x×3×XB×F2=dF2=|dF2siO ×x× ld =Bldusin e d e ldl B 因dl=rd →---- ×0××x fi= BIr sin ode F2=B/(2rcos 0o)j= BIABj 由于F=-BIAB 故F=F+F,=0A C x y r I F1  I l  d  0 B  dF2  I l  d o  0 B 2 d 2 d 2 sin    F = F y = F =  BIdlsin  − = 0 0 π 2 sin d   F BIr   F BI r j BI ABj    2 = (2 cos0 ) = d  因 dl = rd F BI ABj   由于 1 = − 0 F = F1 + F2 =    故