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Explain Why:(A) a body With large reflectivity is a poor emitter.(b) a brass tumbler feels colder than a wooden tray in winter.(c) On optical pyrometry (for measuring high temperatures) caliberated for an ideal black body radiation, gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace.(d) the earth without its atmosphere would be inhospirtably cold.(e) a heating system based on circulation of system are more efficient in warming a building than those based on circulation of hot water. |
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Answer» (a) The body with large reflectivity would be poor c of absorber of radiations. poor absorbers are poor radiators. Hence, a body with large reflectivity is a poor emitter. (b) Brass is a good Conductor of heat. When we touch brass tumbler with our fingers, our body heat is quickly conducted to the brass tumbler and hence temperature of the finger tips is reduced. Thus the brass-tumbler feels colder. On the Other hand, wood is a bad conductor, hence our body heat is not conducted to the eooden tray. (c) The temperature of red hot iron in the Oven is given by E1 = σ. T4 When iron is taken out in the open temperature (T0), its radiation energy is given by, Es = σ. (T4 - T04). Thus, the pyrometer measures low Values is the hot iron in the open. (d) The atmosphere server purpose of a blanket over the earth and it dose not allow earth's heat to be radiated during night. (e) This is due to the fact that steam contains more heat in the form of latent heat (540 calories/gram) than water. |
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