Following the symmetry arguments, we expect that the field lines must be concentric circles, the magnetic flux density must be in the o direction and B, has a constant magnitude along each circle. there are three regions of interested b=aB dl=a dr +ando+a.dz B·dl=Brdp X 2丌 B·dl B,rdo= b, 2rFollowing the symmetry arguments, we expect that the field lines must be concentric circles, the magnetic flux density must be in the  direction ,and B has a constant magnitude along each circle. There are three regions of interested. 2 0 ˆ ˆ ˆ ˆ 2 r z C B a B dl a dr a rd a dz B dl B rd B dl B rd B r            = = + +  =  = =   b a y x 