Specific heat capacity calculation

Question (5 marks): A 2.0 kW electric kettle is used to heat 0.80 kg of water from 18 °C to 100 °C. The specific heat capacity of water is 4200 J/kg°C. Assuming all electrical energy is transferred to the water:

(a) Calculate the energy transferred to the water. (3) (b) Calculate the minimum time taken. (2)

Mark scheme (5): (a)

• (1) Q = m c Δθ.
• (1) Δθ = 100 − 18 = 82 °C.
• (1) Q = 0.80 × 4200 × 82 = 275 520 J ≈ 276 kJ (accept 2.76 × 10⁵ J).

(b)

• (1) t = E / P = 275 520 / 2000.
• (1) t ≈ 138 s (accept 137–138 s, ~2 min 18 s). ECF from (a). No penalty for omitting the assumption restatement; deduct 1 mark for missing units across whole question (capped).