(i) Derivation of expression for the electric potential due to an electric dipole at a point on the axial line.
(ii) Depiction of equipotential surfaces due to an electric dipole.
Potential due to charge at A,
${\mathit{V}}_{\mathit{A}}=\frac{1}{4\mathit{\pi }{\mathit{\epsilon }}_0}\frac{-\mathit{q}}{\left(\mathit{r}+\mathit{a}\right)}$
Potential due to charge at $\mathit{B}$,
${\mathit{V}}_{\mathit{B}}=\frac{1}{4\mathit{\pi }{\mathit{\epsilon }}_0}\frac{+\mathit{q}}{\left(\mathit{r}-\mathit{a}\right)}$


$\mathit{V}={\mathit{V}}_{\mathit{B}}+{\mathit{V}}_{\mathit{A}}$

$=\frac{\mathit{q}}{4\mathit{\pi }{\mathit{\epsilon }}_0}\left[\frac{-1}{\left(\mathit{r}+\mathit{a}\right)}+\frac{1}{\left(\mathit{r}-\mathit{a}\right)}\right]$