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Magnets Through Copper Tube


Consists simply of a copper tube and a powerful cylindrical magnet with an outer diameter just a bit smaller than the inner diameter of the tube. There are three copper tubes available in the demo room. Their lengths aren't exactly the same but are close to 50cm.

A smaller-diameter copper tube with a slit is also available, as well as a pair of aluminum tubes 1) and a long solenoid. 2)


Demonstrate the induction of eddy currents. Demonstrate induced current/ magnetic fields. Demonstrate Lenz's law/ Faraday's law.



There are a couple ways to run this demo. The easiest way is to simply take the copper tube and drop the magnet in, observing the amount of time it takes to descend down the tube versus the amount of time it'd take to fall the same distance (~8s vs <1s). A couple metal cylinders with the same diameter of the magnet are available, so with another tube and a volunteer you can have a 'race', dropping the magnet and the metal cylinder into the tube at the same time.

Another copper tube with a 5mm slit running down it's length is also available. This way you can watch the magnet slowly descend down the tube. Note that this becomes a bit counter-intuitive to explain- the eddy currents don't only go around the circumference of the tube since this tube still slows the magnet down (somewhat less, but still) and the slit would stop those currents. The eddy currents also circle around axes normal to the outside of the tube.


Please take care not to drop the copper tube as dents will not allow objects to pass through.

Demo room information

Location Q2
Maker Unknown
Current State Working
which work, but produce a smaller braking force because the conductivity of aluminum is lower
which at first glance seems like it should work, but doesn't due to the way the induced currents cancel. If you can measure precisely enough, it may be possible to register a (very small) difference.
demonstrations/5_electricity_and_magnetism/5k_electromagnetic_induction/magnets_through_copper_tube/start.txt · Last modified: 2020/01/28 18:25 by demoroom