# A heating engineer installs two identical resistive heating elements in a domestic boiler. In one design, the two elements are connected in series. In a second design, the same two elements are connected in parallel across the same power supply. Explain why the parallel design transfers energy to the water at a greater rate than the series design.

> OCR A-Level Physics B: Advancing Physics (H557) — 3.1 Motion · Explain · 5 marks

> A domestic boiler can be wired so that its two heating elements are connected either in series or in parallel across the same mains supply voltage.

## Mark scheme (5 marks)

1. In a series circuit the total resistance is equal to the sum of the individual resistances, so total resistance is greater than in the parallel circuit
2. In a parallel circuit the total resistance is less than the resistance of either individual element
3. Both designs are connected to the same potential difference (voltage), so the lower resistance in the parallel design results in a greater current
4. Power transferred is equal to current multiplied by voltage (P = IV), so a greater current at the same voltage means more power is transferred
5. Therefore the parallel design heats the water more quickly / transfers energy at a greater rate than the series design

## Key terms

- [series](https://www.gradenine.co.uk/glossary/series)
- [parallel](https://www.gradenine.co.uk/glossary/parallel)
- [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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-heating-engineer-installs-two-identical-8e973db1) · Published by Druglandscape Ltd.