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Proper magnetic monopoles are Things of Mystery, up there with
gravitational waves.
But.
It would seem embarrassingly easy to make a synthetic magnetic
monopole, or at least a monopolar magnet (which may not be quite
the same thing). So easy that I am sure someone will tell me why
this
can't be done, or else will tell me it has been done, or both.
We start, naturally enough, with a Terry's Chocolate Orange (see
link). However, we make this one not out of chocolate, but out of a
samarium-cobalt-nickel alloy - the stuff from which they make very
powerful rare-earth magnets.
We dismantle our orange into its constituent segments. We take the
first segment, and magnetize it such that the North pole is in the
middle of the thin, inner edge, and the South pole is along the wide
outer edge. (In effect, it's just a very wide, short and distorted bar
magnet).
We then take the second segment, and magnetize it in the same
way.
We then take the third segment and - here's the clever bit - we
magnetize it too in exactly the same way. And so on for all the
segments.
We now reassemble the orange. Of course, the segments will repel
eachother (or try to flip around and then stick together in mutually
inverted orientations), but no matter. Even very strong magnets can
be forced together against their repulsion - the force does not climb
to infinity. (In fact, a standard bar magnet can be thought of as two
narrower bar magnets glued together side-by-side, against their
mutual repulsion). We use superduperglue to hold the segments
together.
Lo and viola! We now have a spherical magnet in which the North
pole is all tucked away on the inside, and the outside is pure South
pole!
Such a beast would appear strange, and indeed odd. It may even
have some application.
Terry's Chocolate Orange.
http://1.bp.blogspo...e-Orange-737720.jpg
[MaxwellBuchanan, Jun 30 2010]
Halbach Array
http://en.wikipedia.../wiki/Halbach_array
Not a monopole [csea, Jul 01 2010]
Maxwell's Equations
http://users.aims.a...ll's_equations.html
No monopoles, sorry. At least not without magnetic charge. [ldischler, Jul 01 2010]
No monopoly on monopoles
http://www.sfgate.c...-Magnet-5189984.php
[theircompetitor, Jan 30 2014]
Dirac equation
http://en.m.wikiped...wiki/Dirac_equation
Matrix extrapolation of Erwin's masterpiece. [8th of 7, Jan 31 2014]
Mono....
http://www.scientif...T.mc_id=SA_Facebook
You know..... for poles. [4whom, Jan 31 2014]
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Do you then re-wrap the foil on the outside ? |
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What about the clear plastic bit, and the cardboard box ? |
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The idea is unworkable, since it singularly fails to unify the five fundamental forces; Gravity, Electromagnetism, Strong nuclear, Weak nuclear, and Chocolate; although proponents of the "chocolate" and "fruit and nut" quarks might disagree. |
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The so called "God" particle, the Higgs Boson, is now thought to consist of 30 % Milk, 30% Plain, 30 % White, 8 % hazelnut and 2 % rum. |
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How about using it to make Newton's Cradle of Never Meeting Balls? (that's an idea I've had for a while, but was only thinking of embedding opposing bar magnets through each of the balls) |
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[8th] You're thinking of the Milky Way. |
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<pre-empt>Milky Bar magnets, Mars Bar
magnets</pre-empt> |
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[MaxwellBuchanan] Did you think of this because of
the Tension-Compression balanced Flywheel? |
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Actually the idea had been in my head for a few days, since I
bought some stupidly strong magnets. But oddly, yes, the
Flywheel idea did prompt me to post it. |
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// the idea had been in my head // |
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What a shame it didn't stay there. |
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//What a shame it didn't stay there.// Better out than in. |
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Suppose you make a helical wire and thread a bunch of these
thing on it like doughnuts strung on a telephone handset
cord, but smaller. Now join the ends of the
wire, to make a bracelet, with a lightbulb in place of the
clasp.
Can you make the bulb glow by swinging your wrist? |
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I want to fill a ball pit with these and dive in. |
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I remember this idea was posted before, but it seems to be gone. In any case, you can't build a monopole this way. The field lines will escape. A more interesting arrangement is the Halbach array. Bend it into a cylinder and you can have no field inside, or no field outside. You can even make a Halbach sphere. |
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//Attractive// Shouldn't the subtitle be "Repellant" as each sphere will repel all other similar ones? |
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//The field lines will escape.// |
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I knew there must be a flaw. At what point does it
happen? For example, a hemispherical shell can be
magnetized with one pole on the "inside" face and one on
the "outside" face. Presumably, something which was
slightly more than a hemisphere (ie, a spherical shell with
slightly-less-than-half sliced off) can be similarly
magnetized, and perhaps also something which was even
more of a sphere (ie, a shell with a "window" cut in one
side). |
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So, at what point (as we "grow" the shell towards
completion) does the whole thing stop working? |
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I think it will work fine as long as the fields are "localised" to the centre portions of the inner and outer surface. I'm sure this is possible. |
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Is there any clockwork involved? |
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oh for goodness sake - now I NEED chocolate... |
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//So, at what point (as we "grow" the shell towards completion) does the whole thing stop working?// |
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This is all you need to know: Del dot B = 0
But you should already know that. It comes from Maxwell's equations.
The integral form is a little easier to understand as it says that the integral of flux over any closed surface is zero. So at no point does your shell work. The only way to make a monopole is to start with a monopole and no convincing evidence for monopoles has ever been discovered. |
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//no convincing evidence for monopoles has ever been discovered// |
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I have an old box of monopoles here. It says they were made by John Waddinton Ltd. |
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Given real world assumptions, some section of the magnet will have a slightly weaker magnetization than the rest. This will then become the nominal pole whereby the majority of the flux escapes from the inside of the sphere. |
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Under perfect assumptions with perfectly uniform magnets I can't make up my mind how it would fail. Either, the flux would radiate uniformly throughout the shell, producing an essentially non-magnetic result, or a single point would still be overcome, turning the entire sphere into a simple two pole magnet. |
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//I have an old box of monopoles here. It says they were made by John Waddinton Ltd.// |
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Ah! The rare Egyptian monopoles. |
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//it comes from Maxwell's equations.
The integral form is a little easier to understand as it says
that the integral of flux over any closed surface is zero. So
at no point does your shell work.// |
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First, that would probably my eponymous great aunt,
Maxwell Xavier Buchanan. We didn't talk a lot, even after
they let her out. |
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Second "at no point does your shell work": if you mean
that even a partial shell won't work, then you are
definitely wrong. Imagine, for example, a disc magnet
with its two faces as the poles (these exist - I have many).
Now (conceptually at least), squeeze this magnet a little
to make it into a very shallow dish. Its magnetic
properties will remain intact, but it is now a part of a
spherical shell. |
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So, my question really equates to this: in deforming a
large disc into a dish, a bowl, a hemisphere, and so on
towards becoming a complete sphere, at what point does
the magnetism stop working? |
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well, it obviously works for a horseshoe shape. I wonder if increasing the density as you approached the center would help any... mind you the center of a solid ball would *not* be a happy place. |
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It needn't be solid; in fact I was sort of counting on a small
void in the middle of the Chocolate Monopole. But even a
shell would be fine. A magnetic Easter egg. |
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When I said at no point does the shell work, I meant that there is no characteristic of a monopole at any point in its construction. If you draw a closed surface around it, the net flux through that surface is always zero. If it were a monopole, there would be a net flux. No dipole magnet has a net flux no matter what shape it has. This has nothing to do with "magnetism not working." It has to do with it not acting as a monopole. |
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//It has to do with it not acting as a monopole.//
If I take a piece of paper, white on one side and black on the other, and fold it up until it's a dodecahedron with only black on the outside... then it's a black dodecahedron. |
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I imagine if you had a pentagonal crossection bar magnet, you could chop that up and put it back together as a 12 sided "monopole"... no? |
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no. The magnetic field lines must form closed loops from N to S. A magnetic field line can't just stop. In your example, I would guess the magnetic field lines will just squeeze through the gaps between the magnets. |
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//squeeze through the gap between magnets//... so if you took a standard bar magnet, sliced it longitudinally then glued it back together the same as it was before... ... ? |
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I asked my physics teacher about this when I was in school. My variant of it was to make two hemispherical shells and then squeeze them together. |
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He admitted that he wasn't actually sure what would happen. |
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We ended up thinking that some of the magnetic material would end up getting remagnetised in the opposite direction as the flux lines tried to escape. |
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Quite possibly the result would be no magnetic field I.e. It is all just cancelled out. |
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//It is all just cancelled out.// |
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Right. The source of magnetism is mostly the spin of the electrons, which, in most materials, cancel each other out because they're paired with electrons of opposite spin. Materials like iron have many unpaired electrons so the iron atoms are miniature magnetic dipoles. Point all the atomic dipoles in one direction and you get a macroscopic field but it's still a dipole field. No matter what you do, it's always a dipole field. In the spherical magnet case, if it's perfectly symmetrical, the exterior macroscopic field will disappear even though at the atomic level, the dipole fields will be just as strong. Think of putting a keeper bar on a horseshoe magnet. The exterior field disappears and is channeled into the keeper. In attempting to make a monopole, the field is channeled back into the metal of the sphere. |
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I there was small tail attached to the sphere and one eye painted on it, could it be a mono-tadpole? |
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[ldischler] I could be wrong but I think we're striving for a "monopole" in the sense of say a bowling ball sized sphere where the outside is N and the inside is S, not a *real* monopole. |
