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Thermal Physics

p-V Diagram for the Carnot Cycle

The Carnot cycle can be represented on a graph of pressure against volume (a p-V diagram) as shown below.

 

(The numbers in brackets below refer to the diagrams in the Carnot cycle.)

Curve A (2 to 3)  Isothermal expansion at TH
  Work done by the gas
Curve B (4 to 5) Adiabatic expansion
  Work done by the gas
Curve C (6 to 7) Isothermal compression at TC
  Work done on the gas
Curve D (8 to 1) Adiabatic compression
  Work done on the gas

The product of pressure and volume represents a quantity of work (see the section “Work Done During a Change of Volume of a Gas”). This is represented by the area below a p-V curve.

Therefore, the area enclosed by the four curves represents the net work done by the engine during one cycle.

© David Hoult 2008