<P> The concept of electric potential is closely linked with potential energy . A test charge q has an electric potential energy U given by </P> <Dl> <Dd> U E = q V . (\ displaystyle U_ (\ mathbf (E)) = q \, V. \,) </Dd> </Dl> <Dd> U E = q V . (\ displaystyle U_ (\ mathbf (E)) = q \, V. \,) </Dd> <P> The potential energy and hence also the electric potential is only defined up to an additive constant: one must arbitrarily choose a position where the potential energy and the electric potential are zero . </P>

The si unit of voltage (aka electric potential difference ) is equivalent to