Q38:A long, cylindrical conductor of radius R carries a cur- rent I as shown in Figure P30.38. The current density J, however, is not uniform over the cross section of the conductor but rather is a function of the radius accord- ing to J = br, where b is a constant. Find an expression for the magnetic field magnitude B
(a) at a distance r1 , R and
(b) at a distance r2 . R, measured from the center of the conductor.