Physics notes: SOURCES OF ENERGY For ALP Stage-2 exam 2018 (PART 2)

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2. NON-CONVENTIONAL SOURCES OF ENERGY: Energy sources which are relatively new and whose usage has been recently started are called non-conventional sources of energy, e.g. nuclear power, solar energy, tidal energy etc.
A. SOLAR ENERGY
The energy emitted by the sun in form of heat and light is called solar energy.
Solar Constant = 1.4 (kJ/s.m2)
Outer edge of the earth receives solar energy equal to 1.4 kJ/s.m2 which is known as solar constant.


Uses of solar energy as-
Solar Cooker: Solar cooker is very simple in design and mode of function. It is usually made from mirrors. Plain mirrors are placed inside a rectangular box. The light reflected from the plain mirrors concentrates the solar energy inside the solar cooker which generates enough heat to cook food.
Solar Furnace: Solar furnace is made like a concave mirror. Large solar furnace has many smaller mirrors to compose a very large convex mirror. The thing to be heated is place near the focus of the mirror.
Solar Cells: Solar cells are made from silicon. The solar panel converts solar energy into electrical energy which is stored in a battery; for later use.A large number of solar cells are combined in an arrangement called solar cell panel. 
Limitations of Solar Energy: The technologies for harnessing solar energy are at a nascent stage. At present, the cost benefit ratio for using solar energy is not conducive. Using solar energy is exhorbitantly costly.
B. ENERGY FROM THE SEA
The oceans cover about 70% of the terrestrial area. They contain a lot of energy that can be used for various purposes. Energies which are technically available are the following-
i. TIDAL ENERGY
Due to the gravitational pull of the moon on the spinning earth, the level of water in the sea rises and falls that results in the formation of high and low tides.This difference in sea levels gives us tidal energy.Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy into electricity. 
ii. WAVE ENERGY
The waves are generated by the strong winds that blows across the sea.The kinetic energy of this moving water rotates the turbine of a generator generating electricity. When strong winds stop blowing, the generator stops producing electricity.

iii. OCEAN THERMAL ENERGY
The water at the surface of the sea or ocean is heated by the sun while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean thermal energy conversion plants.
Temperature difference between surface water and water at the depth of 2km should be 20°C or more.The warm surface water is used to boil a volatile liquid like ammonia.The vapours of the liquid are used to run the turbine of generator.The cold water (from deeper layers) is pumped up to condense the vapour into liquid.The power plants used to harness the ocean thermal energy is known as “Ocean Thermal Energy Conversion Plant” (OTEC).

C. GEOTHERMAL ENERGY: The molten rocks from the inside of the earth are pushed in certain regions of the earth. Such regions are called the hot spots of the earth. When groundwater comes in contact with such hot spots, lot of steam is generated. This steam can be harnessed to produce energy. Sometimes, hot water from that region finds outlets at the surface. Such outlets are known as hot springs. Many power plants in New Zealand and USA operate on geothermal energy.

D. NUCLEAR ENERGY
Nuclear energy is the energy which is stored in the nucleus of an atom.
Nuclear energy is of two types
1.Nuclear fission– It is the process during which a nucleus breaks to form two nuclei. The process generates a huge amount of energy. This phenomenon is utilized in nuclear power plants to produce electricity.
U-235 is used as a fuel in nuclear reactor in the form of uranium rods.
2.Nuclear Fusion-  When two lighter nuclei join up to form heavy nucleus and tremendous amount of energy is released, it is known as Nuclear fusion. Hydrogen bomb is based on this phenomenon. Nuclear fusion is the source of energy in the sun and the stars. 

Advantages of Nuclear Energy
1. Large amount of energy is released.
2. In nuclear power plant, the nuclear fuel is inserted once to get energy over a long period of time.
Disadvantages of Nuclear Energy
1. High cost of installation.
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