Electromotive Force (Edexcel AS Physics): Revision Note

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)

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

• This can also be written as:

• 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

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