Re: [Phys-L] breaking magnets

["John Clement" <clement@hal-pc.org>]

Is it really zero at the equator?  A 2 disc stack with N against S acts just
like a fatter disk with stronger field at the ends.  It would be zero around
the equator only if you put N against N, and then the field at the ends
would would also be decreased.  This is looking at the field outside the
magnet.  I think the answer does not distinguish between the two cases.

John M. Clement
Houston, TX 

> -----Original Message-----
> From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of 
> John Denker
> Sent: Sunday, May 04, 2014 3:51 PM
> To: Phys-L@Phys-L.org
> Subject: Re: [Phys-L] breaking magnets
>
> On 05/04/2014 01:28 PM, Ken Caviness asked:
> > is the force at any given distance provided by the combination of 2 
> > disc magnets on some object = twice the force of one disc magnet at 
> > the same distance on the same object?  Or is it greater/less than 
> > twice the force of one disc magnet?  My quick and dirty model says 
> > "=", but "slightly greater" wouldn't surprise me.
>
> That's ill posed!
>
> The "force at any given distance" is not simply a function of 
> distance;  it depends on angle.
>
> In particular, there will be some points where the field due 
> to the two-disk stack is zero, even though the field due to 
> either disk separately would be nonzero.  This happens near 
> the equator of the two-disk stack.
>
> Hint:  Model each disk as a simple current loop.
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