The efficiency of a heat engine is given by the expression [tex] eff =\frac{Q_h-Q_c}{Q_h} [/tex]
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.
[tex] eff =\frac{W}{Q_h} [/tex]
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,
[tex] W=Q_h - Q_c [/tex]
Thus the efficiency is given by, [tex] eff =\frac{Q_h-Q_c}{Q_h} [/tex]
