Q. 4

A piece of charcoal and a piece of shining steel of the same surface area are kept for a long time in an open lawn in bright sun.
A. The steel will absorb more heat than the charcoal.

B. The temperature of the steel will be higher than that of the charcoal.

C. If both are picked up by bare hands, the steel will be felt hotter than the charcoal.

D. If the two are picked up from the lawn and kept in a cold chamber, the charcoal will lose heat at a faster rate than the steel.


Answer :

Steel is a good conductor of heat whereas charcoal isn’t. So, the sunlight falling on the steel surface will make the surface hot and since charcoal is an absorber the incident sunlight would be absorbed by the charcoal. Since charcoal is bad conductor of heat, it won’t be too hot. Therefore, if both are picked up by bare hands, the steel will be felt hotter than the charcoal.
Secondly, Blackbodies are good absorbers of radiation and hence good emitters of radiation. Charcoal is a black body and thus it is a good emitter compared to steel. Hence, If the two are picked up from the lawn and kept in a cold chamber, the charcoal will lose heat at a faster rate than the steel.
Option (a) is incorrect as steel is a bad absorber of heat compared to charcoal as charcoal is a blackbody.
Option (b) is incorrect as temperature is the intensity of heat present in the substance. Steel is hot at the surface but charcoal has more heat intensity absorbed within it.
Thus, options (c) and (d) are the correct options.

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