The infinite number of images of the candle will be formed if it is placed between two parallel plane mirrors.

Question 15.
Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.5. Draw the reflected ray from the second mirror.

Answer.

Question 16.
Boojho stands at A just on the side of a plane mirror as shown in Fig. 16.6.
Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?

Answer.
No, He can see images of objects at P but not of Q and R.

Question 17.
(a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.7).
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?

Answer.
(a) Fig. 16.7 (a)
(b) Yes
(c) Yes
(d) No change as the position of A is not changing

We hope the NCERT Solutions for Class 8 Science Chapter 16 Light helps you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 16 Light, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 15
Chapter Name	Some Natural Phenomena
Number of Questions Solved	12
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena

NCERT TEXTBOOK EXERCISES

Select the correct option in Questions 1 and 2.

Question 1.
Which of the following cannot be changed easily by friction?
(a) A plastic scale
(b) copper rod
(c) An inflated balloon
(d) A woolen cloth.
Answer.
(b) A copper rod.

Question 2.
When a glass rod is rubbed with a piece of silk cloth the rod
(а) and the cloth both acquire a positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire a negative charge.
(d) becomes negatively charged while the cloth has a positive charge,
Answer.
(d) becomes negatively charged while the cloth has a positive charge.

Question 3.
Write T against true and ‘F’ against false in the following statements:
(a) Like charges attract each other. (T/F)
(b) A charged glass rod attracts a charged plastic straw. (T/F)
(c) Lightning conductor cannot protect a building from lightning. (T/F)
(d) Earthquakes can be predicted in advance. (T/F)
Answer.
(a) False
(b) True
(c) False
(d) False

Question 4.
Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
Answer.
The crackling sound is heard because when the sweater is rubbed while taking it off, it acquires a small charge.

Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
Answer.
When we touch a charged body the total charge is transferred into the earth through our body and it loses its charge.

Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer.
The destructive energy of an earthquake is measured on a scale called the Richter scale. An earthquake that measures 3 on the Richter scale Will be recorded by a seismograph. However, it is not likely to cause much damage.

Question 7.
Suggest three measures to protect ourselves from lightning.
Answer.

1. We should not use TV or cable phone during lightning.
2. After hearing the last thunder, wait for at least 30 minutes before coming out of the safe place.
3. A house or a building is a safe place. If you are travelling by car or by bus, you are safe inside with the windows and doors of the vehicle shut.

Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Answer.
A charged balloon is repelled by another charged balloon because both have the same charge. And we know similar charges repel each other. But a charged balloon attracts an uncharged balloon and loses its own charge to the other balloon.

Question 9.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer.
Electroscope: An electroscope is a device used to detect the presence of charge of an object.
Principle: It works on the principle that like charges repel while unlike charges attract each other.

Structure and Working: An electroscope has a metal rod with a thin metal strip or leaf attached to it at the bottom. At the top, the rod enters into a cup. The bottom part of the rod and leaf is enclosed in a glass box for protection. When the knob of the electroscope is touched with a charged ebonite or glass rod, the leaves open out or diverge. The extent of divergence depends upon the amount of charge on the electroscope.

Question 10.
List three states in India where earthquakes are more likely to strike.
Answer.
The states that fall in seismic zones are more earthquake-prone. Jammu and Kashmir, Himachal Pradesh, and Gujarat are a few such states.

Question 11.
Suppose you are outside your home and an earthquake strikes. What precautions would you take to protect yourself?
Answer.

1. Find a safe place, that will be away from buildings, trees and overhead power lines. Do not be on the ground but squat low on it to make yourself the smallest target to be struck.
2. If we are in a car or a bus, we should not come out, as the driver needs to drive slowly to a clear spot. Do not come out till the earthquake stops.

Question 12.
The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer.
No, I would not carry an umbrella. Because the pointed rod of the umbrella can become a target of lightning.

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