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CBL
Lab 12

A Snappy Speed of Sound Measurement 

Goal: To directly determine the speed of sound in air by measuring the time for a sound pulse to echo down a plastic tube.

Equipment / Materials per station:

TI-83 Calculator CBL microphone TI CBL meter stick

TI link cable PHYSICS program group a disposable plastic cup or "clicker"

clear plastic tube(s) ≥ 1m with one capped end [fluorescent light covers work well]

Equipment set-up:

Lay the plastic tube flat on a stable table. The open end should be close at hand and NOT aimed directly toward any significant source of sound. Extraneous noises can cause accidental triggering of the microphone/CBL and produce confusing data. Determine what part of the microphone probe box is the actual microphone. The microphone should be placed close to, but NOT touching the open end of the tube.

Attach your calculator to the CBL using a link cable. Connect the microphone probe in the channel 1 port of the CBL. Turn on the CBL and calculator.

Have the plastic cup nearby. You will be giving the cup a sharp thump near the open end of the tube. This initial thump sound and its echo are the actual sounds you want to record.

Program Execution and Data Collection:

Select and run the PHYSICS program on your calculator by pressing [PRGM] and then selecting PHYSICS and pressing [ENTER].

You will have to set up the method of data collection within the PHYSICS program. To do this, follow the steps below noting that you are given what you see on the screen and the necessary response....

<VERNIER DISPLAY SCREEN>

  

hit [ENTER]

<***MAIN MENU***>

 

  

type 1

OR select 1:SET UP PROBES & hit [ENTER]

<ENTER NUMBER OF PROBES>

  

type 1 OR select 1:ONE & hit [ENTER]

<SELECT PROBE>

 

  

type 4

OR select 4:MICROPHONE & hit [ENTER

<CONNECT PROBE TO CHANNEL 1>

  

check you did this properly and hit [ENTER]

<SELECT MICROPHONE>

 

  

type 1

OR select 1:CBL & hit [ENTER]

<COLLECTION MODE>

 

  

type 2

OR select 2:WAVEFORM/TRIGR & hit [ENTER]

<TRIGGER MODE

PRESS [ENTER] TO READY THE CBL MICROPHONE>

  

hit [ENTER]. The CBL will display READY

until a sound is recorded.

<HOLD SOUND SOURCE CLOSE TO THE MICROPHONE. PRESS [ENTER} WHEN CBL SHOWS DONE>

  

Thump the cup near the open tube end.

When CBL displays DONE, hit [ENTER]

At this point, the collected data will be displayed by the calculator as a graph of Sound Pressure (y axis) vs. time (x axis). Hopefully your graph has two rather sharply defined peaks representing the initial thump and the echo caused by its reflection. Use the left/right arrow keys to scan the data on the graph. Record the time values at the two sound peaks. Be careful when recording the small time values at the beginning of the graph as they will likely be displayed in scientific notation.

The program will give you the option to repeat the measurement without going through the entire set up again. Repeat the data collection and recording several times for a single tube, carefully recording your values, until you have achieved a consistent time interval.

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report form for Name:_______________________________

Speed of Sound Period:___________ Date:_______________

 

Data and Analysis I

Carefully sketch one of your data graphs in the box provided.

 

What do the peaks on the graph represent?

 

 

 

If, for instance, a tube is 1.00m long, what is the distance that a sound pulse travels during its round trip down the tube and back?

 

Explain how you can use the time interval between the initial and reflected sounds and the total distance traveled to determine a value for the speed of sound.

 

 

 

Doing several trials with one tube, fill in the data table below.

Tube Length (m)

Round-trip distance traveled by sound (m)

Initial sound

time (sec)

Reflected sound

time (sec)

echo time = time interval between sounds (sec)

Calculated Speed of Sound (m/sec)
           
           
           
           
           
           
           
           
           
           

AVERAGE CALCULATED SPEED OF SOUND =

  

 

At this point, the collected data will be displayed by the calculator as a graph of Sound Pressure (y axis) vs. time (x axis). Hopefully your graph has two rather sharply defined peaks representing the initial thump and the echo caused by its reflection. Use the left/right arrow keys to scan the data on the graph. Record the time values at the two sound peaks. Be careful when recording the small time values at the beginning of the graph as they will likely be displayed in scientific notation.

The program will give you the option to repeat the measurement without going through the entire set up again. Repeat the data collection twice for each tube, carefully recording your values. Do this for at least five tubes of different length.

--------------------------------------------------------------------------------------------------

report form for Name:_______________________________

Speed of Sound Period:___________ Date:_______________

 

Data and Analysis II

Carefully sketch one of your data graphs in the box provided.

What do the peaks on the graph represent?

 

 

 

If, for instance, a tube is 1.00m long, what is the distance that a sound pulse travels during its round trip down the tube and back?

 

 

 

Doing several trials with several tubes of different length, fill in the data table below.

Tube Length (m)

Round-trip distance traveled by sound (m)

Initial sound

time (sec)

Reflected sound

time (sec)

echo time = time interval between sounds (sec)
         
         
         
         
         
         
         
         
         

Create a plot of round-trip distance (y axis) vs. echo time (x axis). This should yield a linear graph with a slope equal to the speed of sound in the tubes. Sketch your graph below and write the equation of fit.

 

 

 

 

 

 

According to my graph, the speed of sound is ______________________.

 

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