Wednesday, April 11, 2012

#6 Length of a pipe


Objective: 
The purpose of this experiment is to measure the length of a pipe using only the property of sound and standing wave.

Procedures:

1.      Record the frequency of a swing pipe when it reaches a harmonic, that is, a standing wave is created in the pipe.
2.      Record frequency when the swing pipe reaches next harmonic frequency.
3.      Using two frequencies to calculate the length of the swing pipe.


Results:

       Assume the length remains constant and the speed of sound remains to be 340 m/s, the first ω1 = 3859 rad/s, ω2 = 5068 rad/s. Thus, as f = ω / 2 π , f1 = 614 , f2 = 810. v = fλand v = 340 m/s, λ1 =  0.56 m,λ2 = 0.42.

       L = n (0.56) / 2 = (n + 1)(0.42)/2, so n is 3.

       Thus, the length L is 0.84 m


Discussion:
       The experiment conducts well. The tricky part is to understand the first harmonic sound is not actual first standing wave created in the pipe. The calculation is easy and error may occur in rounding the numbers.

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