Demos: 6D-09 Lenz's Law

Two cylindrical objects, identical in appearance, are dropped successively through a long cylindrical aluminum tube. One objects drops freely whereas the other makes its way slowly through the tube. One of the cylinders is magnetized, setting up eddy currents that slow it down as it passes through the tube.

Directions: Hold the long tube in one hand (or have a student volunteer hold it) and drop the unmagnetized cylinder into the tube. Have the student ready to catch it when it comes out of the other end. Then (using deceptive moves, if you wish to add a little mystery to it) drop the other cylinder through the tube, once again having a student ready to catch it. It will take several seconds for this cylinder to fall through.

Suggestions for Presentation: You can create some “magic” here and be as showy as you like. The key is to somehow make the students think that the second cylinder is really the same one just dropped through the tube. A small mark on the cylinder will let you know which is which. After making the presentation, the discussion can go back to the results of Demos 6D - 07 and 6D - 08.

Applications:

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