Q.What is an equipotential surface?

An equipotential surface is a surface on which the electric potential has exactly the same value at every point; for an isolated point charge these surfaces are concentric spheres centred on the charge (since V = kq/r depends only on distance), and for a uniform field they are flat parallel planes perpendicular to the field direction. Two properties follow directly from the definition. First, moving a charge between any two points on the same equipotential surface requires exactly zero net work, since the potential (and hence the potential difference) between those two points is zero. Second, the electric field is always exactly perpendicular to the equipotential surface passing through any given point -- if the field had any component along the surface, that component would do work moving a ch …