Performance of Heat engine:
Performance of HP: It is measured by thermal efficiency that is the degree of useful conversion of heat received into work.
ηth Net work output/ Total Heat supplied = W/Q1 = (Q1 - Q2) / Q1
ηth 1 - Q2/Q1 = 1 - T2/T1;
As Q1/Q2 = T1/T2
Or, Thermal efficiency can be defined as ratio of net work gained(output) from system to heat supplied (input) to the system.