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Magnetization, coil question

  1. Feb 11, 2009 #1
    1. The problem statement, all variables and given/known data
    A bar of soft iron of cross sectional area A and relative permeability μ is bent into
    a ring of radius R. The bar is wound with n turns of a wire carrying a current I. Deduce a value
    for the magnetic field in the iron, explaining your assumptions.

    (b) A narrow gap of width w is sawn into the ring. Find the magnetic field in the gap.

    2. Relevant equations

    3. The attempt at a solution
    For part a. I used Ampere's Law with H to get

    H = nI/(2*pi*r)
    B = μμ0nI/(2*pi*r)

    But part b? I thought of trying to do some sort of superposition. Perhaps working out M in the original problem, and then doing the field due to the original problem plus the field due to a small chunk with opposite magnetization. Is this at all on the right lines?
  2. jcsd
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