**Electrical Potential Energy of a Configuration of Charges**

Two Point Charges

Consider a system of two charges q

Two Point Charges

_{1}and q

_{2}separated by distance r

_{1}. This configuration is associated with a potential energy U

_{1}(say). When the separation is increased to r

_{2}, potential energy becomes U

_{2}.

The work done by electrostatic force can be calculated as follows.

Let the separation at any instant is r. Keeping q

_{1}fixed, q

_{2}is displaced by dr

dW

_{E}= .

dW

_{E}= Fdr cos 0 = dr

By definition of potential energy,

Taking infinity as reference i.e., r

_{1}= and U

_{1}= 0

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