To move a unit test charge
against the direction of the component of the field, work would have to
be done But this is in contradiction to the definition of an equipotential
surface: there is no potential difference between any two points on the
surface and no work is required to move a test charge on the surface The electric field must, therefore, be normal to the equipotential surface
at every point Equipotential surfaces offer an alternative visual picture
in addition to the picture of electric field lines around a charge
configuration