Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538
Demonstrations are cataloged according to PIRA Bibliography
PLEASE REQUEST DEMOS WELL IN ADVANCE
Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.
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Purpose:An example of two high frequency waves with similar frequencies which are combined to produce an audible frequency.
Procedure:The circuit consists of two oscillators each with a frequency of ~400 kHz. The frequency of one of the oscillators can be controlled by changing the capacitance in the circuit. This is accomplished by attaching an antenna to the circuit whose capacitance with respect to the earth depends on the type of material surrounding it. As you move closer to the antenna, its capacitance changes slightly and an audible beat note is generated by mixing the two oscillators and sending the output to a speaker.
Hints:There is an adjustable pot on the back to "zero" the device so that it is silent before placing hand near antenna. A schematic of the circuit can be found here. Here is a full page encapsulated postscript file so you can read the tiny lettering in the schematic. This circuit has been adapted from one found on this site.