1. Sources of Energy Harnessing Solar Energy

2. Direct methods: Collecting solar energy as heat energy with the help of solar heaters and solar cookers. Converting solar energy directly into electrical energy with the help of photovoltaic cells. Harnessing Solar Energy Sources of Energy Indirect methods: The solar energy can be harnessed indirectly by the following methods: By converting solar energy to chemical energy in the form of biomass in plants. By using wind and water energies, tidal energy and ocean thermal energy, etc. Solar energy can be harnessed in the following ways:

3. What is green - house and the greenhouse effect of glass Glass allows infrared radiation of short wavelengths to pass through it, but does not allow the infrared radiation of longer wavelengths to pass through it. This property of glass is used in constructing greenhouse. Sources of Energy Green - House A greenhouse is an enclosure whose walls are made of glass sheets.

4. When the sun-rays fall on the glass walls of a greenhouse, visible and infrared radiation of short wavelength enters the glass enclosure. Sources of Energy Green - House This infrared radiation of short wavelength is absorbed by the plants which get warmer. The warmer plants etc., then start radiating infrared radiation of longer wavelength. The infrared radiation of longer wavelength cannot pass through the glass. So, it gets reflected back into the greenhouse raising the inside temperature further.

5. Greenhouses are used for growing crops in colder places. This heating caused by the trapped infrared radiation of longer wavelengths is called greenhouse effect. Sources of Energy Green - House When the rate of heating and the rate of loss of heat due to radiation becomes equal, the greenhouse attains a steady temperature.