Talk:Meissner effect

message: as I was doing the same mistake in a presentation that a gave about superconductivity, I want to note that the picture with the hovering magnet above a superconductor os not the observation of the Meißner-Ochsenfeld effect. The observation of a flying magnet is due to the creation of vortices in a type II superconductor.. see shubnikov state..
The Meißner effect cannot explain the force that elliminate the gravitation.. since the picture suggests that this effect is the reson for it I would replace it..
cheers
--Xeltok (talk) 18:07, 20 January 2009 (UTC)
thread_title: wrong picture

message: Article needs a section on what the potential practical applications may be for the Meissner Effect.
66.227.84.101 (talk) 21:41, 8 November 2008 (UTC)
thread_title: Article Needs A Section on Potential Applications

message: Much is left to be said about the Meissner effect, including experimental methods for measurement and historical discussion.  Overall, the page is lacking in content.
As in too many of the physics explanations on Wikipedia, the explanation of how the Meissner effect works assumes the reader is nearly a physics expert and is inadequate at best for general science readers with reasonable backgrounds in the physical sciences.   —Preceding unsigned comment added by 75.104.128.58 (talk) 00:19, 18 June 2008 (UTC)
thread_title: Article too brief

message: The meissner effect is distinct from perfect diamagnetism arising from zero resistance. The theory described in the article, as it stands now is wrong. There's no reference to the london equations. I lack the time, so can someone fix it? I'll try editing myself if I have the time siddharth 08:28, 8 June 2006 (UTC)
replies: text: There, I've showed that the meissner effect is distinct from perfect diamagnetism. siddharth 18:07, 14 June 2006 (UTC)
thread_title: Factual inaccuracy in theory

message: How was this discovered?  — Omegatron 01:49, 19 June 2007 (UTC)
thread_title:  History? 

message: from the illustration given, it's unclear whether the Meissner effect can be used to focus a magnetic field (as with a parabolic solar oven focusing light) or if the material used simply stops the magnetic field from going beyond the material's penetration depth.
38.99.84.53 (talk) 17:37, 4 April 2008 (UTC)
replies: text: Like a rock in a stream, the field is simply expelled from the material, and go around it, generally. 150.35.244.246 (talk) 01:14, 13 June 2012 (UTC)
thread_title:  absorption, or reflection? 

message: The article says that "Observation of the Meissner effect is difficult, because the applied fields have to be relatively small (the measurements need to be made far from the phase boundary)."  It also shows a refrigerator magnet levitating over a superconductor.  I assume that what the original author meant is that measurements of the Meissner effect are difficult because using a particular method of calculation requires a small applied field, but I'm no expert. Wnt (talk) 21:46, 21 May 2008 (UTC)
thread_title:  Apparent contradiction 

message: Is the Meissner effect a property of all superconductors or just Type-I superconductors? I ask because Talk:Yttrium barium copper oxide suggests it does not apply to Type-II superconductors. Rod57 (talk) 00:59, 5 September 2008 (UTC)
replies: text: I believe the Meissner effect is a property of all superconductors, and can be derived by the application of Faraday's law of induction to the surface of the superconductor.  As the flux attempts to cut the surface it induces surface currents that cancel out the original field (by Lenz's law). As far as I can see the type II discussion is talking about penetration beyond a certain field strength.  I believe (although am less sure) that this is also common to all superconductors. --Michael C. Price talk 13:26, 30 June 2009 (UTC)

text: Following some of the external links I see that In Type II superconductors the magnetic field is not excluded completely, but is constrained in filaments within the material. So depending on how you define the Meissner effect you could argue it either way, since the interior of the filaments are not superconducting themselves. --Michael C. Price talk 19:26, 30 June 2009 (UTC)
thread_title:  type-II type-I 

