A researcher claims that he has developed an engine, which while working between source and sink temperatures of 377°C and 27° C rejects only 50 % of absorbed heat. What will his engine be? 

Explanation:

Given:

T₂ = 27° C = 300 K, T₁ = 377° C = 650 K, Q₂ = 0.5Q₁

The efficiency of given engine \(= 1 - \frac{{{Q_2}}}{{{Q_1}}}\)

The efficiency of given engine \(= 1 - \frac{{0.5{Q_1}}}{{{Q_1}}}\)

∴ Efficiency of given engine= 0.5 = 50 %

Now,

Efficiency of the reversible engine operating in the same temperature range

\({\left( \eta \right)_{rev}} = 1 - \frac{{{T_2}}}{{{T_1}}} = 1 - \frac{{300}}{{650}} = 0.5384 = 53.84\;\%\)

As \(\eta < {\eta _{rev}}\) which is practical