Zero-Pole Magnets (other than toroid?)
Reality Handbook
I don't know much about magnetism. But I read that a donut-shaped
magnet will not have any poles. I also have read that the magnetic
field exerted by such a shape on the outside is very weak...so perhaps
this means it's not what you would choose if trying to make (for
instance) a strong refrigerator magnet.
Is this correct? If this is the case, is there a way to manufacture a
zero-pole magnet that is very strong...yet if you put a bunch of them
in a box, none would stick together or repel?
-R
FYI: I don't have a practical application in mind...but started
looking into it because of a lucid dream I had:
http://realityhandbook.livejournal.com/36775.html
ji...@specsol.spam.sux.com
> -R
The poles in a donut-shaped (usually called a toroid) exist and
are inside the toroid.
Imagine a rubber bar magnet.
Bend it into a circle and stick the north and south poles together.
You now have a toroid.
--
Jim Pennino
Remove .spam.sux to reply.
s...@microtec.net
> Hello there,
>
> I don't know much about magnetism. But I read that a donut-shaped
> magnet will not have any poles.
All magnets have poles. See below.
> I also have read that the magnetic
> field exerted by such a shape on the outside is very weak...
> so perhaps this means it's not what you would choose if
> trying to make (for instance) a strong refrigerator magnet.
>
> Is this correct?
No this is not correct.
You have many poles configurations possible for donut
shaped magnets. All are as strong at the magnetization
processes and customer specs require.
See:
http://www.magnetcity.net/magnet_specs.htm
The most common type is the loudspeaker magnet,
which is magnetized parallel to thickness. This means
that both poles physically coincide and are located
at the geometric center of the central hole. this is
what allows the loudspeaker coil to easily move
along the axis.
They are VERY strong and will neatly stick to
a refregirator. Watch your fingers!!
> If this is the case, is there a way to manufacture a
> zero-pole magnet that is very strong...yet if you put a
> bunch of them in a box, none would stick together or repel?
There exists no such thing as zero-pole magnets.
André Michaud
Benj
s...@microtec.net wrote:
> On 13 juil, 07:44, Reality Handbook <realityhandb...@gmail.com> wrote:
> > I don't know much about magnetism. But I read that a donut-shaped
> > magnet will not have any poles.
>
> All magnets have poles. See below.
RealityHandbook means external poles. His donut shaped magnet is
identical to two horseshoe magnets stuck together. N-S etc. They
don't have external poles but there are "poles" in the sense that if
you pull them apart each has a N and S pole. Same goes for say a donut
magnet magnetized like the two horseshoes above. No external poles BUT
if you take a hammer and break it into two pieces each half WILL show
poles just like two horseshoe magnets.
> > I also have read that the magnetic
> > field exerted by such a shape on the outside is very weak...
> > so perhaps this means it's not what you would choose if
> > trying to make (for instance) a strong refrigerator magnet.
> >
> > Is this correct?
>
> No this is not correct.
Yes it IS correct! Just TRY to stick two stuck together horseshoe
magnets to a refrigerator. They may stick but don't have much external
field. Now try to stick the two horseshoe halves to the refrigerator.
They stick fine.
> You have many poles configurations possible for donut
> shaped magnets. All are as strong at the magnetization
> processes and customer specs require.
> See:
Yes. The magnetic field is determined by HOW the magnet was magnetized
NOT by the shape of the magnetic material!
> http://www.magnetcity.net/magnet_specs.htm
>
> The most common type is the loudspeaker magnet,
> which is magnetized parallel to thickness. This means
> that both poles physically coincide and are located
> at the geometric center of the central hole. this is
> what allows the loudspeaker coil to easily move
> along the axis.
>
> They are VERY strong and will neatly stick to
> a refregirator. Watch your fingers!!
Yes they DO stick to refrigerator, but the poles (well OK, one needs
to define here what is meant by "poles") actually are on each FACE of
the magnet North on one side, South on the other. This has NOTHING to
do with loudspeaker coil moving easily on the axis!
And the sticking to a refrigerator has to do not only with the
strength of the magnetic field, but ALSO to the rate of change of
field as you increase the distance between the magnet and the iron
refrigerator box.
> > If this is the case, is there a way to manufacture a
> > zero-pole magnet that is very strong...yet if you put a
> > bunch of them in a box, none would stick together or repel?
>
> There exists no such thing as zero-pole magnets.
Well, yes that's sort of true (see comment above about breaking donut
magnets in two pieces), BUT you could fill a box with a bunch of
horseshoe magnet pairs stuck together and they would not especially
interact with each other. However, with magnets there is always
considerable leakage of magnetic fields so there would be SOME
interaction. It should wouldn't be as strong as un-paired magnets.
OK?
Benj
s...@microtec.net
> s...@microtec.net wrote:
> > On 13 juil, 07:44, Reality Handbook <realityhandb...@gmail.com> wrote:
> > > I don't know much about magnetism. But I read that a donut-shaped
> > > magnet will not have any poles.
>
> > All magnets have poles. See below.
>
> RealityHandbook means external poles. His donut shaped magnet is
> identical to two horseshoe magnets stuck together. N-S etc. They
> don't have external poles but there are "poles" in the sense that if
> you pull them apart each has a N and S pole. Same goes for say a donut
> magnet magnetized like the two horseshoes above. No external poles BUT
> if you take a hammer and break it into two pieces each half WILL show
> poles just like two horseshoe magnets.
Ok I see what he means now. But then I think you need two magnets
magnetized separately to obtain this result. I don't see how a single
donut shaped magnet can be magnetezed this way.
Not correct.
I carried out an experiment that shows that two loudspeaker
magnets obey far field behavior (straight inverse cube relation)
which
means that the field is strongest at the geometric center of such
magnets
http://www.wbabin.net/science/michaud2.pdf
> And the sticking to a refrigerator has to do not only with the
> strength of the magnetic field, but ALSO to the rate of change of
> field as you increase the distance between the magnet and the iron
> refrigerator box.
>
> > > If this is the case, is there a way to manufacture a
> > > zero-pole magnet that is very strong...yet if you put a
> > > bunch of them in a box, none would stick together or repel?
>
> > There exists no such thing as zero-pole magnets.
>
> Well, yes that's sort of true (see comment above about breaking donut
> magnets in two pieces),
I think that it is more than "sort of true".
> BUT you could fill a box with a bunch of
> horseshoe magnet pairs stuck together and they would not especially
> interact with each other. However, with magnets there is always
> considerable leakage of magnetic fields so there would be SOME
> interaction. It should wouldn't be as strong as un-paired magnets.
>
> OK?
Yes. This par is ok.
> Benj
André Michaud