Describe schematically the equipotential surfaces corresponding to
(a) a constant electric field in the z-direction,
(b) a field that uniformly increases in magnitude but remains in a constant (say, z) direction,
(c) a single positive charge at the origin, and
(d) a uniform grid consisting of long equally spaced parallel charged wires in a plane.

Explanation

(a) Equipotential surface is always normal to the direction of electric field. Thus, planes parallel to x-y plane are equipotential surfaces for electric field in the z-direction.
(b) Equipotential surfaces are closer in a region of strong electric field. Therefore, planes, parallel to x-y plane are equipotential surfaces for electric field in the z-direction but these planes will get closer as the field uniformly increases.
(c ) For a single positive charge, the spherical shells of any radius with the charge at its centre or centre at the origin will represent the equipotential surface.
(d) Equipotential surfaces for such a uniform grid will be the planes parallel to the grid at longer distance but at smaller distance equipotential surfaces will vary.