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Two charges, each equal to q, are kept at x = −a and x = a on the x-axis. A particle of mass m and charge q0 = q/2 is placed at the origin. If charge q0 is given a small displacement (y << a) along the y-axis, the net force acting on the particle is proportional to

1. y
2. −y
3. 1/y
4. −1/y

Correct answer: y

Solution

The net force acting on the particle is due to the electric fields created by the two charges, which are symmetric about the y-axis. When the particle is displaced slightly along the y-axis, the forces from the two charges will create a restoring force that is proportional to the displacement y, indicating that the force acts in the direction of the displacement.

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