Shoot the ring through the roof after dipping it in liquid N2; Lenz's law induced EMF in metal ring.
What it shows:
The induced current in a metal ring is dramatically increased by lowering the ring's temperature.
How it works:
Here is an extension of the Ring Flinging demo. By placing the aluminum ring in liquid nitrogen, you can decrease its resistance by a factor of about 2. Pull the ring out of the LN2, place it on the solenoid and hit the on switch, and send the ring to the roof.
Setting it up:
Along with the ring flinger, have a dewar with LN2 and a pair of tongs to fish the ring out. The lecturer should be equipped with a safety helmet; this not only adds to the anticipation, it could also prove useful!
See details of the Ring Flinger.