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Magnetic Force of identical shaped box bar magnets

  1. Apr 18, 2010 #1
    I am having a problem with my understanding. I could be incorrect, but I think that the magnetic field emitted from a magnet is consistent and doesn't weaken at points further away. Then could someone explain how magnet force weakens with distance. I would also like to know the math so here is a problem I created.

    Say I have two identical shaped box bar magnets with dimensions (l,w,d) and mass m, and magnetic field b/

    The face of w*d is the side that is directed at each magnet. (ie wxd of magnet_a faces w*d of magnet_b)

    Variable x is the distance between the two magnets.

    So, how can I figure the forces at x.

    Sorry, I accidently put this in wrong forum
    Last edited: Apr 18, 2010
  2. jcsd
  3. Apr 18, 2010 #2

    Vanadium 50

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    Take a refrigerator magnet and hold it 10 meters from a refrigerator. Is there much force? That should tell you something qualitative about the force vs. distance.

    There is no such thing as a "bar magnet with magnetic field b" so the second part has no answer.
  4. Apr 18, 2010 #3
    @Vanadium you are no help. I didn't say if magnets force get weaker I said how does it.

    Also then, why are magnets rated in Teslas. Such as Neodymium which is 1.2-1.6 Tesla at poles.
  5. Apr 18, 2010 #4

    Vanadium 50

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    When you make up your mind, we can talk.
  6. Apr 18, 2010 #5
    Use the Biot-Savart law (http://en.wikipedia.org/wiki/Biot_savart) or Ampere's law (http://en.wikipedia.org/wiki/Ampere_law) to express the magnetic field as fuction of distance, you will find that the magnetic field is inversely proportional to distance.

    To find the magnetic force, you will then need to use the Lorentz force applied on a charged particle moving in a magnetic field (http://en.wikipedia.org/wiki/Lorentz_force).
    Last edited by a moderator: Apr 25, 2017
  7. Apr 18, 2010 #6
    Bio Savart works with a moving charge, but I don't know the speed the electrons. What formulas can be used to determine the repelling or acting force of magnet. And what information do I need about a magnet's strength that will help me.
  8. Apr 18, 2010 #7
    Wow! Your problem is now getting serious but check this out http://en.wikipedia.org/wiki/Magnetic_field
  9. Apr 18, 2010 #8
  10. Apr 19, 2010 #9
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