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The wave model Sinusoidal waves Sound and light waves Energy & Intensity

Chapter 15 Traveling Waves and Sound. The wave model Sinusoidal waves Sound and light waves Energy & Intensity The Doppler effect and shock waves. Topics:. Sample question:.

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The wave model Sinusoidal waves Sound and light waves Energy & Intensity

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  1. Chapter 15 Traveling Waves and Sound • The wave model • Sinusoidal waves • Sound and light waves • Energy & Intensity • The Doppler effect and shock waves Topics: Sample question: The large ears of this bat give us a clue to how it locates its prey: with sound. How do bats use sound to “see” the world around them? Slide 15-1

  2. Reading Quiz • Which of the following is a longitudinal wave? • sound wave • water wave • light wave Slide 15-2

  3. Answer • Which of the following is a longitudinal wave? • sound wave Slide 15-3

  4. Reading Quiz • When the particles of a medium move with simple harmonic motion, this means the wave is • a sound wave • a sinusoidal wave • a standing wave • a harmonic wave • a transverse wave Slide 15-4

  5. Answer • When the particles of a medium move with simple harmonic motion, this means the wave is • a sinusoidal wave Slide 15-5

  6. Reading Quiz • We measure the sound intensity level in units of • watts • joules • candelas • decibels • hertz Slide 15-6

  7. Answer • We measure the sound intensity level in units of • decibels Slide 15-7

  8. Types of Waves Slide 15-8

  9. Wave demonstrations Transverse Waves Longitudinal Waves How does a piece of the spring move? Which way does it oscillate? Slide 15-3

  10. What factors determine wave speed? • Wave speed is determined by the medium • Related to a = Fnet / m • Does not depend on how hard or how fast the wave generator moves Slide 15-3

  11. Waves on Strings and in Air Slide 15-9

  12. Snapshot and History Graphs Slide 15-10

  13. 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 15-11

  14. 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? Slide 15-12

  15. 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 below shows a snapshot graph of the motion of the string? Slide 15-13

  16. 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 below shows a snapshot graph of the motion of the string? Slide 15-14

  17. Examples 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? It is possible to use sound to probe the air temperature of a region of the atmosphere. A source emits a pulse of sound which is then measured by a distant microphone. A measurement of the time between the emission and the reception of the pulse allows a determination of the temperature of the intervening air. Explain how this technique works. Slide 15-15

  18. Example 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? Slide 15-16

  19. Sinusoidal Waves Slide 15-17

  20. 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 15-18

  21. Checking Understanding • For this sinusoidal wave: • What is the amplitude? • 0.5 m • 1 m • 2 m • 4 m Slide 15-19

  22. Answer • For this sinusoidal wave: • What is the amplitude? • 0.5 m Slide 15-20

  23. Checking Understanding • For this sinusoidal wave: • What is the wavelength? • 0.5 m • 1 m • 2 m • 4 m Slide 15-21

  24. Answer • For this sinusoidal wave: • What is the wavelength? • 2 m Slide 15-22

  25. Checking Understanding • For this sinusoidal wave: • What is the frequency? • 50 Hz • 100 Hz • 200 Hz • 400 Hz Slide 15-23

  26. Checking Understanding • For this sinusoidal wave: • What is the frequency? • 100 Hz Slide 15-24

  27. Examples 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 15-25

  28. Energy and Intensity As waves spread out, so does the energy of the wave. The intensity decreases. Slide 15-26

  29. The Decibel Scale Sound intensity level is measured in decibels. Slide 15-27

  30. The Doppler Effect Slide 15-28

  31. Checking Understanding If you are standing 2.0 m from a 100 W lamp, what is the intensity of the radiation on your skin? How does this compare with the intensity of sunlight, approximately 1000 W/m2 at the surface of the earth? Suppose it was so quiet outside that you could detect a sound at the threshold of your perception, 0 dB. Now suppose that someone was playing a stereo with the volume cranked up all the way. How far away could you detect the sound from the stereo? Slide 15-29

  32. Additional Clicker Questions A snapshot and a history graph for a sinusoidal wave on a string appear as follows: • What is the speed of the wave? • 1.5 m/s • 3.0 m/s • 5.0 m/s • 15 m/s Slide 15-30

  33. Answer A snapshot and a history graph for a sinusoidal wave on a string appear as follows: • What is the speed of the wave? • 3.0 m/s Slide 15-31

  34. Additional Examples A 5.0 kg block is hung from the ceiling on a 2.0-meter-long metal wire with a mass of 4 g. The wire is “plucked” at the very bottom, where it connects to the block. How long does it take the pulse to reach the ceiling? The intensity of sunlight is approximately 1000 W/m2 at the surface of the earth. Saturn is about 10 times as far from the sun as the earth. If the earth were moved to the distance of Saturn, what would be the intensity of sunlight at the surface? Suppose you are powering a spacecraft with a 1.0 m2 array of solar cells with an efficiency of 12%. Above the earth’s atmosphere, where the intensity of sunlight is approximately 1300 W/m2, what is the maximum power you could get from the solar cells? How much power could you get if your spacecraft was nearing Neptune, 30 times as far from the sun as the earth? Slide 15-32

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