Re: [Phys-l] [tap-l] Liquid helium experiments

[chuck britton <britton@ncssm.edu>]

Lowering the magnet by a thread is good - but starting with the  
magnet already in the dish is very dramatic also.
Watching the magnet spontaneously rise above the dish got me to  
thinking about a thermo question that is probably more suitable for  
Phys-L
	So I'll cross post there as well

Consider two identical setups, each with a superconducting disk or  
dish and a suitable magnet for demonstrating the Meisser-whoever effect.
One experiment has the magnet placed on the disk when the cooling  
begins - the other has the magnet set off to the side with enough  
separation that its field will not significantly affect the  
superconductor.

Carefully measure the amount of cooling that is required for each  
trial to reach the final equilibrium T.

One magnet is now floating above its superconductor and the other is  
still just sitting there unchanged except in temperature.


		Question:
			Which setup required MORE cooling in order to reach the final  
temperature (and why - of course)



On Oct 31, 2008, at Oct 31(Fri) 11:40 , Bernard Cleyet wrote:

> For a change I tried a tin watch glass, once.
>
> bc forgot the allotrope and doesn't remember how he lowered the  
> magnet (Pb and Sn),