Std 8 SOURCES OF ENERGY

SOURCES OF ENERGY

10 SOURCES OF ENERGY

points to remember :

1. Energy : Energy is needed to do work. Electrical energy, light,

sound, heat, gravitational energy, atomic energy, etc., are

different forms of energy. It can be converted from one form into

another.

2. Fuel : A substance that produces energy on burning is called a

fuel. Lakhs of years ago, remnants of plants and animals got

buried into the earth and were converted into fossil fuels due to

the tremendous pressure of the earth’s layers above them and

the heat inside. Coal, mineral oil and natural gas are fossil fuels.

Their deposits are limited.

3. Sun : The sun is the only source of energy in the solar system.

The energy that we need over one year is provided by the sun in

just 40 minutes. Solar heaters and solar cookers can be used to

heat water and cook food. In a solar cell, solar energy is

converted into electrical energy.

4. Conventional and non-conventional sources of energy :

Coal and mineral oil are conventional or non-renewable sources

of energy. Sun, wind, water falling from a height, biogas,

biodiesel are non-conventional or renewable sources of energy.

5. Energy crisis : The burning of mineral oil, coal, etc., produces

carbon dioxide. This causes a rise in the global atmospheric

temperature. Some gases give rise to pollution and acid rain. The

gravity of these problems can be reduced by the use of renewable

sources of energy. To meet an increasing demand for energy,

atomic energy should be used.

6. Some solutions to meet energy crisis : Finding out new

sources of energy, giving preference to use of renewable sources

of energy, reducing the use of non-renewable sources of energy,

the use of improved burners, stoves, light sources, etc., are some

of the solutions to meet the energy crisis.

Questions and Answers

Q. 1 Answer the following questions :

* (1) What is meant by fuel ?

Ans. A fuel is a substance that produces energy on burning.

* (2) Name the different types of fossil fuels.

Ans. Coal, mineral oil and natural gas are fossil fuels.

(3) Name the materials that can be obtained from mineral

oil.

Ans. Petrol, diesel, kerosene and fuel oil can be obtained from

mineral oil.

(4) Give four examples of natural gas.

Ans. Methane, ethane, propane and butane are examples of

natural gas.

(5) Name two devices/appliances that use solar energy.

Ans. Solar heater and solar cooker use solar energy.

[Note : In these devices/appliances, mirrors are used to collect and concentrate

solar energy.]

(6) What is a solar cell ? Where is it used ?

Ans. A solar cell is a cell that converts solar energy into

electrical energy. It is used at night for lighting.

Answers to the Questions given on page 98 of the textbook

* (1) Which energy is stored in cattle dung?

Ans. Chemical energy is stored in cattle dung.

* (2) Why is solar energy more important in India ?

Ans. In India, solar energy is available in large quantity

and almost throughout the year. Therefore, it is more

important in India.

* (3) What happens to the solar energy absorbed in

water?

Ans. Solar energy absorbed in water is used partly by

aquatic plants and animals. They survive due to this energy.

(7) What is a conventional or non-renewable source of

energy? Give two examples.

Ans. A conventional or non-renewable source of energy is the

one which cannot be produced anew. Its stock is limited.

Examples : (1) Coal (2) mineral oil.

 (8) What is a non-conventional or renewable source

of energy ?

Ans. A non-conventional or renewable source of energy is the

one which is always available.

* (9) Which are the renewable sources of energy?

Ans. Sun, wind, water falling from a height, biogas, biodiesel

are renewable (or non-conventional) sources of energy.

(10) What are the main causes of the energy crisis ?

Ans. Growing population and growing industrialization are

the main causes of the energy crisis.

(11) Why is it necessary to increase the use of renewable

sources of energy ?

Ans. (1) Deposits of conventional sources of energy such as

mineral oil and coal are limited. Their burning produces carbon

dioxide due to which there is a rise in the global atmospheric

temperature. (2) Many gases released in the atmosphere give rise to

a danger like acid rain. (3) Unrestricted cutting down of trees

causes degradation of forests resulting in threatening of diversity

in plant life. Therefore, it is necessary to increase the use of

renewable sources of energy.

* (12) Which element is used for the production of atomic

power?

Ans. Uranium is used for the production of atomic power.

(13) Which particles are used for bombardment of

uranium atoms to obtain energy?

Ans. Neutrons are used for bombardment of uranium atoms

to obtain energy.

(14) State the points on which the government is focusing

to meet the energy crisis.

Ans. To meet the energy crisis, the government is focusing on

the following points : (1) Finding out new sources of energy.

(2) Giving preference to the use of renewable sources of energy.

