Electromotive Force (CIE IGCSE Physics)

• 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

Extended tier only

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

• 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