The intensity I or rate of flow of energy by wave motion through unit area of the medium in a direction perpendicular to the direction of propagation of the wave is given by
If P is the power of an isotopic source of sound at a distance r, the intensity or loudness of sound.
When a wave diverges in all directions from a source, the intensity reduces with the distance from the source according to an inverse square law. This is shown in Fig. 1.10.
Fig. 1.10 In the solid angle shown, the same energy is distributed ...