A harmonic oscillator consisting of a neodymium magnet attached inside a spring is driven through resonance. Eddy currents, induced in pipes surrounding the magnet, result in a damping of the motion of the magnet. Our experiment makes precise measurements of the motion and damping of the magnet as we vary pipe composition, length, thickness, radius, and position. A theoretical analysis combining the standard differential equation for a damped, driven harmonic oscillator and Faraday’s law of electromagnetic induction gives excellent agreement with the experimental results. This analysis allows for the calculation of electromagnetic damping for any pipe configuration which is coaxial with the magnet’s motion and provides strong evidence for the eddy current damping analysis of the common demonstration of dropping a magnet down a conducting tube.
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December 1998
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December 01 1998
Eddy current damping of a magnet moving through a pipe
Kenneth D. Hahn;
Kenneth D. Hahn
Science Division, Truman State University, Kirksville, Missouri 63501
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Erik M. Johnson;
Erik M. Johnson
Science Division, Truman State University, Kirksville, Missouri 63501
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Allen Brokken;
Allen Brokken
Science Division, Truman State University, Kirksville, Missouri 63501
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Steven Baldwin
Steven Baldwin
Science Division, Truman State University, Kirksville, Missouri 63501
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Am. J. Phys. 66, 1066–1076 (1998)
Article history
Received:
December 02 1996
Accepted:
June 06 1998
Citation
Kenneth D. Hahn, Erik M. Johnson, Allen Brokken, Steven Baldwin; Eddy current damping of a magnet moving through a pipe. Am. J. Phys. 1 December 1998; 66 (12): 1066–1076. https://doi.org/10.1119/1.19060
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