1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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

    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:

    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..?

  2. jcsd
  3. Nov 24, 2015 #2


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    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


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    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:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted