Flow of current in a wire is produced and maintained only if
- potential difference is applied across the ends of a wire.
- a constant potential difference is maintained across the two ends of a wire.
The chemical reactions inside the cell generate a difference in potential between the electrodes.
when no current is drawn from the cell ie the cell is not connected in a closed circuit then the potential difference between the electrodes is called emf of the cell.
It is measured by voltmeter.