Re: [Phys-L] breaking magnets

[John Denker <jsd@av8n.com>]

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.