Time period of a block when suspended from the upper plate of a parallel plate capacitor by a spring of stiffness `k` is T, when block is uncharged. If a charge `g` is given to the block then new time period of oscillation will be

Options

A. `T`
B. `gtT`
C. `ltT`
D. `ge T`

Answer

A

Explanation

The force that act on the block are `qE mg `and spring force since `qE` and `mg` are constant force the only variable elactic force change by `kx` where `x` is elongation in the spring
Unbalanced (restoring) force
`F = - kx`
`or - m omega^(2) x = - kx`
`or, omega = sqrt((k)/(m))`
`T = (2m)/(omega) = 2pi sqrt((m)/(k))`