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# Determining magnetic force at a distance

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## Determining magnetic force at a distance

(OP)
Can someone point me in the direction of an equation to determine magnetic force at a given distance?  I'm trying to determine what percentage of magnetic attraction or repulsion remains at a separating distance of 1cm, 2cm, 3cm, etc...  Thank you.
Replies continue below

### RE: Determining magnetic force at a distance

AgainstOdds: There are no equations to calculate force at a distance.  FEA is required.

### RE: Determining magnetic force at a distance

AgainstOdds,
too much depends on the geometry of the magnetic setup, so no general rules can be provided.
For a horseshoe arrangement with a PM (or a coil), you can express the force exerted on the closing iron as a function of the gap, though it is known that, for gaps sufficiently large to be interested in, the actual force may be smaller than the theoretical one by a factor of 2 or more.
Come back if this is what you are looking for.

prex
http://www.xcalcs.com : Online tools for structural design
http://www.megamag.it : Magnetic brakes for fun rides
http://www.levitans.com : Air bearing pads

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