O dB= uor-d/ 2( 2 r+x 2差 R loOR osin 6e.R sin 2R3 R B=[db=LoRoo 0d0=MoRoa 3 写成矢量式:万_2 3 oRa           sin d 2 2 sin d sin 2( ) d d 3 0 3 2 2 2 0 2 2 2 0 2 3 R R R R r x r I B =  = + =        B B R 0 R 0 0 3 3 2 sin d 2 d  = = =   R  o r dI x B  d     B 0 R 3 2 写成矢量式： =