An equipotential surface connects all points at the same potential. Properties: (1) E is always perpendicular to equipotential surfaces (if E had a tangential component, work would be done along the surface, contradicting constant V). (2) No work is done moving a charge along an equipotential: W = q*delta(V) = 0. (3) Equipotential surfaces never intersect (each point has a unique V). (4) Closer spacing of equipotentials indicates stronger E (since E = -dV/dr). For a point charge: concentric spheres. For a uniform field: parallel planes perpendicular to E. For a dipole: complex surfaces, with V = 0 on the perpendicular bisector plane. Every conductor surface in electrostatic equilibrium is an equipotential surface.