The equipotential surface tension means the specific surface has same electric potential at every point. Which means the surface which have equal electric potential at every point. Nothing work is required to do any work to move the charges in equipotential surface. In other, the surface which has equal electric potential at every point is called as equipotential surface.
Electric dipole
Electric dipole means two equal and opposite charges are seperated by the constant distance. Like the charge q1 is at distance of q2 at 2l.
Does electrostatic force obey Newton’s third law?
Yes, it also obeys Newton’s third law. When one charge q1 exerts some force on q2 then q2 also exerts same force on q1. Therefore, the electrostatic force obeys Newton’s third law. Newton’s third law means, every action has equal and opposite reaction.