Efficiency of Carnot Engine #8211; Efficiency (η) of an engine is defined as the ratio of useful heat (heat converted into work) to the total heat supplied to the engine. Thus η = W/Q<sub>1</sub> = Q<sub>1</sub> #8211; Q<sub>2</sub>/Q<sub>1</sub> or (η = 1 #8211; Q<sub>2</sub>/Q<sub>1</sub> = 1 #8211; T<sub>2</sub>/T<sub>1</sub>) [∵ for Carnot cycle, Q<sub>2</sub>/Q<sub>1</sub> = T<sub>2subgt;/T<sub>1</sub>]