Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Light Dimmers and Resonance
Name: Edward M.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 2001-2002

We have several incandescent bulbs that are controlled by dimmers. If the dimmers are slowly moved, there are several positions where the bulb makes a noise. I assume these noises represent some sort of resonant frequency, but what is vibrating? and what property of the changing electrical energy is altering the vibration to set up the resonance? Am I correct in assuming that to maximize bulb life the dimmer should be set to avoid these noises?

Interesting question. Possible sources might be: 1. A "hum" from the dimmer -- presumebaly a transformer -- due to the 60 hertz AC current. This is the very familiar hum you pick up around unshielded AC circuits. 2. The AC current might set up a vibration in the filament, or its wire leads. This would be a much higher frequency pitch. If it is the latter, certainly you would want to avoid those settings.

Vince Calder

I do not know, but I would guess the dimmer decreases the portion of the normal sine wave which will be let through to the bulbs in order to dim the bulbs. Different portions of a sine wave will have different harmonic components. When a large harmonic component is at the frequency of a resonance of the filament, the filament could be made to vibrate more vigorously and even emit noises. I would say that you are absolutely right in that those settings should be avoided for maximum bulb life.

Richard J. Plano

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory