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Homework Help: What is the acoustic power of each pulse?

  1. Sep 27, 2010 #1
    1. The problem statement, all variables and given/known data

    In search for insects, a bat uses an echolocating system based on pulses of high frequency sound. These pulses are 2.0 ms in duration, have a frequency of 50 kHz, and have an intensity level of 100 dB at 1.0 m from the bat's mouth. Assume that the bat produces spherical acoustic waves.

    a.What is the acoustic power of each pulse?
    b. A bug is located 5.0 m from the bat. The effective cross-sectionl area of the insect is 10 mm2. How much of the acoustic power emitted by the bat is intercepted by the insect?

    2. Relevant equations

    I = P/A
    E = Pt

    3. The attempt at a solution

    a. Given intensity level, I can find intensity...

    10log(I/I0) = 100 [I0 = 10-12
    I = 0.01

    P = 0.01 x 4 x [pi] x 12 = 0.13 W

    Textbook has 0.12, so I was wondering if I did it correctly.

    b. I found the intensity of the pulse at 5 m to be 3.8 x 10-4 so...

    P = AI = (0.001)(3.8 x 10-4) = 3.8 x 10-6

    Textbook has it to power -10, so I'm wondering if someone can find a mistake..
  2. jcsd
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