This iron core solenoid is a great demonstration of Lenz's Law. By using AC straight from the wall, it demonstrates how induced current from a magnetic field depends on a change in magnetic flux, and the resulting Lorentz force from these currents causes the rings to levitate! Simply set the device to “float” mode, and place a ring around the core, and it will float. If the device is set to “jump,” then the solenoid will receive a short pulse of electricity, and since that translates to an enormous change in flux, the ring jumps! Classes Used: Phys 102, 108

There are several rings available, various aluminum rings, including one with a slit cut in it to demonstrate that a flowing current is required, a brass ring, and a light bulb connected to many coils that lights up when placed over the solenoid. For the ring with the slit, one can demonstrate that the floating is due to an inductive and not a resistive effect. Connecting alligator clips across the slit will do nothing, but inserting a aluminum sheet into the slit will restore some of the ring's jumping properties (of course there is still a finite air gap between the ring and the inserted sheet metal).