Friday, August 2, 2019

acoustics - Relation of power and intensity of sound/point source wave with distance travelled


I have two conceptual doubts about 3D waves while self-studying,they are:


(1) For a 3D wave,we know that $$ A \propto 1/r $$ Relations for intensity are as follows $$ I \propto A^2 \ and \ I \propto 1/r^2 $$ Shouldn't this imply that $ I \propto 1/r^4$? Please tell me where am I messing up, as I can't figure out whats wrong here.

P.S.- I know the $ A\propto 1/r$ comes from the intensity relations only and I have a feeling thats where im getting my logic wrong.

(2) By same relation $$A \propto 1/r$$ shouldn't the power ($p\propto A$) of a sound/point source wave decrease with distance?




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