# Chapter 19 - Think and Explain: 75

a. The frequency increases. b. The wavelength decreases. c. The speed is unchanged.

#### Work Step by Step

a. The frequency increases because the source is approaching the listener (explained by the Doppler effect). b. The wave speed v, the speed of sound in air, is frequency multiplied by wavelength. $$v = f \lambda$$ In this example, the frequency f increases so the wavelength decreases. Their product remains the same because the wave speed doesn't change. The decrease in received wavelength can also be seen in Figure 19.16, where listener B perceives shorter wavelengths. c. The speed of sound in air is the same.

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