1. The problem statement, all variables and given/known data I need the formula of the intensity of a sound wave at distance r from the source. The wave is spherical, and we know [tex]\rho[/tex], c, the speed of the wave, [tex]\omega[/tex], the pulsation, and A, the amplitude of the wave. 2. Relevant equations The problem text specifies that intensity is the energy [tex]\Delta[/tex]W that passes, during one unit of time, the unit of surface perpendicular to the direction of the propagation of the wave. 3. The attempt at a solution I don't know how to calculate [tex]\Delta[/tex]W.