Lesson: Sources of Energy

Question: 1

Which of the following is a non-renewable source of energy?

(a) Wood

(b) Sun

(c) Fossil fuels

(d) Wind



Question: 2

Acid rain happens because:

(a) Sun leads to heating of upper layer of atmosphere.

(b) Burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere.

(c) Electrical charges are produced due to friction amongst clouds.

(d) Earth atmosphere contains acids.



Question: 3

Fuel used in thermal power plants is:

(a) Water

(b) Uranium

(c) Biomass

(d) Fossil fuels



Question: 4

In a hydro power plant:

(a) Potential energy possessed by stored water is converted into electricity.

(b) Kinetic energy possessed by stored water is converted into potential energy.

(c) Electricity is extracted from water.

(d) Water is converted into steam to produce electricity.



Question: 5

Which is the ultimate source of energy?

(a) Water

(b) Sun

(c) Uranium

(d) Fossil fuels



Question: 6

Which one of the following forms of energy leads to least environmental pollution in the process of its harnessing and utilisation?

(a) Nuclear energy

(b) Thermal energy

(c) Solar energy

(d) Geothermal energy Solution



Question: 7

Geothermal energy:

(a) Energy stored by waves in the ocean.

(b) Temperature difference at different levels in the ocean.

(c) Pressure difference at different levels in the ocean.

(d) Tides arising out in the ocean.



Question: 8

The major problem in harnessing nuclear energy is how to:

(a) Split nuclei?

(b) Sustain the reaction?

(c) Dispose off spent fuel safely?

(d) Convert nuclear energy into electrical energy?



Question: 9

Which part of the solar cooker is responsible for greenhouse effect?

(a) Coating with black colour inside the box

(b) Mirror

(c) Glass sheet

(d) Outer cover of the solar cooker



Question: 10

The main constituent of biogas is:

(a) Methane

(b) Carbon dioxide

(c) Hydrogen

(d) Hydrogen sulphide



Question: 11

The power generated in a windmill:

(a) Is more in rainy season since damp air would mean more air mass hitting the blades.

(b) Depends on the height of the tower.

(c) Depends on wind velocity.

(d) Can be increased by planting tall trees close to the tower.



Question: 12

Choose the correct statement:

(a) Sun can be taken as an inexhaustible source of energy

(b) There is infinite storage of fossil fuel inside the earth.

(c) Hydro and wind energy plants are non-polluting sources of energy.

(d) Waste from a nuclear power plant can be easily disposed off.



Question: 13

In a hydroelectric power plant more electrical power can be generated if water falls from a greater height because:

(a) Its temperature increases.

(b) Larger amount of potential energy is converted into kinetic energy.

(c) The electricity content of water increases with height.

(d) More water molecules dissociate into ions.



Question: 14

Choose the incorrect statement regarding wind power:

(a) It is expected to harness wind power to minimum in open space.

(b) The potential energy content of wind blowing at high altitudes is the source of wind power.

(c) Wind hitting at the blades of a windmill causes them to rotate the rotation thus achieved can be utilised further.

(d) One possible method of utilising the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator.



Question: 15

Choose the incorrect statement:

(a) We are encouraged to plant more trees so as to ensure clean environment and also provide bio-mass fuel.

(b) Gobar-gas is produced when crops, vegetable wastes etc. decompose in the absence of oxygen

(d) Bio-mass is a renewable source of energy.



Short Answer Questions

Question: 16

Why is there a need to harness non-conventional sources of energy? Give two main reasons.


The two main reasons to harness non-conventional sources of energy are as mentioned below:

·         The deposits of the fossil fuels are limited and depleting at a fast pace.

·         The demand for energy is ever-increasing due to increase in quality of life and growth in population.

Question: 17

Write two different ways of harnessing energy from ocean.


(a) Wave energy: The waves possess very high kinetic energy in them. This energy can be converted to generate electricity.

(b) Tidal power: The kinetic energy of the tides can be converted into electricity by utilising the rise and fall of the ocean tides.

(c) Ocean thermal energy- The energy available due to the difference in the temperature of water at the surface of the ocean and at deeper levels results in the formation of the ocean thermal energy (OTE). The ocean thermal energy can be converted into other forms and be put in suitable use.

Question: 18

What steps would you suggest to minimise environmental pollution caused by burning of fossil fuels?


The steps we would suggest to minimise environmental pollution caused by burning of fossil fuels are:

(i) Using catalytic converter: Pollution caused by burning petroleum fuels in vehicles can be controlled by fitting a catalytic converter in the vehicles.

