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 How Do Touch Lamps Work?
Name: judith 
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A


Question:
My sixth grade students are studying electric circuits and want to know how a touch on and off lamp works without a switch. The Clapper also has them wondering. Any explanations?



Replies:
This is going to involve some hand waving and guessing. I am an ex- electrical engineer, but it has been a long time since I have done this stuff. OK, here goes: I think the switch that works in a touch lamp is actually a "capactively coupled field effect transistor". All transistors can be designed to act like little relay switches and FET's are particularly sensitive to residual static charge and subtle potential differences. Basically the touch lamp has a solid state switch. My guess regarding the clapper is that it has an audio amplifier that has a limiter on the input. Any audio signals that are below a particular t threshold will not get through. When the sound pressure level gets above a certain level it triggers the amplifier which is set to clip - switch on. This on signal is the trigger to turn on the lights. The clapper also might have a hi-pass audio filter on it to prevent mis-firing. A sharp noise like a hand clap has more high frequency content than low. By f filtering off the lower frequencies that might be more prevalent in conversation and allowing only "shrill" noises through one would hope to eliminate an false starts on the part of the clapper. However, my bet is that an extremely loud stereo or some serious shouts could confuse a clapper. You might try leaving this query in the "Ask An Engineer" s Section of this BBS. Good luck.

Nick P. Drozdoff



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 (help@newton.dep.anl.gov), or at Argonne's Educational Programs

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

Argonne National Laboratory