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Temperature and frequency in an organ pipe

  1. Nov 7, 2005 #1

    The frequency of the note [tex]{\rm F}_4[/tex] is [tex]f_F[/tex].

    1. If an organ pipe is open at one end and closed at the other, what length must it have for its fundamental mode to produce this note at a temperature of T? The speed of sound is [tex]v_s[/tex].

    I used the equation [tex]f_n = \frac{nv}{4L}[/tex]. Plugging in known values resulted in [tex]L = \frac{1}{4}\frac{v_s}{f_F}[/tex]. This is correct.

    2. At what air temperature will the frequency be f? (Ignore the change in length of the pipe due to the temperature change.)

    I have no idea how to start this.
  2. jcsd
  3. Nov 7, 2005 #2
    will the frequency be f? What's the value of f?

    I know the speed of sound varies at different temperatures. Our book/teacher never gave us a formula though. Velocity of sound is given by v = sqrt(B/rho). Where B is the bulk modulus of air and rho is the density. So if you can figure out how B and rho varie with temperature you should get somewhere.

    Maybe someone else can help further...
  4. Nov 7, 2005 #3
    You're right about temperature affecting velocity; my book made explicit mention of that.

    But, it, too gave no formula for this type of problem in the respective section.
  5. Nov 11, 2005 #4
    I asked my professor and he gave an equation where frequency is 331 + 0.6T.

    I tried this, but was unsuccessful.

    How do I get wavelength from this?
  6. Nov 11, 2005 #5


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    Staff: Mentor

    That formula is for the speed of sound in air at temperature T, where T is in °C, and speed in m/s.
    Ref: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html

    v = [itex]\lambda[/itex] f, where [itex]\lambda[/itex] is wavelength and f is frequency.

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