(ii) Treatment with water in a scrubber: Pollution due to the burning of coal in thermal power and factories can be controlled by washing down the smoke and other pollutants by water in a scrubber.

(iii) Installing electrostatic precipitator in the chimneys of factories:

It prevents the escape of unburnt carbon and ash particles into air.

Question: 19

What is the role of a plane mirror and a glass sheet in a solar cooker?


Plane mirror: It acts as a reflector and reflects the sunlight falling on the top of the solar cooker to the black box where the food is kept.

Glass sheet creates a greenhouse effect in the cooker. Sun’s heat passes through the glass sheet cover and gets trapped in the box. This heat is absorbed by the black interior surface of the cooker box and cooks the food kept inside.

Question: 20

Mention three advantages of a solar cell?


Three advantages of a solar cell are as follows:

(i) It has low maintenance cost.

(ii) It can be set-up in remote areas.

(iii) It does not cause pollution.

Question: 21

What is biomass? What can be done to obtain bio-energy using biomass?


The dead parts of plants and waste materials of animals are called biomass.

The biomass can be best put to use by converting it into biogas by the anaerobic fermentation of the biomass in the presence of water in a biogas plant. Biogas is an excellent fuel. It burns without smoke. It leaves no residue. Its heating capacity is high.

Question: 22

What are the limitations in obtaining energy from wind?


Some of the limitations in obtaining energy from wind are:

(a) It is not available at all times and in equal quantity.

(b) It can be used only at those places where wind blows for the greater part of the year.

(c) It requires large area of land for establishing the wind energy farm.

(d) The initial cost of establishment of wind energy farm is very high.

Long Answer Questions

Question: 23

Which is the process used to harness nuclear energy these days? Explain it briefly.


Nuclear fission can be used to harness nuclear energy these days.

In this process, the nucleus of a heavy atom (such as uranium, plutonium or thorium), are bombarded with low-energy neutrons.

This splits the heavy atoms apart into lighter nuclei. In this process, a tremendous amount of energy is released even if the mass of the original nucleus is just a little more than the sum of the masses of the individual products.

For example, when uranium-235 atoms are bombarded with slow moving neutrons, the uranium nucleus breaks to form two light atoms, barium-139 and krypton-94. In the same reaction, three neutrons are also emitted.

In this fission reaction, some mass of the uranium atom is lost. This mass gets converted into energy.

Question: 24

How can solar energy be harnessed? Mention any two limitations in using solar energy. How these limitations are to be overcome?


The sun is the biggest source of energy for our planet. The sun’s energy consists of light and heat. All of us use sunlight as we do most of work during the day times.

The heat of the sun is utilised with the help of solar heating devices. Some of the solar heating devices are solar cooker, solar heater, solar cell, etc.

Some of the limitations in using solar energy are as follows:

(i) It is available during daytime.

(ii) It requires huge installation cost.

How to overcome

The installation cost remains high and with advancement of technology and large-scale use, it is likely to come down. These limitations of using solar energy can be overcome by using solar cells that convert solar energy into electricity. A large number of solar cells are combined to make a solar cell panel. It can deliver more electricity from the available solar energy. Thus, it ensures better utilisation of the available solar energy.

Question: 25

Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing one non-conventional source of energy.


Conventional sources of energy- Some of the conventional sources of energy are:

·         Fossil fuels

·         Hydro-energy (hydro power plant)

·         Biomass energy

·         Wind energy

Non-conventional sources of energy - Some of the non-conventional sources of energy are:

·         Tidal energy

·         Nuclear energy

·         Solar energy

·         Energy from ocean

·         Geothermal

Geothermal energy

Molten rocks are formed in the deeper hot regions of the earth’s crust. Due to the geological changes, these are pushed upward and are trapped in certain regions called ‘hot spots’.

The earth has abundance of underground water. Steam is generated when the underground water meets the hot spots. The hot water comes out as a hot spring when it finds an outlet.

The steam trapped in rocks is transferred to a turbine through pipes and used to generate electricity. Though the cost of production of electricity by this method is low, yet there are very few commercially viable sites for such a use.

Question: 26

Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea in different ways?


Some of the reasons why the non- conventional sources of energy needs to be harnessed are given below.

(a) Conventional sources like the fossil fuels are limited and are depleting.

(b) Demand for energy is increasing due to increasing population and growing aspirations of people due to improving life style.

