Question

If the heat absorbed by a heat engine is 600 kJ per cycle and it releases 480 kJ of heat each cycle, what is its efficiency?

• A. 20%
• B. 80%
• C. 100%
• D. 30%

Answer 1

The correct option is A 20%

The efficiency of a heat engine is the ratio of the work done per cycle $W$ to the heat absorbed from the high-temperature reservoir $Q_h$.

We can use the relationship between $W$, $Q_h$ & $Q_c$( $W$ = $Q_h$ −$Q_c$ ) to express the efficiency of the heat engine in terms of $Q_c$ and $W$.

$\epsilon =\frac{W}{Q_h}=\frac{Q_h-Q_c}{Q_h}=1-\frac{Q_c}{Q_h}=1-\frac{480}{600}=0.2=20\%$