等電位面と磁力線

No work is required to move a charge along an equipotential surface because the electric potential remains constant, meaning there is no change in electric potential energy. The force on the charge is perpendicular to the displacement along the equipotential, so the work done is zero regardless of the path taken.

Equipotential surfaces are always perpendicular to electric field lines. This perpendicular relationship holds for all charge configurations. Since motion along an equipotential must be perpendicular to the electric field direction, the field lines and equipotential surfaces form orthogonal geometric patterns throughout space.

For an isolated point charge, equipotential surfaces are concentric spheres centered on the charge, with spacing that reflects the inverse relationship between potential and distance. In a uniform electric field, equipotential surfaces are parallel planes perpendicular to the field direction and equally spaced, creating a simpler geometric pattern.

Equipotential lines are closely spaced where the electric field magnitude is higher and farther apart where the field is weaker. This spacing variation provides a visual indicator of field strength: denser equipotential lines correspond to stronger fields, while sparse lines indicate weaker fields in that region.

Electric field lines can be drawn perpendicular to equipotential surfaces. Since the electric field always points away from positive charges and toward negative charges, drawing perpendicular lines to the equipotential surfaces reveals the field direction. Conversely, knowing the field allows you to sketch equipotential surfaces perpendicular to it.

For an electric dipole, equipotential surfaces reflect the asymmetric charge distribution. The potential is higher near the positive charge and lower near the negative charge. The equipotential surfaces are distorted, with denser spacing near the charges and varying potential values throughout the field region.

For two positive charges, equipotential surfaces show a distinctive 8-shaped configuration where two equipotential surfaces intersect. This occurs because the potential from each charge contributes additively, creating a symmetric pattern that reflects the repulsive nature of like charges and the geometry of superposed potential fields.