Carnot designed a theoretical engine. This engine cannot be realised in actual practice.
Carnot cycle : The working substance of the engine undergoes a cycle known as Carnot cycle. It consists of the following four strokes.
(i) Isothermal expansion :
(ii) Adiabatic expansion
(iii) Isothermal compression
(iv) Adiabatic compression
Efficiency of Carnot cycle :
(i) Efficiency of a heat engine depends only on temperatures.
(ii) Efficiency of a heat engine is always lesser than unity, i.e., whole of heat can never be converted into work which is in accordance with second law.
Carnot theorem : Carnot’s reversible engine working between two given temperature is considered to be the most efficient engine.
