15 Gauss’s law: The flux of electric field through any closed surface S is
1/e0 times the total charge enclosed by S The law is especially useful
in determining electric field E, when the source distribution has simple
symmetry:
(i) Thin infinitely long straight wire of uniform linear charge density l
0
ˆ
2
r
ελ
=
π
E
n
where r is the perpendicular distance of the point from the wire and
ˆn is the radial unit vector in the plane normal to the wire passing
through the point (ii) Infinite thin plane sheet of uniform surface charge density s
0
ˆ
2
σ
ε
E=
n
where ˆn  is a unit vector normal to the plane, outward on either side