A sample of ideal gas is taken through steps I, II, and III in a closed cycle, as shown on the pressure P versus volume V diagram above, so that the gas returns to its original state. The steps in the cycle are as follows.
 I. An isothermal expansion occurs from point A to point B, and the volume of the gas doubles.
 II. An isobaric compression occurs from point B to point C, and the gas returns to its original volume.
 III. A constant volume addition of heat occurs from point C to point A and the gas returns to its original pressure.
