Practice Problem 0455
If the speed of sound is 340 m/s and the length of the air column is 0.2 metres, find the
resonant (harmonic) frequencies that this air column would produce when a person
would blow across it.
The first harmonic consists of ¼ of a wavelength
0.2 m
0.2 m = 0.25
0.8 m = 
f = v/
f = 340/0.8
f = 425 Hz
Therefore the first harmonic for this tube is 425 Hz.
The second harmonic consists of 3/4 of a wavelength
0.2 m
0.2 m = 0.75
0.266 m = 
f = v/
f = 340/0.266
f = 1275 Hz
Therefore the first harmonic for this tube is 1275 Hz
Practice Problem 0455
The third harmonic consists of 5/4 of a wavelength
0.2 m
0.2 m = 1.25
0.16 m = 
f = v/
f = 340/0.16
f = 2125 Hz
The third harmonic for this tube is 2125 Hz.
Amazingly, this tube produces many different frequencies,
including the 3 that you just calculated
425 Hz
1275 Hz
2125 Hz
If a tuning fork with a frequency of either 425 Hz, 1275 Hz or
2125 Hz was placed above this tube, a resonance would be heard.