22) By the superposition principle for fields, we add up
the work done on q2 against the two fields (E and that due to q1):
Work done in bringing q2 to r2
1
2
2
2
12
(
)
4
o
q q
q V
εr
=
+
π
r
(2 28)
Thus,
 Potential energy of the system
= the total work done in assembling the configuration
1
2
1
1
2
2
0 12
(
)
(
)
4
q q
q V
q V
εr
=
+
+
π
r
r
 (2 29)
Example 2