+  
=
+
41
0
1
2
12
2
12
1
3
13
2
13
πε
rq q
rq q
ˆ
ˆ
+
+



 ˆ
q q
r
n
n
n
1
1
2
1r
=
=∑
q
q
r
i
i
i
n
i
1
0
1
2
2
1
4πε
ˆr
(1 5)
The vector sum is obtained as usual by the parallelogram law of
addition of vectors All of electrostatics is basically a consequence of
Coulomb’s law and the superposition principle