BCS theory (1 Viewer)

[dawso]

ok, i get the fact that the electrons are put in pairs, but y do they do this? and how does this actually help??

the actual question im tryin 2 answer is:

"explain bcs theory in terms of electron pairs and how they are affected by electrical resistance"

any help much appreciated,

cheers

-dawso

 

[richz]

its due to the phonos, they allow electrons to attach, heres some info,

The BCS theory is based on the idea of Cooper pairs. As the first electron travels through the crystal lattice, it induces phonons in the lattice as it passes. Thus the positive ions move towards the electron, but the electron moves past before it can respond- leading to a momentary concentration of positive charge behind the electron. However, the second electron is attracted to this concentrated positive charge and accelerates towards it. This cause the electrons to travel through the lattice in Cooper pairs; known as phonon-mediated attraction. The BCS theory is adequate for explaining superconductivity, however for high-temperature superconductors, current appears to be carried by both single electrons and Cooper pairs. The BCS theory cannot currently explain these superconductors.

this is from sumone elses notes

 

[richz]

ok heres sum more info, when electrons move through a lattice the postive ions are attracted to it, so these are distorted and the create phonons, therefore electrons travel around in pairs. basically it means that when electrons move into a lattice it will distort postivie ions which inturn attract another electron

hope that helps now

 

[dawso]

cheers man

 

[kako]

This BSC theory is keeping me up–
Everything about it is shitting me. It's a flawed theory that doesn't explain the situation for >50˚K superconductors, is made from really complex maths well beyond the reckoning of any HSC student, and it doesn't even do anything to deepen our understanding of superconductors. Yes, there should be a healthy curiosity as to the details of superconductivity and such, but the general consensus in the scientific community is that it's a bit of a mystery.
The syllabus shouldn't require students to "discuss" the BCS theory, as it is pretty much impossible for any HSC student to have anything but a superficial understanding of the theory. Add to that that there is no reason to understand the theory, as it doesn't apply to most of the superconductors that are used and will be used in society, and the inclusion of it is just plain stupid.

I know venting anger at the stupid Syllabus solves nothing, and I should be focusing on rote-learning some crap to regurgitate in an exam, but this shit just annoys the hell out of me.

 

[rama_v]

This BSC theory is keeping me up–
Everything about it is shitting me. It's a flawed theory that doesn't explain the situation for >50˚K superconductors, is made from really complex maths well beyond the reckoning of any HSC student, and it doesn't even do anything to deepen our understanding of superconductors. Yes, there should be a healthy curiosity as to the details of superconductivity and such, but the general consensus in the scientific community is that it's a bit of a mystery.
The syllabus shouldn't require students to "discuss" the BCS theory, as it is pretty much impossible for any HSC student to have anything but a superficial understanding of the theory. Add to that that there is no reason to understand the theory, as it doesn't apply to most of the superconductors that are used and will be used in society, and the inclusion of it is just plain stupid.

I know venting anger at the stupid Syllabus solves nothing, and I should be focusing on rote-learning some crap to regurgitate in an exam, but this shit just annoys the hell out of me.

Yeah, its even worse than the Planck and black body radiation dotpoint (thats only an identify dotpoint! lol)...

 

[who_loves_maths]

maybe it's so shitty because, like you said, no one really understands how superconductivity works... and obviously that includes the ppl who made the syllabus (who aren't even professors)? so if the scientific community at large is still puzzled by superconductivity, how do you expect the syllabus writers to be able to provide us, yr12 students, with a thorough picture of the explanation? the best anyone can do is the BSC theory, so just live with it... unless you can come up with a better theory yourself?

 

[Antwan23q]

Yeah, its even worse than the Planck and black body radiation dotpoint (thats only an identify dotpoint! lol)...

what do u mean? Planck and black body radiation is relevant because it explains how he discovered that energy is quantanised

 

[who_loves_maths]

Originally Posted by antwan2bu
what do u mean? Planck and black body radiation is relevant because it explains how he discovered that energy is quantanised

i think rama_v is saying that we, as students, are not imparted with enough information of the level of depth one would expect so as to acquire a more thorough provision of understanding into the underlying concepts governing the 'quanta' and quantum theory in general.
for example, it is not of necessity by the syllabus, that student learn to or are required to find out exactly why and how a simplistic concept such as quantised energy could purport the significant change in the theoretical black-body-radiation curve that it does as opposed to the classical Rayleigh-Jeans curve that assumes continuous energy.

of course the reason and explanations for this can't be delivered comprehensively without the involvement of high level applied mathematics - a standard which the HSC mathematics course(s) do not satisfy (esp. taking into the fact that Statistics is not even of major attention in NSW mathematics). in fact, i believe (i heard this from someone) that deriving the Planck black body curve (that is, deriving its mathemtical equation) requires a level of knowledge of Physics beyond uni undergraduate level?! (eg. you have to know things like Statistical Dynamics, etc... before you can fully intepret the significance and implication of the 'quanta' to the real world.)

 

[rama_v]

i think rama_v is saying that we, as students, are not imparted with enough information of the level of depth one would expect so as to acquire a more thorough provision of understanding into the underlying concepts governing the 'quanta' and quantum theory in general.
for example, it is not of necessity by the syllabus, that student learn to or are required to find out exactly why and how a simplistic concept such as quantised energy could purport the significant change in the theoretical black-body-radiation curve that it does as opposed to the classical Rayleigh-Jeans curve that assumes continuous energy.

of course the reason and explanations for this can't be delivered comprehensively without the involvement of high level applied mathematics - a standard which the HSC mathematics course(s) do not satisfy (esp. taking into the fact that Statistics is not even of major attention in NSW mathematics). in fact, i believe (i heard this from someone) that deriving the Planck black body curve (that is, deriving its mathemtical equation) requires a level of knowledge of Physics beyond uni undergraduate level?! (eg. you have to know things like Statistical Dynamics, etc... before you can fully intepret the significance and implication of the 'quanta' to the real world.)

Yes, that is correct. Clearly it is not simple to describe how the theory that energy is quantised explains black body radiation curves...

I have read that Planck used statistical mathematics of a very high degree to come up with a formula to explain the curves. For example take a look at this page: thats complex indeed!

http://en.wikipedia.org/wiki/Planck's_law_of_black_body_radiation

 

[acmilan]

This BSC theory is keeping me up–
Everything about it is shitting me. It's a flawed theory that doesn't explain the situation for >50˚K superconductors, is made from really complex maths well beyond the reckoning of any HSC student, and it doesn't even do anything to deepen our understanding of superconductors. Yes, there should be a healthy curiosity as to the details of superconductivity and such, but the general consensus in the scientific community is that it's a bit of a mystery.
The syllabus shouldn't require students to "discuss" the BCS theory, as it is pretty much impossible for any HSC student to have anything but a superficial understanding of the theory. Add to that that there is no reason to understand the theory, as it doesn't apply to most of the superconductors that are used and will be used in society, and the inclusion of it is just plain stupid.

I know venting anger at the stupid Syllabus solves nothing, and I should be focusing on rote-learning some crap to regurgitate in an exam, but this shit just annoys the hell out of me.

1. There is evidence that BCS theory can explain high temp superconductors, remember its still a relatively new theory, and complete explanations do not get made in short times, we could be talking decades here. There's even thoughts that it might be through pairs of holes rather than electrons, however it has yet to be completely explained. Does this make BCS theory flawed? No, it just shows that it might not be the explanation to all types of superconductivity. Does that mean that it should be ignored since it doesnt explain everything? Again, no.

2. Most, if not all, of the things in HSC physics is made up of complex maths, does that mean they shouldnt be taught?