Day 164: Wavelength of Sound


How long is a sound wave? What is the relationship between the
wavelength of sound from a Boomwacker and the length of the tube?
(Rather than telling students that the wavelength is double the tube
length, they are going to figure it out themselves.)

Part one: Determine the speed of sound in the tubes using a long
Boomwacker, a Vernier microphone and the snap of a finger.

Part two: Hit the Boomwacker in front of the microphone and get the
frequency spectrum. What do you notice about the spectrum (see
picture)? Find the frequency of the lowest resonance (first harmonic).
Calculate the wavelength. Repeat for various length Boomwackers. Graph
wavelength vs. tube length. What’s the pattern? Repeat experiment for
Boomwackers capped at one end.


About Frank Noschese

HS Physics Teacher constantly questioning my teaching.

One response to “Day 164: Wavelength of Sound”

  1. achmorrison says :

    Interesting results here! The issue with interpreting the graph is that you don’t really know how flat the response of the microphone is, nor do you really know how flat the broadband excitation of the boomwhacker is.Suppose, however, that we assume (!) that the mic response and the broadband excitation were both flat. (Probably not too bad of an assumption). We would guess that the relatively thin walls of the tubes damped the lowest few resonances rather significantly.

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