PASCO WA-9612 RESONANCE TUBE - Manual (Page 11)

012-03541E Resonance Tube
7
Experiment 1: Resonant Frequencies of a Tube
EQUIPMENT NEEDED:
— PASCO Resonance Tube
— Function Generator
— Frequency Counter (if your function generator doesn't accurately indicate frequency)
— Oscilloscope (recommended, not necessary)
Introduction
When a speaker vibrates near a tube, there are certain frequencies at which the tube will
amplify the sound from the speaker. These frequencies are called resonant frequencies, and
occur because the dimensions of the tube are such that, at these frequencies, there occurs a
maximum transfer of energy between the speaker and the tube.
Procedure
➀ Set up the Resonance Tube, oscilloscope, and function generator as shown in Figure 1.1.
Turn on the oscilloscope. Set the oscilloscope sweep speed to approximately 5 ms/div and
the gain on channel one to approximately 5 mV/div. Turn on the amplifier and the function
generator. Set the output frequency of the function generator to approximately 100 Hz.
Adjust the amplitude of the function generator until you can distinctly hear the sound from
the speaker. If you use the oscilloscope, trigger on the speaker output.
➤ 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
you may need to reduce the amplitude as you increase the frequency.
➁ Increase the frequency slowly and listen carefully. In general, the sound will become
louder as you increase the frequency because the function generator and speaker are more
efficient at higher frequencies. However, listen for a relative maximum in the sound level—
a frequency where there is a slight decrease in the sound level as you increase the frequency
slightly. This relative maximum indicates a resonance mode in the tube. Adjust the fre-
quency carefully to find the lowest frequency at which a relative maximum occurs. (You
can also find the relative maximum by watching the trace on the oscilloscope. When the
signal is a maximum height, you have reached a resonant frequency.) Record the value of
this lowest resonant frequency as n
0
in Table 1.1
Figure 1.1 Equipment Setup
1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14
WA-9612 RESONANCE TUBE
13 13
SPEAKER INPUT
.1 W MAX
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
ON
OFF
ON
OFF
Oscilloscope
Function generator
Amplifier