19-4 Power and intensity of sound waves u,(x, t)=um sin(kx-ot) as the wave travels each fluid element exerts a force on the fluid element ahead of it. If the pressure increase in the fluid element is AP F=A·AP=A·_Pnsn(kx-ot The power delivered by the element is P=u,F=A·△ Pu sin2(kx-ot) A(△Pn) (19-18) Average over any number of full cycles19-4 Power and intensity of sound waves As the wave travels, each fluid element exerts a force on the fluid element ahead of it. If the pressure increase in the fluid element is , P F A P A P sin( k x t) x =  =  m − The power delivered by the element is: sin ( ) 2 P u F A P u k x t = x x =  m m − v A P P m a v 2 ( ) 2  = (19-18) Average over any number of full cycles. ( ) sin ( ) u x,t um k x ωt x = −