Harnessing Ocean Energy

The energy from the ocean can be harnessed by the following three sources of ocean energy:

·         Energy due to the tides formed in the ocean.

·         Energy possessed by the huge waves near the seashore.

·         Temperature difference between the surface and at certain depth of the seawater.

Energy due to the tides formed in the ocean/ Energy possessed by the huge waves near the seashore-

The first two cases are related to the movement of the ocean water. This energy is harnessed by constructing a dam across a narrow opening to the sea.

A turbine is fixed at the opening of the dam which converts kinetic energy to electricity.

Temperature difference between the surface and at certain depth of the seawater-

A volatile liquid like ammonia is used to tap the energy of hot water at the surface. The warm surface-water boils the volatile liquid. The vapours of the liquid are used to run the turbine of a generator. The cold water, in turn, from the depth of the ocean is pumped up. It condenses the vapour to liquid.

Question: 27

What are the environmental consequences of using fossil fuels? Suggest the steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy.


Environmental consequences of using fossil fuels

Acid rain: Fossil fuels produce acidic gases like nitrogen dioxide and sulphur dioxide. These gases are responsible for acid rain.

Global warming: Burning of fossil fuels result in the release of large amount of carbon dioxide. This contributes to global warming.

Environmental pollution: Burning of fossil fuels produce ash and/or smoke which adds to environmental pollution.

Some of the steps to minimise environmental pollution are:

Using catalytic converter: Fitting vehicles with catalytic converter can control the pollution caused by burning petroleum fuels in vehicles.

Treatment with water in a scrubber: Pollution due to the burning of coal in thermal power and factories can be controlled by washing down the smoke and other pollutants by water in a scrubber.

Installing electrostatic precipitator in the chimneys of factories: It prevents the escape of unburnt carbon and ash particles into the air.

Afforestation: Planting of trees and increase in forest area helps in reduction of carbon dioxide level across the world.

Judicious use of energy: There should be judicious use of energy and it should not be wasted in any form.

Alternate source of energy: Use of alternate and non-conventional sources of energy like solar energy, wind energy, etc. reduce our dependencies on fossil fuels.

Question: 28

Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.


The energy from the sun can be considered to have been derived from the sun. This can be understood from the following examples.

a)   Fossil fuels: Fossils fuels are produced from the remains of plants and animals. The sun has been the source of energy for all living beings on earth.

b)   Hydroelectric energy: Hydroelectric energy is derived from water. The availability of water depends largely on the rainfall and the heating of the glaciers. The sun plays an important role in these physical processes.

c)   Wind energy: Wind is produced due to the uneven heating of the earth’s surface by the sunrays.

d)   Ocean energy: The tide energy, movement of ocean current and ocean thermal energy, etc. are derived from the sun’s energy.

e)   Solar cells: The sun’s energy is directly used for various activities. Solar cells are used to convert solar energy into other forms of energy.

f)    Photosynthesis: It is a primary source of energy of all living beings on earth. Photosynthesis will not be possible if sunlight is not available to green plants.

Question: 29

What is biomass? Explain the principle and working of a biogas plant using a labelled schematic diagram.


Biomass is the dead parts of plants and trees, and the waste material of animals. Biomass contains chemical energy in the form of carbon compounds. Biomass gives a lot of smoke but very less heat on burning. We can improve the efficiency of the fuels by suitable technological inputs in their use.

For example, when wood is burnt in a limited supply of oxygen, volatile materials in it and water get removed and charcoal is left behind.

Charcoal burns without flames. It is comparatively smokeless and has a higher calorific value, i.e., heat generation efficiency.

Biogas plant

Biogas is a mixture of methane, carbon dioxide, hydrogen and hydrogen sulphide. Its major constituent is methane. It is produced as a result of anaerobic fermentation (in the absence of oxygen) of biomass in the presence of water. The degradation is carried out by anaerobic microorganisms. The starting material to make biogas is mainly cow-dung. So, biogas is also known as ‘gobar-gas’.

Working of a biogas plant

A biogas plant is a dome-like structure with bricks having a mixing tank, sealed chamber called digester (with no oxygen), a gas tank and a gas outlet.

Slurry of biomass and water is made in the mixing tank. The slurry is fed into the digester from the mixing tank. It takes a few days for the decomposition process to be complete and generate the gas. The bio-gas is stored in the gas tank above the digester. It is drawn out through pipes, for use, from the digester. The remains of the biogas plant are used as manure in agriculture.