Question

A simple pendulum oscillates slightly above a large horizontal metal plate. The bob is given a charge. The time period?

• A. Has no effect, whatever be the nature of charge
• B. Always decreases, whatever be the nature of charge
• C. Always increases, whatever be the nature of charge
• D. May increases or decreases depending upon the nature of charge.

Answer 1

Answer: (B)

Always decreases, whatever be the nature of charge

When any charge is given to the bob of the pendulum, it induced opposite charge on the metal plate, and hence a net force of attraction acts on the bob. Thus, the effective value of $g$ increases.
So, from $T=2\pi \sqrt{l/h_{eff}}$; the value of $T$ decrease.