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Chapter 17: Q6. (page 482)
A flute filled with helium will, until the helium escapes, play notes at a much higher pitch than normal. Why?
Speed of sound is higher in helium than air.
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A flutist assembles her flute in a room where the speed of
sound is 342 m/s. When she plays the note A, it is in perfect tune
with a 440 Hz tuning fork. After a few minutes, the air inside her
flute has warmed to where the speed of sound is 346 m/s.
a. How many beats per second will she hear if she now plays the
note A as the tuning fork is sounded?
A longitudinal standing wave can be created in a long, thin aluminum rod by stroking the rod with very dry fingers. This is often done as a physics demonstration, creating a high-pitched, very annoying whine. From a wave perspective, the standing wave is equivalent to a sound standing wave in an open-open tube. As FIGURE EX17.21 shows, both ends of the rod are antinodes. What is the fundamental frequency of a 2.0-m-long aluminum rod?
Traditional Indonesian music uses an ensemble called a gamelan that is based on tuned percussion instruments somewhat like gongs. In Bali, the gongs are often grouped in pairs that are slightly out of tune with each other. When both are played at once, the beat frequency lends a distinctive vibrating quality to the music. Suppose a pair of gongs are tuned to produce notes at 151 Hz and 155 Hz. How many beats are heard if the gongs are struck together and both ring for 2.5 s?
FIGURE Q17.3 shows the displacement of a standing sound wave in a 32-cm-long horizontal tube of air open at both ends. a. What mode (m-value) is this? b. Are the air molecules moving horizontally or vertically? Explain. c. At what distances from the left end of the tube do the molecules oscillate with maximum amplitude? d. At what distances from the left end of the tube does the air pressure oscillate with maximum amplitude?
Two loudspeakers in a plane, 5.0 m apart, are playing the same frequency. If you stand 12.0 m in front of the plane of the speakers, centered between them, you hear a sound of maximum intensity. As you walk parallel to the plane of the speakers, staying 12.0 m in front of them, you first hear a minimum of sound intensity when you are directly in front of one of the speakers. What is the frequency of the sound? Assume a sound speed of 340 m/s.
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