Discussion Forum



1)

The figure below depict, two situations  in which two infinitely  long static  line charges of constant positive line charge density λ are kept  parallel to each other

6320217_p4.JPG

 In their resulting electric field, point charges q and -q are kept in equilibrium between them. The point charges are confined to move in the x-direction only. If they are given a small displacement about their equilibrium  positions, then the correct statements is/are


A) both charges execute simple harmonic motion.

B) both charges will continue moving in the direction of their displacement

C) charge +q executes simple harmonic motion while charge -q continues moving in the direction of its displacement

D) charge -q executes simple harmonic motion while charge +q continues moving in the direction of its displacement

Answer:

Option C

Explanation:

 At the shown position net force on both charges is zero. Hence they are in equilibrium. But the equilibrium of +q is a stable equilibrium. So, it will start oscillations when displaced from this position, These small oscillations are simple harmonic in nature. While the equilibrium of -q is unstable. So, it continues to move in the direction of its displacement.