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Meissner Effect

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Image:Meissner effect.jpg thumb|Meissner effect 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''' (or '''Meissner-Ochsenfeld effect''') is the total exclusion of any magnetic flux from the interior of a superconductivity superconductor. It is related to superdiamagnetism perfect diamagnetism but is actually a distinct effect, since the magnetic field will be zero inside the material in the superconducting state regardless of what it was before the material became superconducting. It was discovered by Walther Meißner and Robert Ochsenfeld in 1933. The Meissner effect is one of the defining features of superconductivity, and its discovery served to establish that the onset of superconductivity is a phase transition.

Theory
The Meissner effect is based on two principles - Lenz's Law and superconductivity. Due to Lenz's law the introduction of a magnetic field will cause "screening currents" at the surface of the superconductor. This effect will levitate a magnet as long as the magnetic field does not exceed the critical magnetic field. A magnet that is suspended by the superconductor has two interesting properties; it does not move, and it can spin without friction. The ability for the magnet to stay perfectly still is due to flux pinning, in which the magnetic field is able to penetrate the superconductor by means of impurities in the crystal structure. Note that there is a difference between a perfect diamagnet and a superconductor.

See also
{{Commons|Meissner effect}} * Superdiamagnetism * Superfluid * Diamagnetism

External links

- Meissner Effect (Hyperphysics)
- Superconductor Levitation Kits
- A video demonstrating the Meissner effect and its physical properties Category:Superconductivity Category:Magnetism de:Meißner-Ochsenfeld-Effekt es:Efecto Meissner fr:Effet Meissner it:Effetto Meissner he:×?פקט מייזנר nl:Meissner-effect ja:マイスナー効果 pl:Efekt Meissnera sv:Meissnereffekten vi:Hiệu ứng Meissner see Meissner effect

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