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 _______________?
Correct answer: C
Explanation
For a reversible engine, $\eta = 1 - T_L/T_H$. Then $COP_R = rac{T_L}{T_H-T_L} = rac{\eta}{1-\eta}$ and $COP_{HP} = rac{T_H}{T_H-T_L} = \frac{\eta}{1-\eta} + 1$.