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

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

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.

  • 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.

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