a r=asin 0, dy de sin 0 dE 1a小y 6 1 n(a/sin 0)de sin e 4t(a/sin 8) 4rea in 10 (cos 0, -cos 02) 4丌Ena 同理可得 cos 0de y4兀6061 (sin 0,-sin 0) 4兀 1010     sin 4 1 2 0 r dy dEx =        sin ( /sin ) ( /sin ) 4 1 2 2 0 aa d =  = 21 sin 4 0        d a Ex (cos cos ) 4 1 2 0      = − a 同理可得：  = 21 cos 4 0        d a Ey (sin sin ) 4 2 1 0      = − a r = a/ sin  ,   d a dy 2 sin =  2  1 x oy a