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A body S is continuously supplied heat by an electric heater of power 10 W, and its temperature stabilises at 50 degC while the surroundings are at 20 degC. The heater is then switched off and S cools from 35.1 degC to 34.9 degC in 1 minute. Find the heat capacity of S.

1. 100 J/degC
2. 300 J/degC
3. 750 J/degC
4. 1500 J/degC

Correct answer: 1500 J/degC

Solution

Newton's law gives loss rate proportional to excess temperature; at 15 degC excess the rate is 5 W, and using Q = C*dT over the minute gives C = 1500 J/degC.

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