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[adnan91]

Compare the model for the conduction of electricity in metals at room temperature with the model of the conduction of electricity in superconductors below the critical temperature

zzz tedious questions

metal: there is a sea of free electrons among the metallic lattice. When a potential difference is applied it creates a drift velocity. This velocity is when the electrons move towards to postive terminal. They encounter collisons with themselves and any impurites/imperfections in the lattice. THEY DO NOT COLLIDE WITH THE LATTCE ITSELF. Collisons cause resistance and heat production. Greater temperature the lattice vibrates more thus creating even a higher probability that the conducting electrons with collide with each other...i really cbb for superconduction look up BSC

 

[dolbinau]

THEY DO NOT COLLIDE WITH THE LATTCE ITSELF

Is this a common mistake?

 

[JamesTockuss]

zzz tedious questions

metal: there is a sea of free electrons among the metallic lattice. When a potential difference is applied it creates a drift velocity. This velocity is when the electrons move towards to postive terminal. They encounter collisons with themselves and any impurites/imperfections in the lattice. THEY DO NOT COLLIDE WITH THE LATTCE ITSELF. Collisons cause resistance and heat production. Greater temperature the lattice vibrates more thus creating even a higher probability that the conducting electrons with collide with each other...i really cbb for superconduction look up BSC

Yes they do? The vibrations of the metallic lattice increase the chance of an electron colliding with it, and thus resistance increases with temp?

Next Question: Describe the BCS Theory of superconductivity

 

[helper]

Yes they do? The vibrations of the metallic lattice increase the chance of an electron colliding with it, and thus resistance increases with temp?
[/B]

Bigger problem is it didn't answer the question.

Remember your KEYWORDS. Compare, means to state similarities and/or differences. Just describing what happens won't obtain full marks.

 

[dolbinau]

So it does hit the lattice?

 

[JamesTockuss]

So it does hit the lattice?

I'm pretty sure it does. Otherwise he's saying that if you have a metal free of impurities it wouldn't encounter resistance?

The lattice vibrates due to thermal energy, and these vibrations impede the free flow of electrons through the metal through collisions which scatter the electrons through the crystal.

 

[JamesTockuss]

So it does hit the lattice?

Just called up the HSC advice line - they do yeh

 

[helper]

Just called up the HSC advice line - they do yeh

Once again it comes down to the level you are expected to know at the HSC. Collisions with the lattice would be accepted. Technically it is the collisions with the lattice defects - the structural and vibrational defects

http://books.google.com.au/books?id...&hl=en&sa=X&oi=book_result&resnum=1&ct=result

Which again, isn't saying there isn't collisions with the lattice but the lattice ions.

 

[JamesTockuss]

Once again it comes down to the level you are expected to know at the HSC. Collisions with the lattice would be accepted. Technically it is the collisions with the lattice defects - the structural and vibrational defects

http://books.google.com.au/books?id=KmMYWP56t98C&pg=PA482&lpg=PA482&dq=resistance+in+metals+lattice+collision&source=web&ots=MEMZcskFz6&sig=-zqPVo1_1KDv8vlcvifN64gO_XY&hl=en&sa=X&oi=book_result&resnum=1&ct=result

Which again, isn't saying there isn't collisions with the lattice but the lattice ions.

Well I guess we're not doing Quantum Theory here :S

The guy on the phone said basically what you just said, that we're not expected to know anything more so you can just say it hits the lattice

 

[sonnylongbottom]

Yes they do? The vibrations of the metallic lattice increase the chance of an electron colliding with it, and thus resistance increases with temp?

Next Question: Describe the BCS Theory of superconductivity

• Proposed by Bardeen, Cooper and Schrieffer to explain superconductivity
• When a superconductor reaches its critical temperature, its resistance drops to zero
• As electrons move through the lattice, they induce phonons.
• The positive ions are too slow to respond as they are too big, creating a momentary positive charge
• This charge accelerates the electron behind, forming a Cooper pair
• Cooper pair moves through the lattice unimpeded as the lattice vibrations do not affect them.

Describe how Thomson's experiment deduced the charge to mass ratio.

 

[ashbashness]

Wait, I thought the ions were the lattice - or does the lattice here refer only to the grid-like structure of their arrangement?

Thomson's cathode ray tube had enough air removed in order to visually observe deflection of the cathode ray by electric fields. The anode in thomson's tube was placed near the cathode and had a hole in its centre so that electrons would no longer accelerate down the remainder of the tube. The tube was placed in magnetic field and an electric field perpendicular to the magnetic field in such a way that the cathode ray's motion was pushed up by one and down by the other (would probably use a diagram instead of these convoluted words. I hate words.) The field strengths were set in such a way that the particle was on the whole undeflected from it's initial position, so that Fb=Fe, ie qvB=qE, v=E/B. By turning off the electric field, the motion was circular, and thus qvB=mv2/r, which when rearranged gives q/m=v/Br, and since v=E/B, q/m, the charge to mass ratio could be expressed in known or measurable quantities.

Describe how a galvanometer operates with reference to the relevant physical principles

 

[helper]

Wait, I thought the ions were the lattice - or does the lattice here refer only to the grid-like structure of their arrangement?

The positive ions make up the lattice. The lattice is the structure and influences.

 

[aussiechick007]

Describe how a galvanometer operates with reference to the relevant physical principles

The motor effect is when motion is produced due to a current carrying conductor placed in a magnetic field and the force it experiences according to the right hand palm rule. In the case of a galvanometer, when a current is run through the coil, it experiences a force according to the radial magnetic field around it, of different strengths depending on the amount of current in the coil. The arrow then points in a certain direction depending on the motion of the coil, controlled by the spring, and therefore giving a reading.

In the context of semiconductors, explain the concept of electrons and holes. (8 marks!!)

 

[dolbinau]

Be careful not to state the 'right hand palm rule', It's a guide not a physics law.

 

[m00]

lol im wrong

 

[aussiechick007]

^^ wtf is that physics?? (is that for an option that i dont do? please tell me it is!)

 

[m00]

gfbfgnh im wrong o lol btw that question was quanta to quarks opssss

 

[sonnylongbottom]

In the context of semiconductors, explain the concept of electrons and holes. (8 marks!!)[/quote]

A semiconductor can be doped with either a group III or V element which can change its electrical properties. An example is silicon being doped with a group III element such as boron. As boron has 3 electrons in its valence band, the semiconductor has one less electron in its lattice, hence becoming a p-type semiconductor. This semiconductor has a 'hole' which carries its current as the corresponding electrons moves to fill the hole. The holes move towards the negative terminal and can carry current. When doped with a group V element e.g phosphorus, it becomes an n-type semiconductor. As there is an extra electron, it moves from the valence band to the conduction band, as this electron can carry current, it increases its conductivity.

Discuss two issues which need to be considered for safe re-entry into Earth (4 marks)

 

[aussiechick007]

what do you mean youre wrong? so it was an option question then? which option?

 

[aussiechick007]

Discuss two issues which need to be considered for safe re-entry into Earth (4 marks)

the angle it hits the atmosphere - if it is not big enough, the rocket will 'bounce' off, and if too big re-entry will be too quick, resulting in too much heat and g-forces for the rocket and its occupants to handle. The acceptable angle usually has to be within 2 degrees.

the heat produced on re-entry - due to the friction with the atmosphere, large amounts of heat are produced, which can burn up hte space craft and its occupants. This can be overcome by things such as insulation, and a 'sacrificial skin', which is burnt up on re-entry.

Discuss how superconductors and the effects of magnetic fields have been applieid to develop a Maglev Train. (7 marks)