NCERT Exemplar Class 10 Science Solutions Chapter 14 Sources of Energy

NCERT Exemplar Class 10 Science Solutions Chapter 14-MCQ

Question:1

Which of the following is a non-renewable source of energy?
(A) Wood
(B) Sun
(C) Fossil fuels
(D) Wind
Answer : (C) fossil fuels
A nonrenewable resource is a natural substance that is not replenished with the speed at which it is consumed. It is a finite resource.
Examples: Fossil fuels, Crude Oil, Coal, Uranium, Natural Gas, Steel, Aluminum, Ground Water etc.
Wood – Can be replenished by growing more and more trees
Sun – It is not a finite resource
Fossil Fuels – Thermal power plants make use of fossil fuel for production of electricity and they are considered as non-renewable sources
Wind – It is not a finite resource
Therefore option (C) is correct

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
Answer : (B)
Burning of fossil fuels release oxides of carbon, nitrogen, and Sulphur in the atmosphere which gets dissolved in atmospheric water vapor and rains down as acid rain which damages the plant life, aquatic life, as well as the infrastructure. It has drastic effect on the soil as it changes the nutrition and pH of the soil.
Therefore option (B) is correct

Question:3

Fuel used in thermal power plants is
(A) water
(B) uranium
(C) biomass
(D) fossil fuels
Answer : (D) fossil fuels
Coal and petrol are the fuels used in thermal power plants. These fuels are burnt to produce energy which converts water into vapor which is passed onto turbines to produce electricity.
Therefore option (D) is correct

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
Answer : (A)
Potential energy possessed by stored water is converted into electricity. As the potential energy converts into kinetic energy which rotates the turbine which in turn produces electricity. Hydro power plants are renewable sources of energy.
Therefore option (A) is correct

Question:5

Which is the ultimate source of energy?
(A) Water
(B) Sun
(C) Uranium
(D) Fossil fuels
Answer : (B)
Sun is the ultimate source of energy. Photosynthesis is driven by sunlight. All the producers in a food web make their food by absorbing sunlight. Solar energy has the potential to fulfill all power needs. All our fossil fuels are derived from plants which existed millions of years ago.
Therefore option (B) is correct

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
Answer : (C)
(A) Nuclear reactors do not produce air pollution or carbon dioxide while operating. However, the processes for mining and refining uranium ore and making reactor fuel requires large amounts of energy which leads to environmental pollution
(B) Thermal energy leads to production of thermal gases by burning of fossil fuels and thermal pollution.
(C) Solar energy leads to least environmental pollution as there are no harmful products formed
(D) Methane and carbon dioxide are the most commonly released greenhouse gases which affects the environment. Noise pollution also happens in the case of geothermal energy because of drilling.
Therefore option (C) is correct

Question:7

Ocean thermal energy is due to
(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
Answer : (B)
Ocean thermal energy conversion is a process for producing energy by harnessing the temperature differences between ocean surface waters and deep ocean waters.
Temperature difference at different levels in the ocean is due to the availability of sunlight. As the sunlight is prevalent on the surface which increases the temperature of water but inner layers won’t get the same amount of heat which in turn creates a temperature difference.
Therefore option (B) is correct

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
Answer : (C)
The major problem in harnessing nuclear energy is how to dispose off spent fuel safely. The products are radioactive in nature which affects all the organisms who are exposed. Its effects are not confined to one place but to a major distance as the radiations can travel very long distance.
AERB is in charge of the public safety regarding ionizing radiation & nuclear energy.
Therefore option (C) is correct

Question:9

Which part of the solar cooker is responsible for green house effect?
(A) Coating with black colour inside the box
(B) Mirror
(C) Glass sheet
(D) Outer cover of the solar cooker
Answer : (C) Glass sheet
Glass sheet/plate traps infrared radiations from sunlight and does not allow heat to escape. Solar cookers are covered with a glass plate. Thus this glass plate provides greenhouse effect.
Under identical conditions, a black surface absorbs more heat as compared to a white or a reflecting surface. Solar cookers achieve a higher temperature by using mirrors to focus the rays of the Sun.
Therefore option (C) is correct

