The figures below depict two situations in which two infinitely long static line charges of constant…

The figures 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. 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(s) is (are)

  1. Both charges execute simple harmonic motion
  2. Both charges will continue moving in the direction of their displacement
  3. Charges +q executes simple harmonic motion while charges -q continues moving in the direction of its displacement
  4. Charge -q executes simple harmonic motion while charges +q continues moving in the direction of its displacement

Solution

In first case if q is shifted towards one of the wires, its repulsive force will increase which will bring the charge back. In second case, in same type of displacement attractive force due to wire increases which will make it move further towards wire. `

Asked in: JEE Advanced 2015 (Paper 1)

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