The Meissner Effect (1 Viewer)

[henry08]

Lucid Scintilla has overcomplicated it.

 

[Lucid Scintilla]

Lucid Scintilla has overcomplicated it.

Same result, same method.

Don't post thrice in a row; edit your posts; and, when you do post thrice -- or more than once in a row -- merge your posts.

Edit:

well lucid post up ur answer then so we can all learn from it????????????

Oh, I missed this. My bad.

I did; tbh, it's not great or as well as anyone could answer it.

 

[obimoshman1234]

Edit:
Oh, I missed this. My bad.

I did; tbh, it's not great or as well as anyone could answer it.

lol yea i missed ur answered to which was completly correct

 

[dolbinau]

sorry i straight away assume anyone with reasonable intelligence is male

LOL

 

[Lucid Scintilla]

lol yea i missed ur answered to which was completly correct

Hey, when I do a better job of it, I'll try to post it stat.

I don't think it's good enough, and it could do with improvements.

Edit: Btw, not that it's actually taught in the syllabus, but this is under 9.1, depth of knowledge, I guess; the magnet's kept in place as a result of this "quantum pinning" phenomenon.

 

[syriangabsta]

sorry i straight away assume anyone with reasonable intelligence is male

ROFL

 

[Pwnage101]

can we settle this once and for all guys, if in the HSC we get a questions on WHY a magnet is able to levitate above a superconductor below its critical temp what would we write (if its say 2 marks)?


is it:

- due to the mesisner effect, superconductors expel all magnetic fields permeating them, thus the magnet is able to levitate

OR

- lenz's law, curents induced to oppose, these do not encounter resistance and thus re a perfect mirror of the actual magnet, repelling it

???????

 

[2S1D3]

can we settle this once and for all guys, if in the HSC we get a questions on WHY a magnet is able to levitate above a superconductor below its critical temp what would we write (if its say 2 marks)?


is it:

- due to the mesisner effect, superconductors expel all magnetic fields permeating them, thus the magnet is able to levitate

OR

- lenz's law, curents induced to oppose, these do not encounter resistance and thus re a perfect mirror of the actual magnet, repelling it

???????

Meissner effect but it is basically a 'superconductor' form of Lenz's Law, my bad if I'm wrong

 

[Lucid Scintilla]

Bump, merge.

can we settle this once and for all guys, if in the HSC we get a questions on WHY a magnet is able to levitate above a superconductor below its critical temp what would we write (if its say 2 marks)?


is it:

- due to the mesisner effect, superconductors expel all magnetic fields permeating them, thus the magnet is able to levitate

OR

- lenz's law, curents induced to oppose, these do not encounter resistance and thus re a perfect mirror of the actual magnet, repelling it

???????

Diamagnetism, an intrinsic property of objects, which is predominant and perfect in a sub-critical temperature superconductor.
The top one.

Edit: Dudes and dudettes, TIPS:
BE SURE AS HELL TO ELABORATE YOUR POINT, AND ARGUE, THOROUHGLY, YOUR ARGUMENT AND MAKE SURE YOU HAVE A STRONG CAUSAL LINK BETWEEN YOUR POINTS.
ALSO, ELABORATE AS IN DEPTH AS YOU CAN; DON'T JUST NAMEDROP, EXPECTING TO GAIN MARKS, BECAUSE, YOU WON'T; IN FACT, YOU WILL LOSE MARKS/not gain any -- or the ones you expect you will.
ANOTHER POINT THAT REALLY DOESN'T NEED MENTIONING, BE SURE TO MAKE A PASSING REFERENCE TO LENZ'S LAW, JUST TO DEMONSTRATE 9.1, DEPTH OF KNOWLEDGE. (Brownie points.)
AND, IF YOU WANT, GO NUTS AND TEAR THE SHIT OUT OF THE LENZ'S LAW EXPLANATION.

Edit: Sorry about the over-the-net shouting.

