Question about Superconductivity

[Johnny5]

My question is this.

 

Is the BCS theory of superconductivity permanently wrenched in the minds of today's physicists, or do they expect the theory of high temperature superconductivity to also explain low temperature superconductivity.

 

Thank you

[5614]

Type I superconductors are all low temp superconductors and BCS theory applies to them.

 

Type II superconductors are all high temp superconductors and whilst BCS theory may apply, other effects may be occuring, these are not fully understood yet.

 

==========

 

Or at least the above is what I think, if you can prove me wrong then go ahead.

[Johnny5]

Type I superconductors are all low temp superconductors and BCS theory applies to them.

 

Or at least the above is what I think' date=' if you can prove me wrong then go ahead.[/quote']

 

I thought that BCS theory predicts that high temperature superconductors can't exist, so doesn't that mean its wrong?

 

Thank you

[5614]

Not that I've heard of, then the only thing I have heard of is what I've read on the internet... have you got a reliable source that can back you up?

 

I mean neither, http://hyperphysics.phy-astr.gsu.edu/hbase/solids/bcs.html or http://en.wikipedia.org/wiki/Cooper_pairs mention it, and they are very reliable sites, not to say it doesnt exist, just wondered if I could read about what you say.

[Johnny5]

Not that I've heard of' date=' then the only thing I have heard of is what I've read on the internet... have you got a reliable source that can back you up?

 

I mean neither, http://hyperphysics.phy-astr.gsu.edu/hbase/solids/bcs.html or http://en.wikipedia.org/wiki/Cooper_pairs mention it, and they are very reliable sites, not to say it doesnt exist, just wondered if I could read about what you say.[/quote']

 

I use both those sites.

 

Alternative to BCS

 

I'll look for one which explicitely shows that BCS theory puts a theoretical limit on TC of 50K.

 

Regards

[5614]

One sec, where does the link you gave say that BCS gives superconductors a max temp of 50K ?

[Johnny5]

One sec, where does the link you gave say that BCS gives superconductors a max temp of 50K ?

 

That link doesn't say it, but on page 36 it talks about an alternative to BCS theory. I will find a link for you that does give the BCS prediction for the limit.

 

Regards

 

Here's an argument which shows that BSC theory incorrectly predicts penetration depth:

 

IOP article on penetration depth

[5614]

The link doesn't work.

[Johnny5]

The link doesn't work.

 

It did yesterday, I will try to find another.

 

Regards

[5614]

I still remain confident when I say that BCS theory does not put a limit of 50K on superconductors.

[labview1958]

Hi. I just join. I am interested in superconductivity and LENZ LAW. I am a school teacher turn hobbyist in superconductivity and maglev. Right now I am testing how much lift I can get from a spinning copper/aluminium disk and a magnet. I am a bit confused regarding thickness of the spinning disk. Does levitation force increases or decreases with a thicker disk. I am using 0.5 mm, 1.0 mm copper and aluminium. The results are very CLOSE. In superconductivity does a thicker disk leads to a higher levitation force?

[5614]

I'm a bit confused by what you are actually doing but wouldn't the increased area (bigger thickness) mean that more current could flow, or more induced current could flow so a bigger field?

 

Are you doing this: http://www.fieldlines.com/other/superconductor.html kind of experiment?

 

And also the http://en.wikipedia.org/wiki/Meissner_effect will be related if the above link is what you are doing.

[labview1958]

I have a small aluminum/copper wheel attached to a drill. I have a magnet placed on a digital weighing machine. As the wheel revolves with a high speed the wheel is brought near the magnet from above. A repulsive force between the magnet and the copper/aluminium wheel occurs. As a result the magnet is pushed downwards. At the same time the copper/aluminium wheel slows down as a result of EM drag force.

 

Q1. Does the thickness of the copper/aluminum matters?

Q2. Can we calculate the drag force from how much the wheel has slowed?

Q3. Would replacing the copper/aluminium wheel with a superconducting wheel give similar results?

[labview1958]

Where is everone? Anyone that can direct me to forum with more people regarding superconductivity, Lenz Law, Eddy Current etc.

[labview1958]

Anyone out there?

[5614]

Yeah I'm here.... can't really help you, I mean, there are probably many people who have read it, just it's kinda pointless doing a post like this with no useful info!

 

Try making a new thread for your question... that might help.

[labview1958]

I am trying to connect SUPERCONDUCTIVITY with LENZ LAW through EDDY CURRENT! What more information do you want? One of my questions is does the thickness of a superconductor important in the MEISNER effect?

[5614]

No and yes.

 

Yes: The meisner effect will happen regardless of the thickness of the superconductor, if you had a thicker superconductor it would be able to produce a bigger magnetic field (just like a bigger magnet is more powerful) so I suppose thicker would produce a bigger magnetic field.

 

No: It may play an effect on the meisner effect, but does that make it important? The meisner effect happens regardless of the thickness.

[labview1958]

Thanks. One more question. How small can a superconductor go? Does the smallest superconductor have a diameter of 1mm or 1 micron?

[5614]

Well the smallest "thing" when referring to a substance (ie a superconducting material) would be one atom of it.

 

However within one atom you cannot have a complete circuit to allow for electrons to flow, so I assume the smallest would be two atoms big.

 

Seeing as several supeconductors are compounds as opposed to elements a molecule of the superconductor would be smallest, whether one molecule, comprising of several atoms comprises a circuit I do not know, if so then one molecule, if not two molecules are need for electrons to be classified as flowing (aka current).

[labview1958]

How "small" has a superconductor been made in a lab? What is the current record for the "smallest superconductor" and the "smallest magnet"?

[5614]

I don't know world records like that without looking them up, which you could do if you so wished!

 

It's really not that amazing, a 1 atom magnet would be useless, why bother making one that small?

 

If there's no logical purpose (other than to set a record) no one has probably done it.

[mcoy]

i agree. but hey, people on guiness and ripley's do unbelievable things just for the sake of achieving it. still, making a smallsuperconductor wouldn't have a purpose, or would it? just chek it at gogle, you might find something

[labview1958]

I have tried google etc. but I have not been succesful. I hope one of the forum members can help. I hope MCOY changes her/his ICON. It is not very tasteful.

[Dave]

i agree. but hey, people on guiness and ripley's do unbelievable things just for the sake of achieving it. still, making a smallsuperconductor wouldn't have a purpose, or would it? just chek it at gogle, you might[/b'] find something

 

How about pathways in processor chips? High-temperature superconducting materials in new CPUs would dramatically increase performance with no heat loss - no heatsink required