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15 Traveling Waves and Sound. Slide 15-2. Slide 15-3. Slide 15-4. Slide 15-5. Types of Waves. A transverse wave. A longitudinal wave. Slide 15-12. Waves on Strings and in Air. Slide 15-13. Snapshot Graphs. Slide 15-14. Constructing a History Graph. Slide 15-15.
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15Traveling Waves and Sound Slide 15-2
Types of Waves A transverse wave A longitudinal wave Slide 15-12
Waves on Strings and in Air Slide 15-13
Snapshot Graphs Slide 15-14
Constructing a History Graph Slide 15-15
Checking Understanding The graph below shows a snapshot graph of a wave on a string that is moving to the right. A point on the string is noted. Which of the choices is the history graph for the subsequent motion of this point? Slide 15-16
Answer The graph below shows a snapshot graph of a wave on a string that is moving to the right. A point on the string is noted. Which of the choices is the history graph for the subsequent motion of this point? (b) Slide 15-17
Checking Understanding The graph below shows a history graph of the motion of one point on a string as a wave moves by to the right. Which of the choices is the correct snapshot graph for the motion of the string? Slide 15-18
Answer The graph below shows a history graph of the motion of one point on a string as a wave moves by to the right. Which of the choices is the correct snapshot graph for the motion of the string? (d) Slide 15-19
Conceptual Example Problems A wave travels back and forth on a guitar string; this is responsible for making the sound of the guitar, as we will see. As the temperature rises, the tension in a guitar string decreases. How does this change the speed of a wave on the string? How do you measure the temperature of a flame if the temperature is higher than a probe can handle? One possible solution is to use sound. A source emits a pulse of sound on one side of the flame, which is then measured by a microphone on the other side. A measurement of the time between the emission and the reception of the pulse allows a determination of the temperature. Explain how this technique works. Slide 15-20
A particular species of spider spins a web with silk threads of density 1300 kg/m3 and diameter 3.0 µm. A typical tension in the radial threads of such a web is 7.0 mN. If a fly lands in this web, which will reach the spider first, the sound or the wave on the web silk? Example Problem Slide 15-21
Sinusoidal Waves Slide 15-22
Checking Understanding • For this sinusoidal wave: • What is the amplitude? • 0.5 m • 1 m • 2 m • 4 m Slide 15-23
Answer • For this sinusoidal wave: • What is the amplitude? • 0.5 m • 1 m • 2 m • 4 m Slide 15-24
Checking Understanding • For this sinusoidal wave: • What is the wavelength? • 0.5 m • 1 m • 2 m • 4 m Slide 15-25
Answer • For this sinusoidal wave: • What is the wavelength? • 0.5 m • 1 m • 2 m • 4 m Slide 15-26
Checking Understanding • For this sinusoidal wave: • What is the frequency? • 50 Hz • 100 Hz • 200 Hz • 400 Hz Slide 15-27
Answer • For this sinusoidal wave: • What is the frequency? • 50 Hz • 100 Hz • 200 Hz • 400 Hz Slide 15-28
Example Problems The new generation of cordless phones use radio waves at a frequency of 5.8 GHz. What is the wavelength of these radio waves? A speaker emits a tone of a particular frequency. Suppose the air temperature increases. What happens to the wavelength of the sound? Slide 15-29
Example Problem The water in the open ocean is in constant motion, carrying long-wavelength waves moving at relatively high speeds. Under steady winds, the amplitude of these waves can get quite large. Suppose a boat is at rest in the open ocean. The wind has created a steady wave with wavelength 190 m traveling at 14 m/s. (In fact, the ocean will support a mix of waves, but for steady winds of 30-40 knots, this is the most prevalent wavelength, and the correct speed for a wave of this wavelength in deep water.) The top of the crests of the waves is 2.0 m above the bottom of the troughs. (This wave height is quite typical for windy days in the Atlantic Ocean. The Southern Ocean, with its planet-circling stretch of open water, supports much larger waves—wave heights of 7 m are quite common.) What is the maximum vertical speed of the boat as it bobs up and down on the passing wave? What is the maximum vertical acceleration? Slide 15-30
Example Problem Let’s use the data from the previous problem again. Suppose the boat is sailing at 6.0 m/s in the same direction as the motion of the waves. At t 0 s the boat is at the bottom of a trough. How high above this lowest point will the boat be at t 10 s? Slide 15-31
Sound and Light Waves The speed of sound varies with the medium. Light and other electromagnetic waves in vacuum and in air move at the same speed, 3.00 x 108 m/s. Slide 15-32