Superconductivity Demo - Circuit Diagram

Thanks to http://flanture.blogspot.com/2007/08/howto-flash-content-on-bloggers-blog.html I could post my weird flash animation of the circuit used by Kamerling onnes to demonstrate superconductivity. (Embedding flash in blogger shouldn't be so hard, in fact!)

Observe that initially the switch S1 is closed, while the switch S2 is open. So, no current flows through the mercury.

Now, when the switch S2 is closed, and after a while, switch S1 is open. The currrent that was flowing through the switch S2 keeps on flowing. They call it persistent current. This was achieved when cool Mr. Kamerling cooled the mercury down to 4K. Eventually, Leyden was remarked as 'the coldest spot on the Earth', but hot research on superconductivity was going on.

And here is a vintage photograph of some greatest scientists, assembled during the Solvay congress in 1927.


The event took place in October 1927. In this fifth Solvay International Conference on Electrons and Photons, world's most notable physicists met to discuss the newly formulated quantum theory. It was here that Einstein reportedly said, referring to the Uncertainty Principle, "God does not play dice." Perhaps getting bored of this, Bohr replied, "Einstein, stop telling God what to do." Seventeen of the twenty-nine attendees were or became Nobel Prize winners! And the persevering Marie Curie won Nobel Prizes in two separate scientific disciplines.

Levitation Demo

"It's been nearly 100 years since Kamerling Onnes first demonstrated superconductivity. How many of us have ever seen a simple demonstration of, say levitation due to superconductivity?", asked Professor Asokamani, in one of his Sunday lectures at the Periyar Science and Technology Center, Chennai. Well, how many of us have?

This weekend, we were eager to view the levitation demo. The scheduling of events in the Science and Tech center has a remarkable eccentricity. There was a Science Talent Exam for kids going on, and we were left with no room!

Professor was unyielding, never compromising on his plans and schedules. Then we got the air-conditioned Conference Hall. Yes, the demo started. The audience were but a few - some 4 B.E students, a Ph.D. student, Mr. Raj Mane,a learned man who has ready-made questions and anecdotes, the professor, and myself. The much-awaited liquid Nitrogen emerged, in a thermocoal flask.

First, I had the impression it was boiling and 77 K is the boiling point of liquid nitrogen. Well, at room temperature, it's more than boiling! To learn more about liq. nitrogen, click

And we didn't have an organized plan for the demo. Professor had acquired an 123 superconducting pellet - SmBa2Cu3O(7–delta) - from the Indian Institute of Science, Madras. And there was a strong magnetic pellet, which we expected to jump and levitate magically.

What is levitation?
Levitation (from Latin levare, to raise) is the process by which an object is suspended against gravity, in a stable position, without physical contact.(Wikipedia.org)

The person who bought the liquid nitrogen poured it inside a paper plate, having the superconducting material and the magnet. And we could see nothing but a dense white fume, and were left wondering what really was happening. The levitation was not significant. Nevertheless, we could find the magnet was floating on air when we inserted a paper strip in between the magnet and the superconducing material. The magnet was rotating. Well, that's levitation. Professor explained that the superconducting material would need some more 'oxygenation'.

Each of us enthusiastically probed the gap between the magnet and the superconductor, and exclaimed, 'it's on the air!' And thanks to Professor, I am also fortunate enough to see the hand-drawn picture of the first ever demonstration of superconductivity. I've tried my weird drawing skills to interpret what I saw on that book. And I bet you can never see the basic circuit diagram anywhere else, including google images. All you can see about superconductivity is the Meissner effect, and the I Vs V characteristic curve - showing the transition to superconducting state. Pardon me for my poor drawing skills.



Imagine the switch S1 closed initially, while S2 remains open. After some time, say at 4K, the switch S2 is closed so that the current flows through the mercury in the container. Well, the interesting part is that you open the switch S1. What would happen? How long would the current flow through this circuit. Theoretically (and practically too!) this forms the basis for perpetual current. The current flows through the circuit literally FOREVER - with zero resistivity offered by mercury! All this happened at a temperature of 4K. No wonder when Kamerlingh Onnes performed this achievement after attaining even lower temperature - with the liquefaction of Helium, Leyden, in the Netherlands, was known as the 'coldest spot on the Earth'!

After nearly 100 years, after millions of demonstrations of the experiment worldwide, we performed the astonishing demonstration - for most of us it is the 'first time in my life' experience. We applauded for ourselves, for we had just concluded a beautiful demostration of one of the magical phenomenon of Physics. I couldn't upload the photos yet, but still you can visit this link to see what exactly we too did - something similar!