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[[Image:EfektMeisnera.svg|thumb|right|Diagram of the Meissner effect. Magnetic field lines, represented as arrows, are excluded from a superconductor when it is below its critical temperature.]]
 
The '''Meissner effect''' is an expulsion of a [[magnetic field]] from a [[superconductor]] during its transition to the superconducting state. The German physicists [[Walther Meissner]] and [[Robert Ochsenfeld]] discovered the phenomenon in 1933 by measuring the magnetic field distribution outside superconducting tin and lead samples.<ref name=meissner1>{{Cite journal
| volume = 21
| issue = 44
| pages = 787–788
| last = Meissner
| first = W.
| coauthors = R. Ochsenfeld
| title = Ein neuer Effekt bei Eintritt der Supraleitfähigkeit
| journal = Naturwissenschaften
| year = 1933
| url = http://www.springerlink.com/content/l69w054091n24j14/?p=d517b9e40b344f9bb3fc19ee23a823b3&pi=4
| doi = 10.1007/BF01504252
|bibcode = 1933NW.....21..787M }}</ref> The samples, in the presence of an applied magnetic field, were cooled below their [[Superconductivity#Superconducting_phase_transition|superconducting transition temperature]]. Below the transition temperature the samples cancelled nearly all interior magnetic fields.  They detected this effect only indirectly because the magnetic flux is conserved by a superconductor: when the interior field decreases, the exterior field increases. The experiment demonstrated for the first time that superconductors were more than just perfect conductors and provided a uniquely defining property of the superconducting state.
 
==Explanation==
[[Image:Meissner effect p1390048.jpg|thumb|right|A [[Magnetic levitation|magnet levitating]] above a superconductor cooled by [[liquid nitrogen]].]]
In a weak applied field, a superconductor "expels" nearly all [[magnetic flux]]. It does this by setting up electric currents near its surface.  The magnetic field of these surface currents cancels the applied magnetic field within the bulk of the superconductor. As the field expulsion, or cancellation, does not change with time, the currents producing this effect (called [[Persistent current|persistent currents]]) do not decay with time. Therefore the conductivity can be thought of as infinite: a superconductor.
 
Near the surface, within a distance called the [[London penetration depth]], the magnetic field is not completely cancelled. Each superconducting material has its own characteristic penetration depth.
 
Any perfect conductor will prevent any change to magnetic flux passing through its surface due to ordinary [[electromagnetic induction]] at zero resistance. The Meissner effect is distinct from this:  when an ordinary conductor is cooled so that it makes the transition to a superconducting state in the presence of a constant applied magnetic field, the magnetic flux is expelled during the transition.  This effect cannot be explained by infinite conductivity alone. Its explanation is more complex and was first given in the [[London equations]] by the brothers [[Fritz London|Fritz]] and [[Heinz London]]. It should thus be noted that the placement and subsequent levitation of a magnet above an already superconducting material does not demonstrate the Meissner effect, while an initially stationary magnet later being repelled by a superconductor as it is cooled through its critical temperature does.
 
==Perfect diamagnetism==
Superconductors in the Meissner state exhibit perfect diamagnetism, or superdiamagnetism, meaning that the total magnetic field is very close to zero deep inside them (many penetration depths from the surface). This means that their [[magnetic susceptibility]], <math> \chi_{v}</math> = −1. [[Diamagnetics]] are defined by the generation of a spontaneous magnetization of a material which directly opposes the direction of an applied field. However, the fundamental origins of diamagnetism in superconductors and normal materials are very different. In normal materials diamagnetism arises as a direct result of the orbital spin of electrons about the nuclei of an atom induced electromagnetically by the application of an applied field. In superconductors the illusion of perfect diamagnetism arises from persistent screening currents which flow to oppose the applied field (the Meissner effect); not solely the orbital spin.
 
