Eddy Current Pendulum

Purpose

To show damping of pendula due to eddy currents.
 

Equipment

Eddy current magnet with various pendula.

 

Suggestions

For an extremely dramatic effect, dip the bob into liquid nitrogen before letting it swing; it stops IMMEDIATELY!
 

Images

k2-44

Description

Pendula with bobs of different materials and geometries are swung through the poles of a strong horseshoe magnet. The amount of damping is greater for those bobs in which strong eddy currents can flow. Bobs include, solid copper,copper loop, broken copper loop, laminated copper, copper with central hole, and wood.
 

References

Francis X. Hart and Kenneth W. Wood, Eddy current distributions: Their calculation with a spreadsheet and their measurement with a dual dipole antenna probe, AJP 59, 461-467 (1991)