Thus,
the contribution to the total flux through the pill box
comes only from the outside (circular) cross-section
of the pill box This equals  ± EdS (positive for s > 0,
negative for s < 0), since over the small area dS, E
may be considered constant and E and dS are parallel
or antiparallel The charge enclosed by the pill box
is  sdS By Gauss’s law
EdS = 
0
S
σ δ
ε
E = 
0
εσ
(2