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 36)
Including the fact that electric field is normal to the
surface, we get the vector relation, Eq