How is Gibbs energy (G) related to the cell emf (E) mathematically ?

$-{\mathrm{\Delta }}_{\mathrm{r}}\mathrm{G}={\mathrm{nFE}}_{\text{cell }}^{\mathrm{o}}\text{ (or) }{\mathrm{\Delta }}_{\mathrm{r}}\mathrm{G}=-\mathrm{nFE}\text{ cell }$
where $∆$G = Standard Gibbs free energy change
n = no. of electrons transferred
F = 96500 coloumbs
E = emf of the cell
${\mathrm{\Delta }}_{\mathrm{r}}\mathrm{G}$ = Free energy change
${\mathrm{E}}_{\text{cell }}^0$ = standard electrode potential