23)
The charges q1 and q2 produce a potential, which at any point P is
given by
V
rq
rq
1 2
0
1
1
2
2
41
,
=
+




πε
P
P
(2 24)
Work done next in bringing q3 from infinity to the point r3 is  q3 times
V1, 2 at r3
q V
rq q
q q
r
3
1 2
3
0
1
3
13
2
3
23
41
, (
r)
=
+




πε
(2 25)
The total work done in assembling the charges
at the given locations is obtained by adding the work
done in different steps [Eq (2