Questions i didnt know (1 Viewer)

[helper]

ahaha i thought that question was sinch, obviously related to lenzs law and superconductivity, further more electric magnetic fields..etc.)

Nothing to do with superconductors as highest critical temperature for any material is about -135 degrees celcius and copper is not a superconductor at -50
http://hypertextbook.com/physics/modern/superconductivity/

 

[charismo]

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.

what's with you people??
0 kelvin is the lowest temperature possible in the Universie, anything below this and volume theoretically contract to negative quantities

 

[Wackedupwacko]

aiya.... its a huge trick quesiton in there.... whilst being -50 C does have an impact the copper doesnt superconduct until like..... <30K i which is equivilant to about -230 degrees C or lower. THEREFORE it is NOT in a superconducting state which others have said. HOWEVER because the metalic lattice produces less vibrations it reduces resistivity (remember resistance goes down as temperature goes down until crit temp where it drops to 0). this allows more induced emf created by the magnet similar to the force created in part a however this is greater thus magnet slows more.

at least thats what i put. honestly tho.... it aint gonna happen..... at room temperature.. bs a magnet would slow down to "gently drop onto the copper" or somfin like that..... itll still go *plonk* -.-

 

[sinist4]

i just said: magnetic falling> faradays law of magnetic induction> emf induced into the copper block> lenze states that a current in a dirction will be produced to oppose the orginal field change> two magnetic field interact> block opposes the magnet> resistance is abit lower than explained in part 'a'> magnet falls abit slower than the first....

thats wat i did...

 

[powder.au]

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???

copper is never a superconductor, like some other metallic conductors (gold and silver), and metals don't start superconducting until 7k.
I said lower temp -> less lattice vibration -> less resistance -> stronger induced magnetic field -> slower descent. However how much that change in temperature matters is debateable

Edit: Resistance at -50C is about half that at 25C from here

 

[yaseng1988]

Well, I just think of a plausible explanation. Don't think that it is a superconductor, it's not. So what I answered was:
for 1b).
Copper is an ohmic conductor that obeys Ohm's Law: resistance drops as temperature falls. So, when it is cooled resistance decreases. When the magnet bar falls, magnetic field changes --> induced current flows. Since resistance is low, current flowing is strong, as a result, eddy current produces stronger opposing magnetic field which in turn makes the bar falls more slowly than previously.....

Plausible eh??

 

[Shady01]

Yeah but thing is, in the question was there a current running through anyhting? I cant honeslty remember but i dont think there was, and Lenz law talks about an induced emf opposing action (somthing like that) so how could it have been lenz law? Unless there was a current.
Also it wouldnt! be a superconductor at -50deg. but I assumed it was on its way so I tlaked about what a superconductor does at Tc. and look at that affect and in my head minimsed it serverly for the -50 and said this is what should happen. Even though i think it would go *plonk* to.

 

[XcarvengerX]

For those of you who still think that part (b) is about superconductor, then I say this for clarity:
NO SUPERCONDUCTOR.

Physics reasons have been provided above. (not low enough for critical temperature of copper)

This is the logic reason:
I know most think about superconductor due to it is side by side with superconductor question, BUT there are boxes for our student numbers and centre numbers at the top (if you fail to notice the question number is different for the two questions), SO there will be different markers for the two questions, THEREFORE there are no connection whatsoever.

 

[myeewyee]

Yeah but thing is, in the question was there a current running through anyhting? I cant honeslty remember but i dont think there was, and Lenz law talks about an induced emf opposing action (somthing like that) so how could it have been lenz law? Unless there was a current.

I think you're missing the point. The question stated something along the lines of, a magnet was dropped onto a block of copper- this means that there's relative motion between the two and thus the flux cut by the copper is changing. Because of this, an emf is induced within the copper and Lenz's law simply explains how the currents produced by this emf flow (they flow so as to produce a magnetic field that opposes the changing field of the bar magnet..producing a force that slows its descent)

 

[Shady01]

SHIT! your right, well there goes 6 marks for me big pretty red line through my answers. Dagnamit!

 

[ReaL~]

would the meissner effect be a possible answer for part a) lol

i was thinkig abt the expt with the rare earth magnet sliding dwn the copper tube slowing down.. was abt to write eddy currents ahah but ended up writing meissner noooooo