# A student uses a cell to drive a current through a resistor. Describe the difference between electromotive force (e.m.f.) and potential difference (p.d.), and state the unit in which both are measured.

> Cambridge International IGCSE Physics (0625) — 4.2 Electrical quantities · Describe · 4 marks

## Mark scheme (4 marks)

1. E.m.f. is the electrical work done by the power source (cell) per unit charge moved around the complete circuit.
2. P.d. is the work done per unit charge passing through a component (e.g. the resistor).
3. E.m.f. relates to energy input from the source / p.d. relates to energy output at a component, so e.m.f. drives the circuit whereas p.d. is the energy transferred by a component.
4. Both e.m.f. and p.d. are measured in volts (V).

## Key terms

- [electromotive force](https://www.gradenine.co.uk/glossary/electromotive-force)
- [potential difference](https://www.gradenine.co.uk/glossary/potential-difference)

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-uses-a-cell-to-320da4e7) · Published by Druglandscape Ltd.