Question

In the following diagrams a particle with small charge `-q` is free to move up or down , but not sideways near a larger fixed charge `Q`.The small charge is in equilibrium because in the positions shown ,the electrical upward force is equal to the weight of the particle .Which statement os true?

A. In fig.`(A) ,-q` is in stable equilibrium
B. In fig.`(A) ,-q` is in neutral equilibrium
C. In fig.`(B) ,-q` is in stable equilibrium
D. Neither in fig.`A` nor in `B,-q` is in stable equilibrium

Answer 1

Correct Answer - 3
In first diagram , if we displace `-q` in downward direction , electric force on it decreases , `mg != F_(e )` , it will move down (unstable equilibrium).
In second diagram , if we displace `-q` in downward direction , electric force on it increases , `F_(e ) gt mg` , net force restores `-q` to its original position (unstable equilibrium).