22 The flux through an area element DS is
2
0
ˆ
4
q
r
φ
ε
∆
=
∆
=
∆
π
E
S
r
S
i
i
(1 28)
where we have used Coulomb’s law for the electric field due to a single
charge q The unit vector ˆr is along the radius vector from the centre to
the area element