A simple 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 upwards. If the electrostatic force acting on the sphere is less than gravitational force the period of pendulum is
Options:
(a) `T=2pi[l/(g-(qE)/m)]^(1/2)`
(b) `T=2pi(l/g)^(1/2)`
(c) `T=2pi[l/(g+(qE)/m)]^(1/2)`
(d) `T=2pi[(ml)/(qE)]^(1/2)`