First slide

Refrigerator

Question

The coefficient of performance of a refrigerator is 5. If the temperature inside freezer is $- 20^{o} C$ , the temperature of the surroundings to which it rejects heat is:

Moderate

A

$21^{0} C$
B

$31^{0} C$
C

$41^{0} C$
D

$11^{0} C$

Solution

Coefficient of performance of refrigerator
$COP = \frac{T_{L}}{T_{H} - T_{L}}$
where $T_{L} \to lower temperature$ and $T_{H} \to Higher temperature$
$So, 5 = \frac{T_{L}}{T_{H} - T_{L}}$
$\Rightarrow T_{H} = \frac{6}{5} T_{L} = \frac{6}{5} (253) = 303.6 K$ . Therefore $t_{H} = 30 . 6^{0} C ≃ 31^{0} C$

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