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Author Topic: What produces the pattern of iron filings sprinkled in a magnetic field?  (Read 10997 times)

Offline PAOLO137

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In a typical school experiment, to show the properties of magnetic field, the teacher puts an
horizontal glass over a magnet made like a bar. Then he drops sparsely some iron filings over the glass, and, with a few
light strikes on the glass (to overcome friction), a beautiful pattern of lines appears giving the students an idea on how
the magnetic field is made.
In between the black lines of iron filings there are clean stripes. Why iron filings avoid that space?
« Last Edit: 22/02/2012 19:02:17 by chris »


 

Offline yor_on

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Re: magnetic field lines of force
« Reply #1 on: 22/02/2012 16:15:14 »
That's a good question, why is there space between those magnetic field lines? I'm not sure, maybe it's possible to explain it from the way light can quench and reinforce itself from a wave picture? Or maybe chaos math could have something to say about it? There you have what it called 'attractors' if I remember right. Places that somehow becomes some sort of focus for/in developing patterns?

"Magnetic field lines similarly describe the structure of magnetic fields in three dimensions.They are defined as follows. If at any point on such a line we place an ideal compass needle, free to turn in any direction (unlike the usual compass needle, which stays horizontal--such needles exist, see bottom of page) then the needle will always point along the field line" from Magnetic field lines.

Magnetism is really interesting from a lot of points.
 

Offline syhprum

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Re: magnetic field lines of force
« Reply #2 on: 22/02/2012 16:27:27 »
Of course the magnetic field does not consist of lines of force they a mathmatical atifact the field is continuous. the fillings have a degree of magnetism induced in them and tend to line up with north and south poles together with adjacent lines repeling each other. 
 

Offline yor_on

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Re: magnetic field lines of force
« Reply #3 on: 22/02/2012 16:41:15 »
Hmm. The field lines are what 'attract' electrons, ions and protons around themselves as I understands it. As you say they are described mathematically, but you can also find them in 'reality', as proven by any experiment with iron fillings and a magnet. I'm not sure it's a 'continuous magnetic field' although one might argue so? Maybe it is in a way, same way as you might argue that even though there is 'gravity' everywhere in SpaceTime you can still, in deep space, find patches where that 'gravity' becomes unmeasurable. Or for that sake argue that in any 'uniform motion' gravity disappear.

"Magnetic field--space modified by magnetic forces, so to speak--is one thing, and magnetic field lines are something else again. They are a mathematical description of that field, no more tangible than lines of latitude and longitude which describe the surface of the Earth. One never asks how close THOSE lines are; you can draw any number of them, depends how tightly you are willing to space them.

Magnetic field lines are defined as lines that point everywhere along the magnetic force (in a fluid, a complete analogy is given by flow lines or "streamlines"). They can be described by formulas, in terms of quantities known as Euler potentials or Clebsch functions.

But there also exist intuitive properties: particles threaded by a common field line, tend to share that field line later on as well. Say we have 10 ions numbered 1... 10 sitting on a common spot on the Sun, and therefore sharing there a field line, and destined to come out in the solar wind one day apart. The Sun rotates, so make a drawing with a circle representing the Sun and 9 radial lines coming out about 15 degrees apart. After 10 days, particle #1 is 2.5 inches along the first line, particle #2 2.25 inches on the 2nd one, and so on, down to particle #10 still on the surface: the line conecting the particles is a spiral, so we expect interplanetary field lines to have a spiral shape, and we derived this from intuitive concepts alone (though the same thing can be derived from formulas).
  The details of this excercise are described in http://www.phy6.org/stargaze/Simfproj.htm.

The spacing between field lines is not meaningful (though some engineers speak of "density of magnetic field lines" to describe a quantity commonly known as "flux density.") Suppose you draw two field lines of the Earth, reaching Earth 1 meter or 1 foot apart. Each can have electrons or ions trapped around it. The meaningful question is what is the radius of the circle these electrons or ions describe around their guiding line, and that depends on their energy, and how strong the field is (the circle gets larger in the weak fields far from Earth), but it is generally much more than 1 foot or 1 meter. No problem: densities are so low that such ions or electrons rarely collide, and their orbits can easily overlap. The radius of gyration of auroral electrons can be 100 meters, which is why auroral "curtains"are so thin. On the other hand, solar wind ions entering near the "nose" of the magnetosphere have radii of the order of 500 kilometers, or (say) 350 miles, because the field there is much weaker, and that is therefore the order of the expected thickness of the magnetopause, the boundary between the solar wind and the magnetosphere." From By David P. Stern
 

