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InterviewSolution
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A system S receives heat continuously from an electrical heater of power 10 W. The temperature of S becomes constant at 50°C when the surrounding temperature is 20°C. After the heater is switched off, S cools from 35.1°C to 34.9°C in 1 minute. The heat capacity of S is (a) 100 J/°C (b) 300 J/°C (c) 750 J/°C (d) 1500 J/°C |
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Answer» Correct Answer is: (d) 1500 J/°C Rate of loss of heat ∝ difference in temperature with the surroundings. At 50°C, dQ/dt = k(50 - 20) = 10, where k = constant k = 1/3 At an average temperature of 35°C, dQ/dt = 1/3 (35 - 20) J/s = 5 J/s. Heat lost in 1 minute = dQ/dt x 60 J = 5 x 60 J = 300 J = Q. Fall in temperature = 0.2°C Δθ. Q = cΔθ. Heat capacity = c Q/Δθ = 300 J/0.2°C. |
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