n moles of a perfect gas undergoes a cyclic process ABCA (see figure) consisting of the following processes:

A → B: Isothermal expansion at temperature T so that the volume is doubled from V₁ to V₂ and pressure changes from P₁ to P₂.

B → C: Isobaric compression at pressure P₂ to initial volume V₁.

C → A: Isochoric change leading to change of pressure from P₂ to P₁.

Total work done in the complete cycle ABCA is –