Two parallel sheets each have large area A and are separated by a small distance R. The surface charge densities are σ and -σ . You wish to pull one of the sheets away from the other, by a small distance x. How much work does this require? Calculate this by:
(a) using the relation W = (force) × (distance);
(b) calculating the increase in energy stored in the electric field. Show that these two methods give the same result.