An engine operates by taking $n$ moles of an ideal gas through the cycle $ABCDA$ shown in the figure. The thermal efficiency of the engine is: (Take $C_v = 1.5 R$,where $R$ is the gas constant)

$A$ gas is governed by an equation $V = \frac{aT^3}{P}$,where $P, V$,and $T$ are pressure,volume,and temperature of the gas respectively,and $a$ is a constant. If the temperature of the gas is doubled at constant pressure,then the work done by the gas is: (in $aT^3$)

If a heat engine and a refrigerator are working between the same two temperatures $T_1$ and $T_2$ $(T_1 > T_2)$,then the ratio of the efficiency of the heat engine to the coefficient of performance of the refrigerator is:

Obtain the relation between the coefficient of performance and the efficiency of a heat engine.

$540$ calories of heat converts $1$ cubic centimeter of water at $100\,^oC$ into $1671$ cubic centimeter of steam at $100\,^oC$ at a pressure of one atmosphere. Then the work done against the atmospheric pressure is nearly .......... $cal$.

The figure below shows two paths that may be taken by a gas to go from a state $A$ to a state $C.$ In process $AB,$ $400 \, J$ of heat is added to the system and in process $BC,$ $100 \, J$ of heat is added to the system. The heat absorbed by the system in the process $AC$ will be ...... $J$