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Homework Help: Intensity and dB level

  1. Apr 29, 2015 #1
    1. The problem statement, all variables and given/known data
    The intensity of a certain spherical wave is 8.0 W/m^2 at a distance of 1.0 m from the source. If the medium is isotropic and nonabsorbing, calculate the decibel intensity 100m from the source.

    2. Relevant equations

    3. The attempt at a solution
    I know how to use these equations... And to find the original dB level i use

    Im just not sure what to do to find intensity 100m away?
  2. jcsd
  3. Apr 29, 2015 #2


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    Staff: Mentor

    What do you mean with "original dB level"?

    How does intensity depend on distance for spherical waves without absorption?
  4. Apr 29, 2015 #3


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    Gold Member

    "Decibel" is very confusing because the term is used both for relative and absolute intensities. As far as I am aware, the unit dB always denotes (or should always denote) a relative intensity. If an absolute intensity is intended then it should be qualified to indicate the reference level, like dBm or dBmW.
    Where does your 10-12 come from?
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