Electromotive Force (Cambridge International IGCSE Physics)

Spec point — 4.2.7 · - Define electromotive force (e.m.f.) as the electrical work done by a source in moving a unit charge around a complete circuit (C)

• Know that e.m.f. is measured in volts (V) (Core)

Electromotive force

• Electromotive force (e.m.f.) is the name given to the potential difference of the power source in a circuit
• It is defined as:

The electrical work done by a source in moving a unit charge around a complete circuit

• Electromotive force (e.m.f.) is measured in volts (V)

The e.m.f. is the voltage supplied by a power supply: 12 V in the above case

Calculating electromotive force

Spec point — 4.2.7 · - Recall and use the equation for e.m.f. E = W/Q (E)

Extended Tier Only

• The definition of e.m.f. can also be expressed using the equation:

$E=\frac{W}{Q}$

• Where:

  • $E$ = electromotive force (e.m.f.), measured in volts (V)
  • $W$ = energy transferred to the charges from the power source, measured in joules (J)
  • $Q$ = charge moved, measured in coulombs (C)

• This equation should be compared to the definition of potential difference as the two are closely related