Intensity and dB level

  • Thread starter PCPanos
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  • #1
PCPanos
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Homework Statement


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.

Homework Equations


β=10ln(I1/I0)

The Attempt at a Solution


I know how to use these equations... And to find the original dB level i use
β=(10dB)ln(8.0/10^-12)

Im just not sure what to do to find intensity 100m away?
 

Answers and Replies

  • #2
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What do you mean with "original dB level"?

How does intensity depend on distance for spherical waves without absorption?
 
  • #3
haruspex
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"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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