Also, before you start churning out shit; look at 2007, 23(a-c); 2006, 22a; 2005, 25 (4 marks, in relation to BCS theory), and 22, which is more about losses in energy transmission, and how to reduce them); 2004 (23b).

 

[independantz]

http://www.talent-100.com.au/notes.pdf - page 10, of the physics notes , these guys have people that topped the state so i'm assuming it's right.

 

[Lucid Scintilla]

Good god. Read the fucking marking scheme.
I'm sick of you people.

Joshua and Alex are the names of the guys who topped Physics; we don't live in a dystopic state of conformity. These notes are good (they're not shithouse), in terms of depth, in clarity and expression.
And, what the crap, the look like ... oh, never mind... I get it now. :-/ Tutoring notes... are shit, anyway... now it makes goddamned sense.
Sell out.

You do this; make a statement in your introduction, mentioning the fact that there's a Lenz's law explanation - and, if you want explain it - but[/b] mention it's wrong, and explain cogently that there's an explanation that incorporates diamagnetism.

Look; you guys are making a huge fucking deal out of this simple dot point.
So long as you explain what the fuck you're doing, and so long as it's strongly argued, it flows and makes sense, the markers WILL NOT wrong you.
It is in the marking scheme and critereon for the question.

Sorry to come off as an antagonistic dick and pardon the French, by the way.

Meissner effect but it is basically a 'superconductor' form of Lenz's Law, my bad if I'm wrong

Goddamnit, *pacefalm, facepalm*.

Last thing ITP, what's right in real-life isn't right in BoS, and vice versa.

 

[SkimDawg]

Thank you Lucid Scintilla for finally wrapping up this thread, it should've been answered in like 2 - 3 posts, but no...

 

[Lucid Scintilla]

I've posted in this the most, even with merging posts. What a fucking disgrace. I hate you all.
My school teaches you better; go there. Bleahblahblahbleh, shit thread, close.

I answered this bloody thing a while ago, and post- and pre-dumbfucks posting in it.
The OP is ne'ev a dumbfuck; but a relatively ignorant, confused one.

Tits.

Any more questions? Speak now, or forever hold your peace.

 

[independantz]

Any more questions? Speak now, or forever hold your peace.

So umm... could you explain it again?

 

[Lucid Scintilla]

HoLY SHIT NO IT'S THAT TIME OF THE MONTH RIGHT NOW.

LATER, LATERZ.

 

[Sastrawan]

It's okay, take it easy

I just wanted to sort out a few things; sorry if you feel this is covering old ground.

I don't see why Lenz's law is taking such a beating here... it hasn't been mentioned in any marking scheme I've seen, so I don't know why it's become such a big deal - I don't think you even have to mention it.

Lucid is right to say diamagnetism is the answer; however, this term is also never used in marking guidelines, so, maybe yes, maybe no on actually using that term in an HSC context. Remember, this course isn't about being right, it's about telling them what they want to hear.

Okay, guys, this has to do with the dot pot before (on Cooper pairs), and the fact that superconductors are diamagnetic.
When a magnet is placed over a superconductor's surface, magnetic fields will try to penetrate the superconductor. However, if this does occur, the superconductor's state of having zero B in the interior of the conductor will be destroyed. Thus, to keep the material superconductive, a surface current, produced by the formation of Cooper pairs travelling in loops, is induced to induces a magnetic field which opposes the external magnetic field.

The thing is, there are definitely surface currents on superconductors, which cause the Meissner effect - this is corroborated by all the textbooks, Success One, Charles Sturt, Wikipedia etc. It seems as through these surface currents (whatever direction they go and whether or not Lenz's law is involved), cause magnetic fields to be generated that yield a net zero field WITHIN the superconductor. This too is agreed by all.

The reason that there can be surface currents on superconductors is because, although the interior of the superconductor has net zero field, there is not an abrupt break when the surface of the superconductor stops. Rather, the external magnetic field seeps into the superconductor to a certain very small depth, called the penetration depth, in which these surface currents are formed.

