An electric dipole had been formed by placing two particles each of mass m at the two ends of a light rod of length l. The charges of the two particles are `+q and -q`. This dipole is placed in a uniform electric field E in such a way that its axis is parallel to the direction of the field. The dipole is now deflected through a small angle. Show that for small angular displacement, the dipole will execute angular simple harmonic motion. Calculate the time period of the simple harmonic motion.