(3) Educating the public to use non-renewable sources of energy

responsibly and sparingly. (4) Promoting the use of devices that

consume less fuel such as improved stoves, burners and light

sources using new technology.

Answers to the Questions given on page 101 of the textbook

* (1) Why do renewable sources of energy not cause

pollution ?

Ans. Renewable sources of energy, on burning, do not

produce polluting substances. Hence, they do not cause

pollution.

* (2) With whom does the ownership of renewable

sources of energy rest ?

Ans. The ownership of renewable sources of energy does

not rest with any particular person or nation. Solar energy,

wind energy, etc., can be used by the entire human race.

Q. 2 Give scientific reasons :

* (1) Deposits of fossil fuels are limited.

Ans. Lakhs of years ago, remnants of plants and animals got

buried into the earth. They were converted into fossil fuels due to

the tremendous pressure of the earth’s layers above them and the

heat inside. As this process does not take place in a short time,

but requires lakhs of years, deposits of fossil fuels are limited.

* (2) Solar energy is the source of all forms of fuel.

Ans. The sun is the only source of energy in the solar system.

This energy is absorbed by plants and animals and used for their

nourishment. It is stored in them in the form of chemical energy.

When plants and animals die, this energy becomes available to us

in the form of fossil fuel and other fuels after a long time. Thus,

solar energy is the source of all forms of fuel.

* (3) Natural gas is convenient to use as a fuel.

Ans. (1) Natural gas can be easily transported from its main

sources using pipes over long distances. (2) It lights up quickly and

its burning can be easily controlled. On burning it does not give

smoke and it does not leave any solid substance behind. Thus, it is

convenient to use natural gas as fuel.

* (4) The temperature of the atmosphere is rising.

Ans. (1) With the rise in population, the use of conventional

sources of energy, such as coal and mineral oil increases. Though

these fuels are convenient to use, the resulting emission of carbon

dioxide increases the temperature of the atmosphere. (2) Plants

prepare food using carbon dioxide and solar energy. But

uncontrolled cutting of trees results in degradation of forests.

This results in the decrease in the use of carbon dioxide by plants.

This increases the temperature of the atmosphere.

Q. 3 Answer the following questions in one sentence

each :

(1) Name two forms of energy.

Ans. Electrical energy and light are forms of energy.

(2) Name the substance from which petrol is obtained.

Ans. Petrol is obtained from mineral oil.

(3) Name one renewable source of energy.

Ans. Wind energy is a renewable source of energy.

(4) Name one conventional source of energy.

Ans. Coal is a conventional source of energy.

Q. 4 State whether the following statements are True or

False. If a statement is false, correct it and rewrite :

(1) Light can be converted into electrical energy.

(2) Fossil fuels occur only in the liquid state.

(3) Fossil fuels contain hydrocarbon compounds.

(4) One kilogram wood, used as a fuel, gives about 1700 joules of

energy.

(5) Coal is a renewable source of energy.

(6) Uranium is used to obtain atomic energy.

(7) Fuel oil is used in big furnaces in factories.

Ans. (1) True. (2) False. Fossil fuels occur in all the three

states, solid, liquid and gaseous. (3) True. (4) False. One kilogram

of wood, used as a fuel, gives about 1700 kilojoules of energy.

(5) False. Coal is a non-renewable source of energy. (6) True.

(7) True.

Q. 5 Fill in the blanks :

1. * (1) Charcoal is produced by burning wood in ……… air.

* (2) All fossil fuels contain …… compounds.

* (3) ……… and ……… are renewable sources of energy.

* (4) In Maharashtra, there is an atomic power project at ……….

(5) A substance which produces energy on burning is called

a …….

 (6) ……… wood, on burning, gives about 1700 kilojoules of

energy.

Ans. (1) insufficient (2) hydrocarbon (3) Wind energy,

hydroelectric energy (4) Tarapur (5) fuel (6) 1 kg.

2. (1) ……… is a conventional source of energy.

(2) Petrol, diesel and kerosene are obtained from ……… .

(3) In a ………, solar energy is converted into electrical energy.

(4) The holes in the ……… layer of the atmosphere allow the

passage of harmful rays to the earth.

(5) The unit of energy is the ……… .

Ans. (1) Charcoal (2) mineral oil (3) solar cell (4) ozone

(5) joule.

* Q. 6 Match the following :

‘A’ ‘B’

(1) Mineral oil

(2) Atomic energy

(3) Wind energy

(4) Fossil fuel

(a) Buried plants and animals

(b) Renewable energy source

(c) Uranium

(d) Petrol

Ans. (1) Mineral oil – Petrol (2) Atomic energy –Uranium

(3) Wind energy – Renewable energy source (4) Fossil fuel – Buried

plants and animals.