Key Stage 5
Meaning
Electromotive force (emf) is the amount of work produced per unit charge by a source of electric power.
About Electromotive Force (emf)
- Emf is given by the symbol \(\varepsilon\)
- Emf is measured in volts (V).
- Emf is not actually a force, but a potential difference that drives current around a circuit.
- In a circuit, the emf is equal to the potential difference across the terminals of the power source when no current is flowing.
- The internal resistance of the power source causes the terminal voltage to be less than the emf when current is flowing.
Formulae
The electromotive force is given by the formula:
- \(\varepsilon=\frac{๐}{๐}\)
Where:
The terminal voltage of an electrical cell or battery is related to emf by the following formula:
- \(๐=\varepsilonโ๐ผ๐\)
Where:
- ๐ is the terminal voltage
- ๐ผ is the current through between the terminals
- ๐ is the internal resistance of the power supply