Carnot Engine

The System of Heat

The Carnot Cycle

A conception of Nicolas Léonard Sadi Carnot. Its is a heat cycle in which thermodynamic processes go through numerous stage before returning to their original state. This heat cycle became the basis for the Carnot Engine.

The Stages

Stage one: Isothermic Expansion

  • The engine absorbs heat from a source and the gas begins to expand without changing temperature causing the piston to move as well.

Stage two: Adiabatic Expansion

  • The heat source is removed, and the gas begins to cool, but as it is still at a hotter temperature it keeps expanding.

Stage three: Isothermal Compression

  • As the system becomes cool, the piston begins to return to its original position, re-compressing the gas, decreasing volume, and increasing pressure.

Stage four: Adiabatic Compression

  • The engine stops cooling as the gas returns to the original temperature and the piston to it's original position.

Carnot's Theorem

Maximum efficiency ɳ is defined to be


ɳ =W/QH = 1 – TC/TH



  • W is the work done by the system
  • QH is the heat put into the system
  • TC is the absolute temperature of the cold reservoir
  • TH is the absolute temperature of the hot reservoir