Shows an electric dipole formed by two particles fixed at the ends of a light rod of length 1. The mass of each particle is m and the charges are -q and +q. The system is placed in such a way that the dipole axis is parallel to a uniform electric field E that exists in the region. The dipole is slightly rotated about its centre and released. Show that for small angular displacement, the motion is angular simple harmonic and find its time period.