•无限长载流直导线 讨论 a1=0g2=π •半无限长载流直导线 a1=π/2w2=π B= 4π •直导线延长线上 cosa -cosaz 4π0 •无限长载流直导线 0 1  =  =  2 a I B   2 0 = •半无限长载流直导线 (cos cos ) 4 1 2 0     = − a I B a P 1 I B  讨 论 2 1  =   =  2 a I B   4 0 = •直导线延长线上