Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538
Demonstrations are cataloged according to PIRA Bibliography
PLEASE REQUEST DEMOS WELL IN ADVANCE
Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.
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video - Jumping Ring
Purpose:To illustrate Lenz's Law and the principle of the transformer.
SETUP: Extend iron core no more than 24cm for PHS 203 or 16cm for all other rooms and slip continuous aluminum ring over the core. Press button to turn on power to coil and ring will fly into the air a good distance. Discontinuous ring (with slot) will not jump. Explain. Light bulb in wax can be submerged in water and placed on top of unit with iron core retracted. When energized, bulb will glow. Have student try and hold ring on core as long as he can. Place a small amount of water in the boiling ring and attach it to the binding post. Apply power and soon steam will rise from the ring. One can cool the rings in liquid nitrogen to increase the Eddy currents and get the ring to jump higher.
Hints:Why the ring jumps? A changing magnetic flux induces a current in a metal ring; the magnetic field due to this current opposes the primary field, repelling the ring and flinging it into the air. That's the simple explanation for the beginner student. For a more accurate explanation follow this link. References:
Phys. Teach., Vol. 35, No. 2, February 1997 Pages 80 - 83, Forces on the jumping ring;