Write one process where work is converted into heat and heat is converted into work.

An engine (consisting of one mole of an ideal gas in a cylinder with a piston) follows the cycle shown in the figure. Find the heat exchanged by the engine with the surroundings in each part of the cycle. Given $C_V = \frac{3}{2}R$.
$(a)$ $A$ to $B$: Constant volume
$(b)$ $B$ to $C$: Constant pressure
$(c)$ $C$ to $D$: Adiabatic expansion
$(d)$ $D$ to $A$: Constant pressure

An ideal gas,initially in state $(P_{12}, V_1, T_1)$ is expanded isobarically to $(P_{12}, V_2, T_2)$,then adiabatically to $(P_{34}, V_3, T_3)$. It is then contracted isobarically to $(P_{34}, V_4, T_4)$ and finally adiabatically back to the initial state. The efficiency of this cycle is

Two gases $A$ and $B$ are filled at the same pressure in separate cylinders with movable pistons of radius $r_A$ and $r_B$,respectively. On supplying an equal amount of heat to both the systems reversibly under constant pressure,the pistons of gas $A$ and $B$ are displaced by $16 \ cm$ and $9 \ cm$,respectively. If the change in their internal energy is the same,then the ratio $\frac{r_A}{r_B}$ is equal to

One mole of a diatomic ideal gas undergoes a cyclic process $ABC$ as shown in the figure. The process $BC$ is adiabatic. The temperatures at $A, B$ and $C$ are $400 \ K, 800 \ K$ and $600 \ K$ respectively. Choose the correct statement.

The efficiency of a heat engine is $\eta$ and the coefficient of performance of a refrigerator is $\beta$. Then: