Talk:Diamagnetism

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Physics (Rated Start-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
 

This article has comments here.

possible inaccuracy[edit]

someting is very wrong with the description of diamagnetism, "causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect", this repelling is because the diamagnet is less permeable than air and so the flux desires to go around the diamagnet (easier to go through the air than through the material) which causes the repelling effect. (simular to superconductor Meissner effect) there is an expiriment that demos this by hanging a small bar of glass or a small bar of aluminium between magnet poles the bars align themselves if they are diamagnetic or paramagnetic (Al).information source: http://www.henschke-geraetebau.de/english/Electromagnetic-experiment-apparatus.pdf article should address whichever view is a misconception. finally, shouldnt lenz law repelling cease after magnetism has peaked? and a possible expiriment to confirm is to increase the air pressure, if the reflection on the water is further distorted then the water is not being repelled by the magnet but instead displaced by air. Charlieb000 (talk) 23:33, 19 February 2011 (UTC)Charlieb000 —Preceding unsigned comment added by 121.222.25.57 (talk) 22:32, 19 February 2011 (UTC)

Helium[edit]

I edited the third paragraph to exclude helium. Helium only contains S-shell electrons which have no angular momentum and thus cannot be effected by magnetic fields. Beryllium and magnesium, in their metallic state, have P-shell states which overlap with the S-shell electrons and thus can be paramagnetic at temperatures greater than 0K. —Preceding unsigned comment added by 149.169.54.225 (talk) 20:39, 31 January 2008 (UTC)

Levitating frogs[edit]

I think this article can't be complete until we find a free image of a levitating frog! I'll have a hunt... OK managed to get permission from Nijmegen High Field Magnet Laboratory. CharlesC 14:31, 19 December 2005 (UTC)

I am surprised to be the first to ask this question: since the lab boys now now have gizmo that can levitate anything that can fit inside of it, when can we expect to see a gizmo that can levitate itself?Kalaong (talk) 07:47, 18 April 2008 (UTC)

I think anything that did would have to be Klein bottle-shaped —Preceding unsigned comment added by Tar7arus (talkcontribs) 20:29, 30 August 2009 (UTC)

Explaining the leviation experiment[edit]

(Mouvement, 22 Jan 2005) At the end of the article page, there is a description on how to make a diamagnet leviate. Does anyone know the reason, why this is stable?

I just clarified it, let me know if it does or doesn't make sense.Pkeck 18:54, 6 May 2005 (UTC)

Diamagnetic materials table[edit]

Can you insert a table of diamagnetic materials? i.e.

Bismuth -16.6 Mercury -2.9 Silver -2.6 Carbon (diamond) -2.1 Carbon (graphite) -1.6 Lead -1.8 Sodium chloride -1.4 Copper -1.0 Water -0.91

etc...

Almost everything is diamagnetic. Many metals are para-, a few are ferro-, but dia- is the most common, especially given the wide variety of organic materials. BTW, you forgot the exponents. But here are a few more entries, from Halliday, Resnick, & Krane (ISBN 0-471-54804-9):
Bismuth -1.7 (you have 1.66, which I'll accept) e-5
Mercury -3.2 e-5 (different from yours by ~10%, but HR&K sucks as physics books go)
Silver -2.6 e-5
Carbon dioxide (STP) -1.1 e-8
N2 (STP) -5.4 e-9
And from this site:
Material χv / 10-5
Ammonia -1.06
Bismuth -16.7
Copper -0.92
Hydrogen -0.00022
Silicon -0.37
Water -0.90
Enjoy. --Joel 05:53, 12 May 2005 (UTC)
PS: Whatever compilation table ends up coming together, we should probably mention that the values are volumetric & dimensionless.

I'm not sure why, but the table I got looks like this:

  • Material 2 x(31026)
  • Water 8.8
  • Bismuth metal 170
  • Graphite rod 160
  • Pyrolytic graphite ' axis 450
  • Pyrolytic graphite i axis 85

Tell Me Why!!


This table gives a mu for superconductors of -1E5, but the text says that it should be -1. --Belg4mit (talk) 22:23, 18 April 2011 (UTC)

Never mind, I see that this is to counteract the 1E-5 applied to the table as a whole. It's still potentially confusing and inelegant though. --Belg4mit (talk) 22:35, 18 April 2011 (UTC)

Joel, yes, you or whomever put the table in absolutely should have noted that the values are unitless. --Belg4mit (talk) 22:41, 18 April 2011 (UTC)

Major Cleanup Needed[edit]

I re-added the cleanup and accuracy tags. The tone of the whole article is very informal and inappropriate and there are egregious factual inaccuracies in the superconductor/MRI explanations (for starters). A physicist (or at least someone who really knows what they're talking about) is badly needed to clean this article up. --Deglr6328 04:29, 29 September 2005 (UTC)

