Questions i didnt know (1 Viewer)

[Shady01]

The question that was stright after the impact os superconductors on socitey.

The question asked about a magnet being dropped on a copper block, why did it slow?
was it becuase of a)supconductivity?
b) eddy currents
which is right?

 

[Riviet]

Hmm, I wasn't sure about this one either. Took a guess though and went with the explanation.

 

[Ether]

I didn't relate that questino to superconducitity, although I initialyl thought it did

I talked more about eddy currents being induced more effectively as when a metal is cool its resistance decreases exponentially. That is copper when heated has its resistance increase exponentially. So it was more I think of more production of eddy currents induced which due to Lenz's law induces a magnetic field with a larger strength which effectively intensifies the slowing down of the falling magnet.

But I always feel that I'm wrong, lol

As well, for superconducitivy to occur it has to happen within the negative hundreds of kelvins zone, so I dont think -50C wasit? or -50k on a copper thing would do anything.

 

[Stopsign]

-50 degrees can not be a superconductor.
I mentioned eddy currents, Lenz's law and opposition and then, slowing down!

Who knows?

 

[Ioup]

I took the same approach as Ether, however, I also suggested extremely low temperatures would cause superconductivity. Vagueness is a useful technique.

 

[Sgs2006]

I took the same approach as Ether, however, I also suggested extremely low temperatures would cause superconductivity. Vagueness is a useful technique.

theres no way it would reach critical temperature at -50 degrees

 

[Shady01]

same! becuase of the -50 I talked about superconductor, becuase a magnet being dropped on a copper plate or watever, wouldnt be strong enough to slow the magnet, against g would it? and that question was implying that if strong enough the magnet could hover, whether heated or cooled ( idk which) and i didnt know eddys could cuase that?

and no it didnt say it was its cricitcal temp, it just said what would it do at -50

 

[Stopsign]

Should the magnet fall or hover?

 

[mlinger]

part a) lenz's law..flux threading through copper creates a magnetic feild that oposses the field that created it... repulsion force slows it down... conservation of energy..etc

part b) as temperature cools lattice vibrations reduced... greater currents can be produced therefore greater magnetic forces... magnet takes longer to reach the copper plate (super conductivity doesnt occur in metals until close to 0K so it cant be that)

i think this is rite

 

[Ether]

part a) lenz's law..flux threading through copper creates a magnetic feild that oposses the field that created it... repulsion force slows it down... conservation of energy..etc

part b) as temperature cools lattice vibrations reduced... greater currents can be produced therefore greater magnetic forces... magnet takes longer to reach the copper plate (super conductivity doesnt occur in metals until close to 0K so it cant be that)

i think this is rite

yup that's the one, i answered it as that

what i meant is that -50 wouldnt have caused any form of superconducitivity and i dont think copper has a critical temperature of -50
it was a trick question, note how they put the "imapct of superconductors" a page before to lure us into thinking it would be for the next, nope

mlinger hit it on the head i think

 

[Valtur]

ok guys, cant be superconductor, as many have said, you dont reach critical temp untill *very* low temps, as ether said.. and btw, you cant go below zero kelvin, ether. so basically as the mlinger said, lenz law from induced eddy currents fopr the first part, slows it down as it aproaches, but not stopping to hover - another indication it aint superconductor, and part b, just less lattice vibration, less electrical resistance, strong induced currents, stronger magnetic field produced

 

[shinji]

a) lenz's law - the magnetic field = change in flux and hence, slows down .. lol

b) superconductors. i wrote about superconductor's in part (a) .. and then i had to scribble it allllll out. lol

 

[ianc]

yeah -50 degrees Celsius is 223 degrees Kelvin, so definitely the coppper wasn't a superconductor.

The best ceramic superconductor's critical temp is about 130 degrees K

 

[XcarvengerX]

The last question I attempted on the whole paper... with 3 minutes left. I think I wrote eddy current, oppose, magnetic field, flux and stuff but not Lenz's Law and for b, I got completely wrong because I though the resistance to go down will decrease as temperature decrease due to less particle colliding and stuff, so the magnet falls faster (which is completely opposite to what I think is the correct answer now - mlinger's answer above). How marks for each section? Hopefully get at least half of the marks for this question...

 

[myeewyee]

Yeah you'd want to be talking about lenz's law, eddy currents and interacting opposing magnetic fields producing a retarding force on the magnet to slow it down.

For the second part, my logic went something like : reduced thermal motion within the lattice ---> less electron scattering --> stronger current --> stronger field --> stronger force --> slower descent

I went over the lines on pretty much every question. Except for that damn 'work done' question which stumped me.

 

[lonely_devil]

i doubt copper is a super conductor... i wrote something like... due to the reduced vibration in the lattice under such low temperature, the resistance will be low... hence it's easier for current to flow n the eddy current will b greater and this will slow the magnet even more...

 

[hyparzero]

i doubt copper is a super conductor... i wrote something like... due to the reduced vibration in the lattice under such low temperature, the resistance will be low... hence it's easier for current to flow n the eddy current will b greater and this will slow the magnet even more...

Wrong, Wrong, Wrong, Wrong, Wrong, Wrong, Wrong.

-50*C is a negibile temperature and has absolutely minimal effect on the on the resistivity of the copper.

 

[Angelina88]

I said lenz's law for part a)

Then Meissner's theory/effect for part b)

Yes! thats exactly what i did....did this heavy duty explanation of the Meissner Effect...but i dont think its right after reading all the posts up here

 

[skyline]

ahaha i thought that question was sinch, obviously related to lenzs law and superconductivity, further more electric magnetic fields..etc... dat was a sinch question, but wat bout de projectile motion. arrraaaghhh. got de right stuff down but cudnt find time.. anyone no how to???

 

[angmor]

i talked about lenz law for the part a....

but then i FUCKED FUCKeD FUCKED part b...im so used to thinking that low temps = high resistance due to learning about semiconductors----but didnt realise copper was a metal FUCK FUCK FUCK FUCK