Sources Of Error: closed air column

[n3w ton]

I did an experiment in class to determine the speed of sound. I used the speed of sound in air equation with the room temp at 28°C which was calculated at 348.6m/s. However when doing the experiment I got 329m/s.

I just want to know some source of error that may have caused this?

I have one so far please check it: When performing the experiment (side note; we had different groups doing the experiment, we used a closed air column and a tuning fork and equations to figure out the speed of sound in air that day) there were other groups. Could the other groups tuning forks frequencies been picked up in our closed air column giving us inaccuate resonant lengths?
Please tell me if this is possible, if the closed air column can pick other frequencies from other tuning forks that are being strung by other people thoughout the class.

Also Please give me a possible source of error for this lab, (no human erros please

THANKS!

 

[Drakkith]

I'm willing to bet that you weren't able to keep the conditions of your experiment close enough to what you calculated them to be. This could be due to measurment devices not being accurate enough or something like that. Was your calculation accurate enough for the teacher?

 

[DaveC426913]

That's a 6% margin of error. Is that bad?

 

[n3w ton]

yes the teacher said these results are fine, now I need to find a possible source of error that may have 'decreased' the speed

Also could a change in temperature may have affected the speed of sound? (even though I did not need temp. to find the experimental speed)?[the percentage error calculated is 5.4% which is relatively close to the real value]

 

[DaveC426913]

yes the teacher said these results are fine, now I need to find a possible source of error that may have 'decreased' the speed

Also could a change in temperature may have affected the speed of sound? (even though I did not need temp. to find the experimental speed)?


[the percentage error calculated is 5.4% which is relatively close to the real value]

What are you margins of error for the measurements?

What level of precision can you expect (How many sig digs)? If all your measurements were only two sig digs then your answer is actually 3x10^2, which is the same as the expected answer.

 

[Drakkith]

Sig digs = significant digits correct?

Edit: Also, could you give a few details on how you measured everything? I am not familiar with the experiment. How did you determine that the speed of sounds in your air was 329 m/s?

 

[n3w ton]

The percent margin was 10%, and yes 2 sig digs were used for all measurements. Though the mathematical view to this lab is not such a deal. I am trying to think of possible sources of error that may have been done during the experiment to prevent my getting my 'desired value'

 

[DaveC426913]

The percent margin was 10%, and yes 2 sig digs were used for all measurements. Though the mathematical view to this lab is not such a deal. I am trying to think of possible sources of error that may have been done during the experiment to prevent my getting my 'desired value'

We'd need to know what methods and instruments you used.

 

[n3w ton]

Instrument used:
-Meter Stick
-Resonant Apparatus (closed air column)
-1024Hz tuning Fork

We got a closed air colum (provided by teacher), and we strung the 1024 hz tuning fork with a mallet close to the air column, we pulled the 'plunger' inside the closed air column to find the FIRST resonant length. We did this until we found the 2nd and 3rd resonant length. After I used the resonant length equation for a closed air column L=λ/4 (rearranged to find λ). Then we used the universal wave equation v=f*λ to find the speed.

 

[Andy Resnick]

As DaveC426913 points out, your error is 6%- that's small, less than your measurement accuracy (2 significant digits is not sufficient to quantify a 6% error- never mind 5.4% error!).

In order to turn this experiment into a metrology exercise, you have to account for all kinds of effects, some of which have been mentioned but others include:

Properties of the air in the column- humidity, pressure and temperature will affect the speed of sound in air. For example, what is the effect of a 0.5 degree shift in temperature? What is the effect of a 1% change in pressure? etc..

Measured width of the resonant peak- how well did you locate the peak?

Calibration of the tuning fork- are you sure you are exciting with the frequency you think you are?

We could go on, I'm sure. The smart thing to do at this point is identify the *largest* sources of uncertainties and go down the list.

http://www.nist.gov/itl/sed/gsg/fundamentals_course.cfm

 

[DaveC426913]

Also, perhaps your meter stick was out of calibration. Was part of your setup in relativisitic motion during the experiment?

 

[maimonides]

Dave wins the thread.
On a more serious note: Did you apply end correction? (mouth correction, effective length)
http://www.fonema.se/mouthcorr/mouthcorr.htm

 

[Andy Resnick]

Also, perhaps your meter stick was out of calibration. Was part of your setup in relativisitic motion during the experiment?

Due to budget cutbacks, all of our meter sticks were shortened 15%...