TRANSMISSION OF SOUND 99 



media is assumed to be plane and parallel to the wave front which is also 

 assumed to be plane. 



The boundary conditions are 



1. Continuity of pressure, 



2. Continuity of volume current. 



These conditions may be written 



px + pi = pi 5.59 



where p\ = incident pressure in the first medium, in dynes per square 

 centimeter, 

 p\ = reflected pressure in the first medium, in dynes per square 



centimeter, and 

 p2 = transmitted pressure in the second medium. 



(Ui - U,') ^ U, 5.60 



where Ui = incident volume current in the first medium, in cubic cen- 

 timeters per second, 

 Ui = reflected volume current in the first medium, in cubic cen- 

 timeters per second, and 

 U2 — transmitted volume current in the second medium, in cubic 

 centimeters per second. 



The acoustic impedance of the first medium is 



rAi = Y~ 5.61 



The acoustic impedance of the second medium is 



rA2 = P- 5.62 



U2 



where r,4i = acoustic resistance of the first medium, acoustic ohms, 



rA2 = acoustic resistance of the second medium, acoustic ohms. 



The incident power is 



The transmitted power is 



A = ^ 5.63 



rAi 



ft = 2^ 5.64 



