A dipole is formed by two point charge -q and +q, each of mass m, and both the point charge are connected by a rod of length `l` and mass m. This dipole is placed in uniform electric field `vec(E)` If the dipole is disturbed by a small angle `theta` from stable equilibrium position, prove that its motion will be almost SHM. also find its time period.

Explanation

If the dipole is distributed by `theta` angle,
`tau("net") = -PE sin theta` (here -ve sign indicates that direction of torque is opposite of `theta`)
If `theta` is very small, `sin theta = theta`
`tau("net") = -(PE) theta`
`tau("net") prop (-theta)` so motion will be almost SHM.
`T = 2pi sqrt((I)/(K))`