message: Some friends I know from the nearby University have started studying the Meissner affect. We know it affects magnet, but everything generates magnetism from their mass, so we were wondering if Biological objects like plants or even people can be suspended using this effect?84.92.16.13 (talk) 16:25, 10 November 2008 (UTC)
replies: text: In some sense a superconductor is a perfect diamagnet. Living things tend to be weakly diamagnetic, i.e. they naturally repel magnetic fields to a tiny degree. Good diamagnets such as pyrolytic carbon will happily levitate over a suitable geometry of regular shop-bought Neodymium-Iron-Boron supermagnets. Living things can be magnetically levitated but typically require unusually strong fields. I've seen a video of a frog being levitated inside what I think was an NMR cavity and the same was recently performed with a mouse, attracting some media attention. This could entail anything between 1 and 20 tesla fields. I'm willing to guess that people have studied protists and such in similar conditions. Suffice to say that you can suspend biological objects but it requires tremendously strong fields even for small objects. For comparison, the strongest permanent magnet created thus far has a strength of ~5 tesla. NMRs use Superconducting magnets. Eutactic (talk) 04:53, 2 December 2009 (UTC)
thread_title:  Biological? 

message: The section titled "Observation" is incorrect. First of all, measurement of the Meissner effect, to a satisfactory number of significant figures, predate the 1985 discovery of high-temperature superconductor by a generation or more. For example one might wind a coil of insulated copper wire around the sample (carefully noting the number N of turns). Now place this - in a Dewar containing liquid helium -  between the poles of an electromagnet. Next turn the electromagnet on while the sample is still a normal conductor  and measure the time integral of the induced voltage - using an Integrating Voltmeter. This voltage impulse - in volt-seconds - equals N times the flux admitted - in webers. Now cool the sample through the superconducting transition and obtain the FLUX EXPELLED (Meissner effect), Then compare the two!
The section titled "Observation" also erroneously implies the levitation of a permanent magnet by a superconductor was possible only with high-temperature superconductors. Not so! 
Finally, statements implying that still-photographs of "Levitation of a Permanent Magnet" prove the Meissner effects are erroneous. If you bring the magnet to the superconductor from a distance and it ends up levitating, you have only proved the PERFECT CONDUCTIVITY of the superconductor! On the other hand, if you FIRST place the magnet on the surface of the sample in its normal state and THEN cool it down into a superconductor, THEN, IF IT JUMPS UP AND LEVITATES, or shows that it is trying to do that, with, say, one pole up and the other trapped, THAT WOULD PROVE THE EXPULSION OF FLUX (Meissne effect.) -- Alfred Leitner
:I have undone the deletetion. Before this edit by me it said that the Meissner effect was difficult to observe. And that is true - it took many years after the discovery of superconductivity untill Meissner. And even then it was difficult, usually detected by changes in the magnetic field. The amazing thing with high-Tc was that one could do this in air, on the table. And yes, cooling willmake the magnet go up of course - easily demonstrated with high-Tc's. /Pieter Kuiper (talk) 00:16, 22 September 2009 (UTC)
replies: text: I agree with the deletion. The Meissner effect was discovered long before high Tc (1933). Measuring small changes in magnetic field is not particularly difficult, especially since the advent of the SQUID in the 1960s.Tls60 (talk) 18:55, 13 May 2012 (UTC)
thread_title: Deleted Observation Section

message: The diagram and text show magnetic flux through the blue object for T>Tsubc, and exclusion for T<Tsubc.  What happens when T=Tsubc?
Mea (talk) 23:42, 1 August 2011 (UTC)
thread_title:  What about the equals case 

message: Unless someone edits in quantum levitation 
That is based on Meissner effect (in fact, some magnetic flux tubes still penetrate an extremely thin coating of superconductor, that is what enables such demonstration).  — Preceding unsigned comment added by 86.184.203.17 (talk) 14:51, 18 October 2011 (UTC)
replies: text: "Quantum levitation" is established terminology based upon the casimir force: http://www.st-andrews.ac.uk/~ulf/levitation.html 85.170.167.60 (talk) 18:07, 19 October 2011 (UTC)
thread_title:  The article is not complete 

message: Doing my professional skills III module at the university of york I had great trouble trying to understand what actually causes the meissner effect. In short nobody knows! I've added that "no dynamical explanation of the Meissner effect exists within the conventional understanding of superconductivity"  — Preceding unsigned comment added by Chronus15 (talk • contribs) 02:38, 9 December 2011 (UTC)
thread_title:  Nobody Knows 

