Request a call back

Join NOW to get access to exclusive study material for best results

Class 10 LAKHMIR SINGH AND MANJIT KAUR Solutions Physics Chapter 3 - Sources of Energy

Sources of Energy Exercise 121

Solution 1

Nuclear fuels (like uranium)

Solution 2

The amount of heat produced by burning 1 gram of a fuel completely is known as its calorific value.

Solution 3

Calorific value of LPG is 50kJ/gm means that if 1 gram of LPG is burnt completely, then it will produce 50kJ of heat energy.

Solution 4

LPG, due to its higher calorific value.

Sources of Energy Exercise 122

Solution 5

Ignition temperature of fuel can be defined as the minimum temperature to which a fuel must be heated so that it may catch fire and start burning.

Solution 6

If ignition temp of a fuel is 80oC, this means that minimum 80oC is required for the ignition of the fuel.

Solution 7


Solution 8

A source of energy is one which can provide adequate amount of energy in a convenient form over a long period of time.

Two main categories of the source of energy are:

i. Renewable source of energy

ii. Non- renewable source of energy

Solution 9

A good source of energy is one:

(i) which would do a large amount of work per unit mass,

(ii) which is cheap and easily available,

(iii) which is easy to store and transport,

(iv) which is safe to handle and use.

Solution 10

A non-renewable source of energy is defined as the source of energy which has accumulated in nature over a very, very long time and cannot be quickly replaced when exhausted.

Ex. Coal, petroleum etc.

Solution 11

A renewable source of energy is the one which is being produced continuously in nature and is inexhaustible.

Ex. wind energy, ocean thermal energy etc.

Solution 12

Renewable source of energy can be used again and again endlessly, where as non-renewable source of energy cannot be renewed once used.

Ex. Renewable sources of energy are wind energy, ocean energy.

Non-renewable sources of energy are coal, fossil fuel.

Solution 13

Fossil fuels are known as non-renewable sources of energy because fossil fuels once used cannot renewed or regained.

Solution 14

Air and water, because both air and water can be used again and again endlessly, they never get exhausted.

Solution 15

Petroleum and coal are non-renewable sources of energy because they cannot be used again once exhausted.

Solution 16

(a) Renewable source of energy - wind, tides, wood

     Non- Renewable source of energy - coal, petroleum, natural gas

(b) The above classification is based on the fact that renewable sources are inexhaustible, whereas non-renewable sources are exhaustible.

Solution 17

Coal is a non-renewable source of energy because it has accumulated in the earth over a very. very long time, and if all the coal gets exhausted, it cannot be produced quickly in nature.

Wood is considered as a renewable source of energy because if trees are cut to obtain wood, then more trees will grow in due course of time.

Solution 18

(a) The material which is burnt to produce heat energy is known as a fuel.

Ex. Wood, coal, LPG, kerosene, diesel etc.

(b) Characteristics of ideal fuel:

(i) It should have high calorific value.

(ii) It should burn without giving out any smoke or harmful gases.

(iii) It should have proper ignition temperature.

(iv) It should cheap and easily available.

(c) Fuel A:

    i. Lower calorific value of 55 kJ/g (Disadvantage)

    ii. Moderate ignition temperature of 80oC (Advantage)

    iii. No harmful gases produced (Advantage)

    Fuel B:

    i. High calorific value of 80 kJ/g (Advantage)

    ii. Very low ignition temperature of 10oC (Disadvantage)

    iii. Harmgul gases like CO and SO2 produced (Disadvantage)

Sources of Energy Exercise 123

Solution 30

Fuel B is the most ideal fuel because

(i) it leaves no residue on burning

(ii)  it has high calorific value of 48 kJ/g

(iii) it does not burn explosively

Solution 31

Fuel Y is a better fuel because

(i) it has a moderate ignition temperature of 75oC.

(ii) it produces no harmful gases like CO on burning.

Solution 32

(i) cooking gas - D

(ii) alcohol - E

(iii) wood - B

(iv) hydrogen - C

(v) kerosene - A

Solution 33

Hydrogen gas>Methane>Petrol>Kerosene>Biogas>Wood

Solution 34

Dung cakes<Coal<Alcohol<Diesel<LPG

Solution 35

Hydrogen gas

Sources of Energy Exercise 130

Solution 1


Solution 2


Solution 3


Solution 4

Coal, oil or gas.

Solution 5

Fractions obtained from petroleum:

Diesel, petrol, kerosene, petroleum gas etc.

Sources of Energy Exercise 131

Solution 6

LPG consists mainly of butane, alongwith smaller amounts of propane and ethane.

