5K20.30 Jumping Ring and Variations

PURPOSE: To demonstrate Lenz' Law

DESCRIPTION: A large coil is made to be driven with AC out of the wall socket. It has a cylindrical core which protrudes up a couple of decimeters above the top of the coil. An aluminum ring fits the core loosely. When the power is turned on, the ring floats easily near the top fo the core. The ring with jump up several decimeters into the air if the power is applied suddenly.

SETUP TIME: Medium

COMPONENT LIST:

    


  1.  AC driven coil				?????


  2.  Core with Al Ring				?????

SUGGESTIONS:

REFERENCES: 2122 4.96-4.98 ; PIRA 5K20.30

OTHER NOTES: Variations: 1) Feed the coil with 115 V DC and the ring will float down slowly "in molasses". 2) Discharge a 4 uF, 3000 V capacitor into the coil -- the ring will jump to the ceiling of the Physics lecture halls, and come down hard. Clear the front rows. Have a hammer on hand to straighten the ring when it gets bent. Variation 2 is a potentially dangerous demonstration -- in a league with the capacitor bomb -- and should only be done by someone familiar with high-voltage practice. There is also a danger of someone being bonked by the ring, light as it is.