(iii) Cannot be used at night or on cloudy days.
(iv) Cannot be used to make chapattis for frying as these
require a temperature of 1400C or more.
(Maximum temperature of 1000C only can be
achieved in a solar cooker)
- Other solar devices- Solar water heater, Solar furnace
(4) Geo thermal energy:
(i) Energy harnessed from the heat of the sun is called Geo thermal energy.
(ii) Magma is formed when this heat melts the rocks. The molten rocks and hot gases are called magma
(iii) The magma gets collected at some depths below the earth’s surfaces. These places are called ‘Hot spots”
(iv) When underground water comes in contact these hot spots, it changes into steam, which can be used to generate electricity.
- Advantages of Geo thermal energy:
- Disadvantages of Geo thermal energy:
(i) Only few sites available for harnessing energy.
(5) Nuclear energy:
(i) Energy released when some changes take place in the nucleus of the atom of a
substance, is called Nuclear energy.
(ii) It is used for heat generation, fuel for marine vessels.
- Advantages of Nuclear energy:
(i) Alternative source of energy due to depletion of fossil fuels.
(ii) From a small amount of fuel, a large amount of energy is released.
- Disadvantages of Nuclear energy:
(i) Risk of nuclear waste leakage
(ii) High cost of setting up of nuclear plant
(iii) Pollution of environment.
(6) Energy from the sea-
(A) Tidal energy: Locations inIndia–Gulf of Kutch, Gujrat & W. Bengal
(i) Depends upon harnessing the rise and fall of sea level due to tidal action.
(ii) Dams are constructed across a narrow part of sea and turbine converts tidal
energy into electrical energy.
Disadvantages: Uniform tidal action is not seen
(B) Wave energy:
(i) Kinetic energy of the waves of sea are used to rotate turbines..
(ii) These turbines generate electrical energy
v Important diagrams-
- Hydro power plant
- Bio gas plant
- A wind mill
- A solar cooker
HOTS QUESTIONS (SOLVED)
- Name the materials used for making solar cells.
A. Silicon, Germanium and Selenium
- What fraction of solar energy reaches the earth’s surface?
- Name the process that produces a large amount of energy in the sun.
A. Nuclear fusion
- Why is biogas called a clean fuel?
A. Because it- (i) leaves no ash (ii) does not cause pollution (iii) does not produce any
- Why Hydrogen cannot be used as a domestic fuel?
AHydrogen cannot be used as a domestic fuel, in spite of its high calorific value, because it is explosive in nature and difficult to store & transport.
- What are OTEC power plants? How do they operate?
- (i) It is Ocean Thermal Energy Conversion.
(ii) These plants can operate if the temperature difference between water at the surface and
water at depths up to 2 km is 293K (200C) or more.
(iii) The warm surface water is used to boil a volatile liquid like Ammonia. The vapour of the
liquid is used to turn the turbine.