Conceptual Questions Chap. 14 • A crude model of the human throat is that of a pipe open at both ends with a vibrating source to introduce the sound into the pipe at one end. Assuming the vibrating source produces a range of frequencies, discuss the effect of changing the pipe’s length. • Explain how the distance to a lightning bolt can be determined by counting the seconds between the flash and the sound of thunder. • By listening to a band or orchestra, how can you determine that the speed of sound is the same for all frequencies? • A soft-drink bottle resonates as air is blown across its top. What happens to the resonant frequency as the level of fluid in the bottle decreases? The resonant frequency depends on the length of the pipe. Thus, changing the length of the pipe will cause different frequencies to be emphasized in the resulting sound. The speed of light is so high that the arrival of the flash is practically simultaneous with the lightning discharge. Thus the time delay between the flash and the arrival of the sound of thunder is the time sound takes to travel the distance between the lightning bolt and you. Knowing the speed of sound in air, this information gives you an estimate of the distance to the lightning bolt. If the speed of sound depended on frequency, then the sounds with different frequency could reach your ear at different times, creating a jumble of noise instead of well-timed music. As the length of the air column increases (fluid level decreases), the resonant frequency decreases.