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26. (b)
(i) In an electric bulb, electric energy is converted into light energy and heat energy.
(ii) In an electric iron, electric heater, geyser etc., electric energy is converted into heat energy.
(iii) In an electric fan, electric motor, electric energy is converted into mechanical energy.
(iv) In a hydroelectric power station, potential energy of water is converted ultimately into electric energy.
(v) In a heat engine, chemical energy from coal/oil is converted into mechanical energy.
(vi) In a nuclear reactor, mass is being converted into energy. (vii) In the sun and other stars, mass is being converted into energy, and so on.
Principle of conservation of energy
According to this principle, the sum total of energy of all kinds in an isolated system remains constant at all times. This means that energy can neither be created nor be destroyed. Energy can only be changed from one form to another. The amount of energy appearing in one form is always equal to the amount of energy disappearing in some other form. The total energy thus remains constant, always provided, at all points, we measure the amount of energy present in each form (including mass-which too is a form of energy).
Satish K. Gupta, Modern's A.B.C. of Physics vol. II for class XII, CBSE, p. 1198
"Stellar Energy (Energy generation in the sun and stars)" The sun radiates energy at a tremendous rate of 4 x 1016 Js '. The stars are also radiating a great amount of energy. Further, they have been radiating energy for several billions of years. It has been estimated that the chemical processes like burning or nuclear fission cannot account for such a large quantity of radiation for several billions of years. Whereas no known chemical process can be source of such a large amount of energy, possibility of fission as the cause of this energy is ruled out on the basis of the hypothesis that sun does not have the required abundance of heavy nuclei of fissionable matter. On the other hand, about 90% of the mass of the sun consists of hydrogen and helium.
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