There is an insulator rod of length L and of negligible mass with two small balls of mass m and electric charge Q attached to its ends. The rod can rotate in the horizontal plane around a vertical axis crossing it at a `L//4` distance from one of its ends.
In what position is the rod to be set so that if displaced a little from that position it begins a hormonic oscillation about the axisA?

Options

A.
B.
C.
D.

Answer

A, D

Explanation

Position of option (A) is minimum PE position means stable equilibrium position. Any displacement from this position is opposed by restoring torque.