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How to create 20 000 Gauss?

  1. Oct 19, 2009 #1
    Does the magnetic field around a magnet increase when the distance away from the magnet increases? While using a calculator for magnetic flux I noticed that the magnetic flux increases when the air gap increases. So does this mean the magnetic field of a magnet will increase the further you are away from it???

    For my project I have made a large copper dodecahedron structure that I wish to attach 12 magnets in at various points to create approx. 20 000 gauss inside of it. Is this possible? What size magnets will I need to do this?

    Neodymium magnets have surface gauss of 13000 and ferrite magnets have 4000gauss. which should I use?
  2. jcsd
  3. Oct 19, 2009 #2


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    Staff: Mentor

    You will get the largest magnetic field (all other things equal) when the air gap is the smallest. That's why it's hardest to separate magnets when they are stuck together, and it gets eaiser and easier the fatrher apart you pull them.

    As for creating a magnetic field inside of an object, remember that magnetic field is directional (a vector field). Your field inside the object has to be between two things, fromm one N pole to the other S pole, with the return of the field inside the magnet from S to N.
  4. Oct 19, 2009 #3
    There was a magnet at UC Berkeley that had a 24,000 Gauss central field, The magnet gap was about 20 inches, and the pole tip diameter was about 184" (E. O. Lawrence's cyclotron). I'm told that the field was about 16,000 Gauss iron, and 8,000 Gauss Helmholz coil. It weighed about 4,000 tons.
    Bob S
    [Added] See this GMW electromagnet, and especially the plot of maximum field strength on the specification page.
    The magnet will go to 30,000 gauss, but only with a pole tip gap under 20 mm.
    Last edited: Oct 19, 2009
  5. Oct 20, 2009 #4
    Thanks Berkeman. I had fogotten to consider this directional point.
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