The inner cylinder of a long, cylindrical capacitor has radius ra and linear charge density of +λ. It is surrounded by a coaxial cylindrical conducting shell with inner radius rb and linear charge density −λ. A) What is the electric field? (Hint: use Gauss's law)
B) What is the energy density in the region between the conductors at a distance r from the axis?
C) Integrate the energy density calculated in part B) over the volume between the conductors in a length L of the capacitor to obtain the total electric-field per unit length.