==Consequences==
The discovery of the Meissner effect led to the [[Phenomenology (science)|phenomenological]] theory of superconductivity by [[Fritz London|Fritz]] and [[Heinz London]] in 1935. This theory explained resistanceless transport and the Meissner effect, and allowed the first theoretical predictions for superconductivity to be made. However, this theory only explained experimental observations—it did not allow the microscopic origins of the superconducting properties to be identified.  This was done successfully by the [[BCS theory]] in 1957, from which the penetration depth and the Meissner effect result.<ref>{{cite journal |author1= J. Bardeen |author2= L. N. Cooper |author3= J. R. Schrieffer |year= 1957 |title= Theory of superconductivity |url= http://www.physics.gla.ac.uk/~dtngo/Article/PR_106_162.pdf |journal= [[Physical Review B]] |volume= 108 |issue= 1175 |pages= 162–164 <!--|doi= 10.1103/PhysRev.108.1175--> }}</ref> However, some physicists argue that BCS theory does not
explain the Meissner effect. <ref>{{cite journal |author1= J.E Hirsch |year= 2012 |title= The origin of the Meissner effect in new and old superconductors |url= http://iopscience.iop.org/1402-4896/85/3/035704/|journal= [[Physica Scripta]] |volume= 85 |pages=035704 <!--|doi:10.1088/0031-8949/85/03/035704--> |bibcode = 2012PhyS...85a5704P |doi = 10.1088/0031-8949/85/01/015704 }}</ref>
 
 
<gallery widths="200px">
Image:Tin_4.2K_Electromagnet.jpg|A tin cylinder—in a Dewar flask filled with liquid helium—has been placed between the poles of an electromagnet. The magnetic field is about 8 [[millitesla]]s (80 [[Gauss (unit)|G]]).
Image:Tin_80gauss_4.2K.jpg|''T''=4.2&nbsp;K, '''B'''=8&nbsp;mT (80 G). Tin is in the normally conducting state. The compass needles indicate that magnetic flux permeates the cylinder.
Image:Tin_80gauss_1.6K.jpg|The cylinder has been cooled from 4.2&nbsp;K to 1.6&nbsp;K. The current in the electromagnet has been kept constant, but the tin became superconducting at about 3&nbsp;K. Magnetic flux has been expelled from the cylinder (the Meissner effect).
</gallery>
 
==Paradigm for the Higgs mechanism==
The Meissner effect of superconductivity  serves as an important paradigm for the generation mechanism of a mass ''M'' (i.e. a reciprocal ''range'', <math>\lambda_M:=h/(M c)</math> where ''h'' is [[Planck constant]] and ''c'' is [[speed of light]]) for a [[gauge field]]. In fact, this analogy is an [[abelian (disambiguation)#In physics|abelian]] example for the [[Higgs mechanism]],<ref>{{cite journal |author=P. W. Higgs |title=Spontaneous Symmetry Breakdown without Massless Bosons |journal=Phys. Rev. |volume=145 |issue=4 |pages=1156 |year=1966 |bibcode=2003PhLA..315..474H|arxiv = cond-mat/0305542 |doi = 10.1103/PhysRev.145.1156 }}</ref> through which in [[high-energy physics]] the masses of the [[electroweak]] gauge particles, [[W and Z bosons|{{SubatomicParticle|W boson+-}} and {{SubatomicParticle|Z boson}}]] are generated. The length  <math>\lambda_M</math> is identical with the [[London penetration depth]] in the theory of [[superconductivity]].<ref>{{Cite journal
| volume = 663
| pages = 257–271
| last = Wilczek
| first = F.
| title = The recent excitement in high-density QCD
| journal = Nuclear Physics A
| year = 2000
| doi = 10.1016/S0375-9474(99)00601-6
| arxiv = hep-ph/9908480|bibcode = 2000NuPhA.663..257W }}</ref>
 
==See also==
{{Portal|Physics|Science}}
*[[Superfluid]]
*[[Type-I superconductor]]
*[[Type-II superconductor]]
* [[Flux pinning]]
 
