dM=xdF=ldLBxsin e B x=rsin 6. dl= rde dM=IBR2sin 08 r E R d k X 2 M=IBR- sin-010 P M=1BπR m=ⅠS=I兀R2k b= Bi M=m×B=兀R2B×=ImR2Bd sin d 2 2 M = IBR = 2π 0 2 2 M IBR sin d m ISk I R k    2 = = π B Bi   = M m B I R Bk i I R Bj       2 2 =  = π  = π dM = xdF = IdlBxsin x = Rsin ,dl = Rd 2 M = IBπ R I B  R y z Q J K P o x  x d