Jumping rings: High current AC coil causes rings to jump.

Jumping Rings: High current AC coil causes rings to jump. This is the Elihu Thompson 'Jumping Ring' experiment. The apparatus consists of a cylindrical coil of wire wound around a laminated iron core. Place an aluminum ring over the coil. Pressing the button activates a relay, temporarily placing a pulse of 120 VAC across the coil. The voltage pulse causes eddy currents in the aluminum ring. By Lenz's law, the magnetic field produced by the eddy currents opposes the magnetic field of the coil. The net effect is that the ring jumps several feet in the air. Of the rings supplied, copper works best (jumps 6 feet), aluminum works next best (3 feet), the brass collar barely makes it over the top of the coil, the split aluminum ring and the lead ring do not jump. Cooling the rings in liquid nitrogen greatly enhances the height of the ring jump. CAUTION: The cooled copper ring hits the ceiling with great force. Thus it is preferable to use a cooled aluminum ring. Various Assorted Rings: 1. Soldered brass Collar 2. Aluminum ring (2) 3. Split aluminum ring 4. Copper ring 5. Lead Ring