The force due to the same sphere of charge acting
some test charges (1 u) is shown in the following. It may be verified
the field within the sphere vanishes, and that the field outside
that of a point charge located at the centre and whose magnitude is
the total charge on the sphere. This last property holds in general for
any spherical distribution of charge (it also holds for the
field, and it allows to calculate forces between extended,
spherical, bodies as if they were point masses).