2
=
+
+
+




41
0
1
1
2
2
πε
rq
rq
q
r
n
n
P
P
P (2 18)
If we have a continuous charge distribution characterised by a charge
density r (r), we divide it, as before, into small volume elements each of
size Dv and carrying a charge rDv We then determine the potential due
to each volume element and sum (strictly speaking , integrate) over all
such contributions, and thus determine the potential due to the entire
distribution