例:求Φm b n dx ⑧ B月厅 解:dΦn=B.dS=BcosadS=xhd=,h xdx 2n r 2πx2+(△Z) -0-小广2流 -2me+wr-a2 4π a2+(△Z)2 例:求Φm(t) 2ao(常数) -b 2a 解:等效面积 0 a B=om,Φn0=42aln2 2 =a2+b2+2abcosot,n2=a2+b2-2abcosot ①.0=a1n+6+2 abcosmt 2π a2+b2-2abcosot 22 例:求 m Y b I a h n O X Z I O x dx X r Z B n 解:d m B dS = = = BcosdS hdx r x r I 2 0 2 2 0 2 x ( Z) Ih xdx = m m d a b a x Z Ih xdx 2 2 0 2 ( ) = = a a b x Z Ih ln[ ( ) ] 4 0 2 2 2 2 2 2 0 ( ) ( ) ( ) ln 4 a Z Ih a b Z 例:求 (t) m 2a (常数) I b 2a 解:等效面积 2r b I 1r a t , 1 0 2 2 ln 2 ( ) r r a I t m r2 2 a 2 b 2 2abcost ,r a b 2abcost 2 2 2 1 m (t) = a b ab t Ia a b ab t 2 cos 2 cos ln 2 2 2 2 2 0 a Z