It is this which, it seems to me, is the diamagnetism, or is "implied by" the diamagnetism, so I don't know why this "either/or" situation has occurred between [a] diamagnetism and induced currents. No, there are no currents within the superconductor, but there are surface currents which cause the diamagnetism.

In support of this, Wikipedia: "When the temperature of a superconductor in a weak magnetic field is cooled below the transition temperature, surface currents arise that generate a magnetic field which yields zero net magnetic field within the superconductor. These currents do not decay in time, thus establishing that perfect diamagnetism implies zero electrical resistance. Called persistent currents, they only flow within a depth equal to the penetration depth, whose theory was given in the London equations by the brothers Fritz and Heinz London."

So why the Lenz's Law vs. diamagnetism debate? I realise you're already gotten over this, Lucid, by saying "just bloody say Lenz's law", which is wise

is it:

- due to the mesisner effect, superconductors expel all magnetic fields permeating them, thus the magnet is able to levitate

OR

- lenz's law, curents induced to oppose, these do not encounter resistance and thus re a perfect mirror of the actual magnet, repelling it

But just let me direct Pwnage and some others to this definition of what diamagnetism actually IS: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magpr.html#c2

In particular, "[Diamagnetism] may be viewed as an atomic version of Lenz's Law".


That's my peace. Don't get too worked up about it, Lucid; in the end, we're all just people on the Internet

 

[Lucid Scintilla]

Back to beating a dead horse; it's better than beating it off, though.

It's okay, take it easy

I just wanted to sort out a few things; sorry if you feel this is covering old ground.

I don't see why Lenz's law is taking such a beating here... it hasn't been mentioned in any marking scheme I've seen, so I don't know why it's become such a big deal - I don't think you even have to mention it.

Lucid is right to say diamagnetism is the answer; however, this term is also never used in marking guidelines, so, maybe yes, maybe no on actually using that term in an HSC context. Remember, this course isn't about being right, it's about telling them what they want to hear.

Yes.
I didn't really read it, and really no longer care, as the HSC for Physics is now long-over. Physics is awesome and fun, but this debate and such, it's life-draining.

True that it's not used in the marking scheme. They'll acept anything as long as it makes sense. Aaand that's exactly right; it's about telling them what they wanna hear.

The thing is, there are definitely surface currents on superconductors, which cause the Meissner effect - this is corroborated by all the textbooks, Success One, Charles Sturt, Wikipedia etc. It seems as through these surface currents (whatever direction they go and whether or not Lenz's law is involved), cause magnetic fields to be generated that yield a net zero field WITHIN the superconductor. This too is agreed by all.

Jah.

The reason that there can be surface currents on superconductors is because, although the interior of the superconductor has net zero field, there is not an abrupt break when the surface of the superconductor stops. Rather, the external magnetic field seeps into the superconductor to a certain very small depth, called the penetration depth, in which these surface currents are formed.

It is this which, it seems to me, is the diamagnetism, or is "implied by" the diamagnetism, so I don't know why this "either/or" situation has occurred between [a] diamagnetism and induced currents. No, there are no currents within the superconductor, but there are surface currents which cause the diamagnetism.

In support of this, Wikipedia: "When the temperature of a superconductor in a weak magnetic field is cooled below the transition temperature, surface currents arise that generate a magnetic field which yields zero net magnetic field within the superconductor. These currents do not decay in time, thus establishing that perfect diamagnetism implies zero electrical resistance. Called persistent currents, they only flow within a depth equal to the penetration depth, whose theory was given in the London equations by the brothers Fritz and Heinz London."

So why the Lenz's Law vs. diamagnetism debate? I realise you're already gotten over this, Lucid, by saying "just bloody say Lenz's law", which is wise

What?

But just let me direct Pwnage and some others to this definition of what diamagnetism actually IS: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magpr.html#c2

In particular, "[Diamagnetism] may be viewed as an atomic version of Lenz's Law".

That's my peace. Don't get too worked up about it, Lucid; in the end, we're all just people on the Internet

no wai.
I mean, indeed.

Sorry for an incivility.
Life can be frustraaating.

Raaage, raaage.