Question:10

The main constituent of biogas is
(A) methane
(B) carbon dioxide
(C) hydrogen
(D) hydrogen sulphide
Answer : (A)
Biogas is a renewable energy source composed of methane, carbon dioxide, and other trace compounds produced from anaerobic digestion of organic matter.
Bio gas composition:
Methane CH₄ 55%-75%
Carbon dioxide CO₂ 25% - 40%
Rest are trace gases like hydrogen etc.
Biogas is predominantly made from the excretion of cows and buffalos. This is the reason they produce a lot of methane gas.
Therefore option (A) is correct

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
Answer : (C)
A windmill converts wind power into rotational energy
Power output of a windmill depends on wind velocity as the kinetic energy of the moving wind is used to rotate the mill which is connected to a turbine which produces electricity. The minimum required speed for a windmill to work is 15km/hr
Therefore option (C) is correct

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
Answer : (a,c)
(A) Sun can be taken as an inexhaustible source of energy as the energy is produced through nuclear fusion reaction. The Sun has been radiating an enormous amount of energy at the present rate for nearly 5 billion years and will continue radiating at that rate for about 5 billion years more.
(B) There is a finite storage of fossil fuels.
(C) Hydro and wind energy plants are non-polluting sources of energy as they don’t produce pollutants.
(D) Waste from a nuclear power plant is very difficult to dispose off.
Therefore options (A, C) are correct

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
Answer : (B)
Potential energy is directly proportional to the height. So more the height, more will be the potential energy.
In hydroelectric power plant if water falls from a greater height, a large amount of potential energy is converted into kinetic energy which in turn is converted into electric energy.
Therefore option (B) is correct

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
Answer : (A, B)
(A) It is expected to harness wind power to minimum in open space – Incorrect as in open spaces wind flows easily and wind power is highest.
(B) The potential energy content of wind blowing at high altitudes is the source of wind power – Incorrect as wind power is completely dependent on the wind speed and not the altitude. That’s why we see wind mills in coastal areas due to high wind speeds than in high altitude areas
(C) and (D) are correct.
Therefore options (A, B) are correct

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
(C) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash
(D) Bio-mass is a renewable source of energy
Answer : (C)
(A) Correct. More plants means cleaner and healthier environment. More trees will provide more bio-mass fuel.
(B) Correct. Gobar gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen
(C) Incorrect. The main ingredient of bio-gas is methane and not ethane.
(D) Correct. Bio-mass is a renewable source of energy as it depends on the growth of plants and trees which are renewable.
Therefore option (C) is correct

NCERT Exemplar Class 10 Science Solutions Chapter 14-Short Answer

Question:16

Why is there a need to harness non-conventional sources of energy? Give two main reasons.
Answer:
i) As the population is increasing, energy requirements of the world are constantly increasing and in order to fulfil these requirements, we need to consider non-conventional energy sources.
ii) Majority of sources of energy we use are fossil fuel based which are non-renewable and most of them are damaging the climate by causing pollution. So we need to use non-conventional energy sources which do not damage the environment.

Question:17

Write two different ways of harnessing energy from ocean.
Answer :
1) Tidal Energy: It is the energy obtained from the rising and falling tides. Because of the gravitational pull of the moon on the spinning earth, the level of water in the sea rises and falls. Tidal energy is harnessed by building a dam across a narrow opening to the sea.
2) Ocean Thermal Energy: Energy obtained due to the temperature difference between the deep layers of ocean and upper level of ocean.

Question:18

What steps would you suggest to minimise environmental pollution caused by burning of fossil fuels?
Answer :
1) Afforestation: Converting land into forest by planting trees
2) Use clean fuels like CNG, LPG etc.
3) Use public transport, carpool, electric vehicles etc.
4) Use smokeless appliances and upgrade to fuel efficient systems

Question:19

What is the role of a plane mirror and a glass sheet in a solar cooker?
Answer :
1) Plane Mirror in a cooker is used as a reflector to focus maximum rays of sun in to the cooker.
2) Glass Sheet allows the infrared and visible rays to enter the device. It also does not allow the infrared radiations to move out of the heating device to increase the wavelength of radiation inside the cooker which further increases the temperature.

