n mole a perfect gas undergoes a cyclic process ABCA (see figure) consisting of the following processes.
$\mathrm{A} \rightarrow \mathrm{B} ;$ Isothermal expansion at temperature T so that the volume is doubled from $\mathrm{V}_1$ to $V_2=2 V_1$ and pressure changes from $P_1$ to $\mathrm{P}_2$.
$\mathrm{B} \rightarrow$ C. Isobaric compression at pressure $\mathrm{P}_2$ to initial volume $\mathrm{V}_1$.
$\mathrm{C} \rightarrow$ A is Isochoric change leading to change of pressure from $\mathrm{P}_2$ to $\mathrm{P}_1$.
Total workdone in the complete cycle ABCA is :