PASCO WA-9612 RESONANCE TUBE - Manual (Page 19)

012-03541E Resonance Tube
15
Experiment 4: The Speed of Sound in a Tube
EQUIPMENT NEEDED:
— PASCO Resonance Tube
— Function Generator
— Oscilloscope
Introduction
You can determine the speed of sound in a tube from a standing wave pattern. Create a stand-
ing wave, then determine the wavelength of the sound from the standing wave pattern. You can
then multiply the wavelength by the frequency to determine the speed of the wave (V = ln).
However, you can also measure the speed of sound more directly. In this experiment you'll
measure the speed of sound in the tube by timing a sound pulse as it propagates down the tube
and reflects off the end.
Procedure
➀ Set up the Resonance Tube, oscilloscope, and function generator as shown in Figure 4.1. Move
the piston near the end of the tube. Set the signal generator to approximately 10 Hz square
wave and turn the amplitude up until the speaker is clearly heard making a clicking sound. The
oscilloscope should be triggered with the output from the signal generator, or from a trigger
output of the generator. When viewed at a frequency roughly equal to the frequency of the
signal generator output, the screen should look something like the diagram in Figure 4.2.
1 2 3 4 5
SPEAKER INPUT
.1 W MAX
ON
OFF
ON
OFF
1 2 3 4 5 10 11 12 13 14 11 12 13 14
WA-9612 RESONANCE TUBE
13 13
BK PRECISION 200 Mhz OSCILLISCOPE
MODEL 2120
INTENSITY FOCUS
TRACE NOTATION
TRIG LEVEL
COUPLE SOURCE
SLOPE λ - Y
TIME/DIV
X-POS
VAR VAR
VAR SWEEP
CAL CAL mV V
CH 1 VOLTZ/DIV CH 2 VOLTZ/DIV
CAL mV V
VERTICAL MODE
PULL XS PULL XS
CH 2
∞
CH 1 ∞
AC
DC
AC
DC
AC CH1
CH2
ALT
EXT
POS POS NORM
EXT CH1
CH2 NORM
EXT CH1
CH2
MANUAL AUTO
T X-Y
T X-Y
LINE
CAL EXT CH4
POWER 200V MAX 400V MAX 400V MAX
- + +
-
T T L
H I Ω
G N D
L O Ω
M I N
R A N G E
A D J U S T
M A X
O U T P U T F R E Q U E N C Y
A M P L I T U D E
P I - 9 5 8 7 B
D I G I T
A L F U N C T I O N
G E N E R A T O R - A M P L I F I E R
H E RT Z
W AV E F O R M
I N P U T G N D
E X T E R N A L
Plunger
Time from initial pulse until echo
Figure 4.2 Equipment Setup
Function generator
Oscilloscope
Piston
Figure 4.1 Equipment Setup
➤ WARNING: You can damage the speaker by overdriving it. The sound from the speaker
should be clearly audible, but not loud. Note also that many signal generators become more
efficient and thus produce a larger output as the frequency increases, so if you increase the
frequency, you may need to reduce the amplitude.
➁ Increase the sweep speed of the oscilloscope until you are able to see more clearly the details
of the pulses along one part of the square wave. You should see a series of waves generated by
the initial ringing of the speaker caused by the sudden voltage increase of the square wave.
This will be followed shortly by a similar-looking series of waves representing the returned
sound echoing off the face of the piston at the other end of the tube. The oscilloscope trace
with the faster sweep speed should look something like the lower diagram in Figure 4.2.