Question:20

Mention three advantages of a solar cell?
Answer:
Three advantages of Solar cells:
1. Pollution free
2. Maintenance cost is almost zero
3. It is an unlimited source

Question:21

What is biomass? What can be done to obtain bio-energy using biomass?
Answer:
Bio-mass it is the waste materials of living things (cattle dung etc.) and dead parts of plants, animals and any organic source.
Bio-energy in the form of biogas can be produced from biomass by decomposition in the absence of air. Bioenergy refers to electricity and gas that is generated from organic matter, known as biomass.

Question:22

What are the limitations in obtaining energy from wind?
Answer:
Limitations of wind energy
1) It should be established only in the places where the wind blows throughout the year.
2) Minimum wind speed necessary for wind energy is 15km/hr which is difficult at all times throughout the year.
3) Wind energy farms are expensive to set.
4) Wind Energy farms effect the rainfall patterns.
5) Energy is stored in batteries which is another thing to consider and we cannot completely rely on it as it is constantly varying based on wind speeds.

NCERT Exemplar Class 10 Science Solutions Chapter 14-Long Answer

Question:23

Which is the process used to harness nuclear energy these days? Explain it briefly.
Answer:
Nuclear reaction is a process of making energy from radioactive substances as of now humans harness nuclear energy from nuclear fission process. Nuclear fission is a process where a heavy unstable nucleus breaks in to stable nucleus and releases energy. In a nuclear reactor, uranium nucleus is bombarded with neutrons and the nucleus turns unstable and breaks into two smaller nuclei and releases energy. This energy is used to convert liquid water into high energy steam. Further this steam is passed over turbines which rotates and generates electricity (alternating current)
Nuclear Reaction

E = Δmc² where E = energy released
m = difference in mass of the original nucleus and product nuclei
c = velocity of light [3 x 10⁸ m/s]
This energy is expressed in terms of electron volt [eV]
1eV = 1.602 x 10¹⁹ J
Major draw backs of Nuclear Power:
1) There is no proper, cheap way to dispose nuclear waste as it is bio hazardous.
2) Risk of accidental leakage is very high and it will lead to lot of medical complications.
3) If the reaction is not controlled properly then we will be facing dire consequences.
4) Cost of installation is pretty high and requires high maintenance.

Question:24

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

There are two ways solar energy is harnessed:
Indirect Way: Lot of organisms absorb sunlight and make their food (autotrophs) which are the primary food sources in a food chain. This energy is passed on to higher trophic levels.
Direct Way: Using solar panels to absorb solar energy and converting into electrical energy. The various devices which are used to convert the solar energy into various usable forms are solar cooker, solar heater, solar power plants, solar furnaces and solar cells.
Limitations of solar energy:
1) Cost of initial set up is very high.
2) The distribution of solar energy is not uniform. For example, European nations have less sunlight as they are close to poles but nations like Africa, Saudi Arabia, India has a lot of sunlight all around the year.
3) Takes a lot of area to set up solar energy farms.
4) Solar energy is not available in night time so energy needs to be stored in battery and used in night.
5) Based on moment of sun and clouds lot the energy output of solar panels will vary all the time.
The limitations can be overcome by:
Use of solar cells: Converting solar energy into electrical energy and storing them for future use.
A large number of solar cells combined in an arrangement is called a solar cell panel. It can deliver enough electricity for practical use.

Question:25

Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing one nonconventional source of energy.
Answer:
Conventional sources of energy are non-renewable sources of energy. Non-conventional sources of energy are renewable sources of energy.
Conventional Source of energy:
1. Coal
2. Petrol
3. Wood
4. Hydro Energy
5. Biomass energy
6. Wind Energy
Non-Conventional Energy:
1. Solar Energy
2. Tidal Energy
3. Geothermal energy
4. Nuclear energy
Harnessing of Nuclear Energy: It is a process of making energy from radioactive substances. As of now humans harness nuclear energy from nuclear fission process. Nuclear fission is a process where a heavy unstable nucleus breaks into stable nuclei and releases energy. In a nuclear reactor, uranium nucleus is bombarded with neutrons and the nucleus turns unstable and breaks into two smaller nucleus and releases energy. This energy is used to convert liquid water into high energy steam. Further this steam is passed over to turbines which rotate and generate electricity.

