Intext Questions

Q.1     What is a good source of energy?
Sol.      A good source of energy should be renewable and environment-friendly .

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Q.2     What is a good fuel?
Sol.      A good fuel should have many desirable characteristics. Some of them are as follows:
– It should produce a high amount of energy for each unit of mass or volume.
– It should be easily available and should be easy to transport.
– It should be economical.

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Q.3     If you could use any source of energy for heating your food, which one would you use and why?
Sol.     I will use LPG (Liquefied Petroleum Gas) for heating my food; because it is easily available in my kitchen, gives no smoke on burning and takes less time to do the job.

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Q.1     What are the disadvantages of fossil fuels?
Sol.     Following are the disadvantages of fossil fuels:
(a) They are non-renewable
(b) They produce air pollutants on burning.

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Q.2     Why are we looking at alternate sources of energy?
Sol.      Because of growing population, the energy demand is rising. Fossil fuels are going to be exhausted in the near future and burning them is causing air pollution. Hence, we need to find an alternate source of energy which renewable and environment friendly.

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Q.3     How has the traditional use of wind and water energy been modified for our convenience?
Sol.      Before the beginning of the Industrial revolution, wind and water energy were used for serving many purposes but the ways of their use were not efficient. For example; windmills were used to power smaller mills; like flour mills or saw mills. The flow of water was used for transporting wooden logs. Now-a-days, both wind energy and water energy are being harnessed to produce electricity which means a better and more efficient use of these forms of energy.

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Q.1     What kind of mirror; concave or convex or plain would be best suited for use in a solar cooker? Why?
Sol.      A concave mirror is best suited for use in a solar cooker. The reason for this is the ability of a concave mirror to converge the solar energy at a point. This enables the concave mirror to produce a larger amount of heat; compared to other types of mirror.

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Q.2     What are the limitations of the energy that can be obtained from the oceans? Sol.      Limitations of energy which can be obtained from the oceans:
– These forms of energy can be harnessed only in coastal areas; which would leave a vast portion of the human habitation.
– The technologies for harnessing them are still at experimental stage and hence are very costly and less efficient.

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Q.3     What is geothermal energy?
Sol.      The energy which can be harnessed from the heat of inside of the earth is called geothermal energy.

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Q.4     What are the advantages of nuclear energy?
Sol.      Advantages of nuclear energy are as follows:
– A small amount of radioactive material can generate a huge amount of energy.
– It does not produce air pollution.
– A nuclear power plant is more efficient than other power plants.

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Q.1     Can any source of energy be pollution free? Why or why not?
Sol.      Many sources of energy can be pollution free. When burning of biomass is not involved in production of energy, then there is no chance of pollution. For example; wind energy, hydel energy, solar energy, etc. are pollution free.

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Q.2     Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Sol.      Hydrogen is a much cleaner energy source than CNG. CNG (compressed natural gas) is derived from biomass and hence burning the CNG causes air pollution; albeit on a much smaller scale than coal and petroleum. Use of hydrogen as energy source does not polluting gases.

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Q.1     Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Sol.     Solar energy and wind energy are examples of renewable energy sources because they get quickly replenished.

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Q.2     Gives the names of two energy sources that you would consider to be exhaustible. Give reasons for your choice.
Sol.      Coal and petroleum are exhaustible energy sources because their stock is going to be finished in the near future and it takes millions of years for their formation.

Exercise

Q.1     A solar water heater cannot be used to get hot water on

           (a) A sunny day

           (b) A cloudy day

           (c)  A hot day

           (d) A windy day

Sol.     (b) A cloudy day

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Q.2     Which of the following is not an example of a bio-mass energy source?

           (a) Wood

           (b) Gobar-gas

           (c)  Nuclear energy

           (d) Coal

Sol.     (c) Nuclear energy

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Q.3     Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?

           (a) Geothermal energy

           (b) Wind energy

           (c) Nuclear energy

           (d) Bio-mass

Sol.     (c) Nuclear Energy

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Q.4     Compare and contrast fossil fuels and the Sun as direct sources of energy.

