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How do I calculate the repelling Force of an Electromagnet?

  1. Jun 26, 2015 #1
    Hello everyone, I am working on a project and I am trying to figure out the formula to use. My goal is to calculate the amount of current needed to create an electromagnet with a strong enough field strength to repel a force of 2000 newtons.
    thank you
  2. jcsd
  3. Jun 26, 2015 #2


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    The short answer is: 400000 A/m.
    But of course it depends on:

    * What kind of magnet ( shape ).
    * Dimensions of the magnet and the other magnet to be repelled. ( for example unmagnetized iron will always be attracted ).

    So you need to fill out "All known data:".
    Last edited: Jun 26, 2015
  4. Jun 26, 2015 #3
    Thanks. Actually I just found this formula. I can reverse solve for m1 and m2 which is the pole strength of each electromagnet I would be using for the project. 4f895116f8bde4cf60497d348294918b.png and then solve for the current I need.
  5. Jun 26, 2015 #4


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    I don't recognize this formula. What is m1 and m2: Masses, or?

    Say you have two magnets kept apart with a distance, s. The cross section areas of the magnets are A. The energy density within the airgap will be

    Edens = ½*B*H [ J/m3 ] ( = ½*μ0*B2 )

    The energy in the airgap will be E = ½*B*H*Volumeairgap = ½*B*H*s*A

    Now, you can find the force: F = dE/ds = ½*B*H*A.

    But what is the size of A?
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