Just a couple of questions........ (1 Viewer)

[stiggles0]

Hey everyone, just a few questions bout superconductors.....
1. What is the difference between Type I and Type II superconductors?
2. How much do we need to know bout the BCS theory?

Thanks in advance and good luck to everyone on Wednesday!

 

[jumb]

1) http://hsc.csu.edu.au/physics/core/implementation/9_4_4/944net.html

"Superconductivity describes the state reached in a conductor when the resistance to electron movement in a conductor drops to zero. Research has shown that there are two types of superconductors. For a number of pure metals, superconductivity occurs at temperatures from close to absolute zero and up to 23K (Type I). For another group of conductors, ones that have been manufactured using alloys of metals and metal oxides, superconductivity (Type II) has been demonstrated to occur at higher temperatures (in the range of 120 K)."

2) just the theory behind it (phonons and such)

 

[tennille]

Well, the syllabus dot point states "discuss the BCS theory", so i'm assuming you should know a fair bit.

 

[Jezzabelle]

BCS Theory suggests that superconductors have zero electrical resistance below their critical temperatures because at such temperatures the electrons pass unimpeded through the crystal lattice and therefore lose no energy. The theory states that the supercurrent in a superconductor is carried by many millions of bound electron pairs, called Cooper pairs.
These pairs form when one electron passing between adjacent positive ions in the lattice attracts the ions, causing them to move slightly inwards and to create a region of increased positive charge density. Due to the elastic properties of the lattice, this region of increased positive charge density propagates through the lattice as a wave. A second electron passing through the lattice is attracted into this moving region of increased positive charge density and is effectively swept along by the lattice wave created by the first electron. Thus, by pairing off two by two, the electrons pass more smoothly through the lattice.

Cooper pairs continually form, break and re-form. Since random lattice vibrations break up Cooper pairs, the temperature needs to be low enough to keep such vibrations to a minimum.

NOTE: this is a very simplified description, as the actual theory is way beyond the scope of the HSC physics course

 

[dingding]

http://webs.mn.catholic.edu.au/physics/emery/hsc_ideas_implementation.htm#BCS

 

[tennille]

That site is cool. I went on there this morning.

 

[Jezzabelle]

http://webs.mn.catholic.edu.au/physics/emery/hsc_ideas_implementation.htm#BCS

just steal my resources so i dont look smart anymore

 

[Jase]

Whoa what the hell?? they continually break and reform? I thought they were in a constant superfluid state directly due to the cold temperature... not because of "random lattice vibrations"

 

[Xayma]

Yes they continually break and reform once one electron is through there is no need for the cooper pairs to remain and a new cooper pair forms through the exchange of a phonon.

 

[BillyMak]

You do not need to mentions phonons.

 

[tennille]

But it is part of the BSC theory. Hence, you should mention phonons.

 

[BillyMak]

My physics teacher is a senior marker and on more than one occasion has been on the board writing the physics HSC paper. He has never mentioned the word "phonons".

 

[tennille]

Some books mention it, some don't.

hsc.csu.edu.au mentions phonons.

 

[mojako]

also
-> the electrons in each pair is not one behind the other.. the two electrons are well separated by hundreds to thousands of atoms
-> the electrons in the pair move in opposite direction, but one moves with greater speed so overal electrons drift in one direction

but dont mention this in the exam because then the idea of "pair" is somewhat destroyed
mmm u can..

 

[sub]

what's thsi about phonons? we never learnt of them in class...do we need to? can u pls explain if so?

 

[tennille]

phonons are sound waves that cause vibrations in the lattice. When an electron distorts the lattice, another electron approaches. The vibration in the lattice occurs like a waave which is finally absorbed by the second electron. The exchange of phonons keeps the cooper pairs together.

 

[DavidB]

yup since the electron passes through the metal lattice the cations are attracted to the path of the electrons. SO as the cooper pairs join together, it causes a distortion in this lattice and the cations begin to vibrate about a position.
This vibrational (sound) energy is stored in phonons ( basically a rip-off of photons) and they are "used" by the cooper pairs, accelerating them, thus enhancing conductivity....and wah do yah know ... its a bird, its a plane no no its SUPERCONDUCTOR!

(i give this theory another 10 yrs b4 its disproved....such BS)

peace out.

 

[CrashOveride]

little qquestion:

In the dot point section "2" of I2I, whats the diff between identify einstteins contribution.....and the other one in the other colums "assess eintstein's contribution...."

 

[helper]

In the second one you are suppose to access your own information and then make a judgement of how important his work is.

So your answer would be the same to start and then a personal opinion.
Eg
Einstein did not produce new theoretical knowledge but rather extended the ideas of Planck, and explained the physical meaning of these ideas.