Four point charges q, q, q and – q are placed at the vertices of a square of side length a. The configuration is changed and the charge are positioned at the vertices of a rhombus of side length a with – q charge at the vertex where angle is `120^(@)`. Find the work done by the external agent in changing the configuration.

Answer

`W=-(Kq^(2))/(a)(1-(1)/(sqrt(2)))`