Two charges 2 µC and -2 µC are placed at points A and B, 6 cm apart.

What is the direction of the electric field at every point on this surface?

According to the formula, E dr = dV, the value of dV = 0 at each point of equipotential surface.

.-. E.dr=0

So, the angle between electric field vector and distance vector will be 90°. Thus, the electric field is always normal to the plane passing through AB.