Note the following generic facts (1)B y sammet try B is independent of and z (2)Be=0: Taking a cylinder of length I and radius P, which is either inside or outside the solonoid /sB.d=0. The integral on the l h.s. is 2TplBp( the two end faces cancel), so Be=0 (3 B2 inside is independent of p.(see a rectangular path a in Fig 9-6)