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State (i) Stefan-Boltzmann law and (ii) Wein’s displacement law. |
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Answer» (i) The Stefan-Boltzmann law : The rate of emission of radiant energy per unit area or the power radiated per unit area of a perfect blackbody is directly proportional to the fourth power of its absolute temperature. OR The quantity of radiant energy emitted by a perfect blackbody per unit time per unit surface area of the body is directly proportional to the fourth power of its absolute temperature. (ii) Wien’s displacement law : The wavelength for which the emissive power of a blackbody is maximum, is inversely proportional to the absolute temperature of the blackbody. OR For a blackbody at an absolute temperature T, the product of T and the wavelength λm corresponding to the maximum radiation of energy is a constant. λm T = b, a constant. Notes: (1) The law stated above was stated by Wilhelm Wien (1864-1928) German Physicist. (2) The value of the constant b in Wien’s displacement law is 2.898 × 10-3 m.K. |
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