An electric dipole is placed at an angle of $30^{\circ}$ with an electric field of intensity $2 \times 10^{5} \mathrm{NC}^{-1}$. It experiences a torque equal to $4 ~\mathrm{N~m}$. Calculate the magnitude of charge on the dipole, if the dipole length is $2 \mathrm{~cm}$.