In the figure, the cross-section of a hollow
conducting tube and an infinitely long, thin
wire are shown. The hollow tube has an inner
radius a and an outer radius b. Both the tube
and the wire are aligned along the z-axis,
which serves as their common axis. The tube
carries a current with a density
vec(J)=(-I)/(2\pi (b-a)\rho )vec(a)_(z)(A)/(m^(2)), while the wire carries
a total current Ivec(a)_(z)A. Determine the magnetic
field vec(H) at all points in space.