Solution 7

Compressed Natural Gas (CNG)

Solution 8

(i) LPG-Liquified Petroleum Gas

(ii) CNG-Compressed Natural Gas

Solution 9

(i) Main constituent of petroleum gas is butane.

(ii) Main constituent of natural gas is methane.

Solution 10


Solution 11

Uses of natural gas:

(i) As a fuel in thermal power plants

(ii) As a fuel in transport vehicles

Solution 12

CNG is used as a fuel in transport vehicles

Solution 13


Solution 14

Natural gas is considered to be a good fuel because it has a high calorific value, burns with a smokeless flame, causes no air pollution and does not produce any poisonous gas.

Solution 15

The traditional sources of energy which are familiar to most people are called conventional source of energy.

Ex. Wood, coal etc.

Solution 16

In a thermal power plant, heat produced by burning coal is used to boil water to form steam. The steam, at high temperature and pressure, rotates the turbine and its shaft, which drives the generator to produce electricity.


Solution 17

Disadvantages of burning the fossil fuels are:

(i) The burning of fossil fuels produce acidic gases.

(ii) The burning of fossil fuels produce large amount of CO2 gas, which increases greenhouse effect.

(iii) The burning of fossil fuels produce smoke and leaves behind a lot of ash.

Solution 18

Burning of fossil fuels leads to the production of many acidic gases like sulphur-dioxide and nitrogen dioxides. These gases causes acid rain which damages trees, plants and buildings, reduces fertility of soil, and poses danger to aquatic life. The burning of fossil fuels puts a poisonous gas carbon monoxide in air. It also produces large amount of CO2 gas which damages the environment in the long run by increasing the greenhouse effect. Also, burning of fossil fuels produces smoke and a lot of ash.

Solution 19

Pollution caused by the burning of fossil fuels can be controlled by the increasing the efficiency of combustion process and by using various techniques to reduce the escape of harmful gases and ash into the surrounding air.

Solution 20

We will use LPG due to its high calorific value and smokeless flame.

Solution 21

LPG is considered as good fuel because it has a high calorific value gives a smokeless flame.

Solution 22

LPG is considered as a better fuel than coal because it has a higher calorific value, while burning it does not produce any smoke.

Solution 23

For the detection of leakage, a foul smelling substance called ethyl mercaptan is added to the LPG.

In case of LPG leakage in the kitchen, following steps must be taken:

1. The door and windows should be opened at once to allow the gas to escape.

2. The source of gas leakage should be checked and then set right with the help of a gas mechanic.

Solution 24

(a) Natural fuels formed deep under the earth from the pre-historic remains of the organisms (like plants and animals) are called fossil fuels.

Ex. Coal, petroleum and natural gas.

(b) The plants and animals which died millions of years ago and got buried deep in the earth, away from the reach of oxygen, got converted into fossil fuels due to the chemical effects of pressure, heat and bacteria.

(c) Sun is considered to be the ultimate source of fossil fuels because it was the sunlight of long ago that made plants grow and the animals which got buried in the earth also ate plants. So, plants and animals which were originally made by sun's energy only have been converted into fossil fuels.

(d) Petroleum and natural gas

(e) Coal

Sources of Energy Exercise 132

Solution 37

(a) X = Carbon

(b) Another element which is usually found in combination with carbon in fossil fuels is hydrogen.

Solution 38

Petrol is obtained from petroleum, which is a fossil fuel. Fossil fuels were originally made by sun's energy because it was the sunlight of long ago that made plants and animals grow. So, the energy in petrol originally came from the sun.

Solution 39

(a) X is ethyl mercaptan

(b) Ethyl mercaptan has a foul smell that can be detected easily.

Solution 40

(a) Catalytic converter

(b) It converts poisonous carbon monoxide into non-poisonous carbon dioxide and harmful nitrogen oxides into harmless nitrogen gas.

Sources of Energy Exercise 140

Solution 1

Potential energy into electrical energy

Solution 2

Kinetic energy

Solution 3

Kinetic energy of water.

Solution 4


Solution 5

15 km/hr

Solution 6

Use of wind energy

(a) in the past - in flour mills

(b) at present - for generating the electricity through wind-powered generators.

Solution 7

Copper tube of solar water heater is painted black because black colour is good absorber of heat.

Solution 8

Nuclear fusion

Solution 9

Solar water heater

Solar cooker

Solar cell

Solution 10

Plane mirror reflector

Solution 11

About 1000C to 1400C

Solution 12

Solar cell

Solution 13

Solar constant is 1.4kW/m2 or 1.4 kJ/s/m2.

