1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Finding displacement amplitude given frequency and pressure

  1. Oct 19, 2011 #1
    1. The problem statement, all variables and given/known data

    What is the displacement amplitude of a sound wave of frequency 160.0 Hz in air at 20 °C at the pain-threshold pressure amplitude of 29.0 Pa?

    f = 160 Hz
    Vs = 343 m/s
    ΔP = 29 Pa

    2. Relevant equations

    ΔP(x,t) = (ΔP)cos(kx - wt) = β*s*k*cos(kx - wt)
    k = f/Vs

    3. The attempt at a solution

    ΔP = βsk

    Therefore, s = ΔP/(β*k) = (ΔP*Vs)/(f*β)

    β = 1.4 * 10^5 Pa

    So the answer I got was 4.44*10^-4 m which is wrong. Am I missing something here?
  2. jcsd
  3. Oct 20, 2011 #2
    k=f/Vs is not accurate, since k is 2π/λ

    λf = Vs

    ω/k = Vs
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook