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NCERT Exemplar Class 10 Science Chapter 14 Sources of Energy Solutions

NCERT Exemplar Solutions for Class 10 Science Chapter 14 Sources of Energy covers all the important questions and answers as well as advanced level questions. It helps in learning about the Conventional Sources of Energy or traditional Sources of Energy, Fossil fuels, Thermal power plant and Hydropower plants.

The NCERT Exemplar solutions for class 10 science is very important for board exams. NCERT Exemplar Solutions for Class 10 Science Chapter 14 Sources of Energy is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like Non-Conventional Sources of Energy, Biomass, Wind Energy, Solar energy, Tidal energy, Ocean thermal energy and Nuclear energy.


Chapter Name

Chapter 14 Sources of Energy

Book Title

NCERT Exemplar for Class 10 Science

Related Study

  • NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy
  • Revision Notes for Class 10 Science Chapter 14 Sources of Energy
  • MCQ for Class 10 Science Chapter 14 Sources of Energy
  • Important Questions for Class 10 Science Chapter 14 Sources of Energy

Topics Covered

  • MCQ
  • Short Answers Questions
  • Long Answers Questions

NCERT Exemplar Solutions for Chapter 14 Sources of Energy Class 10 Science

Multiple Choice Questions

1. Which of the following is a non-renewable source of energy?
(a) Wood
(b) Sun
(c) Fossil fuels
(d) Wind

Solution
(b) Sun

Sources of energy which are present in limited amount and can’t be recycled once used are known as non-renewable sources of energy. Fossil fuels are non-renewable source of energy.


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

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

When rain water mixes with the oxides of carbon, nitrogen and sulphur in the atmosphere, acid rain takes place.


3. Fuel used in thermal power plants is
(a) water
(b) uranium
(c) biomass
(d) fossil fuels

Solution
(d) fossil fuels 

Coal is the major fossil fuel used in thermal power plants. Along with coal natural gas and petroleum are also used.


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

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

Water in the dams possesses potential energy. This potential energy converts into kinetic energy when the water is released. This kinetic energy turns the turbines. Turbines in turn produce electricity.


5. Which is the ultimate source of energy?
(a) Water
(b) Sun
(c) Uranium
(d) Fossil fuels 

Solution
(b) Sun

Plants use solar energy to produce food. Fossil fuels are produced from dead plants. Hence directly or indirectly, sunlight is the source of all energy.


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
(c) Solar energy

In nuclear energy, metals like uranium are used which release harmful rays. In thermal energy, coal is used as a fuel. Burning of coal releases sulphur and carbon dioxide which causes air pollution. In geothermal energy, the energy is absorbed by the pressure which can sometimes be extremely hot and dangerous.


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

Solution
(b) temperature difference at different levels in the ocean

Energy from the surface of the ocean is used to boil volatile liquids. Vapors from these are used to turn the turbine.


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?

Solution
(c) dispose off spent fuel safely?

Nuclear plants produce highly radioactive materials. Thus disposing the nuclear waste in the environment will pose a major threat to the living organisms. Therefore, safe disposal of nuclear waste is a major problem in harnessing nuclear energy.


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

Solution
(c) Glass sheet 

The trapping of heat by the atmosphere leads to the greenhouse effect. Same thing happens in a solar cooker. Solar energy gets trapped which is then reflected by the glass sheet, this helps in cooking the food.


10. The main constituent of biogas is 
(a) methane 
(b) carbon dioxide 
(c) hydrogen 
(d) hydrogen sulphide 

Solution
(a) methane 

Methane gas is the major product of biogas. Around 70% of the gas is methane and remaining is ammonia and carbon dioxide.


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

Solution
(c) depends on wind velocity

High speed winds will turn the turbine at a higher speed. This in turn will increase the production of electricity.


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

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

Fossil fuels are exhaustible energy sources. Hydro and wind energy plants can change the environment and affect the land use, homes, and natural habitats there by having a large environmental impact. The disposal of waste from a nuclear power plant is the major issue faced by nuclear plant.


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

Solution
(b) larger amount of potential energy is converted into kinetic energy


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

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

Kinetic energy of the wind runs the wind power.


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

Solution
(c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash

Methane is the main product of a biogas. Biogas burns with less smoke and does not produce residual ash.


Short Answer Questions 

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

Solution
Following are the reasons to harness non-conventional sources of energy:

  • In the near future, the conventional sources will get exhausted.
  • Non-conventional source of energy do not cause environmental pollution.


17. Write two different ways of harnessing energy from ocean.

Solution
Different ways of harnessing energy form the ocean are:

  1. Tidal energy
  2. Ocean thermal energy


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

Solution
Steps to minimise pollution caused by burning of fossil fuels are as follows.

  • Use of non-conventional sources of energy.
  • Afforestion should be adopted to control air pollution.
  • Smokeless appliances should be used.


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

Solution
Plane mirror increases the intensity of solar energy as it reflects the sunlight. Glass sheet prevents the escape of heat from the solar cooker.


20. Mention three advantages of a solar cell?

Solution
Advantages of a solar cell areas follows.

  • They are the source of renewable energy.
  • They do not cause pollution.
  • They require minimum maintenance.


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

Solution
Biomass is the fuel obtained from organic material. The methods to obtain bio-energy using biomass are as follows:

  • Using firewood as a fuel.
  • Preparing cow dung cakes and using them as a fuel.
  • Preparation of gobar gas.


22. What are the limitations in obtaining energy from wind?

Solution

Limitations in obtaining energy from wind are as follows:

  • No continuous and consistent production.
  • Area required for installation of wind power mill is large.
  • Minimum wind speed should be 15 km/hour.


Long Answer Questions 


23. Which is the process used to harness nuclear energy these days? Explain it briefly.
Solution
Nuclear energy is harnessed in nuclear power plants. A nuclear power plant has a nuclear reactor, a boiler and a turbine.
  • Nuclear fission takes place in the nuclear reactor. This produces a large amount of energy.
  • Energy produced by nuclear fission is utilized to boil water, in order to generate steam.
  • Steam is then utilized to turn the turbines which produce electricity.

24. How can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?
Solution
Solar energy can be harnessed by the following methods:
  1. Solar Cookers and solar water heaters:
    Black surfaces are good absorbers of heat as compared to a white or a reflecting surface. This is used in solar cookers and solar water heaters. Solar cookers are covered with a glass plate. Solar energy trapped within the solar cooker gets reflected by the glass plate and this helps in cooking the food.
  2. Solar Cell
    A typical cell when exposed to sunlight develops a voltage of 0.5–1 V and produces about 0.7 W of electricity. Solar panels are a large number of solar cells that deliver enough electricity for practical use.
Limitations of solar energy:
  • Cannot be harnessed beyond a certain latitude.
  • Cannot be harnessed during the night.
  • Can only be harnessed at places where there is plenty of sunlight.
  • It is an expensive source of energy.
Cheaper technologies must be discovered. Batteries can be used to store electrical energy form photovoltaic cells.

25. Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing one nonconventional source of energy.
Solution
Coal, petroleum, fire wood and tidal energy are conventional sources of energy. Solar energy, nuclear energy, Biogas, Tidal energy, Ocean thermal energy, wave energy etc. are non-conventional energy sources.
The various methods to harness non-conventional energy sources are:
  • Solar cookers, solar water heaters, solar cells and solar panels harness the solar energy.
  • Nuclear reactors convert nuclear power to electric energy.
  • The sun heats the water at the surface of the sea while the water in lower sections is relatively cold. This temperature difference is exploited to obtain energy in ocean-thermal-energy conversion plants.
  • The kinetic energy possessed by huge waves near the seashore can be trapped to generate electricity.

26. Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea in different ways?
Solution
Following are the reason for the need to harness non-conventional sources of energy:
  • In the near future, the conventional sources of energy will get exhausted in the near future.
  • Non-conventional source of energy do not cause environmental pollution. 
Energy can be harnessed from the sea in following ways:
  • Tidal energy: Tidal energy is harnessed by construction of a dam. A turbine fixed at the opening of the dam converts tidal energy to electricity.
  • Wave energy: Near the sea shore, the kinetic energy possessed by huge waves can be harnessed to generate electricity. Strong winds blowing across the sea, generate the waves.
  • Ocean Thermal Energy: The sun heats the water at the surface of the sea or ocean while the water in deeper layers is relatively cold. This temperature difference can be used to obtain energy in ocean-thermal-energy conversion plants.

