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Total Magnetic Flux Density Law Problem

  1. Feb 2, 2015 #1
    We know Total Magnetic Flux B = B_0 + B_m

    Where, B_0 is the external field and B_m is the field inside a material.

    Now, we get,

    B = B_0 + μ_0*M (M is the magnetization)

    My question is -

    Do I always have to use μ_0 ? If yes then Why?

    The material isn't free space, is it?

    & also

    B = μ_0*(H + M) , where H is the Magnetic Field Intensity/Strength

    Same problem here. Do I always have to use μ_0 here too? Why not only μ ??

    The main problem is we know Magnetic Field inside a material is B_m = μ_0*M

    Why we are using μ_0 here while the material isn't free space!?

    This problem is the main reason of those 2 questions I asked before.

    Please help..
  2. jcsd
  3. Feb 2, 2015 #2

    Simon Bridge

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    The answer to your question is "no". Sometimes the material has a susceptability different from that of a vacuum. The definitions of the terms should answer your questions for you.
  4. Feb 2, 2015 #3


    Staff: Mentor

    This equation is the definition of H in SI units. The H field is defined as the quantity that makes that equation true.

    In that equation we always use ##\mu_0##. The purpose of ##\mu_0## is simply to convert the SI units of M and H into the SI units of B. The purpose is not to describe the material, that is done by M.
  5. Feb 2, 2015 #4

    Simon Bridge

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    ... ah, yes: a niggly feeling had been building over that one.
    Dalespam is correct

    You'll see:
    ##\vec B = \mu_0(\vec H+\vec M)##
    ##\vec B = \mu \vec H##
    ... which can lead to confusion.
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