# When is the efficiency of a heat engine maximum?

(a) temperature of source is greater than that of sink
(b) temperature of sink is greater than that of source
(c) temperature difference of source and sink is minimum
(d) temperature difference of source and sink is maximum

Toolbox:
• Efficiency of a heat engine, $\eta = \frac{T_2 - T_1}{T_2}$
Answer: temperature difference of source and sink is maximum
Since, efficiency of a heat engine, $\eta = \frac{T_2 - T_1}{T_2}$
Thus, Efficiency is more when temperature difference between source ($T_2$) and sink ($T_1$) is large.