Sol.      Sun is the direct source of energy, while fossil fuels are formed because of the solar energy stored in them. When green plants prepare food, they convert the solar energy into chemical energy which is stored in the form of biomass. The same biomass gets transferred to the animals. Thus, the energy in the form of biomass which is stored in fossil fuels has come from the sun.

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Q.5     Compare and contrast bio-mass and hydroelectricity as sources of energy.

Sol.      Biomass and hydroelectricity are different in many aspects. Hydroelectricity is generated using the kinetic energy from moving water, while the energy from biomass is generated by decomposition of farm waste. Since biomass is composed of organic compounds so energy from biomass results in air pollution. Hydroelectricity, on the other hand, is pollution free.

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Q.6    What are the limitations of extracting energy from:

          (a) Wind

Sol.    Large tract of land is required for establishment of wind farms. They can be established only at those places where wind speed is high enough. Initial cost of establishing a wind farm is very high and the cost of maintenance is also high.

          (b) Waves

Sol.    Energy from waves can be harnessed only at selected places; only in coastal areas.

          (c) Tides

Sol.    Energy from tides can be harnessed only at selected places; only in coastal areas.

Technologies for harnessing energy from waves and tides are still at experimental stage and hence are less efficient and very costly.

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Q.7     On what basis would you classify energy sources as:

           (a) Renewable and non-renewable

           (b) Exhaustible and inexhaustible

           Are the options given in (a) and (b) are the same?

Sol.     Options given in (a) and (b) are almost same. An energy source which can be quickly renewed is called renewable or inexhaustible. On the other hand, the energy source which cannot be renewed in foreseeable future are called non-renewable or exhaustible.

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Q.8     What are the qualities of an ideal source of energy?

Sol.     Characteristics of an ideal source of energy:

– It should be able to do large amount of work for each unit of mass or volume.

– It should be easily accessible.

– It should be easily transported.

– It should be economical.

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Q.9     What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Sol.     Advantages of Solar Cooker:

– They are environment friendly.

– Use of a solar cooker does not involve recurring expenses on fuel.

Disadvantages of Solar Cooker:

– Solar cooker is very slow.

– Solar cooker can work only during summer months and is useless during winters and on cloudy days.

– Solar cooker can be useful at those places which receive plenty of sunshine. This is useless in colder climates.

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Q.10     What are the environmental consequences of increasing demand for energy? What steps would you suggest to reduce energy consumption?

Sol.       Environmental consequences of increasing demand for energy are as follows:

– Use of fossil fuels is increasing air pollution which is not good for our health.

– Air pollution is causing much damage to the ecosystem.

– Greenhouse effect has resulted in global warming which is manifesting itself in strange changes in the weather pattern around the world.

– Too much exploitation of fossil fuels is going to create a situation when there would be not fossil fuel.

Steps to reduce energy consumption:

– Judicious use of energy is the only way.

– Use public transport instead of private modes of transport.

– Use bicycle whenever possible.

– Walk for short distance commute.

– Avoid unnecessary use of modern gadgets which consume lot of energy.

– Get a solar water heater installed for winter.

Exemplar

Multiple Choice Questions

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

(a) Wood

(b) Sun

(c) Fossil fuels

(d) Wind

Sol. (c)

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Q.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

Sol. (b)

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Q.3 Fuel used in thermal power plants is

(a) Water

(b) Uranium

(c) Biomass

(d) Fossil fuels

Sol. (d)

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Q.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

Sol. (a)

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Q.5 Which is the ultimate source of energy?

(a) Water

(b) Sun

(c) Uranium

(d) Fossil fuels

Sol. (b)

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Q.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

Sol. (c)

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Q.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

Sol. (b)

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Q.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?

Sol. (c)

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Q.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

Sol. (c)

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Q.10 The main constituent of biogas is

(a) Methane

(b) Carbon dioxide

(c) Hydrogen

(d) Hydrogen sulphide

Sol. (a)

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Q.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

Sol. (c)

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Q.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

Sol. (a)

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Q.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

Sol. (b)

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Q.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

Sol. (b)

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Q.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

Sol. (c)