穿过外管的全磁通: N,LI =NIBdS=NB. S 12内 2R|2R 2·R Z R N 2 又:工1=1mn1 (2")2l·zR2=12nRi ER R R2 2 1 2 2 1 2 R l N N I M    = = 又： 2 1 1 2 1 2 1 1 ( ) l R l N L = n V =   2 1 2 1 R l N =   2 2 2 2 2 R l N L =   1 2 1 2 L L R R M = N1 N2 l 2 2R1 2R L1 L2 穿过外管的全磁通： 1 2 2 1 1 2 1 2 N B dS N B S s =   =  内    2 2 2 1 2 I R l N N =  