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 FIGURE 2 9 For a
single charge q
(a) equipotential
surfaces are
spherical surfaces
centred at the
charge, and
(b) electric field
lines are radial,
starting from the
charge if q > 0