why work done by a electric force is negative of the work done by the external force?

can somebody give me a brief about the concept of work done by a external force and electric force..

Dear student,

While finding out the potential energy stored when a body is diplaced against an electric field, we calculate the work done by an ‘external force’ which is opposite to the electric force acting on the particle and put it equal to the gain in potential energy. Since this external force is assumed to have magnitude equal to that of electric field at all times and opposite in direction. Hence work done by them is also negative of each other.

Approved