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 alternatly 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. |
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