(a) (i) Draw equipotential surfaces for an electric dipole. (ii) Two point charges $q_1$ and $q_2$ are located at $\vec{r}_1$ and $\vec{r}_2$ respectively in an external electric field $\vec{E}$. Obtain an expression for the potential energy of the system. (iii) The dipole moment of a molecule is $10^{-30} \text{ Cm}$. It is placed in an electric field $\vec{E}$ of $10^5 \text{ V/m}$ such that its axis is along the electric field. The direction of $\vec{E}$ is suddenly changed by $60^\circ$ at an instant. Find the change in the potential energy of the dipole, at that instant.