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I sort of covered this one with Gyrosphere. I never did get a satisfactory answer about why it wouldn't work, other than the magnetic fields would cancel each other out over time. |
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Spheres within spheres within spheres within... |
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//I could be wrong but I think we're striving for a "monopole" in the sense of say a bowling ball sized sphere where the outside is N and the inside is S, not a *real* monopole.// |
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Yes, I know. And it's impossible by Maxwell's law as I said before. Del dot B = 0 |
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I'm happy with LDischler's answer, though I am still curious as
to what actually happens. If I made the "shell" as described,
but left a small hole in it, would all the field lines from the
inside squeeze out through the hole and wrap around to the
outside? Would the field in the hole be very strong? I mean,
like, just, what?? |
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And what's meant to happen in the case of a *real*
monopole? What do its field lines do? |
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so.... you're saying (or claim that Maxwell's saying) that if you have a magnet embedded in a steel plate (like say a cabinet door) N on one side, S on the other, that it won't work because there's no clear path between physical poles |
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The integral form of "Del dot B = 0" says if you draw a closed control surface in three dimensions, then the flux going in equals the flux going out. So a magnet is fine, it has a net flux through that surface of zero. Half a magnet is fine too, as the net flux is also zero. A million magnets are fine. Throw in chunks of steel and wood, that's fine. But you never have a case where those magnets look like a monopole with flux going out but not coming in, no matter what the geometry. They always look like a dipole (or quadapole, etc.), or else they're nonmagnetic. |
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You can modify the equation to account for the possibility of a real monopole (ie, a particle with magnetic charge) but it still gives you a zero net flux for ordinary matter. |
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If you have that magnet imbedded through a steel plate, you will find that the steel itself develops a magnetic polarization, such that the section around the north end of the magnet is south and vice versa. The net result will pass the magnetic field through the steel plate. |
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If you're worried about flux escaping, just post
some Rottweilers |
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I'm still curious. If I had a magnetic monopole in my hand,
how would it behave? Would it attract iron things? Would it
repel one pole of a bar magnet and attract another? Would it
induce a current if I moved it across a wire? |
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Well [MB}, according to [ldischler], whatever was in your hand would have no flux, and so would be magnetically inert... have we just proved that a magnetic monopole is impossible, or that it is non-magnetic? |
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I suspect it might be very lonely... |
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In any case, there are about 7 monopoles: the top hat, boot,
racing car, couple of others I can't remember, and the wee
Scotty dog. |
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Actually, there's only one significant monopole - brut. |
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But still curious about what a monopole is like. |
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In some ways, electric fields are analagous to magnetic - and there is basic electric theory for point charges. Just pretend that they're the same, in terms of attraction & repulsion of other magnetic nodes (like +ve & -ve charges). |
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If your curiosity extends to other effects then it might get a bit more hairy. That's where the various Maxwell's equations will kick in and the pretence above might fall apart. |
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I've left behind all my undergrad knowledge of Maxwell's & appropriate physics but I think that the basic aspect that you have to get your head round is that while a point charge (e.g. electron) would have uniform electric field lines eminating out perpendicularly to the surface of an imaginary sphere, equi-centred on the charge, the magnetic 'point' (and monopole candidate) at atomic level will have the magnetic field eminating like a torroid - North at one end, looping round to the South at the other. |
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//the magnetic 'point' (and monopole candidate) at atomic
level will have the magnetic field eminating like a torroid -
North at one end, looping round to the South at the other// |
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But I thought the point of a monopole was that it only had
one pole? |
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So where is the other pole if it doesn't have it? |
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[Jinbish] train motorbike tank? |
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[pocmloc]: hmmm... Not sure. They don't ring any bells. At
this rate I'll have to look it up on the intarweb. |
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[MaxwellB]:?I'm really pushing the cogs in my head now... No.
The point of a monopole is that it is a theoretical Pooh Stick.
Imagine you
have a magnet, with an understanding of the flux density
surrounding it. To calculate the force applied, in theory, to
another magnetic object, you perform the calculation with a
single point as if it were a monopole and then integrate... |
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{Cripes. I've just realised it is over 12 years since I studied
*any* of this...} |
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The issue with an actual existing monopole is that it would be
akin to saying that something had a top, but not a bottom.
Magnetic flux lines run in, through, and out of a magnet.
