Skip to main content

Superconducting Electrons as a Frictionless Superfluid

While doing research for an article I'm writing about Janet Tate and her Gravity Probe B experiment[4], I found a few cool things regarding superconductors, frictionless bearings, and the Egg of Columbus experiment this morning.

The Egg of Columbus demonstration was first performed by Nicola Tesla in 1893 at the World's Columbian Exposition[1].  Here's a brief video from MIT showing a modern day version of the demonstration[2]:


The MIT site[2] describes the apparatus as follows:
"A toroid with three different wire windings is connected to 220 VAC 3-phase voltage. The voltage phase of each of the three windings lags 120 degrees behind the next, creating a changing induced magnetic field. The changing field causes metal objects to rotate when placed inside.
Motors using this principle are very common. In fact, power lines are often seen in sets of three because they are carrying three phases. For more information on 3-phase voltage,"
Alfred Leitner made use of a similar apparatus to demonstrate one of the properties of liquid helium.  Interstingly he points out that the rotating cylinder in the liquid helium Dewar is made of copper,(a non-superocnducting matieral).



Today's interesting find has to do with what happens when you replace the copper with a superconductor, a lead sphere in this case.  I. Simon reported[3] that while their Egg of Columbus style apparatus worked just fine, spinning a  lead sphere at room temperature, when the lead was cooled to its superconducting state, the sphere would no longer spin!  As long as care was taken not to trap residual magnetic fields in the superconductor as it cooled, the transverse magnetic field of the stator coils was unable to effect the cylinder in the least!


References:
1. Tesla's Egg of Columbus on Wikipedia
https://en.wikipedia.org/wiki/Tesla%27s_Egg_of_Columbus
2.  MIT demonstration of the Egg of Columbus
http://techtv.mit.edu/collections/physicsdemos/videos/718-physics-demo-magnetic-motor
3.  Simon, I, "Forces Acting on Superconductors in Magnetic Fields", Journal of Applied Physics, 24, (1953), p. 19
http://scitation.aip.org/content/aip/journal/jap/24/1/10.1063/1.1721125
4.  Tate, J, "Precise Determination of the Cooper-Pair Mass", Physical Review Letters, 62, (1989), 845
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.62.845





Comments

Popular posts from this blog

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla



to the nabla for another coordinate system, say… cylindrical coordinates.



What we’ll need:

1. The Cartesian Nabla:



2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:



3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:



How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…

Unschooling Math Jams: Squaring Numbers in their own Base

Some of the most fun I have working on math with seven year-old No. 1 is discovering new things about math myself.  Last week, we discovered that square of any number in its own base is 100!  Pretty cool!  As usual we figured it out by talking rather than by writing things down, and as usual it was sheer happenstance that we figured it out at all.  Here’s how it went.

I've really been looking forward to working through multiplication ala binary numbers with seven year-old No. 1.  She kind of beat me to the punch though: in the last few weeks she's been learning her multiplication tables in base 10 on her own.  This became apparent when five year-old No. 2 decided he wanted to do some 'schoolwork' a few days back.

"I can sing that song... about the letters? all by myself now!"  2 meant the alphabet song.  His attitude towards academics is the ultimate in not retaining unnecessary facts, not even the name of the song :)

After 2 had worked his way through the so…