Paul wrote:
Stephen A. Lawrence wrote:
> And we don't
> have any sufficiently whizzy bar magnets here to
> let me test it
> macroscopically.
There you go again with your cigarette dipoles. ;-)
OK, I finally got the point WRT the shape...
>
> Ummm hmmmm so it is, the field strength ratio at
> the end versus the side
> is something like 2:1, and, if the dipole is
> allowed to align with the
> field, the net force it feels is always in the
> direction of increasing
> field strength.
For a point charge it is. Of course if for example
the dipole is 1 cm in diameter and
you're testing the field right up against the wire
millimeters away then it doesn't make
sense you'll get 2:1 ratio.
Did you try to field
dipole moment calculator?
http://www.netdenizen.com/emagnet/offaxis/iloopcalculator.htm
Yes, I took a look at it, but I already knew the shape of the dipole
field, at least for small dipoles. In geometrized cgs units it's
http://www.physicsinsights.org/dipole_field_1.html#eqn-16
which is pretty clear.
The primary point I missed was that my "mental model" of a tiny dipole
wasn't spherically symmetric, so rotations also involved major changes
in |r|.
