Additional Info

• ID Code: K2-42
• Purpose: Demonstrates Lenz's law
• Description:
  

  Two arrays of magnets, containing five strong disc magnets each with small aluminum spacers between the magnets, are dropped through a vertical aluminum tube. One set, having its poles North-to-South, has very little external field, and falls very quickly through the tube. The other set, having its poles arranged North-to-North, then South-to South, etc., has a large external field. A solid aluminum bar of the same size is also available for comparison.

  Background

  As the magnetic array falls, it induces large currents in the aluminum tube. According to Lenz's law, these currents interact with the falling magnet array so as to oppose its (falling) motion, and the array takes several seconds to fall about two meters through the tube. By comparison, the aluminum rod falls much more quickly. For advanced students, compare the two different magnetic arrays, to show the relationship between the amount of slowing and the changing flux. For the simpler form of the demonstration, just use the aluminum rod and the North-North South-South array (marked with a red dot) to maximize the difference.

  Optionally, a smaller portable handheld of this demonstration is available upon request, suitable for small groups.

• Availability: Available
• Loc codes: FS2