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Frequency change with velocity change

  1. Apr 10, 2014 #1
    Does the received frequency at a location differ from the transmitted frequency when the medium velocity differs at the two locations?

    To give a concrete example, a sub-sea pinger is transmitting at 37.5 Khz 4,000 metres below sea level and at a particular pressure, salinity, and temperature. A receiver nearer the surface detects the signal at a different pressure, temperature, and salinity. Finally a surface vessel detects the signal under yet another set of pressure, temperature and salinity.

    For reference the velocity of sound in the oceans can vary by up to 10% due to these factors.

    My intuitive guess is that sound transmitted in a high velocity domain will increase in frequency when it hits a low velocity domain?
  2. jcsd
  3. Apr 10, 2014 #2


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    No ... frequency does not change with the media; only the wavelength changes.

    Speed = frequency x wavelength; so if the speed changes (due to the media), then the wavelength must change.

    Frequency is the driver ...
  4. Apr 10, 2014 #3
    Suppose for simplicity there existed a distinct boundary between the two mediums. And further suppose that we watched the crest of the wave from the time it hit the boundary and traveled onward in the lower velocity medium. This crest will not have traveled a full wave length by the time the following crest hits the boundary. This has the effect of shortening the wave length. But since the speed also is shortened then the frequency remains constant.
    Last edited: Apr 10, 2014
  5. Apr 10, 2014 #4
    The Frequency of the wave ONLY depends on the source producing it, If the source makes 30 thousand complete oscillations in one second then all the particles affected by the waves will make 30 thousand complete oscillations and the frequency will be 30 kHz,
    the velocity of propagation of the wave ONLY depends on the medium while the wave length depends on both the frequency and the velocity of the wave according to this equation velocity = frequency x wave length
    Last edited: Apr 11, 2014
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