Total
work done (W) by the external force is obtained by integrating Eq (2 6)
from r¢ = ¥ to r¢ = r,
W
Q
r
dr
Q
r
Q
r
r
r
= −
′
′ =
′
=
∞
∞
∫ 4
4
4
0
2
0
0
π
π
π
ε
ε
ε
(2 7)
This, by definition is the potential at P due to the charge Q
0
( )
4
Q
V r
εr
=
π
(2