$A$ Carnot heat engine has an efficiency of $10 \%$. If the same engine is worked backward to obtain a refrigerator,then the coefficient of performance of the refrigerator is

An ideal heat engine has an efficiency $\eta$. The coefficient of performance of the engine when driven backward will be

The efficiency of a reversible heat engine working between two temperatures is $50 \%$. The coefficient of performance of a refrigerator working between the same two temperatures but in reverse direction is

If the coefficient of performance of a refrigerator is $\beta$ and the heat absorbed from the refrigerated space is $Q$,then the work done on the system is:

Is the coefficient of performance of a refrigerator constant?

In a cold storage,ice melts at the rate of $2 \ kg$ per hour when the external temperature is $20^{\circ} C$. The minimum power output of the motor used to drive the refrigerator which just prevents the ice from melting is (latent heat of fusion of ice $= 80 \ cal \ g^{-1}$) (in $W$)