message: I suggest we merge the rather redundant Superdiamagnetism page into this one.  Circuitboardsushi (talk) 20:32, 29 December 2011 (UTC)
replies: text: Agree - since there are no objections I'm going ahead with the merger, with superdiamagnetism becoming a redirect to Meissner effect. Tls60 (talk) 19:52, 13 May 2012 (UTC)
thread_title:  Merge superdiamagnetism here 

message: The article currently does not explain why the magnet stays in place in the leveitation examples, rather than sliding over the expelled field, this is explained at Flux pinning - perhaps a few sentences here would be helpful? 192.12.81.1 (talk) 15:52, 8 April 2013 (UTC)
thread_title:  Flux pinning 

message: As many astronomical bodies do have a Magnetic Field, and there may be Magnetic Fields more or less intense all across the universe, if a Magnet, i.e., something having a Magnetic Field, levitates over a Superconductor, the phenomenon could be reversed, the way the shape of a Wankel engine housing was changed by an inversion, from the early designs where both housing and piston rotated, to the currently used ones, with a rotating piston and a fixed stator, epitrochoid or housing; thus, is it possible that a superconducting body or a superconducting part inside a bigger device may levitate on the existing natural magnetic fields, if the adequate power or any other differential physical dymension is implemented or applied?  Salut † --Jgrosay (talk) 14:26, 23 October 2013 (UTC)
thread_title:  Upside down, boy you turn it, inside out, and round and round 

message: From my brief reading here, it seems to me that a very fine distinction exists between perfect diamagnetism of a perfect conductor and the Meissner effect of a superconductor. I intend to address the inconsistencies I see here.
A superconducting pellet (good ol' Y123) is brought below its transition temperature with LN2 in a styrofoam cup. A small rare-earth magnet (NdFeB) is placed above the pellet, and is observed to levitate at a fixed spacing. Attempts to push the magnet closer to the SC pellet show that the magnet prefers to return to it's original spacing above the pellet. This is the Meissner effect, as I have been informed by faculty.
My professor's attempt to articulate the theory led me to believe that surface-depth eddy currents induced in opposition to the applied B field are the cause of the so-called Meissner effect. He disclaimed expertise over the minutae of BCS theory and left it there in class. However, from what I read here, what my professor described is in fact perfect diamagnetism and not the "exclusion of internal B" via the Meissner effect. 
My difficulty in understanding arises here: has there ever been a material observed to display perfect diamagnetism that does not display the Meissner effect? Moreover, is there any material which is a perfect conductor but not a superconductor? It seems to me like perfect diamagnetism is an older explanation for what is observed to be B field internal exclusion when observations are performed on a sample already below Tc. The two effects would not be distinguishable unless the transition temperature was traversed while a constant applied B
So my question stands: has perfect diamagnetism ever been observed without the presence of the Meissner effect? It seems to me like perfect diamagnetism is merely an overly simple explanation which appeals to the formulae of Lenz and Faraday. If indeed there has been such an observed "internal freezing of an external B field", I would most love to be aware of it. Otherwise, the distinction seems redundant.  — Preceding unsigned comment added by 147.26.87.13 (talk) 16:54, 6 March 2014 (UTC)
thread_title:  A distinction must be made 

message: I think one should not mention J. Hirsch's complaints about BCS theory. These are extremely fringe theory -- I think a poll among practicing physicists would find 99.999% disagree with such fringe theories.
However, scientific truth is not decided by polls. In 1542, 99.99% of practicing astronomers agreed with Ptolemy's model of the solar system.
I agree with the opinion that we should remove fringe theories.   Although scientific truth may not be decided by opinion -- the truth of wikipedia (and what we teach our students) should be given by the consensus view until the fringe theory is proven to be more correct.  — Preceding unsigned comment added by 82.17.71.110 (talk) 16:07, 23 April 2018 (UTC)
replies: text: Removed the fringe.  Jähmefyysikko (talk) 09:39, 23 February 2024 (UTC)
thread_title:  Hirsch 

message: Superdiamagnetism article seems to be just another name for Meisner effect.MaoGo (talk) 20:05, 26 November 2017 (UTC)
thread_title:  redirect/merge with Superdiamagnetism