5K20.10 - Magnetic and Electromagnetic Damping

Code Number:
Demo Title:
Magnetic and Electromagnetic Damping
Eddy Currents in a Pendulum, Magnetic Induction
Area of Study:
Electricity & Magnetism
Alnico Horn Magnet, Pendulum Frame, Disks and Rings (Broken and Unbroken), 3 Table Rods (Pendulum Frame), Electromagnet (5th Floor), 70 Volt DC Power Supply (5th Floor), Switch, and Made Up Pendulum and Rings.

Set up the permanent magnet demo as shown.  Attach an unbroken ring or disk to the pendulum and observe the damping.  Replace with a broken ring, slotted plate, or nonmagnetic material and observe no damping of the pendulum.

Take the long flat piece of aluminum and move it back and forth between the poles of the magnet and feel the damping force.

The electromagnetic damping is arranged as shown.  The pendulum pivot may need to be oiled.  Turn on the circuit breaker of the power supply.

NOTE: The power supply should already be pre-set at approximately 35 AC volts, or 50 DC volts on the output.

Start the pendulum swinging.  As the pendulum swings between the poles of the electromagnet turn on the switch and the magnet will have built up enough of a magnetic field to stop the pendulum as it comes back between the poles again.  PRACTICE is needed to get the timing down.

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Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.