10.1.3—The electromotive force (e.m.f.) of a source as energy transferred per unit
- Syllabus
- 9702–2028–2029
- Objective
- 10.1.3
- Level
- AS
Electromotive force is the energy supplied by a source per unit charge
The e.m.f. ε of a source is the energy supplied by the source per coulomb as charge moves through it: ε=W/Q.
E.m.f. describes the source’s energy rise, whereas terminal potential difference can be lower when internal resistance causes a drop.
A 12 V ideal source supplies 12 J per coulomb; a real source may show less terminal voltage while delivering current.
E.m.f. is not a force in newtons and is not always identical to the voltage measured across a working battery.
ConceptA-Level CAIE Physics AS