How to calculate the force between magnets?

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For example at the surface of both magnets, the field strength is 1.5Tesla. Suppose the top magnet plus the weight it's supporting is 1 Newton, what is the height that I need to separate both magnets of like facing poles so that the top magnet hovers?
 

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  • #2
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For example at the surface of both magnets, the field strength is 1.5Tesla. Suppose the top magnet plus the weight it's supporting is 1 Newton, what is the height that I need to separate both magnets of like facing poles so that the top magnet hovers?
Hint: The magnetic field B by a given pole of a bar magnet at a point (assume unit north pole) r cm away from its centre is given by,

B= (μoqm/4π(r-l)2)

Where qm is the pole strength of bar magnet. l is the "half length" of the bar magnet.

Hence classically the force between two poles of bar magnet is defined by F = Bqm. This formula is valid if the poles are mere points.
 
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  • #3
Hence classically the force between two poles of bar magnet is defined by F = Bqm. This formula is valid if the poles are mere points.
So what if the poles aren't points like in the example that I gave. Suppose the magnets facing each other are circular. Would the difference between points and a circle area of 3cm2 be significant? If so, then how would you calculate it? (Forgive me if this post was already answered. I used the search function and came up with nothing related to this situation).
 
  • #4
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What about intregrating the differential forces between differential areas on each magnet? Would it work? Do you know what I mean?
 
  • #5
What about intregrating the differential forces between differential areas on each magnet? Would it work? Do you know what I mean?
Yup I was also thinking the same, although I don't know how to do it. It's a bit above my math level.
 
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