Two charges $+2\mu C\text{and}-2\mu C$ are placed at points A and B, 6 cm apart (a) Identify an equipotential surface of the system. (b) What is the direction of the electric field at every point on this surface ?

Solution: (a) the situation is represents in the given figure

An equipotential surface is plane on which total potential is zero everywhere. This plane is normal to line AB. The plane is located at the mid-point of line AB because the magnitude of charges is the same .
(b) the direction of the electric field at every point on this surface is normal to the plane in the direction of AB.