Question

The heat rejected per cycle by a heat engine to the surroundings is $60\%$ of the heat supplied. Find the efficiency of heat engine.

• A. $40\%$
• B. $60\%$
• C. $20\%$
• D. $75\%$

Answer 1

The correct option is A $40\%$

Given, heat rejected$\left(Q_2\right)$ per cycle is $60\%$ of the heat supplied$(Q_1$
$\Rightarrow Q_2=0.6Q_1$
From conservation of energy on heat engine,
$\Rightarrow Q_1=Q_2+W$
$W=Q_1-Q_2$
$\Rightarrow W=Q_1-0.6Q_1=0.4Q_1$
Substituting $W$ in the formula of efficiency we get,
$\eta =\frac{W}{Q_1}\times 100$
$\therefore \eta =\frac{0.4Q_1}{Q_1}\times 100=40\%$