df=df cos e 10112Rcos6 2t d+rcos e d F,=dF'sin o-uoL. Rsin 0d0 2πd+ RCOS 6 F=Ho 1 2R ran cos eie B dF dF 2兀0d+Rcos dF d-R d0130Ldl R F=20412km2sm闭0 0 2π0d+Rcos     cos sin d 2π d d sin 0 1 2 d R I I R Fy F + = =      cos cos d 2π d d cos 0 1 2 d R I I R Fx F + = = x y F  Fy d  d Fx  d O 2 I 1 I d  I l  d2 R d (1 ) 2 2 0 1 2 d R d I I − =  −  + = 2π 0 0 1 2 cos cos d 2π     d R I I R Fx 0 cos sin d 2π 2π 0 0 1 2 = + =      d R I I R Fy . B 