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Explain why:

(i) A body with large reflectivity is a power emitter.

(ii) A brass tumbler feels much colder than a wooden tray on a chilly day.

(iii) An optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot piece in the open, but gives a correct value for the temperature when the same piece is in the furnace.

(iv) The earth without its atmosphere would be inhospitably cold.

(v) Heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water.

Asked by Topperlearning User 16th April 2015, 9:43 AM
Answered by Expert

(i) The body having a large reflectivity (or bright surface) is a poor absorber of heat radiations. Poor absorbers are poor radiators. Therefore, a body with a large reflectivity is a poor emitter.

(ii) Brass is a good conductor of heat. When we touch the brass tumbler, heat is quickly transferred from the fingertips to the tumbler. Thus, we feel cold while touching the brass (or any other) tumbler on a chilly day.

(iii) The temperature of the red hot iron in the oven is given by . However, when the iron is taken out in the open (To), then its radiant energy is given by . Therefore, the pyrometer will measure a low value for the red hot iron in the open.

(iv) The atmosphere acts as a blanket over the Earth and does not allow its heat to be radiated during the night.

(v) Because steam contains more heat in the form of latent heat (540 cal/g) than water.

Answered by Expert 16th April 2015, 11:43 AM
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