ndl (2)de=dE cose cOS 6 4x9 dl= acsc ede a+l=a csc6 ∴E 4To. COS0- na 0e 2 cOs cos 0de 4丌a2cSc2b 4丌a de= de sin 0= 4zo sin 6de (3)E3 dE x4丌a Sin B-sin 0 ); E, -dE (cos 0,-cos 02) 14a (4)E (sin 02-sin 0)i+(cos 0,-cos 02)j 4丌a 讨论:一无限长均匀带电细棒E=E, 2 丌aL(cos cos ) 4 (sin sin ); 4 (3) 2 1 1 2 2 1 2 1               = = − = = −   a E dE a Ex dEx y y  i j a E    (sin sin ) (cos cos ) 4 (4)  2 1 1  2    = − + − j a E E j y       2 讨论：一无限长均匀带电细棒 = =       d a dEy dE sin 4 = sin =      cos 4 (2) cos 2 r dl dEx = dE =    2 2 2 2 2 2 csc csc r a l a dl a d = + = =                 d a a a d r dl dEx cos 4 cos 4 csc csc cos 4 2 2 2 2  = = =