ENERGY SOURCES - II :BRIEF ANSWERS

ANSWER IN BRIEF

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1. 'A very minute part of sun's energy reaches the earth.' Justify giving details.
   

   ANS:
   

   
   
   • Sun is the ultimate source of energy for earth. Tremendous amount of energy is continuously produced in sun due to thermonuclear fusion process and this energy is radiated by the sun into the space.
     
   • The sun releases 3.8 x 10²⁶ joule of heat energy per second in all directions.
     
   • Only 1.7 x 10¹⁷ joule of heat energy per second reaches the surface of the earth which is only 0.000000045792% of sun's energy output.
     
   • Thus, a very minute part of sun's energy reaches the surface of the earth.
     

   
   

   
   
2. Mention two categories of solar appliances with examples.
   

   ANS:Solar appliances are classified into two categories on the basis of principle of their working.
   (1)Devices that convert solar energy into heat energy : for example, solar cooker and solar water heater.
   (2)Devices that convert solar energy into electricity : for example, solar cells.
   

   
   
3. Distinguish between renewable and nonrenewable sources of energy.
   

   ANS:
   

   
   
   
4. How are smokeless chulhas more efficient than the traditional chulhas ?
   

   ANS:Only 8 - 10% of the energy of the fuel(firewood) is used when burnt in traditional chulhas as the supply of oxygen is less. In smokeless chulhas, the fuel gets more oxygen and the efficiency is increased. Moreover, incomplete combustion of fuel in traditional chulhas creates pollution due to smoke.
   

   
   
5. How was petroleum formed ?
   

   ANS:Many aquatic plants and animals were buried down in the earth centuries ago (in fact, millions of years ago). The high temperature and pressure created due to the layers of earth formed above them converted their fossils into petroleum. Usually it is formed under sedimentary rocks and its formation involves complicated reactions.
   

   
   
6. Mention Uses of Natural gas.
   

   ANS:
   
   The uses of natural gas are:
   

   
   
   • As a fuel in industries and power stations.
     
   • In the manufacture of artificial fertilisers like ammonia and urea.
     
   • As a source of hydrogen gas.
     
   • As a source of methane for use as domestic fuel.
     

   
   

   
   
7. Give reason: The calorific value of wood is lower than that of the hydrocarbons.
   

   ANS: The calorific value of hydrogen is the highest. The calorific value of a fuel is higher if its hydrogen content is high. The hydrocarbons are made of carbon and hydrogen only whereas wood is made of carbohydrates. Carbohydrates contain oxygen in addition to carbon and hydrogen. Oxygen does support combustion but it does not burn itself. Therefore, it does not contribute to the energy released. Thus, the calorific value of wood is lower than that of the hydrocarbons.
   

   
   
8. Explain how the energy obtained from nuclear fusion is better than that obtained from fission reactions.
   

   ANS:The energy obtained from nuclear fusion is better than that obtained from fission reactions because of the following advantages of fusion process:
   

   
   
   • The fuel for nuclear fusion is cheaper and easily available.
     
   • There is no requirement of disposing off of the nuclear waste.
     
   • It is comparatively pollution-free.
     

   
   

   
   
9. State the advantages and limitations of a solar cooker.
   

   ANS:Refer to the long answer on Solar cooker.
   

   
   
10. Distinguish between petrol and diesel.
    ANS:
    
11. Distinguish between petrol and kerosene.
    ANS: