Demo Day 2017

Yesterday, I participated in a demo day for elementary school-aged girls, hosted by FEMMES.  I always have tons of fun showing off the department's cool physics demos, and I thought I'd talk a bit about the one I was showing this time: A levitating superconductor.

Most materials fall into two categories: conductors, which allow electric current to flow through them; and insulators, which don't.  Even though conductors allow current flow, there's always some resistance – The electrons lose energy as they move.  Superconductors, however, allow charge to move with zero resistance, which leads to some interesting effects.

For the purposes of the demo, we used a "high-temperature" ceramic superconductor:

The temperature where it transitions to a superconducting state is only high compared to other superconductors – It needs to be cooled to 77 Kelvin, or about -321°F.  Luckily, that's the temperature of liquid nitrogen, which is a common tool in science labs.

This is a type-II superconductor, which means that when it is cooled to the proper temperature, it can "pin" the magnetic flux passing through it.  In simpler terms, it remembers the magnetic field it was in when it was cooled.  That means if we set up a magnetic track like this,

we can make the superconductor levitate!  On the left is a styrofoam cup holding the superconductor in liquid nitrogen.  Underneath the cup are magnets arranged in a pattern that matches the one on the track to the right.  When the superconductor is set on the track, it settles into the exact field it was in when pinned, resulting in levitation:

Big thanks to the Demo Lab for providing the equipment, and FEMMES for organizing the event!