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Due to the ever increasing demand for energy, we need to develop specific devices that can harness energy from non-conventional sources like - solar energy, energy from the sea, geothermal energy and nuclear energy.
We shall discuss each non-conventional source of energy in detail.
Sunlight falling on the earth's surface equals 50,000 times the energy used each year by man. Almost all our energy comes from sun.
The sun's energy is responsible for the tidal energy, heat energy stored in water, the chemical energy stored in plants, and the kinetic energy stored in the wind, from which we can obtain electrical energy. This is the indirect use of solar energy. We can also harness solar energy directly. Solar water heater and solar cells directly harness solar energy.
Only a small part of the solar energy reaches the outer layer of the earth's atmosphere. Nearly half of it is absorbed while passing through the atmosphere and the rest reaches the earth's surface.
The amount of solar energy received per second by one square metre of the near earth space (exposed perpendicularly to the rays of the sun) at an average distance between the sun and the earth is called solar constant.
Solar constant = 1.4 kW/m2
The experiment described below shows that a black surface absorbs more heat than a white one.
| Take two conical flasks and paint one white and the other black
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The thermometer in the black conical flask records higher temperature
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This is because black surface absorbs more heat than any other surface under identical conditions
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| Fill them with equal amount of water and place them in sunlight for one hour
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The above concept is used in designing the device called the solar cooker
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| Touch the flasks and find out which one is hotter
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| You may also use a laboratory thermometer to record the exact temperature
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The peculiar property of glass which results in the green house effect is the principle involved in the working of the solar cooker.
Peculiar Property of Glass
Glass allows the heat rays of shorter wavelength to pass through it but does not allow the heat rays of larger wavelength to escape from it and thus it is able to trap heat inside a container.
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