Potential difference is a measure of the transfer of energy by charge carriers; its unit is the volt where one volt is the p.d.
across a component when 1J of energy is transferred per unit charge passing through the component.
In this equation, V is the p.d. measured in volts, Q is the charge in coulombs, and W is the energy transferred by charge Q. P.d. is measured with a voltmeter (always connectedm in parallel); an ideal voltmeter should have an infinite resistance.
Electromotive force is the energy transferred from chemical energy (or another form) to electrical energy per unit charge; it is the energy that charge carriers gain when work is done on them.
In this equation, is the e.m.f. measured in volts, Q is the charge in coulombs, and W is the energy transferred to charge Q.
- Distinction in terms of energy transfer:d. is used when charge carriers lose energy in a component because they do work. E.m.f. is used when the charge carriers gain energy because work is done on them, e..g. by a power supply or cell.
- Energy transfer is given by
