Two particles, carrying -q and +q and having equal masses m each,

Two particles, carrying $-q$ and $+q$ and having equal masses $m$ each, are fixed at the ends of a light rod of length a to forma dipole. The rod is clamped at an end and is placed in a uniform electric field $E$ with the axis of the dipole along the electric field. The rod is slightly tilted and then released. Neglecting gravity find the time period of small oscillations.