Question

An ideal heat engine exhausting heat at ${77}^{0}C$ is to have a 30% efficiency. It must take heat at:

• A. ${127}^{0}C$
• B. ${227}^{0}C$
• C. ${327}^{0}C$
• D. ${673}^{0}C$

Answer 1

The correct option is B ${227}^{0}C$

We know,

$\eta =1-\frac{T_1}{T_2}⟹\frac{30}{100}=1-\frac{77+273}{T_2}⟹\frac{350}{T_2}=1-\frac{3}{10}⟹T_2=\frac{350\times 10}{7}=500K$

Or, It must take heat at $500-273=227°C$