Chapter 20, Problem 50P

(a) Use Ampere’s law to show that the magnetic field between the conductors of a coaxial cable (Fig. 20-6115) is $B={\mu }_0//2\pi r$ if r(distance from center) is greater than the radius of the inner wire and less than the radius of the outer cylindrical braid (= ground) (b)Show that B = 0 outside the coaxial cable

Figure 20-61