You're not the first to say that, and yet no one gives any examples of what they think is wrong. I don't see any informal tone or factual errors. — Omegatron 13:45, 29 September 2005 (UTC)
The diamagnetic levatation section reads like a science fair project when it should actually be a lucid explanation of the physics behind said phenomenon and after that should come a demonstration section. --Deglr6328 23:19, 29 September 2005 (UTC)
Also, in the diagram of the suspended magnet, field lines cross. Field lines NEVER cross. I do not have the means to fix this mastodon 21:55, 26 November 2005 (UTC)

I agree that a major clean-up is required. For instance, the claim that "[a]ll materials, except helium, show a diamagnetic response in an applied magnetic field" is false. Not only is helium actually diamagnetic, there are also many substances that are paramagnetic (e.g. molecular oxygen) or ferromagnetic (iron, nickel, cobalt). Oleg Tchernyshyov (talk) 23:33, 2 February 2008 (UTC)

Also, the section which states "an external magnetic field alters the orbital velocity of electrons around their nuclei" is is an incorrect, classical picture of the electron behaviour. We need a version which gives a quantum mechanical description. I don't expect anyone else to write it, perhaps I'll get around to it. —Preceding unsigned comment added by 202.36.29.1 (talk) 03:15, 14 August 2009 (UTC)

Explanation involving electromagnetic force rather than Faraday's Law[edit]

We changed the explanation of the cause of diamagnetism to reflect the fact that it does not result from electromagnetic induction as described by Faraday's Law. Faraday's Law is an induced electromotive force that results from a changing magnetic field. Diamagnetism exists whether the external field is changing or not; it is the result of the qvxB electromagnetic force on individual electrons. This is incorrectly explained in about half the Physics textbooks we've seen. Any suggestions?

Quantum Spin Coherence In modelling electron correlation effects in close-coupled pairs, I have developed a new thesis of coherent distributed matter-wave spinor interactions. This model, the quantum spin coherence (QSC) model, has interesting ramifications not only in elucidating the underlying physics of diamagnetism, but also - ! - is relevant to the extremely weak orienting force between massive objects that we know of as gravity. see http://homepage.mac.com/blinkcentral/Menu7.html (Paper being presented at 17th AIP Conference, Brisbane Dec 3-8, 2006) [1]--peter g burton 23:53, 14 November 2006 (UTC)

Lorentz force does NOT change the speed of the moving charged particle because the force is always perpendicular to the velocity! Only the direction changes which effectively changes the size of the "current loop" of the orbitting electron (classical picture). Changing the loop size would change the magnetic flux hence current is induced whose field will oppose the applied field.
"Lorentz force does NOT change the speed of the moving charged particle because the force is always perpendicular to the velocity!" 1) That's true only if the electric component of the Lorentz force is zero. 2) An object composed of a multitude of charges having different velocities (i.e. different speeds and directions) can certainly change speed. However, the apparent acceleration or deceleration of a magnetized such object under the influence of a magnetic field only is due to change of the direction, or deflection, of its constituent individual charges converging toward a common direction, which can be achieved without changing any of the speeds of the charges. Thus, the basic cause of the attraction and repulsion of magnets can be explained in an entirely classical sense, though any specifics as a far as the magnitude, structure, and dynamics of such magnets must include a quantum mechanical explanation.siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 + talk
00:51, 18 July 2011 (UTC)

Effect of diamagnetism on water[edit]

Sorry for this being a bit off topic, but I couldn't think of a better place to ask: Using no special equipment, is there any way to demonstrate diamagnetism of water with just a standard magnet?

My ideas were things like putting a magnet into a fine mist, and watch for changes in the density of the mist. Would that work? —The preceding unsigned comment was added by Wierdy1024 (talkcontribs) 23:13, 7 December 2006 (UTC).

A common demonstration of this is to put a very strong NIB permanent magnet (N45 or more if you can find it, and a half inch or more across) at the bottom of a petri dish, and add just enough water to slightly cover the magnet. Google shows several sites with photos of this, such as http://www.matchrockets.com/water/diamagh2o.html ... --Splarka (rant) 08:10, 8 December 2006 (UTC)


I have taken a long soda straw, filled it with water, and frozen it. Then I suspend the straw on a string. Using a powerful rare earth magnet, I can show that the end of the straw is repelled by the magnet. Freezing *really* helps and it seems, the colder, the better. I am using an half pound rare earth magnet that is very powerful...arguably dangerously so. This may not qualify as a "standard magnet". Paul Hite

You don't necessarily need a neodynium magnet to show the effect of diamagnestism. Try filling a petri dish with just enough water to cover the surface, then shine a laser on the water so that you can see the reflection some distance away. Moving even a magnet that is relatively weak compared to neodynium magnets should be able to show an effect by movement of the laser reflection. SunflashX (talk) 05:13, 12 January 2009 (UTC)

vector field terminology[edit]

"Diamagnets are also attracted to field minima, and there can be a minimum..." Wouldn't the diamagnetic be repelled too the field minima rather than attracted to it?