Solar energy received by 1 m2 area in 1 s = 1.4 kJ

Solar energy received by 1 m2 area in one hour (or 3600 s) = 1.4 x 3600 = 5040 kJ

Solution 14

sunlight; electrical

Solution 15

(a) Difference between thermal power plant and hydro power plant:

Thermal power plant uses non-renewable sources of energy like coal, oil or gas; whereas hydro power plant uses renewable source of energy i.e. water.

Thermal power plant causes pollution due to the burning of fossil fuels; whereas hydro power plant is environment friendly.

(b) Thermal power plant causes serious air pollution because it emits harmful gases and fly-ash into the air.

Sources of Energy Exercise 141

Solution 16

Sun is a renewable source of energy, where as fossil fuels are non-renewable sources of energy.

Solution 17

Concave and plane mirrors are used for making solar cooker because concave mirror converges a large amount of sun's rays at a point that is required for high heating and plane mirror reflects the rays of light in the form of a strong beam of sunlight on the top of the box that is required for moderate heating.

Solution 18

(a) Glass sheet cover

(b) A plane mirror reflector is used in a box type solar cooker so as to get a strong beam of sunlight after reflection from the mirror.

Solution 19

(a) Advantages of using solar cooker

(i) It saves precious fules like coal, kerosene etc.

(ii) It does not produce any smoke or ash.

(iii) The food cooked in a solar cooker has all its nutrients intact.

(b) Disadvantages of using solar cooker

(i) Solar cooker cannot be used during night time.

(ii) If the day-sky is covered with clouds, it will not be possible to cook the food using solar cooker.

(iii) Direction of reflector has to be changed from time to time to keep it facing the sun.

Solution 20

(a) Solar cell is a device which converts solar energy directly into electrical energy.

(b) Silicon

(c) Use of solar cell:

i. To provide electricity in artificial satellites and space probes.

ii. To provide electricity to remote areas where normal electricity transmission lines do not exist.

iii. To provide electricity to light houses

iv. To operate traffic signals, watches, calculators and toys.

Solution 21

(a) Advantage of solar cell

(i) They have no moving parts and require no maintenance.

(ii) They can be set up in remote and inaccessible areas

(b) Disadvantage of solar cell

(i) They are very expensive.

(ii) They are less efficient. They can convert only about 25 % of light falling on them into electricity.

(iii) They cannot work during night time.

Solution 22

Solar cell panel consists of a large number of solar cells joined together in a definite pattern. It is used to convert solar energy into electricity.

Advantages of solar cell panel are:-

1. It provides much more electric power than a single solar cell.

2. It is used to provide electricity in remote and inaccessible rural areas.

Solution 23

(a) The amount of solar energy received per second by one metre square area of the near earth space (exposed perpendicularly to the sun rays) at an average distance between the sun and the earth, is known as solar constant. Its value is 1.4 kJ/s/m2.

(b) Area, A=5m2; time,t=10 min=600sec; E=4200 kJ

Solar constant =E/(Axt)


=1.4 kJ/s/m2

Solution 24

Traditionally, the energy of flowing water has been used for rotating the water-wheels and for driving water-mills to grind wheat to make flour. The traditional use of energy of flowing water has been modified by improvements in technology and it is now used to generate electricity.

Solution 25

Traditionally, wind energy was used through windmills to pump water from a well and to grind wheat into flour. But the traditional use has been modified and now it is used for the generation of electricity.

Solution 26

(a) The electricity generated from hydro power plant is known as hydro electricity.

           Water is collected in a reservoir at a height, so the water has potential energy stored in it. When the water flows down through this large height, its potential energy gets converted into kinetic energy. The fast flowing water rotates the turbine which is connected to generator through its shaft. The generator produces electricity.

(b) Advantage of producing hydroelectricity:

(i) It does not cause any environmental pollution.

(ii)  It uses the energy of flowing water, which is a renewable source of energy

(c) Disadvantage of producing hydroelectricity

(i) Large areas of land are required.

(ii) Large eco-systems get destroyed.

Solution 27

(a) Construction and working of solar cooker

A solar cooker consists of an insulated metal box or wooden box which is painted all black from inside. There is a thick glass sheet cover over the box and a plane mirror reflector is also attached to the box.

The food to be cooked is put in metal containers which are painted black from outside. These metal containers are then placed inside the solar cooker box covered with the glass

sheet. The sun's rays fall on the reflector, get reflected into the box through the upper glass and get trapped within it.