Chapter 14 Sources of Energy

Sun is the ultimate source of energy. Sun is important for the sustainability of this living world. Nowadays in this modern era each and every activity is dependent on energy sources. Combustion of Coal and Petroleum increases and due to various hazardous activities causing increase in pollution so to overcome, this non traditional source of energy is used like solar energy for production of electricity. In this chapter we will discuss various forms of energy, their use on a daily basis.

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Exercise 1

  • Q1 What is a good source of energy?

    Good sources of energy are

    (I) It should have high calorific value.

    (II) It does a huge amount of work per unit mass.

    (III)  It should be easy to  handle.

    (IV)  It should be easy to store and transport.

    (V) It  must be cheap.

    (VI) It produces less amount of smoke  and is eco friendly.


    Q2 What is a good fuel?

    A good fuel should have a high calorific value that is  the amount of heat produced  on burning, does not produce a lot of smoke, and is easily available.


    Q3 If you could use any source of energy for heating your food, which one would you use and why?

    Natural gas  is a good source of energy and can be used for heating and cooking food because it is a clean source of energy burn without smoke. Although it is highly inflammable, it is easy to use, transport, and has high calorific value.


Exercise 2

  • Q1 What are the disadvantages of fossil fuels?

    The fossil fuels  disadvantages are as follows:

    (a) coal and petroleum while burning  produces a lot of pollutants that cause air pollution.

    (b) They release oxides of carbon, nitrogen, sulphur, etc. that cause acid rain, which affects the soil fertility and potable water.

    (c) Burning of fossil fuels produce gases such as carbon dioxide that causes global warming.


    Q2 Why are we looking at alternate sources of energy?

     Non conventional sources of energy are better than Fossil fuels, which have been traditionally used by human beings as energy sources, are non-renewable sources of energy. These sources of energy are limited and cannot replenish on their own. They are being consumed at a large rate. If this rate of consumption continues, then the fossil fuels would be exhausted from the Earth. Therefore, we have to conserve the energy sources. Hence, we should look for alternate sources of energy.


    Q3 How has the traditional use of wind and water energy been modified for our convenience?

    Nowadays, windmills are used to generate electricity whereas earlier they were used to harness wind energy to do mechanical work such as lifting/drawing water from a well.. Through windmills, the kinetic energy of wind is  converted into electricity. The rotatory motion of the blades turns the turbine of the electric generator to generate electricity.    waterfalls potential energy is converted to electricity with the help of turbines. Since waterfalls are few in number, water dams have been constructed in large numbers. Nowadays, hydro-dams are used in order to harness potential energy of stored water. In water dams, water falls from a height on the turbine, which produces electricity.

Exercise 3

  • Q1 What kind of mirror – concave, convex or plain – would be best suited for use in a solar cooker? Why?

    A concave mirror  is a converging mirror therefore it would be best suited in a solar cooker because it converges the sunlight in a very small area of the solar cooker and a high temperature is produced in it which is sufficient to cook the food.

    Q2 What are the limitations of the energy that can be obtained from the oceans?

    The various forms of energy can be obtained from the ocean these are:

    a. ocean thermal energy
    b. wave energy and
    c. tidal energy

    Limitations of Tidal Energy:

    i. Limited areas around the world which are suitable for building tidal dams.
    ii. During high and low tides the rise and fall of sea-water is not enough to generate electricity on a large scale.

    Limitations of Wave Energy:

    In the world there are limits where the waves strike the shore lines with sufficient power that is sufficient to generate electric energy from the kinetic energy of the waves.

    Limitations of Ocean Thermal Energy:

    Ocean thermal plant involves high cost. To convert ocean thermal energy into electricity, a great variation in temperature difference of 20°C (or more) between the surface water of the ocean and deeper water is needed for operating OTEC power plants.

    i. Limited areas around the world which are suitable for building tidal dams.
    ii. During high and low tides the rise and fall of sea-water is not enough to generate electricity on a large scale.

    Q3 What is geothermal energy?