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.

Solution
The various environmental consequences of using fossil fuels are:
  • Increased levels of carbon dioxide in the atmosphere lead to global warming.
  • Sulphur oxides causes acid rain.
  • Accumulation of smog in big cities which in turn reduces visibility
  • Air pollution which might cause health hazards to humans and animals.
The steps to minimize the pollution caused by various sources of energy including non-conventional sources of energy are as follows:
  • Use of public transport
  • Use of vehicles like electric bikes and bi-cycle
  • Adopting the 3R’s policy-reduce, reuse and recycle
  • Planting of trees

28. Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.
Solution
Energy from various sources is considered to have been derived from the sun. This statement can be justified by the following points: 
  • Plants trap sunlight and produce food which ultimately forms the biomass. Biomass gets converted to fossil fuels. So, in general the energy derived from the fossil fuels is indirectly harnessed from sunlight.
  • Biomass helps in obtaining wood and gobar gas.
  • The kinetic energy of the sun circulates the water on the earth.
  • The heating of water in the oceans causes waves and tides. Therefore, sun is indirectly responsible for harnessing tidal, wave and geothermal energy.

29. What is biomass? Explain the principle and working of a biogas plant using a labelled schematic diagram.
Solution
The fuel obtained from organic material is known as biomass. The anaerobic decomposition of cow-dung, various plant materials, vegetable waste and sewage gives bio-gas.
The biogas plant has a dome-shaped structure built with bricks. A slurry of cow-dung and water is made in the mixing tank which is then fed to the digester. The digester does not any supply of oxygen. Anaerobic micro-organisms decompose the complex compounds of the slurry. The decomposition process is completed in a few days and gases like methane, carbon dioxide, hydrogen and hydrogen sulphide are generated. This gas is stored in the gas tank above the digester from which it can be drawn through pipes for use.
Bio-gas contains up to 75% methane, hence it is an excellent fuel. It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning. The heating capacity of bio-gas is also high.
The slurry left behind can be used as a manure as it is rich in nitrogen and phosphorous.

NCERT Exemplar Chapter 14 Sources of Energy Class 10 Science Solutions

NCERT Exemplar Class 10 Science Chapter 14 Sources of Energy Solutions

NCERT Exemplar Solutions for Class 10 Science Chapter 14 Sources of Energy covers all the important questions and answers as well as advanced level questions. It helps in learning about the Conventional Sources of Energy or traditional Sources of Energy, Fossil fuels, Thermal power plant and Hydropower plants.

The NCERT Exemplar solutions for class 10 science is very important for board exams. NCERT Exemplar Solutions for Class 10 Science Chapter 14 Sources of Energy is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like Non-Conventional Sources of Energy, Biomass, Wind Energy, Solar energy, Tidal energy, Ocean thermal energy and Nuclear energy.


Chapter Name

Chapter 14 Sources of Energy

Book Title

NCERT Exemplar for Class 10 Science

Related Study

  • NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy
  • Revision Notes for Class 10 Science Chapter 14 Sources of Energy
  • MCQ for Class 10 Science Chapter 14 Sources of Energy
  • Important Questions for Class 10 Science Chapter 14 Sources of Energy

Topics Covered

  • MCQ
  • Short Answers Questions
  • Long Answers Questions

NCERT Exemplar Solutions for Chapter 14 Sources of Energy Class 10 Science

Multiple Choice Questions

1. Which of the following is a non-renewable source of energy?
(a) Wood
(b) Sun
(c) Fossil fuels
(d) Wind

Solution
(b) Sun

Sources of energy which are present in limited amount and can’t be recycled once used are known as non-renewable sources of energy. Fossil fuels are non-renewable source of energy.


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

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

When rain water mixes with the oxides of carbon, nitrogen and sulphur in the atmosphere, acid rain takes place.


3. Fuel used in thermal power plants is
(a) water
(b) uranium
(c) biomass
(d) fossil fuels

Solution
(d) fossil fuels 

Coal is the major fossil fuel used in thermal power plants. Along with coal natural gas and petroleum are also used.


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

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

Water in the dams possesses potential energy. This potential energy converts into kinetic energy when the water is released. This kinetic energy turns the turbines. Turbines in turn produce electricity.


