Heat Transfer
The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of 'n' is exactly 4 for

Black painted bodies only
Polished bodies only
A black body
All bodies

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Heat Transfer
Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the

Average temperature of the fin
Constant temperature equal to that of the base
Temperature of the fin end
Surrounding temperature

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