Oscillations and Waves > Instruments > Air Columns DCS# 3D30.10


plexiglas cylinder 202-17-F
copper tank  202-17-F
rubber tubing with clamp  202-17-F
HP 200AB audio oscillator  202-08-G
small speaker  202-07-E4
2-liter beaker to fill tank  101-01-C
microphone 201A
oscilloscope with camera 202

DESCRIPTION Show resonance two ways: 1) fixed air column length, tune through frequencies,
2) fixed frequency, raise or lower reservoir and you hear the resonance as it goes through the proper length.

Like a closed organ pipe, might show the end correction.

Demonstrates both resonance and the harmonic content of a distorted sine wave.  Use f = 680 Hz, so wavelength is about 0.5 m. First put maximum generator output into scope, to show it is distorted.  Then connect scope to speaker, watch scope and listen to sound as air column length increases from about 5 to 40 cm.  Expect first fundamental resonance for about 12.5 cm, but it comes at 9 or 10 due to end correction.  Next fundamental one is at about 35 cm, but between these two you hear and see others (higher in frequency) due to the higher Fourier components, whenever the relationship f = odd integer x v/4L is satisfied.

NOTES If using VIZ audio generator, use matching transformer to reduce harmonics.

Add water just before demo is needed -- plexiglas tube leaks.