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Homework Help: Sound Intensity of a trumpet

  1. Feb 25, 2009 #1
    1. The problem statement, all variables and given/known data

    When playing fortissimo (very loudly), a trumpet emits sound energy
    at a rate of 0.800 W out of a bell (opening) of diameter 12.7 cm. (a) What is the sound
    intensity level right in front of the trumpet? (b) If the trumpet radiates sound waves
    uniformly in all directions, what is the sound intensity level at a distance of 10.0 m?

    3. The attempt at a solution

    My only question for the following question has to do with area. I know that I = P / A.. However, for a), since it is at the very end of the trumpet, would the area be pi*r^2, rather than the area for a sphere?

    I know that for b) it is the area of a sphere, but I was thinking for a) it would be a circle. Apparently this question is supposed to be hard, so that's why I was thinking that.

  2. jcsd
  3. Feb 25, 2009 #2


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    Homework Helper

    You are quite right on all counts.
  4. Feb 25, 2009 #3
    Thank you. I was a bit unsure about the area for a), but it's nice to have some clarification that it is a circle.
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