at a distance r from the source Q. So, integrating and using Coulomb's law for the force:
:Now, use the relationship
:

To show that the external work done to move a point charge q+ from infinity to a distance r is:
:This could have been obtained equally by using the definition of W and integrating F with respect to r, which will prove the above relationship.

In the example both charges are positive; this equation is applicable to any charge configuration (as the product of

1.Previous
3.Next