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ERIC Number: EJ1295701
Record Type: Journal
Publication Date: 2021-Apr
Pages: 4
Abstractor: ERIC
ISBN: N/A
ISSN: ISSN-0031-921X
EISSN: N/A
Rotation of Spherical Magnet Falling through a Slit Copper Pipe
Behroozi. F.
Physics Teacher, v59 n4 p243-246 Apr 2021
The stately fall of magnets through conducting pipes is a favorite classroom and laboratory activity used in teaching electromagnetic induction, Lenz's law, eddy currents, electromagnetic braking, and even Newton's third law. When a neodymium magnet is used, the terminal velocity is reached in just a few milliseconds as the induced eddy currents brake the fall and limit the speed to just a few centimeters per second. When the pipe is whole, the induced eddy currents in the vicinity of the poles form the circumferential current loops ahead and behind the falling magnet. When a slit is cut along the entire length of the conducting pipe, the induced eddy currents near the poles follow a path along the cut slit to complete a closed double loop. In this case the braking action is less effective so the magnet falls with a greater terminal velocity to generate the required eddy currents to balance the gravitational force. To explore experimentally the braking action due to each of the two types of induced eddy current, the terminal velocity of two neodymium magnets is measured, one cylindrical and one spherical, each falling through two identical copper pipes, one of which has a cut slit. The experiments are repeated with another set of copper pipes with the same outer dimensions as the first set but with a thinner wall to explore the effect of wall thickness. This article describes the experimental data, equation of motion, and outcomes of the experiments.
American Association of Physics Teachers. One Physics Ellipse, College Park, MD 20740. Tel: 301-209-3300; Fax: 301-209-0845; e-mail: pubs@aapt.org; Web site: http://aapt.scitation.org/journal/pte
Publication Type: Journal Articles; Reports - Descriptive
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A
Grant or Contract Numbers: N/A