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!

Doppler Effect + Wavelength problem! Help Please

  1. Dec 4, 2011 #1
    1. The problem statement, all variables and given/known data

    A sound source emits sounds of frequency 210 Hz that travel through still air at 340 m/s. The listener moves at 85 m/s relative to still air toward the stationary source. What is the wavelength of the sound between the source and the listener?

    2. Relevant equations

    f' = f[1+ Vlistener/Vsound]
    v=(wavelength)f

    3. The attempt at a solution
    well using the doppler effect since the listener is moving towards the stationary source i know it will be f'=f[1+Vlistener/Vsound]

    i find the f' right... but when using v=wavelength*frequency, which frequency do i actually use. because i know although im solving for f' , im just wondering if its a trick or something because i'm a little confused on the concept.

    so for f' i get 262.5 Hz

    then i plug it in to the v=wavelength*freq , but which velocity do i use? the speed of sound or the speed of the listener moving?

    using the speed of sound i get 340 m/s = wavelength * 262.5 and end up with 1.295m as the wavelength.
     
  2. jcsd
  3. Dec 4, 2011 #2
    If the source is not moving the waves are unchanged and their wavelength is simply given by v/f where v is their speed in still air and f the original frequency.
    The frequency of the sound heard by the moving listener is higher because he passes through the approaching waves at a higher rate than if he were stationary. The Doppler formula will give this new frequency.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Doppler Effect + Wavelength problem! Help Please
Loading...