consider a long coaxial cable consisting of a conducting wire of radius r and a concentric conducting thick shell with internal and external radii r1 and r2, respectively (fig. 1). the wire and the shell carry equal and opposite steady currents i parallel to the axis. assuming that the currents are uniformly distributed inside the conductors, calculate the magnetic field as a function of the distance r from the axis of the wire. sketch the magnitude of the magnetic field as a function of r.