Jumping Ring with Adjustable Core

PIRA 5K20.30

The jumping ring coil shown at right has an iron core that can be adjusted up or down.  The current and voltage across the coil can be monitored through connections on the base. A variety of rings (lower picture) can be placed on top of the coil with the core through their middle.  The current in the coil is AC, and will induce currents in any metal ring.  Metal rings will be alternately attracted to the coil and repelled.  Because of a phase shift between the induced emf and the current, and hysteresis effects in the iron core, the average repulsion is stronger than the attraction.  Metal rings will jump as little as a few inches or as high as 12', depending on the adjustment of the core.

The switch may be kept on for two minutes before the coil gets too hot.  If a metal ring is held in place with the switch on, it will quickly get very hot because of joule heating from the induced currents.

One of the aluminum rings has a gap.  There is not a complete circuit for induced current, so it will not jump.

If the ring is cooled in liquid nitrogen first, it will shoot almost twice as high.