Physics 2225 Minilab 1: A Look at Sound
Purpose
• Visualize the wavelike nature of sound by using a
sound-to-voltage transducer (otherwise known as a
microphone….).
• Measure the speed of sound in a variety of ways.
Physics 2225 Minilab 1: A Look at Sound
Activity I: The Nature of Sound
Microphone (converts sound to electric voltage)
Sound 
Pasco 750 Interface
Computer/Data Studio : Used as an oscilloscope
Physics 2225 Minilab 1: A Look at Sound
Data Studio as a 1-Channel Oscilloscope
adjust vertical axis by
clicking on black
triangles
adjust trigger level
here by sliding
triangle
up or down
adjust horizontal axis by clicking on black triangles
Physics 2225 Minilab 1: A Look at Sound
T (period)
1
f 
T
1ms
1 ms
div
Physics 2225 Minilab 1: A Look at Sound
Activity II: Standing Waves and the Speed of Sound
tuning fork
L
Procedure:
 Adjust pipe location until the sound from the
tuning fork is amplified.
 Measure L as shown on the left.
 Think about the relationship between the
wavelength l and the length L.
 Determine wavelength l.
 Calculate the speed of sound using
vs  f l
Note: f is written on the tuning fork.
Physics 2225 Minilab 1: A Look at Sound
Review: Uncertainty from Repeated Measurements (e.g., Q8)
 Calculate the average speed of sound v from
several measurements.
 Determine the standard deviation sv
 Calculate the standard deviation of the mean:
sv 
sv
( N is the number of measuremen ts)
N
Result  v  s v
Physics 2225 Minilab 1: A Look at Sound
Activity III: Measuring the Speed of Sound with Microphones
Microphone 2 (plugged into port B !!)
d
Microphone 1 (plugged into port A !!)
stand
distance d
v

time
t
Clap !
table
Physics 2225 Minilab 1: A Look at Sound
How We Measure “t”
The basic idea:
 Sound first hits microphone 1  Triggers the oscilloscope
 Measurements on both microphones are started
simultaneously and displayed in Data Studio (acts now as a 2Channel oscilloscope).
 Sound pattern is seen on Channel A first, then Channel B.
 Time shift in sound pattern (Ch A versus Ch B) is “t”.
Physics 2225 Minilab 1: A Look at Sound
Data Studio as a 2-Channel Oscilloscope
adjust vertical axis of
Channel A or B.
Make Ch. A 5 Volts/div
Make Ch. B 2 Volts/div
Suggested values:
Please play with
these adjustments
as needed.
adjust horizontal axis to 0.5 ms/div
Physics 2225 Minilab 1: A Look at Sound
After a Successful Clap … Identify Repeat Pattern
t
It may require several
clap attempts before
you can reliably
recognize the
same pattern in
Channel B as in
Channel A.
Physics 2225 Minilab 1: A Look at Sound
Activity IV: Measuring the Speed of Sound with an Echo
Microphone 1
(plugged into port A !!)
Clap !
Stand
d
Table
distance 2 d
v

time
t
Hollow cardboard tube
Physics 2225 Minilab 1: A Look at Sound
Identify a repeated pattern…you may need several attempts
t
Echo
First passage
Physics 2225 Minilab 1: A Look at Sound
% Difference (e.g., Q 13)
measured value  theoretical value
% difference 
100
theoretical value
Physics 2225 Minilab 1: A Look at Sound
Important
 In the lab manual the data studio activities are called:
“Sound1.ds”, “Sound2.ds”, “Sound3.ds”
The actual files are called:
“A Look at Sound 1.ds” ….etc…
 Whenever you launch a new Data Studio file, you must
first close all other existing Data Studio files. Then launch
the new one. Still, sometimes the “Start Button” won’t
work. If that happens, close the file and launch it again.