Tuesday, 2 September 2014



1. RENEWABLE SOURCES OF ENERGY: are those , which do not get exhausted with time or can be     
   regenerated over a reasonable period of time. For example, solar energy, energy due to flowing water, wind energy, thermal energy of earth and biomass are renewable sources of energy

2. NON RENEWABLE SOURCES OF ENERGY  are those which take millions of years for the formation and   Cannot be regenerated over a small span of time. For example,coal and petroleum products are nonrenewable sources of energy.

3.Solar energy (i) provides energy to wind ,tidal waves and sea waves(ii) is responsible for large scale evaporation of water which causes rain,(iii) is responsible for photosynthesis so vital  for plants and hence animals.

4. Solar energy is harnessed by man by using devices such as solar cookers ,solar furnaces, solar water heaters, and solar electric power plants.

5. Collection of solar energy in solar cookers can be enhanced by (i) Painting their surface black (ii) by using glass cover (iii) by using reflector, such as plane mirror.

6 .Photo voltaic cell directly convert solar energy into electric energy.

7.In a solar cell , semiconductors of germanium or silicon are used. These semiconductors are doped with traces of phosphorous or boron .The semiconductors doped with boron are called P-type semiconductors. They attract the electrons towards themselves. The semiconductors doped with Phosphorous are called n-type semiconductors. They have surplus of electrons.

8. Wind energy can be harnessed in the form of mechanical energy in sail boats and windmills, which may be used in lifting underground water or  for grinding gran.Wind energy can also be harnessed in the form of electrical energy, by coupling an electric generator to the windmill.

9. Wind energy is undependable as the wind  does not blow all the time at a given place. Furthermore, the speed of  wind changes from time to time.

10.Hydel energy is used in the generation of electricity .Water stored at higher level (in dam) is made to fall on the blades of turbine, connected to electric generator. As the coil of generator rotate in the magnetic field the mechanical energy changes to kinetic energy.

11. Nuclear energy is obtained by splitting the nucleus of uranium by slow moving neutrons in a special device called Nuclear reactor.  The Heat energy so liberated is used in in raising steam. The steam is made to run the turbine, which is coupled to the generator. In the generator  the mechanical energy changes into electrical energy.

12. The waste products of nuclear power plants are highly radioactive. If not handled properly, they can cause diseases  like cancer, leukaemia.Furthermore, there is always a small chance of nuclear explosion.

13. Tidal energy of sea waves is harnessed by constructing hydroelectric dams at the mouth of narrow bays along the sea coast.

14. Biogas mostly consists of methane .It is obtained by the fermentation of cow dung and farm
     wastes by anaerobic bacteria in Biogas plants. The spent slurry left after the generation of  
      Biogas is an     excellent Manure.

15. Air gets polluted by burning (i) biomass in insufficient supply of air (ii) by the burning of fossil fuels  in     big factories and automobiles.

16. Air pollution can be mnimised by using electric precipitators in coal burning factories and by using           improved engines or CNG in automobiles.