Offline yor_on

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Re: magnetic field lines of force
« Reply #4 on: 22/02/2012 17:07:30 »
If I assume that radiation is the 'carrier' of EM, and then state that there is no limit to a photons propagation, then I also have to conclude that there should be no limit to a magnetic fields 'propagation', that is if I'm thinking right here. Doing so I then live in a SpaceTime filled with Gravity, Electricity and Magnetism (EM aka photons). And assuming that the magnetic fields are limitless, as well as each one filling 'all space' no matter what the iron fillings show me, SpaceTime becomes a very magnetic vision :)
« Last Edit: 22/02/2012 17:34:56 by yor_on »
 

Offline wolfekeeper

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In between the black lines of iron filings there are clean stripes. Why iron filings avoid that space?
What's happening is that each of the iron filings become magnetised by the field, so they produce north and south poles at each end, other iron filings that are nearby get magnetised, not only by the overall field, but also by the other filings, and so they tend to stick- end-to-end.

If there's a lot of filings they're just happy to just fill up the space, but if you lower the amount of filings, they prefer to stick end-for-end, rather than side-to-side because that would involve two similar poles being close to each other, and by sticking end-for-end they form the 'field lines' that you see.

The shape of the field lines isn't quite the same as when the filings aren't there though, the filings tend to short circuit the field, because the magnetic permeability of filings is much higher than free space, so the field becomes closer to the magnet when they're present.
« Last Edit: 23/02/2012 13:38:24 by wolfekeeper »
 

Offline JP

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If I assume that radiation is the 'carrier' of EM, and then state that there is no limit to a photons propagation, then I also have to conclude that there should be no limit to a magnetic fields 'propagation', that is if I'm thinking right here. Doing so I then live in a SpaceTime filled with Gravity, Electricity and Magnetism (EM aka photons). And assuming that the magnetic fields are limitless, as well as each one filling 'all space' no matter what the iron fillings show me, SpaceTime becomes a very magnetic vision :)


You've discovered field theory, Yor_on.  ;)

Field theory is an area of physics that describes the properties of fields by assuming they fill all space-time and take on values at different points in space-time.  Knowing those values, as well as rules governing the behavior of the fields (how they move about and interact with matter and other fields) allows physicists to model their behavior. 

Classical field theory doesn't use quantum mechanics.  You could view Maxwell's equations for electromagnetism as describing classical fields.  The electric and magnetic field fill all space-time and have properties given by Maxwell's theories.  Maxwell's equations do not predict a smallest piece of the fields: you could take smaller and smaller energy pieces without limit.  When scientists discovered quantum mechanics, they naturally asked what the smallest pieces of energy in electromagnetic fields were, and came up with photons, which led to QED, which is a quantum field theory.  QED explains the connection between photons and the larger-scale structure of fields.
 

Offline wolfekeeper

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FWIW far from being a magnetic universe, Einstein was of the view (which I agree with, given the apparent non existence of magnetic monopoles- so far) that magnetic fields don't really exist; all known magnetic fields are associated with moving charges, and from the point of view of a charged particle that you might think is being curved by a magnetic field, it's always a net electrical field that it actually feels, not a magnetic field that is accelerating it(!)
« Last Edit: 23/02/2012 14:41:04 by wolfekeeper »
 

Offline syhprum

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Wolfkeeper

May I refer you to my post of 22/02/2012 16:27:27 where I said exacly the same thing.
« Last Edit: 23/02/2012 16:27:19 by syhprum »
 

Offline wolfekeeper

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More or less. Actually the lines don't tend to repel each other very much, because the North and South poles tend to cancel each other out, but they do attract each other quite strongly at the ends, aligned with the field, so most of the metal ends up along the lines.
 

Offline greeniemax

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Iron filings don't leave space but space is created when iron filings line up with the magnetic field.

If you put huge amount of filings you wouldn't see any spaces between the two lines, if you are asking why is that line left its because of most iron filings line up in the line that was created, iron filing is better conductor of magnetism compared to air and thus two iron filings like to align with each other than randomly.
 

Offline yor_on

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Ah, but didn't Einstein also say that, as I see it, due to frames of reference you can define a purely magnetic field without any electrical component? I remember reading that somewhere? And it been stuck in my mind since then :). It all goes to question how seriously you should take a 'frame of reference' if I now remember right. We all live 'locally', with our own ruler and clock defining SpaceTime, so, assume that you find a magnetic field in the manner described.. Is it 'real' or would you call it a 'illusion'.

