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Homework Help: Solenoid (magnetising current)

  1. Aug 6, 2017 #1
    1. The problem statement, all variables and given/known data

    Part d of attached question
    2. Relevant equations
    Solenoid equations
    B=uo n i

    3. The attempt at a solution
    B (absence)=B (presence)
    Uo n (i+im)=u n i
    But answer is 794A.

    Attached Files:

  2. jcsd
  3. Aug 6, 2017 #2


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    Staff: Mentor

    I don't understand what you calculated, but such a small difference looks like a rounding error.
  4. Aug 6, 2017 #3

    rude man

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    The answer should be M/H x 2A.
  5. Aug 7, 2017 #4
    Can you guys give a formula for magnetising current for solenoid?Every book gives for transformer but not for solenoid
  6. Aug 7, 2017 #5

    rude man

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    I just did, in post 3.

    But you raise a good point: magnetizing current in a transformer is fundamentally different from magnetizing current in a solenoid. The latter term is actually rarely encountered. Why? Because it's a fictitious current whereas for a transformer it's very real.

    For a solenoid, magnetizing current is defined to be the extra current that would be needed to restore the flux if the high-permeability core were removed.

    For a transformer it's the actual primary current with the secondary open. It's the current needed to establish the flux given by Faraday's emf = -N d phi/dt. Note that emf = applied voltage - primary losses voltage drops.
    Last edited: Aug 7, 2017
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