Question

Why electric field lines are always normal to equipotential surface?

Answer 1

Equipotential lines are curved lines on a map which mark out lines of identicalaltitude. The altitude pertains to electric potential or voltage. Equipotential lines are always perpendicular to the electric field. The lines creates equipotential surfaces in a three dimensions. Movement along an equipotential surface needs no work since such movement is always perpendicular to the electric field. 

Answer 2

Answer:

Explanation:

Suppose if electric field were not normal to the the surface but at some angle theta , then by resolving it into vectors ...it would have a component along the surface ...which tends to move the charges present on surface ....( no force to counteract this force is present ) constituting electric current ...which is in contradiction to the case of electrostatics where charges tends to remain at rest . So electric field lines must be normal to equipotential surface .