5K20.30 - Lenz's Law - Jumping Rings

Code Number:
5K20.30
Demo Title:
Lenz's Law - Jumping Rings
Condition:
Excellent
Principle:
Induction
Area of Study:
Electricity & Magnetism

Disclaimer

Equipment:
Electromagnet Coil, Iron Cores, Variac, Pulse Switch, and Rings (Assorted).
Procedure:

Video Credit: Jonathan M. Sullivan-Wood.

Connect the electromagnet coil to a Variac.  Insert the iron core and place a ring over the core.  As you turn up the Variac the ring will appear to float.  Use a split ring or non-ferromagnetic ring and observe no effect.  Unplug the coil from the Variac and plug it into the pulse switch.  This allows you to input 110 volts AC instantaneously.  Place a ring over the core and hit the switch and the ring will jump about 20 feet into the air.

References:
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  • Arthur R. Quinton, "The AC Repulsion Demonstration of Elihu Thomson", TPT, Vol. 17, #1, Jan. 1979, p. 40.
  • Paul J. H. Tjossem and Elizabeth C. Brost, "Optimizing Thomson's Jumping Ring", AJP, Vol. 79, #4, Apr. 2011, p. 353.
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  • B-260: Ring - Jumping and Heating", DICK and RAE Physics Demo Notebook.
  • "B-270: Attraction of Levitating Rings", DICK and RAE Physics Demo Notebook.
  • "B-265: Variable Levitation of Rings", DICK and RAE Physics Demo Notebook.
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  • Jearl Walker, "6.22: Turning in the Shade of a Magnetic Field", The Flying Circus of Physics with Answers.
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  • Brian Jones and Matt Fackelman, "Ring Shooter", Don't Forget the Duct Tape, p. 125 - 128.
Operating Instructions for Cenco Ring Launcher

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.