In this article you will get CBSE Class 10 Science chapter 14, Sources of Energy: NCERT Exemplar Problems and Solutions

Find below the NCERT Exemplar problems and their solutions for Class 10 Science Chapter, Sources of Energy:

Multiple Choice Questionsjmnth

Question 1. Which of the following is a non-renewable source of energy?

(a) Wood

(b) Sun

(c) Fossil fuels

(d) Wind

Answer. (c)

Explanation: 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.

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) the earth atmosphere contains acids

Answer. (b)

Explanation: The oxides of carbon, nitrogen and sulphur that are released by burning fossil fuels form acidic oxides. These lead to acid rain which affects our water and soil resources.

Question 3. Fuel used in thermal power plants is

(a) Water

(b) Uranium

(c) Biomass

(d) Fossil fuels

Answer. (d)

Explanation: Large amount of fossil fuels are burnt every day in power stations to heat up water to produce steam which further runs the turbine to generate electricity.

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)

Explanation: The water stored in dams has potential energy associated with it. Potential energy possessed by stored water is converted into electricity

Question 5. Which is the ultimate source of energy?

(a) Water

(b) Sun

(c) Uranium

(d) Fossil fuels

Answer. (b)

Explanation: Sun is the ultimate source of energy as many of the sources (like wind energy etc) ultimately derive their energy from the Sun.

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)

Explanation: Solar energy leads to least environmental pollution in the process of its harnessing and utilization.

In case of nuclear energy, the major concerns of pollution are while storage and disposal of spent fuels where there is always a risk of leakage of radiation.

In case of thermal energy, enormous amount of air pollution is produced.

Even in case of geothermal energy a little amount of pollution is produced.

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) pessure difference at different levels in the ocean

(d) tides arising out in the ocean

Answer. (b)

Explanation: The temperature difference between the water at the surface and water at depths up to 2 km is 20 K (20°C) or more. The warm surface-water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of generator. The cold water from the depth of the ocean is pumped up and condenses vapour again to liquid.

Question 8. The major problem in harnessing nuclear energy is how to

(a) split nuclei

(b) sustain the reaction

(c) dispose of spent fuel safely

(d) convert nuclear energy into electrical energy

Answer. (c)

Explanation: The major hazard of nuclear power generation is the storage and disposal of spent or used fuels – the uranium still decaying into harmful subatomic particles (radiations). Improper nuclear-waste storage and disposal result in environmental contamination.

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

Answer. (c)

Explanation: Solar cookers are covered with a glass plate which traps infrared radiations (heat) from sunlight and does not allow them to escape. In other words we can say that it provides greenhouse effect.

A black surface absorbs more heat as compared to a white or a reflecting surface under identical conditions.

Solar cookers achieve a higher temperature by using mirrors to focus the rays of the Sun.

Question 10. The main constituent of biogas is

(a) methane

(b) carbon dioxide

(c) hydrogen

(d) hydrogen sulphide

Answer. (a)

Explanation: Bio-gas is an excellent fuel as it contains up to 75% methane. It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning. Its heating capacity is high. Bio-gas is also used for lighting.

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)

Explanation: Power generated in a windmill depends on the velocity with which wind is moving.

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)

Explanation: 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. So, it can be taken as an inexhaustible source of energy.

Fossil fuels inside the earth are present in very limited amount.

Hydro and wind energy plants run with the help of air and do not cause any pollution.

It is very difficult to dispose waste from a nuclear power plant.

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)

Explanation: Water at greater height has more potential energy. When it falls it will have greater kinetic energy associated with it. A larger amount of potential energy is converted into kinetic energy due to which more electric power will be obtained.

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 utilizing the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator

Answer. (a), (b)

Explanation: Maximum wind power is harnessed in open space hence, option (a) is wrong.

Moving air have kinetic energy which on hitting at the blades of a windmill causes them to rotate.

To generate wind power, we require wind at a very high speed. Due to this motion it possess kinetic energy and as such they are capable of doing mechanical work by virtue of its motion.

The energy possessed by the wind is due to its high speed. When the blowing wind strikes across the blades of a windmill, it exerts a force on them due to which the blades of the windmill start rotating. This rotational motion of the blades is used to run the turbine of an electric generator. Thus, the option (b) is the incorrect statement.

Question 15. Choose the incorrect statement.

(a) We are encouraged to plant more trees so as to ensure clean environment and also provide biomass fuel

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

(c) The main ingredient of biogas 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)

Explanation: The main ingredient of biogas is methane. Except option (c), all other options are correct.

Long Answer Type Questions

Question 23. Which is the process used to harness nuclear energy these days? Explain it briefly.

Answer.

Nuclear fission process is used to harness nuclear energy these days.

The fission of an atom of uranium, for example, produces 10 million times the energy produced by the combustion of an atom of carbon from coal.

In a nuclear fission, the difference in mass, Δm, between the original nucleus and the product nuclei gets converted to energy E at a rate governed by the equation E = Δm c² , where c is velocity of light.

In a nuclear reactor designed for electric power generation, such nuclear ‘fuel’ can be part of a self-sustaining fission chain reaction that releases energy at a controlled rate. The released energy can be used to produce steam and further generate electricity.

Question 24. How can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?

Answer.

Solar energy can be harnessed directly by using solar cooker, solar hater or solar cells.

In solar cooker the heat energy by sun is used to for cooking purposes. In solar heater, heat energy is used to heat the water. In solar cells it is converted to electricity.

Limitations in using solar energy are:

• Solar energy is not available in night or when the sun is hidden under clouds.
• The domestic use of solar cells for production of electricity is not possible due to high cost.

These limitations can be overcome by following ways:

• First limitation can be overcome by converting solar energy into electrical energy and storing them for future use.
• Second limitations can be overcome by taking certain steps by government to reduce price of solar cells.

