Derive an expression to measure of a battery.

Explanation

Electromotive force (emf) is defined as the work done by the chemical force to move unit positive charge from negative terminal to positive terminal of the battery.
1. Let this chemical force be `F_(e).`
2. This chemical force does some work to move a negative charge 'q' from positive terminal to negative terminal against the electric `F_(e)` Let this work be 'W'.
3. The work done by the chemical force to move 1 coulomb of charge from the terminal to negative terminal is give by `(W)/(q)=(F_(e)d)/(q).`
This `(W)/(q)` is know as emf `(epsilon)` of the battery.
`thereforeemf(epsilon)=(W)/(q)=(F_(e)d)/(q)
This S.I unit of emf is 'volt' and is measured using volt meter.