# A student is investigating two electric heaters, Heater A and Heater B, which are connected to the same mains supply. Heater A has a greater resistance than Heater B. Both heaters are ohmic conductors operating at constant temperature. Explain which heater transfers energy to the surroundings at a greater rate, and describe what happens to the rate of energy transfer for both heaters if the potential difference of the mains supply is increased.

> OCR A-Level Physics A (H556) — 3.3 Work, energy and power · Explain · 5 marks

> Two electric heaters, Heater A and Heater B, are connected to the same mains potential difference. Heater A has a greater resistance than Heater B. Both heaters behave as ohmic conductors at constant temperature.

## Mark scheme (5 marks)

1. Power is the rate at which energy is transferred (by an appliance / to the surroundings)
2. Because they share the same potential difference, the heater with lower resistance draws greater current (Heater B has lower resistance so carries greater current)
3. Heater B transfers energy at a greater rate (has greater power) because it has lower resistance and therefore higher current
4. Increasing the potential difference increases the current through each heater (since they are ohmic conductors / current is proportional to potential difference)
5. The rate of energy transfer (power) increases for both heaters when the potential difference is increased, because power depends on both current and potential difference (P = IV, both of which increase)

## Key terms

- [potential difference](https://www.gradenine.co.uk/glossary/potential-difference)
- [resistance](https://www.gradenine.co.uk/glossary/resistance)
- [ohmic conductor](https://www.gradenine.co.uk/glossary/ohmic-conductor)

## Related

- [Revision notes for OCR A-Level Physics A (H556)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-is-investigating-two-electric-91eebb91) · Published by Druglandscape Ltd.