Electric field due to the charge rDV is
given by Coulomb’s law:
2
0
1
ˆ
4
V
'
r'
ρ
ε
∆
∆
=
π
E
r
(1 26)
where r¢ is the distance between the charge element and P, and  ˆr¢ is a
unit vector in the direction from the charge element to P By the
superposition principle, the total electric field due to the charge
distribution is obtained by summing over electric fields due to different
volume elements:
2
0
1
ˆ
4
all
V
V
'
r'
ρ
ε
∆
∆
≅
Σ
π
E
r
(1 27)
Note that r, r¢,  ˆ′r  all can vary from point to point