Northwestern Physics Demos                                 Go back to Magnetism
DCS# 5K20.30NWU# E-34Location:    1 ?
title: Repelling Rings
aka: Jumping ring on Elihu Thompson apparatus

A coil with an iron core is connected to a variac set to 70%.  The AC magnetic field induces current flow in rings placed on the pole of the apparatus.  Since there is inductance in the ring, the current flow lags behind the change in magnetic field, resulting in a repulsion.
The ring can be flung much higher if it is cooled in LN.  The ring also gets quite warm when held down in the field.

    What happens when the ring is split and current cannot flow?
     What happens when two rings are placed next to each other on the pole?
pix of set uppiecesring floating