Question

A system receives heat continuously from an electrical heater of power 10 W. The temperature of becomes constant at 50°C when the surrounding temperature is 20°C. After the heater is switched **, cools from 35.1°C to 34.9°C in 1 minute. The heat capacity of * is

(a) 100 J/°C

(b) 300 J/°C

(c) 750 J/°C

(d) 1500 J/°C

Answer 1

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

uf05c k = 1/3

At an average temperature of 35°C, dQ/dt = 1/3 (35 - 20) J/ = 5 J/.

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.