Meissner effect: Difference between revisions
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==What is the Meissner Effect== | ==What is the Meissner Effect== | ||
The Meissner effect is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state, discovered by German physicists Walther Meissner and Robert Ochsenfeld in 1933. | The Meissner effect is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state, discovered by German physicists Walther Meissner and Robert Ochsenfeld in 1933. They discovered it by measuring the magnetic field outside superconducting tin and lead. | ||
[[File:Meissner effect1.png|200px|thumb|right|alt text]] | [[File:Meissner effect1.png|200px|thumb|right|alt text]] | ||
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A super conductor with little or no magnetic field within it is said to be in the Meissner state and breaks down when the magnetic field is too large | A super conductor with little or no magnetic field within it is said to be in the Meissner state and breaks down when the magnetic field is too large | ||
A superconductor is fundamentally different from a conductor, because Faraday’s law of induction alone does not explain magnetic repulsion by a superconductor. At a temperature below its Critical Temperature, Tc, a superconductor will not allow any magnetic field to freely enter it. This is because microscopic magnetic dipoles are induced in the superconductor that oppose the applied field. This induced field then repels the source of the applied field, and will consequently repel the magnet associated with that field. This implies that if a magnet was placed on top of the superconductor when the superconductor was above its Critical Temperature, and then it was cooled down to below Tc, the superconductor would then exclude the magnetic field of the magnet. This means that a magnet already levitating above a superconductor does not demonstrate the Meissner effect, while a magnet that is initially stationary and then repelled by a superconductor as it is cooled through its critical temperature does. | A superconductor is fundamentally different from a conductor, because Faraday’s law of induction alone does not explain magnetic repulsion by a superconductor. At a temperature below its Critical Temperature, Tc, a superconductor will not allow any magnetic field to freely enter it. This is because microscopic magnetic dipoles are induced in the superconductor that oppose the applied field. This induced field then repels the source of the applied field, and will consequently repel the magnet associated with that field. [[File:Floating magnet.png|200px|thumb|right|alt text]]This implies that if a magnet was placed on top of the superconductor when the superconductor was above its Critical Temperature, and then it was cooled down to below Tc, the superconductor would then exclude the magnetic field of the magnet. This means that a magnet already levitating above a superconductor does not demonstrate the Meissner effect, while a magnet that is initially stationary and then repelled by a superconductor as it is cooled through its critical temperature does. | ||
==What did it lead to?== | ==What did it lead to?== | ||
The theory of the Meissner effect led to the phenomenological theory of superconductivity by Frits London and Heinz London in 1935. This theory explained resistance less transport and the Meissner effect, and allowed the first theoretical predictions for superconductivity to be made as seen below. | The theory of the Meissner effect led to the phenomenological theory of superconductivity by Frits London and Heinz London in 1935. This theory explained resistance less transport and the Meissner effect, and allowed the first theoretical predictions for superconductivity to be made as seen below. | ||
[[File: | [[File:London equations.png]] | ||
==History== | ==History== | ||
Revision as of 23:59, 30 November 2015
claimed by ooshinowo3
What is the Meissner Effect
The Meissner effect is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state, discovered by German physicists Walther Meissner and Robert Ochsenfeld in 1933. They discovered it by measuring the magnetic field outside superconducting tin and lead.
Some materials tend to expel a magnetic field, materials that do this are called diamagnetic, but the effects of this diamagnetism are weak. For example, water and the human body are diamagnetic materials.
In superconducting material the Meissner effect creates currents which completely oppose the magnetic field applied by a magnet, in other words they will repel a magnet. This consequently makes a superconductor in the Meissner state a perfect diamagnet.
A Mathematical Model
What are the mathematical equations that allow us to model this topic. For example [math]\displaystyle{ {\frac{d\vec{p}}{dt}}_{system} = \vec{F}_{net} }[/math] where p is the momentum of the system and F is the net force from the surroundings.
A Computational Model
How do we visualize or predict using this topic. Consider embedding some vpython code here Teach hands-on with GlowScript
How does it Work?
A super conductor with little or no magnetic field within it is said to be in the Meissner state and breaks down when the magnetic field is too large
A superconductor is fundamentally different from a conductor, because Faraday’s law of induction alone does not explain magnetic repulsion by a superconductor. At a temperature below its Critical Temperature, Tc, a superconductor will not allow any magnetic field to freely enter it. This is because microscopic magnetic dipoles are induced in the superconductor that oppose the applied field. This induced field then repels the source of the applied field, and will consequently repel the magnet associated with that field.
This implies that if a magnet was placed on top of the superconductor when the superconductor was above its Critical Temperature, and then it was cooled down to below Tc, the superconductor would then exclude the magnetic field of the magnet. This means that a magnet already levitating above a superconductor does not demonstrate the Meissner effect, while a magnet that is initially stationary and then repelled by a superconductor as it is cooled through its critical temperature does.
What did it lead to?
The theory of the Meissner effect led to the phenomenological theory of superconductivity by Frits London and Heinz London in 1935. This theory explained resistance less transport and the Meissner effect, and allowed the first theoretical predictions for superconductivity to be made as seen below. File:London equations.png
History
Put this idea in historical context. Give the reader the Who, What, When, Where, and Why.
See also
Superconductors and magnetic flux
Further reading
Books, Articles or other print media on this topic
External links
https://www.youtube.com/watch?v=44mVZdnR6Yc
References
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