Question

In a heat engine, Qh and Qc represents high temperature substance and low temperature substance respectively. Which of the following expressions is correct for the efficiency of the heat engine?

Answer 1

The efficiency of a heat engine is given by the expression $eff =\frac{Q_h-Q_c}{Q_h}$

The efficiency of a heat engine is the ratio of the work done by the engine to the heat given as the input to the engine.

$eff =\frac{W}{Q_h}$

The heat engine absorbs Q h from the hot reservoir , performs a work W on the absorbed heat and rejects Qc to the cold reservoir.

Therefore, the work done  is given by,

$W=Q_h - Q_c$

Thus the efficiency is given by, $eff =\frac{Q_h-Q_c}{Q_h}$