A family is trying to reduce their electricity bill. They compare two electric heaters that produce the same amount of heat. Heater A has a power-rating of 3 kW and Heater B has a power-rating of 2 kW. Explain why choosing Heater B would reduce the family's electricity costs, referring to the kilowatt-hour in your answer.

Eduqas GCSE Physics — 1.4 Domestic electricity · Explain · 4 marks · View as Markdown

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

Both heaters are used for 4 hours each day.

Model answer (4 marks)

1. The kilowatt‑hour (kWh) is the unit used to measure domestic energy consumption.
2. The amount of kWh used by an appliance depends on its power‑rating (kW) and the time (h) it is operated.
3. Heater B has a lower power‑rating (2 kW) than Heater A (3 kW), so for the same 4 h of use it consumes fewer kWh.
4. Using fewer kWh means the cost of electricity is lower, so the family’s bill is reduced.

Examiner tips

  • Use the exact term ‘kilowatt‑hour’ and explain its role as a unit of energy. Show the relationship: kWh = kW × h. State the power‑ratings of both heaters and the time used. Conclude that lower kWh = lower cost.
  • common_mistakes
  • :
  • Confusing power (kW) with energy (kWh). Failing to mention the 4‑hour usage period. Using informal wording such as ‘less energy’ instead of ‘fewer kWh’.

Mark scheme (4 marks)

  1. The kilowatt-hour is the unit used to measure domestic energy consumption
  2. The number of kilowatt-hours used depends on the power-rating of the appliance (and the time it is used)
  3. Heater B has a lower power-rating (2 kW) so it uses fewer kilowatt-hours than Heater A (3 kW) in the same time period
  4. Because fewer kilowatt-hours are used, the cost of electricity is lower / the electricity bill is reduced

Key terms in this question

power-rating · kilowatt-hour

Related

More Domestic electricity questions

▶ Try answering this question with AI marking (free) →