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A refrigerator works between 4°C and 30°C. It is required to remove 600 calories of heat every second in order to keep the temperature of the refrigerated space constant. The power required is: (Take 1 cal = 4.2 joules)

1. 2.365 W
2. 23.65 W
3. 236.5 W
4. 2365 W

Correct answer: 23.65 W

Solution

The efficiency of a refrigerator is determined by the Carnot cycle. The temperatures in Kelvin are T1 = 30 + 273 = 303 K and T2 = 4 + 273 = 277 K. The coefficient of performance (COP) is T2 / (T1 - T2) = 277 / (303 - 277) = 277 / 26 ≈ 10.65. The work required is W = Q / COP = (600 × 4.2) / 10.65 ≈ 23.65 W.

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