解:1「B·l=「B=2mB=M B=uo N/2rr RumI 2.中B●dS hdr Ri 2Tr uo Nh R 2rr RI R7 解：1. B dl Bdl rB NI = = 2 = 0  •    B  NI 2r = 0 1 0 2 0 ln 2 2 2. 2 1 R R r NIh hdr r N I B dS R R     = • =     I h R1 R2