A family is trying to reduce the amount of energy they use at home. They notice that their electric kettle has a higher power-rating than their slow cooker. Explain what power-rating means and describe how an appliance with a higher power-rating affects the cost of running it for the same amount of time.

WJEC GCSE Physics (Wales) — 1.4 Domestic electricity · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

An electric kettle has a power-rating of 3 kW. A slow cooker has a power-rating of 0.3 kW.

Model answer (4 marks)

Power‑rating is the maximum rate of energy transfer of an appliance.
A higher power‑rating means more energy is transferred per second, or in a given time.
More energy used in the same time means a greater number of kilowatt‑hours are consumed.
Therefore the appliance with the higher power‑rating costs more to run for the same amount of time.

Examiner tips

  • Use the exact phrase "maximum rate of energy transfer" for power‑rating. Show the link between power (kW) and energy (kWh) over time. Explain that cost is proportional to energy used.
  • Mention that the same running time is assumed.

Mark scheme (4 marks)

  1. Power-rating is the maximum rate of energy transfer of an appliance
  2. A higher power-rating means more energy is transferred per second / in a given time
  3. More energy used in the same time means a greater number of kilowatt-hours are consumed
  4. Therefore the appliance with the higher power-rating costs more to run for the same amount of time

Key terms in this question

power-rating

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