A coaxial cable consists of a copper wire, radius a surrounded by a concentric copper tube of inner radius e (Fig. 4.26). The space between the two conductors is partially filled (from radius b to radius c) with a linear dielectric material of dielectric constant Er. The gap from a to b has permittivity co. Find the capacitance per unit length of this cable.

A coaxial cable consists of a copper wire, radius a surrounded by a concentric copper tube of inner radius e (Fig. 4.26). The space between the two conductors is partially filled (from radius b to radius c) with a linear dielectric material of dielectric constant Er. The gap from a to b has permittivity co. Find the capacitance per unit length of this cable.