大学物理 规范作业解答25(8)

µ0 I B= + B2 2πxr r µ0 I dφ = B dS = ( + B2 )ldx 2πxφ = ∫ dφ = ∫a +b+vt a +vt

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µ0 I ( + B2 )ldx 2πx

µ0 Il a + b + vt = ln + B2lb a + vt 2πdφ µ0 Ibvl dB ε = |t =0 = bl dt 2πa(a + b) dt