(a) The potential on the surface of a charged sphere of radius R is equal to
where
is the Coulomb's constant,
is the charge on the sphere's surface.
For the generator mentioned in the problem, the charge is
, while the radius is
. Using these values in the formula, we can calculate the potential at the surface:
(b) The potential generated by the sphere at a certain distance r from the centre of the sphere is given by
the problem asks at which distance
. Substituting in the previous formula we can find the value of r:
(c) An oxygen atom with 3 missing electrons has a positive charge of +3e, with e being the elementary charge.
The electric potential energy of a charged particle located at some point with voltage V is
where q is the charge of the particle, which is in our case
. So we can calculate the energy of the oxygen atom at the distance found in part b, which corresponds to
and a voltage of
: