Two positive point charges each of magnitude q are placed on y axis at the points (0,a) and (0,-a). If a positive charged particle of charge q· and mass m is dispalced slightly from the origin in the direction of the negative x axis.

Hi Srijit,

If the positive charged paticle comes closer to any one of the charge then there will be more repulsion from the nearest one.....this makes it to move in the oppsite direction and finally the charge will oscillate about the origin...the origin is said to be stable equilibrium for positive charge along x-axis.