Now the normal to the surface 3 at every point is
perpendicular to E, so by definition of flux, f3 = 0 Further, the outward
normal to 2 is along E while the outward normal to 1 is opposite to E Therefore,
f1 = –E S1,     f2 = +E S2
S1 = S2 = S
where S is the area of circular cross-section Thus, the total flux is zero,
as expected by Gauss’s law