cΦ=Bds=Nhdr 死r Φ=∫a地=uNInRdr 2元 int) 2 w=NP -HNIhIn(Ra) 2元 R L-号-a 2饥 π ( ) = ln R1 μ R2 2 N Ih Ψ =NΦ = μ 2π N Ih 2 ( ) ln R1 R2 L = Ψ I π μ 2 N h 2 ( ) ln R1 R2 = dΦ B. = dS π = dr μ 2 r NI h Φ = dΦ π R = 1 R 2 r μ 2 N Ih dr 