Question

A simple pendulum has time period $T$. The bob is given negative charge and surface below it is given positive charge. The new time period will be:

• A. less than T
• B. greater than T
• C. equal to T
• D. infinite

Answer 1

Answer: (A)

less than T

Answer 2

Opposite charges attract each other. For SHM a restoring force acts on the bob this restoring force is accompanied by electrical force. Hence, restoring force changes from $-m g \sin \theta$ to $-m g' \sin \theta$ where $g'=g+\frac{F_{e}}{M}$. Also $T=2 \pi \sqrt{\frac{\text { displacement }}{\text { acceleration }}}$ Since, acceleration increases time period decreases.