Q. from 2002 paper (Superconductors) (1 Viewer)

[Skywalker]

Some materials become superconductors when cooled to extremely low temperatures. Identify THREE properties of superconductors.

I don't have the exemplar responses...I know
i) Zero resistance below the superconducting temperature and
ii) the Meissner effect

Anyone know what the third is?

Thx in advance

Edit: Ok whoops fuk dat I found the exemplars on the main site. They say the third property is "being brittle". Hmm. Are there any other besides that?

 

[+:: $i[Q]u3 ::+]

there are two types of superconductors.. extremely pure metals but these have a very low critical temperature. (eg. Al has critical temp of like 1.2 K).
Type 2 superconductors have critical temperatures that are higher.. eg. "YBCO" which has critical temp 90K. But these are ceramic compounds (YBa2Ca3O7) which is why they're brittle.
that explains the 'brittle' bit, but sory, i can't think of anything else. =P

 

[jm1234567890]

lol, if there were anymore it would be in the examplar response

 

[SmokedSalmon]

Apparently I rang up the 'advice line' and the teacher informed me that the third answer would be..

if the temperature rose above the critical temperature then it would become just like a normal conductor.
I hope that is right.

 

[Constip8edSkunk]

well thats kind of the same as i)

its like saying 'young' and 'not old' are 2 descriptions of bob

 

[-X-]

What about magnetic field cant pass through it? But thats almost the same as ii.

 

[inasero]

yep....i just thought of another property......

if the external magnetic field is too high, then a superconductor loses its conducting properties although i forgot how exactly that wroks...perhaps someone would like to clarify.....

 

[Constip8edSkunk]

again thats like the meissner effect, which states that the superconductor will expel magnetic fields as long as its below the critical flux density...

but its a dodgy question from the beginning i reckon, cuz the brittleness only refers to the ceramic superconductors, while the q is generic... besides the ceramic superconductors dun even expel all the magnetic fields, but let them pass through in vortexes or sumfin...

 

[Rahul]

yeh, ugly question. what about metal or metal alloy superconductors?
they arent brittle.

here are the 3 properties regarding the success one book:
1. negligible resistance
2. meissner effect
3. they become sc at a certain critical temperature. and it will remain as one as long as it is below that temp.

sounds ok

 

[wogboy]

Or how about saying something along the lines of: Once a current is started in a superconducting wire, it can flow indefinitely, even when the voltage source is deactivated (unlike a normal conductor)

This property may have quite a few potential uses, such as in long term electrical energy storage etc