Magnet inserted and withdrawn from copper ring causes ring to swing.

A magnet is inserted and withdrawn from a solid copper ring. Eddy currents induced in the copper ring create a temporary magnetic field opposing that of the magnet, causing the ring to recede when magnet approaches and attract when magnet is moved away. This effect is small when ring is at room temperature but if the ring is dipped in liquid nitrogen the effect is magnified very greatly and repeated insertion and removal of magnet will cause a dramatic swing to begin. Gloves are worn when doing this demo with LN2.
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The copper rings associated with the jumping ring experiment D+15+20 stored in 21-1 in Le Conte and 45-1 in Pimentel work well.