Chapter 12, Problem 73PP

BIO Waves on vocal cords. In the larynx, sound is produced by the vibration of the vocal cords. The diagram in Figure 12.44 is a cross section of the vocal tract at one instant in time. Air flows upward (in the +z direction) through the vocal tract, causing a transverse wave to propagate vertically upward along the surface of the vocal cords. In a typical adult male, the thickness of the vocal cords in the direction of airflow is d = 2.0 mm. High-speed photography shows that for a frequency of vibration of f = 125 Hz, the wave along the surface of the vocal cords travels upward at a speed of u = 375 cm/s. Take t to be time, z to be displacement in the + z direction, and λ to be wavelength.

Figure 12.44 Problems 72–74.

73. Which of the following is a possible mathematical description of the wave in Problem 15.72?

1. A.    A sin [2пf(t + z/u)]
2. B.     A sin [2пf(t − z/u)]
3. C.     A sin (2пft) cos (2пz/λ)
4. D.    A sin (2пft) sin(2пz/λ)