"Explain the Meissner effect" (2 Viewers)

[mrpotatoed]

If you got a 3-4 marker on the title, how would you go about answering it? What would the 'key words' that you pretty much have to mention to get full marks be?

 

[Drsoccerball]

Previously it was thought that the meisner effect was just the result of change in flux in the superconductor which thus repelled the rare earth magnet. However, this was proved wrong when it was discovered that the rare earth magnets magnetic field did not penetrate the superconductor but went around it. Therefore as the magnetic field of the rare earth magnet travels around the superconductor below its critical temperature it creates a lifting force which is dubbed as the "meisner effect."

 

[leehuan]

For some reason, whilst mention of the inability of magnetic field lines to penetrate the superconductor is still taught, some sources still speak about eddy currents.

 

[Drsoccerball]

For some reason, whilst mention of the inability of magnetic field lines to penetrate the superconductor is still taught, some sources still speak about eddy currents.

It's because the fact was recently discovered and textbooks/ past papers before about 2010-2012 didn't know this fact.

 

[keepLooking]

So wait, when they ask you to explain how a magnet levitates above a superconductor, you are actually meant to talk about Meissner effect not the surface eddy currents?

 

[Drsoccerball]

so wait, when they ask you to explain how a magnet levitates above a superconductor, you are actually meant to talk about meissner effect not the surface eddy currents?

there is no eddy currents because there is no change in flux

 

[leehuan]

It's because the fact was recently discovered and textbooks/ past papers before about 2010-2012 didn't know this fact.

I suppose that makes sense. I didn't know that the discovery was that recent though. Because either the 2011 or 2012 CSSA paper was talking about eddy currents as well and that made me more confused than ever.

 

[mrpotatoed]

Is the meissner effect related to the operation of Maglev trains? If so, does that mean Lenz's Law, Faraday's law, all the stuff to do with induced currents, has nothing at all to do with superconductors?

 

[leehuan]

I never knew induced currents had anything to do with superconductors.......

 

[Drsoccerball]

Is the meissner effect related to the operation of Maglev trains? If so, does that mean Lenz's Law, Faraday's law, all the stuff to do with induced currents, has nothing at all to do with superconductors?

They have zero relations since the magnetic field doesn't penetrate the superconductor.

 

[Drsoccerball]

And yes maglev trains use superconductors only to lift the train

 

[leehuan]

If I recall correctly propagation occurs by switching the polarity of the magnets on the rails at coordinated intervals?

 

[Drsoccerball]

If I recall correctly propagation occurs by switching the polarity of the magnets on the rails at coordinated intervals?

Yes by the process of magnetic attraction and repulsion magnets on the track are switch on with electromagnets at the exact time such that one magnet is attracted foward and the other is pushed foward.

 

[mrpotatoed]

If induced currents have nothing to do with the operation of a maglev train.. how does it work? My teacher said maglev trains don't use the meissner effect and stressed that we don't make the mistake of thinking they do use it.

 

[Mathsisfun15]

If induced currents have nothing to do with the operation of a maglev train.. how does it work? My teacher said maglev trains don't use the meissner effect and stressed that we don't make the mistake of thinking they do use it.

there are 2 types of maglev train
One uses superconductors for levitation which uses the Meissner Effect
The other which simply uses two very strong electromagnets

 

[keepLooking]

Maglev trains do not use the Meissner effect because - Maglev trains do not explicitly have to use superconductors.

Leehuan has answered your question above:

If I recall correctly propagation occurs by switching the polarity of the magnets on the rails at coordinated intervals?

 

[Drsoccerball]

If induced currents have nothing to do with the operation of a maglev train.. how does it work? My teacher said maglev trains don't use the meissner effect and stressed that we don't make the mistake of thinking they do use it.

Does your teachers last name start with an L ? Because my teacher stresses that it doesn't use it but then why would the dot point ask about superconductors? IT uses superconductors to levitate the train as the train is extremely heavy.

 

[Drsoccerball]

Maglev trains do not use the Meissner effect because - Maglev trains do not explicitly have to use superconductors.

Leehuan has answered your question above:

They need it to be lifted from the beginning.

 

[keepLooking]

They need it to be lifted from the beginning.

Can they not work with extremely strong magnets as mentioned by Mathsisfun?

 

[Drsoccerball]

Can they not work with extremely strong magnets as mentioned by Mathsisfun?

The energy required would be significantly less with superconductors. You can but why waste heeps of energy?