# A building uses two types of electric heaters in its entrance hall. Heater X is connected in a series circuit and Heater Y is connected in a parallel circuit with an identical heater. Both circuits are powered by the same mains supply. Explain how connecting Heater Y in parallel with an identical heater affects the total resistance of that circuit and, as a result, the power transferred by Heater Y compared to Heater X operating alone.

> OCR A-Level Physics B: Advancing Physics (H557) — 3.3 Work, energy and power · Explain · 5 marks

> Power is the rate at which an appliance transfers energy. For a circuit component, power is equal to the product of the current passing through it and the potential difference across it. When resistors are connected in parallel, the total resistance is less than the lowest individual resistance.

## Mark scheme (5 marks)

1. Connecting Heater Y in parallel means both heaters share the same potential difference (from the supply)
2. The total resistance of the parallel circuit is less than the resistance of a single heater alone
3. Lower total resistance means a greater total current is drawn from the supply
4. The potential difference across Heater Y is the same as across Heater X (full supply voltage), so the power transferred by Heater Y is the same as Heater X
5. The total power transferred by the parallel circuit is greater than that of Heater X alone, because both heaters transfer power simultaneously

## Key terms

- [parallel](https://www.gradenine.co.uk/glossary/parallel)
- [total resistance](https://www.gradenine.co.uk/glossary/total-resistance)
- [power](https://www.gradenine.co.uk/glossary/power)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](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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