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How to find the magnetic flux of this magnet?

  1. Jul 11, 2015 #1
    I am looking to find the magnetic flux of a cylindrical magnet as it passes through a coil. I am aware of the complexity of magnetism, however, i am only looking for a conservative approximation of the magnetic flux. I found the formula ΦB = B · A, but is my understanding that the magnetic field will not be constant over the loop. How do I account for this in the calculation? Also, is the equation asking for the cross-sectional area of the solenoid, or the area of the actual piece of wire used to make the coil?
     
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  3. Jul 12, 2015 #2

    Hesch

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    More information is needed: Is the coil loaded somehow? If not, the flux in the magnet will not change when it passes through the coil, no current will flow in the coil.
    The magnetic flux density (B) will change over the loop, but the flux (Φ) will not. The "cross section area" of the B-field will change over the loop, being expanded outside the magnet.
    Yes, presumably.
     
  4. Jul 12, 2015 #3
    Ok, I am having a hard time understanding what you mean by "the "cross section area" of the B-field will change over the loop, being expanded outside the magnet." Can you explain how this happens?
     
  5. Jul 12, 2015 #4

    Hesch

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    Actually I cannot speak of a "cross section area" as for the B-field because it is infinite. Some extremely sensitive instrument could sense your magnet field on the moon.

    But this illustrates what I mean:

    ad47be8696067dd04e99f783722ecfe7.png

    It is a solenoid, but it could be your magnet as well. You can see that the field-curves spread out outside the solenoid, indicating that the B-field is weaker here. Contrary the are close to each other inside the solenoid/magnet.
     
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