Example 26.7: Figure 26.41 shows a coaxial cable, widely used in electronics to minimize interference either with or from signals carried on the cable. The cable consists of an inner solid conductor of radius a and a hollow outer conductor of inner radius b and thickness c. The two conductors carry equal but opposite currents I, distributed uniformly over their cross-sectional areas. Find expressions for the magnetic field strength as a function of radial position r (a) within the inner conductor, (b) between the inner and outer conductors, (c) within the outer conductor, and (d) beyond the outer conductor.