Chapter 12, Problem 72PP

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.

72. What is the wavelength of the wave that travels on the surface of the vocal cords when they are vibrating at frequency f?

1. A.    2.0 mm
2. B.     3.3 mm
3. C.     0.50 cm
4. D.    3.0 cm