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. Equally spaced x-y planes.
b. x-y planes getting closer and closer along the z-direction.

c. Concentric spherical surfaces gradually increasing in spacing.
d. A periodically varying shape near the grid which gradually reaches the shape of the planes parallel to the grid at far distances.