Question

Derive an expression for the potential energy of a system of point charge

Answer 1

The extension produced x is directly proportional to the force applied to extend or compress the spring. F=kx were k is spring constant. The work done to stretch or compress the spring is stored as its PE W= integral 0 to x (Fdx) =0 to x (kxdx) =1/2 kx^2

Answer 2

We have to consider two charges q1, q2, located at r1,r2, respectively.The workdone in bring charge q1 from infinity to r1 is zero because there is no pontential in abesense of electrical field. Workdone in bring the charge q2 from infinity to r2 against the field due to charge q1 is = q1V when V is pontential point r2 due to the charge q1.