Discuss the Carnot cycle of operation and reduce the expression for efficiency. Carnot engine is works on the principle of Carnot cycle made up of four stages are represented as shown in (PV) diagram. 

  1) Isothermal expansion (LM):  The gas is permitted to expand isothermally. During the expansion gas absorb an amount of heat Q₁ from the source at T₁. 

 (2)Adiabatic expansion (MN): The gas is permitted to expand adiabatically till the temperature of gas falls to T₂, the temperature of the sink, 

 (3) Isothermal compression (NO): The gas is compressed slowly at constant temperature T₂. During this method a certain amount of heat Q₂ is rejected into the sink, 

  (4) Adiabatic compression (OL): The gas is further compressed adiabatically till it returns to its initial state L.  The cycle of operations, LM, MN, NO and OL is known as the Carnot cycle. It is shown by the closed loop LMNOL.