25)],
U
rq q
rq q
q q
r
=
+
+




41
0
1
2
12
1
3
13
2
3
23
πε
(2 26)
Again, because of the conservative nature of the
electrostatic force (or equivalently, the path
independence of work done), the final expression for
U, Eq (2 26), is independent of the manner in which
the configuration is assembled