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Finding Air Temperature

  1. Oct 14, 2006 #1
    Hey guys, need some help here with a problem. I've gotten half way thru and don't know where to go next. Here's the problem:

    The wavelength of a 40,000-Hz ultrasound wave is measured to be 0.868cm. Find the air temperature.

    Using v = frequency(wavelength)
    40,000-Hz(0.868cm) = v
    v = 347 m/s

    I'm not sure where to go from here? ...Thanks for any advice!
  2. jcsd
  3. Oct 14, 2006 #2

    Andrew Mason

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    You will need to know the relationship between the speed of sound in air and temperature.

    [tex]v = \sqrt{\gamma RT/M}[/tex] so

    [tex]T = Mv^2/R[/tex]

    where M is the molar weight of the gas (28.95 grams/mole for air) and [itex]\gamma[/itex] is Cp/Cv = 7/5 for a diatomic gas such as air.

    See this link to the hyperphysics site

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