    The  heat energy of the Earth  is used to generate electricity by geothermal plants . This heat energy of the Earth is known as geothermal energy.When there are geological changes, the molten rocks present in the core of the earth are pushed to the earth’s crust. This forms regions of hot spots. Steam is generated when the underground water comes in contact with these hot spots forming hot springs. This trapped steam is used to generate electricity in the geothermal power plants.


    Q4 What are the advantages of nuclear energy?

    The nuclear energy advantages  are as follows:

    a) Fusion of four hydrogen atoms produces a huge amount of energy approximately equal to 27 MeV.

    b) Large amount of energy is produced per unit mass.

    c) It does not produce smoke. It is clean energy.

    d) Fission of one atom of uranium produces 10 million times the energy released by burning of one atom of carbon.


Exercise 4

  • Q1 Can any source of energy be pollution-free? Why or why not?

    Yes ,  no source of energy can be pollution-free. They might cause adverse effects on the environment to some extent. It is considered that solar cells are pollution-free. However, even their making causes environmental damage indirectly.

    Also, in the case of nuclear energy, there is no waste produced after the fusion reactions. However, it is not totally pollution-free. To start the fusion reactions, approximately 107 K temperature is required, which is provided by fission reactions. The wastes released from fission reactions are very hazardous. Hence, no source of energy is pollution-free.

    Q2 Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

    Hydrogen Gas is cleaner to  CNG.  hydrogen is waste-free. The fusion of hydrogen does not produce any waste. Whereas CNG contains hydrocarbons. Therefore, it has carbon contents. Carbon is a form of pollutant present in CNG. Hence, hydrogen is cleaner than CNG.


Exercise 5

  • Q1 Name two energy sources that you would consider to be renewable. Give reasons for your choices.

    Two renewable sources of energy are as follows:

    (a) Wind: Wind energy is derived from air blowing with high speed. Wind energy is harnessed by windmills in order to generate electricity. Air blows because of uneven heating of the Earth. Since the heating of the Earth will continue forever, wind energy will also be available forever.

    (b) Sun: The energy derived from the Sun is known as solar energy. Solar energy is produced by the fusion of hydrogen into helium, fusion of helium into other heavy elements, and so on. A large amount of hydrogen and helium is present in the Sun. Therefore, solar energy can replenish on its own. The Sun has 5 billion years more to burn. Hence, solar energy is a renewable source of energy.


    Q2 Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.

    Two exhaustible energy sources are as follows: coal and wood


    (a) Coal: It is formed from the remains of dead plants and animals that have been buried under the earth’s crust for millions of years. It takes millions of years to produce coal. Industrialization has increased the demand of coal. However, coal cannot replenish within a short period of time. it is a nonrenewable or exhaustible source of energy.

    (b) Wood: It is obtained from forests. Deforestation at a faster rate has caused a reduction in the number of forests on our planet. It takes hundreds of years to grow a forest. If deforestation is continued at this rate, then there would be no wood left on the Earth. Hence, wood is an exhaustible source of energy.


Exercise 6

  • Q1 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.

    (b) during cloudy days solar heater cannot be used  because , A solar water heater uses solar energy to heat water. It requires bright and intense sunlight to function properly. On a cloudy day, the sunlight reflects back in the sky from the clouds and is unable to reach the ground. Therefore, solar energy is not available for the solar heater to work properly.

    Q2 Which of the following is not an example of a bio-mass energy source?       (a) wood                     (b) gobar-gas       (c) nuclear energy      (d) coal

    (c) nuclear energy is not a biomass. 

    Biomass is a source of energy that is obtained from plant materials and animal wastes.Wood is a plant material, gobar gas is formed from animal dung, and coal is a fossil fuel obtained from the buried remains of plants and animals, these are biomass products.  Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atom is bombarded with low-energy neutrons. Hence, uranium atom splits into two relatively lighter nuclei. This reaction produces huge amount of energy. In nuclear fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. This reaction produces a tremendous amount of energy. 


    Q3 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.

    C) Nuclear energy is not derived from sun energy.

     Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atoms are bombarded with low-energy neutrons, uranium atoms split into two relatively lighter nuclei. This reaction produces a huge amount of energy. In nuclear fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. The energy required to fuse the lighter nuclei is provided by fission reactions. This reaction produces a tremendous amount of energy. These reactions can be carried out in the absence or presence of sunlight. There is no effect of sunlight on these reactions. Hence, nuclear energy is not ultimately derived from the Sun's energy.

    Geothermal energy, wind energy, and biomass are all ultimately derived from solar energy.


    Q4 Compare and contrast fossil fuels and the Sun as direct sources of energy.

    Coal and petroleum  are Fossil fuels and are energy sources,obtained from the Earth’s crust. They are directly available to human beings for use.So , fossil fuels are the direct source of energy. These are non-renewable sources of energy because these cannot be replenished in nature. Fossil fuels take millions of years for their formation. If the present fossil fuel of the Earth gets exhausted, its formation will take several years. Fossil fuels are also very costly.

    On the other hand, solar energy is a renewable and direct source of energy. The Sun has been shining for several years and will do so for the next five billion years. Solar energy is available free of cost to all in unlimited amounts. It replenishes in the Sun itself.


    Q5 Compare and contrast bio-mass and hydro electricity as sources of energy.

    Both Biomass and hydro-electricity are renewable sources of energy. Biomass is derived from remaining  plants and animal wastes.So , it is naturally replenished. Wood, gobar gas, etc. are some of the examples of biomass.

    Hydro-electricity, on the other hand, is obtained from the potential energy stored in water at a height. Energy from it can be produced again and again. It is harnessed from water and obtained from mechanical processes.


    Q6 What are the limitations of extracting energy from—    (a) the wind?          (b) waves?          (c) tides?

    (a) limitations of extracting energy from wind is that a windmill requires wind of speed more than 15 km/h to generate electricity. Also, a large number of windmills are required, which covers a huge area.

    (b) Strong ocean waves are required in order to extract energy from waves.

    (c) Very high tides are required in order to extract energy from tides. Also, occurrence of tides depends on the relative positions of the Sun, moon, and the Earth.


    Q7 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) the same?

    (a)That source of energy that replenishes in nature is known as a renewable source of energy. Sun, wind, moving water, biomass, etc. The source of energy that does not replenish in nature is known as a non-renewable source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non-renewable sources of energy.

    (b)those sources of energy, which will deplete and exhaust after a few hundred years are exhaustible . Coal, petroleum, etc. are the exhaustible sources of energy.Inexhaustible resources of energy are those sources, which will not exhaust in future. These are unlimited. Biomass is one of the inexhaustible sources of energy.

    Yes. The options given in (a) and (b) are the same.


    Q8 What are the qualities of an ideal source of energy?

    An ideal source of energy must be:

    i) Easy to store and transport

    ii) Easily accessible

    iii) Environment friendly

    iv) high calorific value 

    v) cheap


    Q9 What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

    Solar cooker uses the Sun's energy to heat and cook food. It is an inexhaustible and clean renewable source of energy. It is free for all and available in unlimited amounts. Hence, operating a solar cooker is not expensive.

    Disadvantage of a solar cooker is that it is very expensive. It does not work without sunlight. Hence, on cloudy days, it becomes useless.

    The places where the days are too short or places with cloud covers round the year, have limited utility for solar cookers.


    Q10 What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

    Due to Industrialisation the demand for energy increases . Fossil fuels are easily accessible sources of energy that fulfil this demand. The increased use of fossil fuels has an adverse  effect on the environment. Large consumption of fossil fuels increases the greenhouse gas in the atmosphere, resulting in global warming and a rise in the sea level.

    It is not possible to reduce the consumption of fossil fuels. However, some  preventive measures can be taken such as using electrical appliances wisely and not wasting electricity. Unnecessary usage of water should be avoided. Public transport systems with mass transit must be adopted on a large scale. These small steps may help in reducing the consumption of natural resources and conserving them.


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