(e)(3%) What is the dispersion effect for electromagnetic wave propagation?

1.(20%) The radius of the solid inner conductor and the inner radius of the very thin outer conductor of an air coaxial transmission line are ri and ro, respectively. A uniform current I flows in the inner conductor and returns via the thin outer conductor in the other direction. The permeability of free space μ0 is H/m. Determine the stored magnetic energy per unit length of the line.