Heat Transfer
Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer co-efficient is 3k/l. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?

35.5
81.25
43.75
48.25

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Heat Transfer
The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are

(COP)R = 1.5; (COP)HP = 2.5
(COP)R = (COP)HP = 2.5
(COP)R = (COP)HP = 0.6
(COP)R = 2.5; (COP)HP = 1.5

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