5H40.23 - Lamp Filaments, Magnet & AC/DC

Code Number:
5H40.23
Demo Title:
Lamp Filaments, Magnet & AC/DC
Condition:
Excellent
Principle:
Magnetic Field Surrounding Wires with AC or DC Electricity
Area of Study:
Electricity & Magnetism
Equipment:
40 Watt Light Bulb with Long Filament, Variac, Neodymium Magnet, and 150 Volt DC Power Supply.
Procedure:

Connect the light bulb to the DC power supply and turn on.  When the magnet is brought near the bulb nothing happens.  Then connect the Variac and turn on the bulb.  When the magnet is brought near the bulb this time, wild oscillations of the filament due to the 60 cycle AC are observed.

NOTE: Bringing the magnet too close to the bulb when doing the AC part of the experiment may break the hot filament.

References:
  • Bruce Bernero, "A Demonstration of Magnetic Force upon a Current-Carrying Wire", TPT, Vol. 25, #2, Feb. 1987, p. 88.
  • John Kwasnoski, "Mechanical Resonance with an Incandescent Filament", TPT, Vol. 12, #5, May 1974, p. 302.
  • Wallace A. Hilton, "E-7d", Physics Demonstration Experiments.
  • Jodi and Roy McCullough, "Electromagnetism with a Flickering Bulb", The Role of Toys in Teaching Physics, p. 4.198.
  • Robert Ehrlich, "M.6. Deflection of a Light-bulb Filament", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 161 - 162.
  • Brian Jones and Matt Fackelman, "Dancing Light Bulb", Don't Forget the Duct Tape, p. 33 - 36.

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.