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Analysis of the Motion of a Permanent Magnet Ring Falling Outside a Conductive Pipe
New Phys.: Sae Mulli 2020; 70: 161~167
Published online February 28, 2020;
© 2020 New Physics: Sae Mulli.

Sungwook HONG*

Department of Science Education, Daegu University, Gyeongsan 38453, Korea
Correspondence to:
Received December 9, 2019; Revised January 7, 2020; Accepted January 9, 2020.
cc This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
In this study, the motion of a permanent magnet ring falling outside a conductive pipe was analyzed. The magnetic dipole moment of the magnet ring was found to be 162.97 Am$ ^{2}$ by measuring the magnetic fields at a distance from the center of the ring. The terminal velocity was determined using an infrared sensor and an Arduino board. The actual relationship between the thickness of the conductive pipes and the drag constants corresponded well with the theoretical result of the falling motion of a magnetic moment within a conductive pipe. The effective magnetic moment of the permanent magnet ring and the effective inner radius of the conductive pipe were 1.41 Am$ ^{2}$ and 5.87 mm, respectively. The falling motion of a magnetic ring outside a conductive rod can be considered as the falling motion of a magnetic moment within a conductive tube with a very high thickness.
PACS numbers: 01.40.-d, 01.40.Fk
Keywords: IR sensor, Arduino, Physics education, Faraday’s law, Terminal velocity

March 2020, 70 (3)
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