5. Which is the ultimate source of energy?
(a) Water
(b) Sun
(c) Uranium
(d) Fossil fuels 

Solution
(b) Sun

Plants use solar energy to produce food. Fossil fuels are produced from dead plants. Hence directly or indirectly, sunlight is the source of all energy.


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
(c) Solar energy

In nuclear energy, metals like uranium are used which release harmful rays. In thermal energy, coal is used as a fuel. Burning of coal releases sulphur and carbon dioxide which causes air pollution. In geothermal energy, the energy is absorbed by the pressure which can sometimes be extremely hot and dangerous.


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

Solution
(b) temperature difference at different levels in the ocean

Energy from the surface of the ocean is used to boil volatile liquids. Vapors from these are used to turn the turbine.


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?

Solution
(c) dispose off spent fuel safely?

Nuclear plants produce highly radioactive materials. Thus disposing the nuclear waste in the environment will pose a major threat to the living organisms. Therefore, safe disposal of nuclear waste is a major problem in harnessing nuclear energy.


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

Solution
(c) Glass sheet 

The trapping of heat by the atmosphere leads to the greenhouse effect. Same thing happens in a solar cooker. Solar energy gets trapped which is then reflected by the glass sheet, this helps in cooking the food.


10. The main constituent of biogas is 
(a) methane 
(b) carbon dioxide 
(c) hydrogen 
(d) hydrogen sulphide 

Solution
(a) methane 

Methane gas is the major product of biogas. Around 70% of the gas is methane and remaining is ammonia and carbon dioxide.


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

Solution
(c) depends on wind velocity

High speed winds will turn the turbine at a higher speed. This in turn will increase the production of electricity.


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

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

Fossil fuels are exhaustible energy sources. Hydro and wind energy plants can change the environment and affect the land use, homes, and natural habitats there by having a large environmental impact. The disposal of waste from a nuclear power plant is the major issue faced by nuclear plant.


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

Solution
(b) larger amount of potential energy is converted into kinetic energy


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

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

Kinetic energy of the wind runs the wind power.


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

Solution
(c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash

Methane is the main product of a biogas. Biogas burns with less smoke and does not produce residual ash.


Short Answer Questions 

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

Solution
Following are the reasons to harness non-conventional sources of energy:

  • In the near future, the conventional sources will get exhausted.
  • Non-conventional source of energy do not cause environmental pollution.


17. Write two different ways of harnessing energy from ocean.

Solution
Different ways of harnessing energy form the ocean are:

  1. Tidal energy
  2. Ocean thermal energy


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

Solution
Steps to minimise pollution caused by burning of fossil fuels are as follows.

  • Use of non-conventional sources of energy.
  • Afforestion should be adopted to control air pollution.
  • Smokeless appliances should be used.


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

Solution
Plane mirror increases the intensity of solar energy as it reflects the sunlight. Glass sheet prevents the escape of heat from the solar cooker.


20. Mention three advantages of a solar cell?

Solution
Advantages of a solar cell areas follows.

  • They are the source of renewable energy.
  • They do not cause pollution.
  • They require minimum maintenance.


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

Solution
Biomass is the fuel obtained from organic material. The methods to obtain bio-energy using biomass are as follows:

  • Using firewood as a fuel.
  • Preparing cow dung cakes and using them as a fuel.
  • Preparation of gobar gas.


22. What are the limitations in obtaining energy from wind?

Solution

Limitations in obtaining energy from wind are as follows:

  • No continuous and consistent production.
  • Area required for installation of wind power mill is large.
  • Minimum wind speed should be 15 km/hour.


Long Answer Questions 


23. Which is the process used to harness nuclear energy these days? Explain it briefly.
Solution
Nuclear energy is harnessed in nuclear power plants. A nuclear power plant has a nuclear reactor, a boiler and a turbine.
  • Nuclear fission takes place in the nuclear reactor. This produces a large amount of energy.
  • Energy produced by nuclear fission is utilized to boil water, in order to generate steam.
  • Steam is then utilized to turn the turbines which produce electricity.