Diamagnetism in the home[edit]

There is a source that can be cited for the last paragraph in the entry: http://www.unitednuclear.com/magnets.htm The second last section on that page is about Diamagnetism and a bismuth display setup kit. 143.117.120.104 (talk) 09:21, 16 January 2008 (UTC)


superconductors are not diamagnetic![edit]

The article states, confusingly, that superconductors may be viewed as perfect diamagnets. However the origin of their magnetization opposing the applied magnetic field is completely different from that of ordinary diamagnets. While in an ordinary diamagnet, such as water, the opposing field is caused by eddy currents. In superconductors it is caused by electron-lattice interactions (cooper pairs). I've added this note to the sentence.

A superconductor acts as an essentially perfect diamagnetic material when placed in a magnetic field and it excludes the field, and the flux lines avoid the region

Superconductors may be considered to be perfect diamagnets (\ \chi_{v} = −1), since they expel all fields from their interior due to the Meissner effect.

Changed to:

A superconductor acts as an essentially perfect diamagnetic material when placed in a magnetic field and it excludes the field, and the flux lines avoid the region

Superconductors may be considered to be perfect diamagnets (\ \chi_{v} = −1), since they expel all fields from their interior due to the Meissner effect. However this effect is not due to eddy currents, as in ordinary diamagnetic materials, see the article on Superconductivity.

--Jaapkroe (talk) 16:40, 18 September 2009 (UTC)

quantum mechanical explenation[edit]

should we get into more detalied QM explaination for how the property arise in the first place in this article? —Preceding unsigned comment added by ArielGenesis (talkcontribs) 20:36, 9 June 2010 (UTC)

The other side to diamagnetism[edit]

"Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field...." This is correct, but it doesn't tell you that:

  • "Diamagnetism is the property of an object which causes it to create a magnetic field in alignment to an externally disapplied magnetic field...."

The cause of diamagnetism is the effect that Lenz's law has on underlying spin currents of matter. Diamagnetism involves resistance to the changes in the magnetic field, and thus diamagnetic materials repel incoming magnetic fields and attract outgoing magnetic fields. This explains why supercooled diamagnetic materials will levitate on a magnetic rail without falling off even when the rail is flipped upside down (click here for examples).siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 + talk
21:16, 12 April 2011 (UTC)

Superconductors don't merely oppose changes in the magnetic field. They expel any magnetic field that is in the body before it becomes superparamagnetic. RockMagnetist (talk) 13:20, 13 April 2011 (UTC)
How is "expelling" magnetic fields mathematically different than subtracting out, in its entirety, the magnetic field (whether pre-existing or not) cutting through the body? I think that any real magnetic field will not be perfectly constant, even in a superconductor, so any increases in the conductivity would seem to act against any magnetic field changes inside the body by allowing Lenz's law to take effect more rapidly, allowing charges to become responsive even to very small fluctuations in the magnetic field, and thereby "deleting" many of the magnetic fields inside the body.siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 + talk
21:46, 13 April 2011 (UTC)
Kmarinas, you're speculating, and plausible as your speculations sound, they're wrong. Superconductivity is a quantum effect.RockMagnetist (talk) 00:08, 14 April 2011 (UTC)
Where did I say that it wasn't a quantum effect? Isn't a superconductivity subset of diamagnetism?siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 + talk
00:37, 18 July 2011 (UTC)

Bad Article[edit]

This whole article is horrible. It was clearly not written by a competent physicist. The mixing of classical Lenz's law statements with Quantum mechanical ideas is childish. Then, the author throws is a description of what fields lines are doing !!! Field lines are NOT Real - they thus do not move. They are a mathematical description. In many classical cases deducing physics from field line 'motions' leads to the wrong answer. This article is such crap that it should be removed in its entirety as it trashes basic physics. Leave physics to physicists. — Preceding unsigned comment added by 165.201.140.13 (talk) 15:42, 20 February 2012 (UTC)

Your objections seem to apply mainly to the lead paragraph (which I agree needs rewording) and a figure. Do you disagree with any other part of the article? Wikipedia authors have many authors. If you don't like the way this article is written, you could edit it. RockMagnetist (talk) 17:42, 20 February 2012 (UTC)

Magnetic levitation[edit]

Earnshaw's theorem seems to preclude the possibility of static magnetic levitation. However, Earnshaw's theorem only applies to objects with positive moments, such as ferromagnets (which have a permanent positive moment) and paramagnets (which induce a positive moment).

Is Earnshaw's theorem even relevant? From what I gather, it only applies in the absence of other forces. For example, take a glass cylinder, and put in two permanent magnets of an opposite orientation, of the same size as the cylinder's diameter. The second magnet will levitate above the first (the magnetic force offsetting the Earth's gravity), and won't be able to move sideways because of the cylinder. - Mike Rosoft (talk) 10:25, 7 July 2012 (UTC)