I think ..
 

Offline yor_on

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Yeah JP :), I like fields, but ? I don't really know what it means. Assume all those bosons we can't 'measure', are they a 'field' too, or 'corpuscles'. We say that light (radiation) are waves and 'photons', what if it is a field, neither waves nor 'photons'?
 

Offline wolfekeeper

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Ah, but didn't Einstein also say that, as I see it, due to frames of reference you can define a purely magnetic field without any electrical component? I remember reading that somewhere? And it been stuck in my mind since then :). It all goes to question how seriously you should take a 'frame of reference' if I now remember right. We all live 'locally', with our own ruler and clock defining SpaceTime, so, assume that you find a magnetic field in the manner described.. Is it 'real' or would you call it a 'illusion'.

I think ..
It's an illusion. In the rest frame of a charged particle, the existence or non existence of a magnetic field is irrelevant, since the Lorentz equation is:

F = q( E + v x B )

but if v is zero the B is zeroed out, and it becomes:

F = qE

So any acceleration, in any other frame, must have been caused by the electrostatic potential in the charged particles rest frame. So we can see that the B is fictitious and is caused by us not being in the rest frame of the charged particle. B is basically just an accountancy thing that humans have invented to deal with that.

That doesn't quite prove that there's no B field, but it's pretty strong evidence I think. If there was a magnetic monopole the argument would fail though, because a moving magnetic monopole would create an electric field, and in that monopoles rest frame, the electric field would not affect it.
« Last Edit: 26/02/2012 20:53:11 by wolfekeeper »
 

Offline yor_on

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Moving magnet and conductor problem.

In it it states "The observable quantity in the experiment, the current, is the same in either case, in accordance with the basic principle of relativity, which states: "Only relative motion is observable; there is no absolute standard of rest"."

That one seems questionable to me. If motion, excluding accelerations, is relative the 'observer', then that is a 'local' statement of the same dignity as when a observer defines something as being 'still' relative himself. What I mean there is that if you have no way of proving 'who' is moving relative whom, then you're free to define it all possible ways, including defining something as being 'at rest' relative your 'relative motion'.
« Last Edit: 26/02/2012 22:21:43 by yor_on »
 

Offline origami

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Fields were invented to explain action at a distance. The only difference is that they are graduated therefore their strengths can be measured. For millennia people have played with magnetic iron filing patterns which suggest that something emanates from one pole and travels around to the other. When it was discovered that a current spinning around a solenoid also generated the same effect on iron filings as magnets did early scientists adopted the same polar principles. They were so committed to the old science that they simply ignored the blindingly obvious fact that the magnetism spins parallel to the current. Thus magnets have clockwise and anticlockwise magnetic poles. They generate magnetic vortexes which obey Bernoulli principles. Co-parallel flows attract, anti-parallel flows repel. Magnets are a construct of thousands of same spinning magnetic vortex columns held together by atomic forces. The magnetism is moving anti-parallel at the interface between neighbouring columns therefore the columns are mutually repulsive. When the vortexes emerge from the poles they are free of atomic restraints so they spray out. Some of them unite with the sprays from the other end. They are self repulsive so spaces occur between filing lines.
 

Offline wolfekeeper

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Yes, what you say origami is pretty much true. It's just the motion of the electrons in the magnetic material creating an electrostatic field that appears when there's external motion (including motion within other magnetic materials), but disappears, cancels when there's none. The 'vortexes' as you put it don't leave the magnetic material.
« Last Edit: 27/02/2012 12:16:31 by wolfekeeper »
 

Offline yor_on

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Offline origami

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Wolfekeeper
If as you claim the vortexes donít leave the magnets, how do counter the simplicity of describing the forces on a charge moving through a magnetic vortex. Co-parallel motions attract and anti-parallel motions repel. If it goes in one direction diagonally through the vortex, it is both pulled up from above and pushed up from below; in the reverse direction it is pulled and pushed down. There is no insane right hand screw rule required. Conventional magnetic theory has magnetism incorrectly running perpendicular to the event. This is not the first time science has got it wrong. viz Copernicus.
 

Offline JP

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Origami, you seem to be heading in the direction of proposing a new theory there.  This forum is primarily for answering science Q&A in terms of established theories.  To prevent topics from being derailed, I'd like to ask you to take discussions about overturning mainstream physics to the New Theories forum:
http://www.thenakedscientists.com/forum/index.php?board=18.0

Thanks,
JP (moderator)
 

Offline Razza

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Perhaps origami is reading Taylor's work on magnetic ether flow
 

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