Q104 / 125 · BITSAT 2010 · Physics
An ideal refrigerator has a freezer at a temperature of $13^{\circ} \mathrm{C}$. The coefficient of performance of the engine is $5 .$ The temperature of the air (to which heat is rejected) is
- A$320^{\circ} \mathrm{C}$
- Correct answerB$39^{\circ} \mathrm{C}$
- C$325 \mathrm{~K}$
- D$325^{\circ} \mathrm{C}$
Solution
$\mathrm{T}_{2}=273-13=260$,
$$
\mathrm{K}=\frac{\mathrm{T}_{2}}{\mathrm{~T}_{1}-\mathrm{T}_{2}} ; \quad 5=\frac{260}{\mathrm{~T}_{1}-260}
$$
or $\mathrm{T}_{1}-260=52 ; \quad \mathrm{T}_{1}=312 \mathrm{~K}$
$\mathrm{T}_{2}=312-273=39^{\circ} \mathrm{C}$
Hence, the correct answer is option: 'B'.