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A Level Specific Heat Capacity Questions

 

Q6.

(a) A 2.0kW heater is used to heat a room from 5 °C to 20 °C. The mass of air in the room is 30 kg. Under these conditions the specific heat capacity of air = 1000 J kg-1K-1.

Calculate

(i) the gain in thermal energy of the air,

ΔQ = mcΔθ

ΔQ = 30 × 1000 × 15

ΔQ = 4.5 × 105J

(ii) the minimum time required to heat the room.

P × t = 4.5 x 105

t = 45 x 105/2000 = 225 s

(4 marks)

(b) State and explain one reason why the actual time taken to heat the room is longer than the value calculated in part (a)(ii).

Heat is lost to surroundings or other objects in room or to heater itself therefore more (thermal) energy is required from heater [or because convection currents cause uneven heating or rate of heat transfer decreases as temperature increases]

(2 marks)

(Total 6 marks)