As you drop neodymium magnets down these large diameter, thick-walled copper and aluminum tubes, you can watch them twist and turn as they slowly fall. A moving magnetic field creates a surprisingly strong opposing magnetic field in these tubular conductors. Each tube kit listed below contains a thick-walled Eddy Current Tube and sample neodymium magnets. Please see below for details. The length of the heavy-walled aluminum tube is calculated so that magnets take the same time to fall as the shorter copper tube.
Read more on our Blog - Focus on Lenz's Law Read more on our Blog - Bring Some Magic Into Your Classroom! Read more on our Blog - Eddy Current Tubes with Video
| Material || Approx. Dimensions || Approx. Fall Time || Included Neodymium Magnets || Item Number |
| Copper || 18 cm (7 in.) 34 mm Dia || 4 sec || 2 rings || ED-100 |
| Aluminum || 36 cm (15 in.) 34 mm Dia || 4 sec || 2 rings || ED-125 |
| Copper || 60 cm (24 in.) 26 mm Dia || 18 sec || 1 sphere || ED-140 |
Download the pdf of this lesson!
- An eddy current is a current set up in a conductor in response to a changing magnetic
field. Lenz's law predicts that the current moves in such a way as to create a magnetic
field opposing the change; to do this in a conductor, electrons swirl in a plane
perpendicular to the changing magnetic field.
Because the magnetic fields of the eddy currents oppose the magnetic field of the
falling magnet; there is attraction between the two fields. Energy is converted into
heat. This principle is used in damping the oscillation of the lever arm of many
mechanical balances. At the end of the arm a piece of flat aluminum is positioned to
move through the magnetic field of a permanent magnet. The faster the arm
oscillates, the greater the eddy currents and the greater the attraction to the permanent
magnet. However, when the arm comes to rest, the attraction is negligible.
- If a single neodymium magnet has the same mass as a single cow magnet, the
neodymium magnet will fall at a slower rate because its magnetic field strength is
- Two neodymium magnets fall at a slower rate than one because the magnetic field
strength has increased. The time of fall within the tube increases with the addition of
other magnets. There is a point where the effect of the increase in mass becomes
greater than the increase in magnetic field strength. Then, the group of magnets falls
- Thicker tubes increase the falling time due to stronger eddy currents from the greater
number of conducting electrons. Suggest an experiment to determine the thickness of
the tube by determining the rate of fall of a magnet within the tube.
- Determine the time for one magnet to fall through the 7 inch copper tube and measure
the time for the same magnet to fall through the 15 inch aluminum tube. The falling
times should be approximately the same. Relate the length of the tubes to the
conductivity of the metals.
Areas for investigation:
- How will magnets of different magnetic field strengths affect falling time? Try dropping 2 cow magnets that have the same mass but different magnetic field strengths down the same tube one at a time.
- How does the falling time of neodymium magnets compare to the falling time of cow magnets?
- Allow multiple neodymium magnets to attract together. How does changing the
number of magnets affect the falling time?
- Do both single and multiple neodymium magnets fall down the tube at a constant velocity?
- How does changing the thickness of the tube affect falling time?
- How does changing the length of the tube affect falling time?
- How does changing the material of the tube affect falling time?
- How does cooling the tube down with liquid nitrogen affect falling time?
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Jun 16, 2016 | By James of NYC, NY United States
Sep 16, 2015 | By Mark Carter of Phoenix, AZ United States
Aug 20, 2015 | By Darla Dee Turlington of Palm Coast, FL United States
May 28, 2015 | By Jerry Petrey of Tucson, AZ United States
Nice eddy current demo, needs larger magnet
Mar 22, 2014 | By Lyndie Chiou of Union City, CA United States
Mar 11, 2014 | By Kevin Eckhart of Oxnard, CA United States
Very good copper tube
Feb 26, 2014 | By Ruggero of Milano, Italy
Feb 20, 2013 | By Al Evans of DeLand, FL United States
Captivating Magnet Races
May 20, 2012 | By Lissa Vincent of Montgomery Village, MD United States
Eddy Current Tubes
May 16, 2012 | By Brian of Tucson, AZ United States
What, Come On!!
May 16, 2012 | By Roy of Dallas, TX United States