Question

A pendulum bob carriers a negative charge - A positive charge +q is held at the point of support. Then, the time period of the bob is

• A. greater than $2 \pi \sqrt{ \frac{ L}{ g}}$
• B. less than $2 \pi \sqrt{ \frac{ L}{ g}}$
• C. equal to $2 \pi \sqrt{ \frac{ L}{ g}}$
• D. equal to $2 \pi \sqrt{ \frac{2 L}{ g}}$

Answer 1

Answer: (C)

equal to $2 \pi \sqrt{ \frac{ L}{ g}}$

Answer 2

There is no change in the restoring force as the electrostatic forces are the central forces. Negative and positive charges at the two extremeties of the string affect tension $T$ which does not affect the restoring force.
So that the time period of bob is
T = $2 \pi \sqrt{ \frac{ L}{ g}}$