==References==
{{Reflist}}
 
==Further reading==
*{{cite journal |author= Albert Einstein |authorlink= Albert Einstein |year= 1922 |title= Theoretical remark on the superconductivity of metals |arxiv= physics/0510251v2 |bibcode = 2005physics..10251E }}
*{{cite book |author=[[Fritz Wolfgang London]] |title=Superfluids |series=Structure of matter series |volume=1 |contribution=Macroscopic Theory of Superconductivity |year=1950 |oclc=257588418}}.  Revised 2nd edition, Dover (1960)  ISBN 978-0-486-60044-4.  By the man who explained the Meissner effect.  pp.&nbsp;34–37 gives a technical discussion of the Meissner effect for a superconducting sphere.
*{{cite book |author=Wayne M. Saslow |title=Electricity, Magnetism, and Light |publisher=Academic |year=2002 |isbn=978-0-12-619455-5 |oclc=51032778}}.  pp.&nbsp;486–489 gives a simple mathematical discussion of the surface currents responsible for the Meissner effect, in the case of a long magnet levitated above a superconducting plane.
*{{cite book |author=Michael Tinkham |title=Introduction to Superconductivity |edition=2nd |series=Dover Books on Physics |year=2004 |isbn=978-0-486-43503-9 }}.  A good technical reference.
 
==External links==
{{Commons|Meissner effect}}
*[http://www.magnet.fsu.edu/education/tutorials/slideshows/maglev/index.html Maglev Trains] Audio slideshow from the National High Magnetic Field Laboratory discusses magnetic levitation, the Meissner Effect, magnetic flux trapping and superconductivity.
*[http://www.youtube.com/watch?v=44mVZdnR6Yc Meissner Effect (Science from scratch)] Short video from Imperial College London about the Meissner effect and levitating trains of the future.
*[http://www.alfredleitner.com/superconductors.html  Introduction to superconductivity] Video about Type 1 Superconductors: ''R''=0/Transition temperatures/'''B''' is a state variable/Meissner effect/Energy gap (Giaever)/BCS model.
*[http://hyperphysics.phy-astr.gsu.edu/hbase/solids/meis.html Meissner Effect (Hyperphysics)]
 
{{DEFAULTSORT:Meissner Effect}}
[[Category:Magnetic levitation]]
[[Category:Quantum magnetism]]
[[Category:Superconductivity]]

Latest revision as of 10:23, 30 December 2014

Cessna 210 is an aircraft with six-seats, retractable €"gear, and has a single-engine. At first this plane has solely 4 seats. In 961 its fuselage and wing had been redesigned. This Cessna was manufactured in 26 mannequin variants. One in every of this is the Cessna 210 Centurion which is a great heavy hauler and it's also a speedster. And there are quite a lot of Cessna 210 on the market online.

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The tires on the market are USED, until noted as "New" or "By no means Mounted" within the description. Some tires could also be professionally patched and noted within the description. We do not do sidewall repairs or plugs. Every tire is visually checked for holes, punctures, or damaged belts earlier than listed on the market. Every tire is air checked at forty psi for leaks and/or damaged belts after it is bought and before it is shipped. Large rig, semi vehicles, tractor semi, semi sleeper are provided on the market through this particular. These semi truck specials provided on the market are going to be a weekly update for buyers in search of that special deal. These three listed in this blog are solely a small sample available in immediately's trucking market. Save even more cash whenever you buy tires on-line.

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The consultants of Nitto tires additionally implemented multi-angled blocks in order to improve the gripping power of the tires in case of dry and moist street surfaces. It also helps to evacuate the level of water from the tires in order to increase efficiency within the wet roads. Thus, these Nitto all-terrain tires are developed for the fanatic who wishes for an all-round excellent efficiency. Due to this fact, the Nitto Tires For Sale enhanced as dominate all terrains, whether it's filth, rocks or mud. Hence, the Nitto tires or SUV tires presents extreme consolation and longer tread-life along with lowered noise.

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Once your tires are chosen and paid for, they'll either be picked up personally by you in the event you ought to occur to reside close sufficient, or they can be shipped to an area installer in your area. The installer will then contact you when your tires have arrived, and you'll take your tractor to their place of work to have them installed. If that's the case, how then do you determine which tires are the best or a minimum of among the best in your express want? Not everyone's tires needs are the same. And if we can break down the completely different wants, we are going to higher establish a better form of tire to fulfill the wants an individual has. How to Match Bigger Tires to Your Mountain Bike How to Choose the Greatest Tires for Your Automotive, SUV or Minivan Value of the Tire

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