Intensity and dB level

1. Apr 29, 2015

PCPanos

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
β=10ln(I1/I0)

3. 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?

2. Apr 29, 2015

Staff: Mentor

What do you mean with "original dB level"?

How does intensity depend on distance for spherical waves without absorption?

3. Apr 29, 2015

haruspex

"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?