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Iron core solenoid questions

  1. Nov 24, 2015 #1
    1. The problem statement, all variables and given/known data

    Iron core solenoid, with 50 turns per cm (5000 per metre)
    Current = 0.2A
    Measured B field = 1.58T

    Calculate:
    i) The applied field, Bapplied
    ii) The magnitude of magnetisation, M, of iron alloy

    2. Relevant equations

    For a long solenoid, Bapplied0nI
    And, generally, B=Bapplied0M

    3. The attempt at a solution

    I'm actually confused mainly on the first part because the answer isn't as it seems.

    For a solenoid, the applied field is:
    B=μ0nI

    So I get B = 1.26E-6 * 5000 * 0.2 = 1.26mT

    This would then suggest, for part ii), that the magnetisation for the iron alloy is (1.58 - 0.00126)T = 1.579T

    It seems the iron alloy has been rather hugely magnetised by such a small applied field!
    I worry if this is actually correct, or I've done something wrong..?

    Thanks
     
  2. jcsd
  3. Nov 24, 2015 #2

    TSny

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    Homework Helper
    Gold Member

    Is this the value for M or for μ0M?

    Yes. Ferromagnetic materials are amazing! :smile:
     
  4. Nov 25, 2015 #3
    Ah, oops, yeah I missed out the μ0 term.

    Still I was shocked by the seemingly huge resultant B field from such a tiny current in the solenoid.

    So M = (B-Bapp)/μ0 = (1.58-0.00126)/μ0

    However I'm now shocked again because this gives a magnetisation of 1.25E6... which is huge! (Or is it...?) I can't seem to find any examples online with actual numerical values for me to consider as a reference towards my own answer.

    Simply, I don't know what a typical magnetisation value should look like. Should it be as huge as that?

    Thanks :oldsmile:
     
  5. Nov 25, 2015 #4

    TSny

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    Gold Member

    Yes, your numbers look reasonable for iron. It is amazing and it shows what a large group of entities (atoms) can accomplish when they cooperate.
     
  6. Nov 25, 2015 #5
    Great stuff, thanks :angel:
     
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