Meissner Effect in a strong field?

[f95toli]

Strange, having the flux lines penetrating the superconductor is the result of flux pining I assume?
Initially, when the superconductive state occurs with the type II SC, the flux lines are penetrated correct?

Based on the graph posted earlier, the superconductor of Type II will have nothing penetrating it, however, it will in the vortex state?

In order to get the "floating" effect you (usually) need to put the magnet on top of the SC BEFORE it goes below Tc (i.e. before you pour liquid nitrogen on it). If you just cool a SC and THEN try to "balance" a magnet on top of it you will find that it is very difficult, and it is a bit like trying to balance magnet on top of another. This is due to the fact that unless you cool the SC in a magnetic field there won't be any pinned flux lines and there is no "minima" for the magnet to rest in. If you move the magnet around above the SC you will feel a resistance not only when you try to push it down, but also when you move it sideways.
This is why it is stable.It IS possible to arrange things so that you can levitate a magnet above a type I superconductor (this is "permitted" since the SC behaves like a perfect diamagnet), it is just very difficult.

 

[Wiz700]

There's nothing here in what you've said that made it wrong. It is backed by both experiment, and theoretical description. I get the SAME effect from two ordinary magnets.
Zz.

I need to study from better resources... I was slacking off and watched this video.
His descriptions are quite brief.

I used to believe that there is no force related between a superconductor and the external magnetic field. Mainly because the fields cancel out... But I need to study more and more.

Thank you all for pointing out my misconceptions.

 

[Wiz700]

2. It then means that it has a dependence on distance. At some point, the repulsive magnetic force equals the weight of the superconductor.

Zz.

A force between a magnet and a superconductor for example, is equal to the weight of the superconductor separated by a distance r?
While reviewing the concept. I realized... That indeed there is a force, as explained earlier, to expel the magnetic field lines there has to be energy, This is where the repulsive force comes into play.

I knew its a magnetic repulsive force... But is it the same force you'd get from two dipoles?
Meaning, the repulsive force generated by a magnet and a superconductor is equal to the force generated by to magnets?

A perfect dimagnet will always repel an external field?

I believe the repulsive force between a superconductor and a strong magnetic field from a magnet is very very weak.

 

[ZapperZ]

I think you still don't have an understanding of the Meissner effect.

The physics mechanism on how a magnetic field is excluded from a superconductor is due to the presence of supercurrent loops that generate its own field in response to the external magnetic field. The result of these two fields generally cancels out the external magnetic field that would have penetrated the superconductor. That is why you were told repeatedly that in such a state, the superconductor behaves as a perfect diamagnet!

However, as a result of this, the superconductor will also produce its own external magnetic field, and it results in a repulsive force between it, and the magnet.

You need to look up the definition of a perfect diamagnet. It is defined NOT as "always repel an external field", but rather has does has NO magnetic field inside its relevant volume.

Zz.

 

[Wiz700]

I think you still don't have an understanding of the Meissner effect.

The physics mechanism on how a magnetic field is excluded from a superconductor is due to the presence of supercurrent loops that generate its own field in response to the external magnetic field. The result of these two fields generally cancels out the external magnetic field that would have penetrated the superconductor. That is why you were told repeatedly that in such a state, the superconductor behaves as a perfect diamagnet!

However, as a result of this, the superconductor will also produce its own external magnetic field, and it results in a repulsive force between it, and the magnet.

You need to look up the definition of a perfect diamagnet. It is defined NOT as "always repel an external field", but rather has does has NO magnetic field inside its relevant volume.

Zz.

Im sorry, but I've struggled a lot while studying only EM...
So dealing with this idea is quite... Strang hence why I'm struggling here as well!

 

[Wiz700]

Magnetic field lines don't like to be compressed, or stretched either. There's an electromagnetic stress tensor that describes this mathematically. But intuitively, field lines behave like rubber bands. Bowing out the field lines near a superconductor takes energy, and indicates the presence of a repulsive force (pressure) between the object and the external field source.

Amazing amazing explanation! Because now I can use this explanation why when a high permeability piece of metal like soft iron, concentrates the flux lines through a certain point. Which explains the attraction between them!

I know this has no relevance to the Meissner effect, but it's nice to relate the ideas :)

 

[Wiz700]

I wonder...
If there are two type II superconductors facing a magnet, then cooled and reach the superconducting state. Will the magnetic flux lines penetrate BOTH conductors? Assuming the distance between each is r.

I'm guessing that indeed the magnetic flux will penetrate BOTH SC's.
Also, the time it takes to reach its superconductive state when exposed to a cooling source, would it be fast? How fast?

 

[ZapperZ]

I wonder...
If there are two type II superconductors facing a magnet, then cooled and reach the superconducting state. Will the magnetic flux lines penetrate BOTH conductors? Assuming the distance between each is r.

I'm guessing that indeed the magnetic flux will penetrate BOTH SC's.
Also, the time it takes to reach its superconductive state when exposed to a cooling source, would it be fast? How fast?

This has now become a meandering thread where you are just making things up as you go along.

If you wish to actually learn, start from the basic. Try Lenz's law, and brush up on your E&M. Otherwise, I can only see you asking these things just for the sake of asking.

A set of disjointed pieces of information does not a knowledge make!

Zz.

 

[Wiz700]

If you wish to actually learn, start from the basic. Try Lenz's law, and brush up on your E&M.

Done(Thank you for the advice!)
Now, I'll ask again(I couldn't figure this out!):

Type II superconductor will allow some of the flux lines from the external field to penetrate it, what is the best way to calculate the penetrating flux lines?
I'm wondering how many lines have really penetrated the superconductor.

 

[Wiz700]

2. It then means that it has a dependence on distance. At some point, the repulsive magnetic force equals the weight of the superconductor.

This is really confusing, generally. I know that magnetic force depends on the Strength of B and the distance. Why is the weight of such importance?

 

[Wiz700]

Just when I thought I've understood the magnetic force...

 

[Vanadium 50]

This has now become a meandering thread where you are just making things up as you go along.

Which makes this a good time to close it.