Eddy Current Brake - Lab Experiment

Lab Experiment

In physics education a simple experimental configuration is sometime used to illustrate Lenz's law. When a magnet is dropped down a conducting pipe, eddy currents are induced in the pipe, and these retard the decent of the magnet. As one set of authors explained

If one views the magnet as an assembly of circulating atomic currents moving through the pipe, Lenz’s law implies that the induced eddies in the pipe wall counter circulate ahead of the moving magnet and co-circulate behind it. But this implies that the moving magnet is repelled in front and attracted in rear, hence acted upon by a retarding force.

Laboratory work ranges from comparison of time-of-fall with a magnet in a cardboard tube, to oscilloscope reading of current in a loop wound around the pipe, to use of multiple magnets.