electric field in a cylindrical conductor
you think of these thin cylindrical shells as resistors in series, since the same current flows through each shell, for which you add the resistances.
then dR=ρdr/(2πrL) where resistivity ρ=1/σ
now dV=IdR
and E=-dV/dr = -IdR/dr = -Iρ/(2πrL)
now...