24. How can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?
Solution
Solar energy can be harnessed by the following methods:
  1. Solar Cookers and solar water heaters:
    Black surfaces are good absorbers of heat as compared to a white or a reflecting surface. This is used in solar cookers and solar water heaters. Solar cookers are covered with a glass plate. Solar energy trapped within the solar cooker gets reflected by the glass plate and this helps in cooking the food.
  2. Solar Cell
    A typical cell when exposed to sunlight develops a voltage of 0.5–1 V and produces about 0.7 W of electricity. Solar panels are a large number of solar cells that deliver enough electricity for practical use.
Limitations of solar energy:
  • Cannot be harnessed beyond a certain latitude.
  • Cannot be harnessed during the night.
  • Can only be harnessed at places where there is plenty of sunlight.
  • It is an expensive source of energy.
Cheaper technologies must be discovered. Batteries can be used to store electrical energy form photovoltaic cells.

25. Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing one nonconventional source of energy.
Solution
Coal, petroleum, fire wood and tidal energy are conventional sources of energy. Solar energy, nuclear energy, Biogas, Tidal energy, Ocean thermal energy, wave energy etc. are non-conventional energy sources.
The various methods to harness non-conventional energy sources are:
  • Solar cookers, solar water heaters, solar cells and solar panels harness the solar energy.
  • Nuclear reactors convert nuclear power to electric energy.
  • The sun heats the water at the surface of the sea while the water in lower sections is relatively cold. This temperature difference is exploited to obtain energy in ocean-thermal-energy conversion plants.
  • The kinetic energy possessed by huge waves near the seashore can be trapped to generate electricity.

26. Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea in different ways?
Solution
Following are the reason for the need to harness non-conventional sources of energy:
  • In the near future, the conventional sources of energy will get exhausted in the near future.
  • Non-conventional source of energy do not cause environmental pollution. 
Energy can be harnessed from the sea in following ways:
  • Tidal energy: Tidal energy is harnessed by construction of a dam. A turbine fixed at the opening of the dam converts tidal energy to electricity.
  • Wave energy: Near the sea shore, the kinetic energy possessed by huge waves can be harnessed to generate electricity. Strong winds blowing across the sea, generate the waves.
  • Ocean Thermal Energy: The sun heats the water at the surface of the sea or ocean while the water in deeper layers is relatively cold. This temperature difference can be used to obtain energy in ocean-thermal-energy conversion plants.

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.

Solution
The various environmental consequences of using fossil fuels are:
  • Increased levels of carbon dioxide in the atmosphere lead to global warming.
  • Sulphur oxides causes acid rain.
  • Accumulation of smog in big cities which in turn reduces visibility
  • Air pollution which might cause health hazards to humans and animals.
The steps to minimize the pollution caused by various sources of energy including non-conventional sources of energy are as follows:
  • Use of public transport
  • Use of vehicles like electric bikes and bi-cycle
  • Adopting the 3R’s policy-reduce, reuse and recycle
  • Planting of trees

28. Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.
Solution
Energy from various sources is considered to have been derived from the sun. This statement can be justified by the following points: 
  • Plants trap sunlight and produce food which ultimately forms the biomass. Biomass gets converted to fossil fuels. So, in general the energy derived from the fossil fuels is indirectly harnessed from sunlight.
  • Biomass helps in obtaining wood and gobar gas.
  • The kinetic energy of the sun circulates the water on the earth.
  • The heating of water in the oceans causes waves and tides. Therefore, sun is indirectly responsible for harnessing tidal, wave and geothermal energy.

29. What is biomass? Explain the principle and working of a biogas plant using a labelled schematic diagram.
Solution
The fuel obtained from organic material is known as biomass. The anaerobic decomposition of cow-dung, various plant materials, vegetable waste and sewage gives bio-gas.
The biogas plant has a dome-shaped structure built with bricks. A slurry of cow-dung and water is made in the mixing tank which is then fed to the digester. The digester does not any supply of oxygen. Anaerobic micro-organisms decompose the complex compounds of the slurry. The decomposition process is completed in a few days and gases like methane, carbon dioxide, hydrogen and hydrogen sulphide are generated. This gas is stored in the gas tank above the digester from which it can be drawn through pipes for use.
Bio-gas contains up to 75% methane, hence it is an excellent fuel. It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning. The heating capacity of bio-gas is also high.
The slurry left behind can be used as a manure as it is rich in nitrogen and phosphorous.

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