Final answer:
Equipotential surfaces are perpendicular to the electric field at a given point, which means they are normal to the direction of the field lines and no work is done when moving a charge along an equipotential surface.
Step-by-step explanation:
For any charge configuration, the equipotential surface through a point is perpendicular to the electric field at that point. Equipotential surfaces are always normal to electric field lines, meaning they cross at right angles. This is because the work done in moving a charge along an equipotential surface is zero, and thus there is no component of the electric field along the direction of movement on an equipotential surface. When charges are present in a conductor and an external electric field is applied, the free charges move until the electric field inside the conductor is balanced and the field becomes perpendicular to the surface. This is in equilibrium with the electrostatic forces.