First slide

Refrigerator

Question

An ideal refrigerator has a freezer at a temperature of $- 13^{0} C$ . The coefficient of performance of the engine is 5. The temperature of the air (to which heat is rejected) will be

Moderate

A

$325^{0} C$
B

325K
C

$39^{0} C$
D

$320^{0} C$

Solution

Coefficient of performance
K = $\frac{T_{2}}{T_{1} - T_{2}} \Rightarrow 5 = \frac{(273 - 13)}{T_{1} - (273 - 13)} = \frac{260}{T_{1} - 260}$
$\Rightarrow 5 T_{1} - 1300 = 260 \Rightarrow 5 T_{1} = 1560$
$\Rightarrow T_{1} = 312 K \Rightarrow t_{1} = 39^{0} C$

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