College of Liberal Arts & Sciences
6B40.10 - Variac and Light Bulb
See also 6B40.10 in Astronomy.
Video Credit: Jonathan M. Sullivan-Wood.
Put the 1 KW light bulb onto the variac and turn up slowly. At low voltages the large filament area should look red to a dull orange. As you now slowly turn up the voltage the filament will get hotter and the corresponding color will be more and more towards white.
- D. C. Agrawal, Harvey S. Leff, and V. J. Menon, "Efficiency and Efficacy of Incandescent Lamps", AJP, Vol. 64, #5, May 1996, p. 649.
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.