PURPOSE: To show damping of pendula due to eddy currents.
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, aluminum, and wood.
Compare how the bobs swing in the absence of a magnetic field using an identical pivot on the back of the post (seen portruding out the left of the post in the picture at the left above).
SUGGESTIONS: For an extremely dramatic effect, cool the bob in liquid nitrogen before letting it swing; it stops IMMEDIATELY!
Click on the following for mpeg videos of:
See Question of the Week #136, Question #137, and Question #138 for information on using this demonstration to enhance class involvement.
REFERENCES: (PIRA 5K20.10)
EQUIPMENT: Eddy current magnet with various pendula.
SETUP TIME: None.
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