question_answer

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

Correct Answer: A

Solution :

Key Idea: 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\[-\,mg\text{ }sin\text{ }\theta \]to\[\text{ }-\text{ }mg'\text{ }sin\text{ }\,\theta \] Where \[g'=g+\frac{{{F}_{e}}}{M}\] Also  \[T=2\pi \sqrt{\frac{\text{displacment}}{\text{acceleration}}}\] Since, acceleration increase time period decrease