Question

An ideal heat engine exhausting heat at ${77}^{\circ }C$ is to have a 30% efficiency. It must take heat at

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

$\eta =1-\frac{T_2}{T_1}\Rightarrow \frac{30}{100}=1-\frac{350}{T_1}$

$\Rightarrow \frac{350}{T_1}=1-\frac{50}{100}=\frac{70}{100}=\frac{7}{10}\Rightarrow T_1=500K={227}^{\circ }C$