# Wavelength from pressure graph

1. Apr 29, 2004

### Evgeny

Today in class we were performing an experiment to determine the speed of sound using a pitch-fork, a mic, a long tube, and a ti calculator.
We ended up with a very nice uniform wave-pattern on the pressure/time graph. Now that we have figured that out, we need to figure out the wavelength to complete the experiment. (using v = wavelength * frequency, frequency being the inverse of period which we can easily find)
Problem is, I'm not sure how to go about figuring out the wavelength only given the pressure/time data table. Or am I missing something completely in finding the speed of sound using given data?

-Evgeny

2. Apr 30, 2004

### Integral

Staff Emeritus
You do not give much information about your experiment. Remember, all that we know about what you did we learn from what you tell us. There is much that must be assumed in order to help you.

Let me guess. You used the tunning ford to induce vibrations in the tube, then you used the mic to find loud and quite spots in the tube?

What is the pressure time graph? I would think that you would generate a sound intensity vs position graph? Please tell us what you plotted and how you took your data? Without more information there is no way to help you.

3. May 1, 2004

### ophecleide

Integral is right, your description of the experiment was very vague. How/where were you measuring the pressure? Do you know the length of your tube? Do you know the frequency of the pitchfork, or is that what the pressure vs. time graph was for? Based on the statement "Or am I missing something completely in finding the speed of sound using given data?" I'm guessing you aren't using a given value for the speed of sound. Please elaborate.

4. May 1, 2004

### Parth Dave

For this particular lab the objective was to determine the speed of sound using any means necessary (except for measuring the temperature and using the formula).

What we did (i am evgeny's lab partner btw) was set up a system with a long tube (we do have the length); on one side we had a vernier microphone, on the other side we had a tuning fork. We used the tuning fork to create a (relatively) constant sound. The data from the microphone was sent to a TI-83 graphing calculator which then created a pressure vs time graph for us. According to the instruction manual for the mic, it will graph pressure vs time. However, other people in the class did different experiments (still using the mic) and attained sound intensity. So it may be sound intensity vs time. The only difference with theirs is that they used the LoggerPro program on imac computers, whereas we used the Datamate program on either a TI-83 or TI-89 graphing calc. We are not given values for anything. We have to determine wavelength and frequency and then calculate the speed of sound. The Frequency is no problem. However we are having trouble finding the wavelength. The question is - is it possible to find it? And if so, how? (if you need any more information, feel free to ask, ill see how i can help)

One other thing we were looking at to determine the wavelength was the sound resonance in the tube. Im not exactly sure how to do this, but I will be doing some research to see if i can find something.

5. May 2, 2004

### Integral

Staff Emeritus
I do not see that you have taken any data that will give you the wavelength. I am assuming that you positioned your mic at a OPEN end of a tube with the source (Tuning fork) that the other end. If you were able to vary the length of the tube and find resonate lengths you would have the information you need. Otherwise it is not clear what you have.

{Begin Rant}
I seems that your school has lost sight of how to teach Physics. You are given lots of sexy technology and expected to figure out the physics simply because you have sexy technology. The way I have done this lab was with a glass tube slowly filled with water, marking the position of each resonance. The separation of the resonances contains your wavelength information. The equipment needed is a sound source, a glass tube, some water, a grease pencil and a meter stick. The students were not simply handed the equipment and expected to figure out the physics on their own. The procedure was carefully described.

Your school has some fancy equipment, now if you only had a teacher that knew how to use it. I can imagine some wonderful stuff that could be done if the emphasis was on the PHYSICS and not the equipment.

{/rant}

Last edited: May 2, 2004