Edexcel A Level Physics

Revision Notes

3.15 Electromotive Force

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Electromotive Force

  • When charge passes through a power supply such as a battery, it gains electrical energy
  • The electromotive force (e.m.f.) is defined as:

The amount of chemical energy converted to electrical energy per unit charge when charge passes through a power supply

  • e.m.f. is measured in Volts (V)


emf definition, downloadable AS & A Level Physics revision notes

Definition of e.m.f. with regards to energy transfer

  • This can also be written as:

Emf energy equation


  • E.m.f. is:
    • represented by the symbol ε (greek letter epsilon)
    • not actually a force, but a measure of energy transferred per coulomb of charge
    • is measured in volts (V), which is J C−1 in S.I. units

  • e.m.f. is also the potential difference across the cell when no current is flowing
  • e.m.f. can be measured by connecting a high-resistance voltmeter around the terminals of the cell in an open circuit

 Measuring emf, downloadable AS & A Level Physics revision notes

e.m.f. is measured using a voltmeter connected in parallel with the cell


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