WBJEE 2013 Physics Solved Paper

A particle of mass M and charge q is at rest at the midpoint between two other fixed similar charges each ofmagnitude Q placed a distance 2d apart. The system is collinear as shown in the figure. The particle is now displacedby a small amount x (x ≪ d) along the line joining the two charges and is left to itself. It will now oscillate about themean position with a time period (ε0 = permittivity of free space)