Demo Number 197
Location Shelf 37
Description This is a metal disk that has been balanced on a pin-sized tip to eliminate friction. When a spinning magnetic field (magnet mounted in a drill) is applied to the disk as shown in the picture, it starts spinning via the induction current formed on the disk. When a strong magnet is held around the rim of the disk, it will start slowing down due to magnetic braking.
 Related Demos 337
  • Procedure: Hold the magnet-drill assembly close to the balanced disc and operate the drill. The magnet exerts a torque (via eddy currents) on the disc, causing it to spin in the same direction as the magnet. The disk can be brought up to high speed very very quickly.
  • This demonstrates one method used in speedometers.
  • There is also a second disk made of the same material that has slits cut along it to eliminate eddy currents from forming.
  • For best results, remove the aluminum disc from the magnet, oil the base at the contact point, and hold the magnet very close to the disc.

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This Demo is Part of the following Categories: 5K20 Eddy Currents