Question

A smple pendulum consists of a small sphere of mass m suspended by a thread of length l. The sphere  carries a positive charge q. The pendulum is placed in a uniform electric field of strength E directed vertically  downwards. Find the period of oscillation of the pendulum due to the electrostatic force acting on the  sphere, neglecting the effect of the gravitational force.

Answer 1

`a_(eff) = g +(qE)/m`

`T = 2 pi sqrt(l/g_(eff)) = 2 pi  sqrt(l/(g + (qE)/m)`