NCERT IN-TEXT QUESTIONS SOLVED
1.  What is a good source of energy?
Ans. The energy which is easily available, cheap, does not produce pollution is said to be good source.
2.  What is a good fuel?
Ans. A good fuel is one which is cheap, easily available, easy to handle, transport, has proper ignition temperature and high calorific value.
3.  If you could use any source of energy for heating your food, which one would you. us? and why?
Ans. If sun�s ,heat is accessible then solar cooker or else CNG.
4.  What are the disadvantages of fossil fuels?
Ans. Disadvantages of fossil fuels are:
       (a) They are non-renewable resources
       (b) They cause pollution which can lead to
             (i) Acid rain
             (ii) Smoke
             (iii) Green house effect due to CO2
             (iv) Fly ash suspended in air.
5.  Why are we looking at alternate sources of energy?
Ans. The sources of energy we are using now is fossil fuel i.e., petrol and petroleum products, and coal which are exhaustible and non-renewable. The demand of energy is increasing due to increased population and better technology that has added many machines, appliances to add comfort to life style. Hence ,the. demand for energy is increasing day by day. To overcome this problem we are looking for alternate sources of energy.
6.  How has the traditional use of wind and water energy been modified for our convenience?
Ans. (i) The traditional use of water energy has been modified and we have built dams, turbines and dynamos to generate electricity with the help of flow of water.
           (ii) Wind; energy is used to rotate the wind mills, turbines and generate electricity by constructing wind fans.
7.  What kind of mirror-concave, convex or plain-would be best suited for use in a solar cooker? Why?
Ans. Concave minor would be best suited for use in solar cooker. As it is a converging mirror and would converge sun�s heat radiation at one focussed point.
8.  What are the limitations of the energy that can be obtained from the oceans?
Ans. The limitations of ocean energy are:
           (i) Few limited sites/places where this wave, tidal or ocean thermal energy can be obtained.
           (ii) The cost of construction of plants is very; high
           (iii) The efficiency of producing energy is also low
9.  What is geothermal energy?
Ans. The heat energy obtained in the form of steam from under the earth�s crust is called geothermal energy
10.  What are the advantages of nuclear energy?
Ans. The advantages of nuclear energy are:
           (i) A very small amount of radioactive material can produce large amount of energy which can be controlled and converted into usable form e.g., 1 kg Uranium = 25 thousand tonnes of coal.
           (ii) It does not release any smoke or harmful gases in the air. Hence it can, curbthe global warming that is caused due to green house effect.
11.  Can any source of energy be pollution free? Why or why not?
Ans. Yes, there can be a source of energy that can be pollution free in using it. e.g., sun�s energy that is used in solar cooker, solar water heater, solar cell panels.
12.  Hydrogen has been used as a rocket fuel. Would you consider It a cleaner fuel than CNG? Why or why not?
Ans. Hydrogen is a cleaner fuel than CNG because hydrogen on burning/combustion form water whereas CNG that contain methane burns to produce carbon dioxide.
13.  Name two energy sources that you would consider to be renewable. Give reasons fur your choices.
Ans. Solar energy-it will not get exhausted it can be used for multipurpose-heating, burning and producing electricity. It will not cause any pollution, it is cheap and easily available.
           Energy from water-Energy can be obtained from water in various form i.e., for producing electricity without pollution.
QUESTIONS FROM NCERT TEXTBOOK
1.  A solar water heater cannot be used to get hot water on
       (a) a sunny day.       (b) a cloudy day.       (d) a windy day.       (c) a hot day.
Ans. (b) a cloudy day.
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
Ans. (c) nuclear energy.
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
Ans. (c) nuclear energy.
4.  Compare and contrast fossil fuels and the Sun as direct sources of energy.
Ans.
Sun Fossil fuels
1. It is renewable source of energy. It is non-renewable source of energy.
2. It does not cause pollution. It causes pollution in the environment.
3. It is cheap, easily available for most of the time and at most of the places. It is expensive, not easily available ai1y time and anywhere.
5.  Compare and contrast bio-mass and hydro electricity as sources of energy.
Ans.
Bio-mass as Energy Source Hydro electricity as Energy Source
1. It causes pollution. It does not cause pollution.
2. It is cheap and easily available. It is expensive and not easily available.
3. Initial cost for building the bio-gas plant is very cheap and its maintenance is also cheap. The initial cost of building the power plant is expensive, its maintenance is also expensive.
6.  What are the limitations of extracting energy from:
       (a) the wind?       (b) waves?       (c) tides?
Ans. (a) The Wind
                   (i) It can be extracted only at limited sites where the wind blows most of the time in a year.
                   (ii) The minimum speed of wind should be 15 km/h.
                   (iii) Large area is required to build the wind farm/wind mills which is expensive affair.
                   (iv) Efficiency, is low.
           (b) Waves
                   (i) The place and time is limited when the waves are strong.
                   (ii) Initial setup cost is expensive.
                   (iii) Efficiency is low.
           (c) Tides
                   (i) The areas where tidal energy can be harnessed is less.
                   (ii) The efficiency is very low.
                   (iii) The plants are not cost effective.
7.  On what basis would you classify energy sources as
       (a) renewable and non-renewable?
       (b) exhaustible and inexhaustible?
Ans. Both (a) and (b) options are same:
Renewable/Inexhaustible Non-renewable/Exhaustible
1. They are also called inexhaustible They are also called as exhaustible
2. The energy source that will not finish and can be renewed or made again and again is called renewable source of energy e.g., sun, wind, water. The energy source that will finish and will get exhausted and cannotrbe made very soon or takes million of years for its formation e.g., fossil fuels-petrol, coal.
8.  What are the qualities of an ideal source of energy?
Ans. he ideal source should have the following qualities:
           1.  should be cheap, easily available and easy to handle.
           2.  It can be transported easily.
           3.  It should have high calorific value.
           4.  It should have proper ignition. temperature.
           5.  It should not cause any environmental pollution.
9.  What are the advantages and disadvantages of using a solar cooker.? Are there places where solar cookers would have limited utility?
Ans. Advantages of solar cooker:
           (a) It is cheap and easy to handle.
           (b) It does not need any fuel for cooking food.
           (c) It is pollution free.
           Disadvantages of solar cooker:
           (a) It is very slow, takes long time for cooking.
           (b) It is dependent on sun�s light, cannot work on cloudy day.
           (c) The reflectors position need to be monitored so as it reflects the sunlight at the centre focused point of the solar cooker.
                Yes-the places where sun�s energy not sufficient, the use of solar cookers would be limited
10.  What are the environmental �consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Ans. Due to increasing demand of energy the available sources of energy are depleting at fast rate. The use of fuels on large scale is releasing lot of gases and unwanted particles in the air. The gases like SO2, NO2 are causing acid rain that is destroying monuments, iron articles, bridges etc. The CO2 released in air is causing green house effect that is leading to global warming which will melt the ice and sea-level will increase submerging coastal areas and islands. To reduce energy consumtion we should look for alternative source of energy which can help us to overcome all these problems.