In the lowest normal mode of sound waves in a PVC tube open at both ends, the tube
length is essentially one half-wavelength. (There is a small "end correction," so that the
tube length is actually about one tube diameter less than a half-wavelength.) The velocity
of sound is about 330 m/sec. Your tuning fork is 440 Hz. By holding your tuning fork at
one of the tube so that it acts like a transmitter, vary the tube length (by sliding one tube
inside the other) until you find the resonance. Verify that the total length at resonance
makes sense.
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