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?
Answer:
Non-conventional sources of energy are renewable sources of energy. Examples:
1. Solar Energy
2. Tidal Energy
3. Geothermal energy
4. Nuclear energy
Reasons for harnessing non-conventional sources energy:
1. Demand for energy is increasing day by day. Increasing human activities and increasing demand of electricity has to be met. Changing life-styles, rapid industrialisation and population explosion demands increase in human needs.
2. All the predominant forms of energy we use are fossil fuel based and are responsible for pollution and global warming. Moreover, these are non-renewable resources.
Different forms from which energy can be harnessed from sea:
1. Tidal energy: Harnessing energy from the mechanical energy of the tides in sea. This method is not used predominantly but the tides are regular all the time so has a potential to be an alternative for fossil fuels.
2. Ocean Thermal energy: Ocean thermal energy conversion is a process for producing energy by harnessing the temperature differences between ocean surface waters and deep ocean waters.
Temperature difference at different levels in the ocean is due to the availability of sunlight. As the sunlight is prevalent on the surface which increases the temperature of water but inner layers won’t get the same amount of heat which in turn creates a temperature difference.

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.
Answer:
Environmental consequences of using fossil fuel:
1) Burning of fossil fuel leads to air pollution and incomplete combustion produces health hazard gases like carbon monoxide etc.
2) Oxides of nitrogen and carbon will lead to acid rains.
3) Generation of greenhouse gases lead to global warming.
Some of the steps to minimize pollution:
1) Reduce the consumption of fossil fuels by using public transport and use of non-conventional resources like solar, wind etc.
2) Converting vehicles from petrol and diesel to liquid petroleum gas and compressed natural gas and even using electric vehicles.
3) Using energy efficient equipment like 5 star or 4 star rated electrical equipment.
4) Plant more trees as they consume carbon dioxide and release oxygen into atmosphere.

Question:28

Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.
Answer:
Yes, sun is the ultimate source of energy as all the producers on earth make their food using sunlight and rest of the organisms consume or feed on producers.
Non-renewable resources like coal, petrol and natural gases are living organisms which got buried in the ground and due to high pressure and temperature in the earth, has turned into fossil fuels. But they got their initial energy form sun only.
Renewable sources are also indirectly dependent on sun.
Wind energy: Harnessing energy from wind is wind energy and wind is possible due to the uneven heating of earth’s surface. For example, land gets heated easily compared to water which in turn produces hot and cold gas which is nothing but high energy and low energy gas respectively.
Bio energy: Harnessing energy from living organisms like wood, cow dung etc. into biogas which are products of life. These are dependent directly on sun or indirectly on sun by feeding on producers.
Wave energy: Harnessing energy from waves which are dependent on the wind speed which is a phenomenon due to uneven heating of earth’s surface.
Solar energy: Harnessing energy form Sun’s radiation is directly dependent on Sun.
So yes, we can conclude that Sun is the source for all the forms of energy on this planet directly or indirectly.

Question:29

What is biomass? Explain the principle and working of a biogas plant using a labelled schematic diagram.
Answer:
Bio mass means the organic fuel obtained from plants and animal’s waste like cow dung, dry wood, vegetable waste and sewage etc.
Cow-dung, various plant materials like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen to give bio-gas or locally called as ‘gobar-gas’ due to the predominant use of cow dung.
Bio gas plant has a dome-like structure built with bricks. A slurry of cow-dung and water is made in the mixing tank from where it is fed into the digester. The digester is a sealed chamber in which oxygen is completely absent. Anaerobic micro-organisms that do not require oxygen to decompose complex compounds of the cow-dung slurry. After a few days for the decomposition process is complete and generate gases like methane, carbon dioxide, hydrogen and hydrogen sulphide. All this gas is known as bio gas which is stored in the gas tank above the digester from which they are drawn through pipes for use.