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The speed of sound in a classroom is 343m/s.

A) A tuning fork of frequency 512Hz is struck. What length of open air tube is required to create a resonant sound at the 1st harmonic?
wavelength=v/f=343/512=0.67m
L=.5wavelength=.5(.67)= 0.335m

B) Fore the same tube, what tuning fork frequency is needed to generate a resonant tone at the 3rd harmonic?
L=1.5wavelength
Therefore: .335=1.5wavelength
wavelength= .223m
f=v/wavelength=343/.223= 1538.12Hz

C)In the same classroom, what is the lowest resonant frequency for a closed air tube of length 45cm?

wavelength=L/.25=.45/.25=1.8
f=V(wavelength)=343(1.8)=617.4Hz

I'm having a really hard time with waves... So I just want to make sure I'm on the right track. Thanks a bunch :)

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6 answers
  1. http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/opecol.html

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  2. so A yes .335
    B yes 1536
    C
    well lambda = 1.8 meters all right
    but
    1.8 = v T = v/f
    f = v/1.8 = 343/1.8 = 1.91 Hz
    keep that distance = speed *time in mind

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  3. 191 Hz

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  4. Oh I mixed up my formula!! Thank you for catching that :) I hate mistakes that I should know better than.

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  5. When in danger or in doubt, keep the units and make sure they come out right.

    meters = meters/second * seconds :)
    L = v T

    f = 1/seconds
    so
    f = v/L = (meters/ second) / meters
    = 1/seconds

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  6. Ok, that's a good idea, I struggle with the units sometimes so I should try & keep track anyways. Thanks again :)

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