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NEET 2015 (AIPMT) · Heat Engines, Refrigerators & Second Law

Heat Engines, Refrigerators & Second Law question from NEET 2015 (AIPMT)

Q69NEET 2015 · AIPMTMedium

Heat Engines, Refrigerators & Second Law

The coefficient of performance of a refrigerator is 5. If the temperature inside freezer is $-$ 20oC, the temperature of the surroundings to which it rejects heat is

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Answer: (c)

$\beta = \frac{T_2}{T_1 - T_2}$ with $T_2 = -20^\circ\text{C} = 253$ K.
$5 = \frac{253}{T_1 - 253} \Rightarrow T_1 - 253 = 50.6$
$T_1 = 303.6\text{ K} \approx 31^\circ\text{C}$
So the answer is (c) $31^\circ\text{C}$ .

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