Thermodynamics - Result Question 39
41. The coefficient of performance of a refrigerator is 5 . If the inside temperature of freezer is $-20^{\circ} C$, then the temperature of the surroundings to which it rejects heat is
[2015 RS]
(a) $41^{\circ} C$
(b) $11^{\circ} C$
(c) $21^{\circ} C$
(d) $31^{\circ} C$
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Answer:
Correct Answer: 41. (d)
Solution:
- (d) Coefficient of performance,
Cop $=\frac{T_2}{T_1-T_2}$
$5=\frac{273-20}{T_1-(273-20)}=\frac{253}{T_1-253}$
$5 T_1-(5 \times 253)=253$
$5 T_1=253+(5 \times 253)=1518$
$\therefore T_1=\frac{1518}{5}=303.6$
or, $T_1=303.6-273=30.6 \cong 31^{\circ} C$
