等電位面と磁力線

An equipotential surface is a 3-dimensional surface on which all the points have the same potential. If a test charge Q is moved on such a surface, its potential energy remains constant.

Therefore the work done to move from one point to another on equipotential surfaces is zero. The equipotential surface is always perpendicular to the electric field lines.

For a uniform electric field, parallel and equally spaced lines, equipotential surfaces are parallel planes perpendicular to the electric field.

The equipotential lines are the 2-dimensional representation of equipotential surfaces.

For an isolated charge, the electric field is radial and equipotential surfaces are concentrated spheres of different potentials with charge being at the center.

The equipotential lines are closely spaced where the electric field magnitude is higher and farther apart where the electric field is weaker.

For an electric dipole, the potential will be higher near the positive charge and lower near the negative charge.

For two positive charges, equipotential surfaces show a single 8-shaped surface where two equipotential surfaces intersect.