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.

Answer.

Conventional Sources of Energy

• Fossil fuels
• Hydro-electric Power Plant
• Thermal Power Plant
• Bio-mass

Non-Conventional Sources of Energy

• Solar Energy
• Tidal Energy
• Nuclear Energy
• Ocean Thermal Energy

Harnessing nuclear energy:

Nuclear energy is a non-conventional source of energy and can be harnessed by a process called nuclear fission. The nucleus of a heavy atom (such as uranium, plutonium or thorium), when bombarded with low-energy neutrons, can be split apart into lighter nuclei. When this is done, a tremendous amount of energy is released if the mass of the original nucleus is just a little more than the sum of the masses of the individual products. The fission of an atom of uranium, for example, produces 10 million times the energy produced by the combustion of an atom of carbon from coal. In a nuclear reactor designed for electric power generation, such nuclear ‘fuel’ can be part of a self-sustaining fission chain reaction that releases energy at a controlled rate. The released energy can be used to produce steam and further 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.

The population of the world is increasing at a very rapid rate due to which demands for energy is increasing day by day.  As, fossil fuels like coal, petroleum, are present in a limited amount which and are likely to finish one day so the need for alternative sources of energy is essential.

Use of conventional sources of energy (coal, petroleum etc.) causes pollution. To reduce pollution use of non-conventional sources of energy is essential.

The energy from the sea energy be harnessed from the sea in different ways

Tidal Energy

Due to the gravitational pull of mainly the moon on the spinning earth, the level of water in the sea rises and falls. This phenomenon is called high and low tides and the difference in sea-levels gives us tidal energy. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.

Wave Energy

The kinetic energy possessed by huge waves near the seashore can be trapped to generate electricity. The waves are generated by strong winds blowing across the sea. Wave energy would be a viable proposition only where waves are very strong. A wide variety of devices has been developed to trap wave energy for rotation of turbine and production of electricity.

Ocean Thermal Energy

The water at the surface of the sea or ocean is heated by the Sun while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean-thermal-energy conversion plants. These plants can operate if the temperature difference between the water at the surface and water at depths up to 2 km is 20 K (20°C) or more. The warm surface-water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of generator. The cold water from the depth of the ocean is pumped up and condense vapour again to liquid. The energy potential from the sea (tidal energy, wave energy and ocean thermal energy) is quite large, but efficient commercial exploitation is difficult.

Question 27. What are the environmental consequences of using fossil fuels? Suggest the steps to minimize the pollution caused by various sources of energy including non-conventional sources of energy causes global warming.

Answer.

Followings are the environmental consequences of using fossil fuels:

• The burning of fossil fuels produces greenhouse effect of gases like carbon dioxide and results in global warming.
• The burning of fossil fuels also releases oxides of nitrogen and sulphur that are released by burning fossil fuels are acidic oxides. These lead to acid rain which affects our water and soil resources.

The steps to minimize the pollution caused by various sources of energy including non-conventional sources of energy causes global warming.

Pollution caused by combustion of coal, petroleum (conventional sources) and biomass (non-conventional sources) can be reduced by increasing the efficiency of the combustion process and using various techniques to reduce the escape of harmful gases and ashes into the surroundings.

The effect of green house gases released by burning of fossil fuels and biogas can be minimized by planting more trees.

Pollution due to nuclear waste can be minimized by properly disposing nuclear wastes.

Question 28. Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.

Answer.

Yes, I agree by the statement that energy from various sources is considered to have been derived from the sun, reasons for which are:

Wind Energy: As we know that warm air rises up andcold air settles down. By similar principal, due to uneven heating of the earth’s surface by the sun rays at two different adjoining places a pressure difference is created and wind is produced.

Wave energy: Strong winds are generated due to the sun and the waves are generated by strong winds blowing across the sea.

Ocean thermal energy: The difference between the water at the surface and water at depth in seas and oceans is due to the sun.

Energy from fossil fuels: Fossil fuels (coal, petroleum etc) are formed when large plants and ancient creatures are buried deep inside the earth crust under the effect of a lot of pressure and heat.

Solar energy: The phenomenon of photoelectric effect (generation of electricity by light) is possible only in the presence of sun.

Bio-mass: Plants converts the solar energy into chemical energy with the help of inorganic substances (i.e. air, water etc).  These plants are consumed by plants and animals and produce wastes from which energy is obtained.

Energy from flowing water: Water from sea and rivers evaporate and fall at different places of the earth as snow and rainfall. This water collected in a dam and when allowed to flow rotates turbine of generator and electricity is produced. 

Question 29. What is bio-mass? Explain the principle and working of a biogas plant using a labelled schematic diagram.

Answer.

Biomass refers to those living and non-living organic materials that can be used as sources of energy in the form of fuel. Some examples of biomass fuels are biogas, wood, crops, and organic garbage. The chemical energy in biomass is released as heat on burning.

Bio-mass refers to the organic fuel obtained from plants and animal wastes like wood, cow-dung, residue after harvesting the crop, vegetable waste and sewage, etc. It has been used as a fuel for a long time. These fuels, however, do not produce much heat on burning and a lot of smoke is given out when they are burnt.

Principle

When substance likes cow-dung, vegetable waste etc undergoes anaerobic (in absence of air) decompositionthen these complex substances are broken down into simpler substances and gases like methane, Carbon dioxide etc are produced.

Working

The 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 there is no oxygen. Anaerobic micro-organisms that do not require oxygen decompose or break down complex compounds of the cow-dung slurry. It takes a few days for the decomposition process to be complete and generate gases like methane, carbon dioxide, hydrogen and hydrogen sulphide. The bio-gas is stored in the gas tank above the digester from which they are drawn through pipes for use.