A plane longitudinal harmonic wave propagates in a medium with density p. The velocity of the wave propagation is v. Assuming that the density variations of the medium, induced by the propagating wave, ∆p = p, demonstrate that (a) The pressure increment in the medium ∆p = pv2 (∂ε/∂x), where ∂ε/∂x is the relative deformation;
(b) The wave intensity is defined by Eq. (4.3i).