Specific Heat Capacity and Latent Heat Questions - GCSE standard

Q13.

An electric kettle was switched on. The graph shows how the temperature of the water inside the kettle changed.

(a) When the kettle was switched on the temperature of the water did not immediately start to increase.

Suggest one reason why.

The heating element of the kettle takes time to heat up itself.

[1 mark]

(b) The energy transferred to the water in 100 seconds was 155,000 J.

Given that the specific heat capacity of water = 4200 J/kg °C, use the graph to determine the mass of water in the kettle.

Give your answer to 2 significant figures.

Δθ = 78 °C (see graph)

E = mc Δθ

155,000 = m × 4200 × 78

m = 155,000 / (4200 × 78)

m = 0.4731 kg

m = 0.47 kg (to 2 sf)

[5 marks]

Gradient of the graph = ∆θ/t

Now

E = mc Δθ

dividing both sides by t

E/t = mc Δθ/t

But

E/t = P

so,

P = mc x gradient of the graph

[3 marks]

(9 marks total)