This is a question in my book: A point charge q is rotated along a circle in the electric field generated by another point charge Q . The work done by the electric field on the rotating charge in one complete revolution is? The answer in my book says that regardless of whether Q is at the center of the circle work done will always be zero.
Now I can understand why work done is zero when Q is at the centre, since the circle will be an equipotential surface for charge Q, field of Q always being perpendicular to displacement of q at each instant. But why is work done still zero even when Q is not located at the centre of the circle but somewhere else?