Energy Transfers

2 marks · Easy

A kettle transfers 320 kJ of energy to water, and 40 kJ is wasted as heat to the air. Calculate the efficiency of the kettle. Give your answer as a percentage.

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89% (±1)

Also accept: 88.9%

Common mistakes: 12.5%; 80%

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Uses the correct formula for efficiency: (useful energy output / total energy input) × 100%. (follow-through)

A1 · 1 mark · Obtains the correct numerical value (accept rounding 88.9% or 89%). (follow-through)

Worked solution

Total energy input = 320 kJ + 40 kJ = 360 kJ