Electric flux lines radiate out. |
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//The issue with an actual existing monopole is that it would be akin to saying that something had a top, but not a bottom. // |
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No, that’s not the issue. Magnetic charge is perfectly analogous to eclectic charge. If you modify Maxwell's equations to allow for magnetic charge, they become symmetrical, and symmetrical equations are more likely to be the real equations. So they make sense and the equations are prettier with them than without them, but that’s not enough to make them real. |
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OK, as I understand it, monopoles may exist but haven't
been convincingly shown. I also understand (soooooorta)
the idea that a regular magnet is only a regular magnet
because the flux lines run from one pole to another, and
therefore my pseudomonopole won't work because the
flux lines can't run from its external "south" pole to the
internal "north" pole. |
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First question: what if I make my "shell", but leave a
teeny hole in one side? Do all the flux lines dive through
the teeny hole? And if so, is the field very strong around
the hole? |
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Second question: if I did have a monopole in the palm of
my hand, how would it affect iron filings, "normal"
magnets, and suchlike? |
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I don't know much about monoples but here's what I reckon (for what it's worth). |
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//First question: what if I make my "shell", but leave a teeny hole in one side? Do all the flux lines dive through the teeny hole? And if so, is the field very strong around the hole?// |
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//Second question: if I did have a monopole in the palm of my hand, how would it affect iron filings, "normal" magnets, and suchlike?// |
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If a monopole attached to a piece of iron then that piece of iron would act as a monopole. If a monopole was in the vicinity of a magnet it would be attracted to – and stick to – one end of the magnet. |
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//If a monopole attached to a piece of iron then that piece of iron would act as a monopole// so the monopole and the iron filing would then repel each other? |
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//First question: what if I make my "shell", but leave a teeny hole in one side? Do all the flux lines dive through the teeny hole? And if so, is the field very strong around the hole?// |
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You'll reach a maximum flux density as you shrink the hole and then it will begin to decline and reach zero as you close it off. At that point your perfectly spherical magnet will show no magnetic field at all. A less symmetrical situation is to press the flat faces of two cylindrical magnets together. If you press like poles together, that ought to reduce the sticking power of the opposite poles, esp. if the magnet is much wider than it is long. You could also use modeling clay or a stiff epoxy to assemble 6 square magnets into a cube, making a crude version of your mono-sphere and see what happens. |
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//Magnetic charge is perfectly analogous to eclectic
charge.// |
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I'd once been charged with being eclectic, but the
charges didn't stick because I was too one-sided. |
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//First question: what if I make my "shell", but leave a teeny hole in one side? Do all the flux lines dive through the teeny hole? And if so, is the field very strong around the hole?// Yes (but no) and yes. |
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I have a way of explaining this in terms of superposition that to me seems fairly simple to understand. I don't know if it is actually accurate, but it makes sense to me and I don't know of anything contradicting it. |
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My understanding is that there is no way to block or distort the magnetic field from a magnetic dipole. You can add other magnetic fields that partially or even fully cancel out the magnetic field when they are added together, and if you put a real magnet in a strong enough field you may be able to cause the magnetic dipoles inside the magnet to move either temporarily or permanently, but if you could sum up the fields from all of the dipoles in their current orientation, you could calculate the resulting field. |
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I saw one site that said superposition of magnetic fields does not work exactly except in a vacuum, but my understanding is that is does work as long as you take all the dipoles in the material into account. These dipoles will change alignment in the presence of another magnetic field, and their magnetic field will cancel and/or augment the other fields. The way the dipoles move relative to external fields depends on the property of the material (ferromagnetic, diamagnetic, etc). |
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When you construct the perfect sphere, nothing amazing has to happen. There is no need for there to be "leakage" through cracks or demagnetization. It's just that if you have a perfect sphere of uniform magnets, all of the magnetic fields from all of the magnets will perfectly cancel. |
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When you have one magnet missing, the field in that hole is really intense, because the magnets that are in place are creating a perfect inverse of the field of the magnet that is missing. The field in the hole has a higher flux density than the field from the missing magnet because you can only measure the field on the exterior of the single magnet, but you can measure the field in the interior of the hole. |
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So back to your original question: "Do all the flux lines dive through the teeny hole?" If I just answered that question with a yes, someone might infer that the flux density would approach infinity as the hole became arbitrarily small. Based on my explanation, the flux density approaches the flux density in the core of a piece of the magnetic material being used. When you shrink the hole by adding more magnets around the edge of the hole, the field from those magnets does increase the flux density in the hole, but a lot of that field is going around canceling out other bits of field. As the hole gets smaller, each magnet added causes less and less increase in the flux density. Of course if you draw the flux lines, all of them _will_ be diving through the hole, but as the hole gets smaller, there will be fewer and fewer lines until the hole finally closes and there are no lines at all. |
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No, that's an invalid argument, because
you're proposing that delta-x -> 0 for any
minimal value of r which contradicts the
Dirac equation (q.v.) |
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People are actually now implying that this new B-E condensate monopole is actually this orange as mention in the idea. |
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On reflection, I'm against magnetic monopoles.
Everyone should be free to use magnets. |
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I was pondering monopoles again (the hypothesized particles
this time, not artificial ones made out of magnets). I was
wondering whether a smattering of monopoles of a single
polarity (eg, all south) would be enough to explain dark
energy. |
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Also, why are pondering and pandering not pronounced to
rhyme with wondering and wandering? |
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