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Homework Help: Calculating the speed of an ultrasound wave in an unknown liquid

  1. Sep 2, 2007 #1
    1. The problem statement, all variables and given/known data

    An ultrasound unit sends a 2.40 MHz sound wave into a 25.0-cm-long tube filled with an unknown liquid. A small microphone right next to the ultrasonic generator detects both the transmitted wave and the sound wave that has reflected off the far end of the tube. The two sound pulses are 4.40 divisions apart on an oscilloscope for which the horizontal time sweep is set to 100μs/division

    What is the speed of sound in this liquid?

    2. Relevant equations


    3. The attempt at a solution

    Honestly, I have no clue...
  2. jcsd
  3. Sep 2, 2007 #2


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    Staff Emeritus
    Science Advisor

    The microphone detects the transmitted and reflected wave.

    Time interval between signals (transmitted and reflected pulses) is 4.4 div * 100μs/division or _________ μs?

    The wave had to travel 2 lengths (down and back) of a 25 cm tube in that time. Make sure units are consistent.
  4. Sep 2, 2007 #3

    i had figured that it was 440μs but didnt know where to go from there...

  5. Sep 2, 2007 #4
    As reference to anyone else who may need this problem:

    50cm = 0.5m
    4.3 divisions * 100μs/division = 440μs
    440μs = 4.4*10^-4 seconds

    0.5/(4.4*10^-4) = 1136.363636363636363636.... m/s
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