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Homework Help: Power and Amplitude of sound wave

  1. Nov 6, 2005 #1
    For my homework,
    To find Amplitude of the wave,
    for a longitudinal wave travelling down a copper rod.
    Given: frequency, radius of copper rod, average power, Young's constant, density, wavelength.
    what equation should I consider?
    I'm thinking something like P=(omega*amplitud)^2 because I know power is proportional to amplitude and frequency of the wave....but I know that's wrong.
  2. jcsd
  3. Nov 7, 2005 #2


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    The displacement amplitude A is given by:

    [tex]A\,=\,\frac{\Delta{p_o}}{\omega\,\rho\,c}[/tex], where

    [itex]\Delta{p_o}[/itex] is the pressure amplitude,

    [itex]\omega[/itex] is the angular frequency given by [itex] 2\,\pi\,f[/itex],

    [itex]\rho[/itex] is the material density, and

    c = speed of sound in the material, which is given by -

    [tex] c = \sqrt{\frac{E}{\rho}}[/tex]

    where E is Young's (Elastic) modulus.

    The intensity of the sound wave is I = P/a, where P is the power of the wave per unit transverse area, a, and

    P = 1/2 [itex]\omega^2[/itex]A2[itex]\rho[/itex] c
    Last edited: Nov 7, 2005
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