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Read the following statements: A. When small temperature difference between a liquid and its surrounding is doubled, the rate of loss of heat of the liquid becomes twice. B. Two bodies P and Q having equal surface areas are maintained at temperature 10°C and 20°C. The thermal radiation emitted in a given time by P and Q are in the ratio 1: 1.15. C. A Carnot Engine working between 100 K and 400 K has an efficiency of 75%. D. When small temperature difference between a liquid and its surrounding is quadrupled, the rate of loss of heat of the liquid becomes twice. Choose the correct answer from the options given below

1. A, B, C only
2. A, B only
3. A, C only
4. B, C, D only

Correct answer: A, B, C only

Solution

A: rate of heat loss is proportional to temperature difference (Newton's law of cooling), so doubling DeltaT doubles the rate -> true. B: emission ratio = (283/293)^4 = 0.87, i.e. P:Q = 1:1.15 -> true. C: Carnot efficiency = 1 - T_cold/T_hot = 1 - 100/400 = 0.75 = 75% -> true. D: quadrupling DeltaT quadruples the rate, not doubles -> false. Correct statements: A, B, C.

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