Derive an expression to measure emf of a battery

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 ${ F }_{ c }$.
  2. This chemical force does some work to move a negative charge ‘q’ from positive terminal to negative terminal against the electric force Fe. 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 given by W/Q = ${ F }{ c }$d / q
    Where ‘d’ is the distance between the terminals.
    If we assume Fc = Fe ,
    then = W/q = Fed/q
    This W/q is known as emf of battery.
    Therefore , emf = W/q = ${ F }
    { c }$d / q
    This S.I unit of emf is volt and is measured using voltmeter