Physics 434
Autumn 2006
Module 3
Finding resonances in a Kundt’s Tube (lab due to and
thanks to Toby Burnett)
Introduction
This module explores the waveform capabilities of the NI DVI data acquisition board,
and the corresponding driver VI’s. We will generate a sine wave of a given frequency,
use it to excite a physical system (the Kundt’s Tube), and measure the result.
We will also do some analysis of the results, demonstrating the capability of LabVIEW to
perform standalone data analysis.
The tubes that we use for this purpose have a loudspeaker in one end, and a small hole at
the other end for a microphone to measure the sound wave amplitude.
There is also a
small box containing amplifiers for the speaker and microphone.
The point will be to find some of the resonances, and estimate the speed of sound, and
measure the damping.
We begin by considering the sound resonances of an ideal organ pipe, or thin tube, of
length L closed at both ends.
Such a tube should show resonances under the following
conditions:
2L = n
λ
(129
where
L
is the length of the tube,
n
is an integer,
n
= 1,2,3, .
.. and
λ
is the wavelength of
the sound. Standing waves are established such that at the ends of the tube, the pressure
amplitude is maximal.
Such regions are known as (pressure) antinodes. As Figure 1
shows, there are also nodes (regions of the tube where the pressure amplitude is zero).
For n = 1, there is one pressure node at the center of the tube at L/2, while for n = 2, there
are two nodes at L/4 and 3/L4 and so on for higher values of n.
1
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View Full DocumentPhysics 434
Autumn 2006
Figure 1. Standing Waves in a closed thin tube of Length L.
The wavelength of the sound wave,
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 Fall '10
 LESLIEROSENBERG
 Physics, Frequency, Qn

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