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APPARATUS

At a moderate volume, vary the signal generator frequency near resonance until a folded paper strip on the rim of the glass vibrates wildly and the microphone signal increases sharply in amplitude.  At resonance, the microphone signal should be 90 degrees out of phase with the signal generator voltage.  Turn up the volume a bit to show the standing waves around the rim using the strobe light and video camera.  Turn up the volume to about 3/4 max for about a second and glass should shatter.

Select a clean thin-walled beaker or glass with a high Q and not having two closely-spaced resonant frequencies.  Find its resonance frequency by pinging the rim - it should be between about 800-1000 Hz.  The laptop with the sound card scope can be used instead of an ordinary scope to identify the resonance frequency.

Set strobe to just above or below a submultiple of the resonance frequency.

Display both driving frequency and microphone signal.  Trigger on function generator.  

Protect speaker with 2 A fuse.

Input to amplifier should not exceed 1 V.

Set the beaker within 1/2 cm of the speaker.  Set microphone 90 degrees from speaker.  Illuminate beaker from above with strobe light and position camera to display rim.

REFERENCES

 

AJP 47(9), 828,

TPT 28(6), 418,

TPT 38(5), 259.