1. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The wave model Sinusoidal waves Sound and light waves Energy & Intensity The Doppler effect and shock waves Chapter 15 Traveling Waves and Sound 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. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Energy and Intensity As waves spread out, so does the energy of the wave. The intensity decreases. Slide 15-26

3. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Decibel Scale Sound intensity level is measured in decibels. Slide 15-27

4. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Doppler Effect Slide 15-28

5. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Doppler Effect Slide 15-28

6. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Physics of Speech and Hearing Slide 16-15

7. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Checking Understanding Two waves on a string are moving toward each other. A picture at t = 0 s appears as follows: How does the string appear at t = 2 s? Slide 16-9

8. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Two waves on a string are moving toward each other. A picture at t = 0 s appears as follows: How does the string appear at t = 2 s? Slide 16-10 Answer

9. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Standing Wave Modes Slide 16-11

10. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 1.A particular species of spider spins a web with silk threads of density 1300 kg/m3 and diameter 3.0 µm. A passing insect brushes a 12-cm-long strand of the web, which has a tension of 1.0 mN, and excites the lowest frequency standing wave. With what frequency will the strand vibrate? 2.Two strings with linear densities of 5.0 g/m are stretched over pulleys, adjusted to have vibrating lengths of 50 cm, and attached to hanging blocks. The block attached to string 1 has a mass of 20 kg and the block attached to wire 2 has mass M. When driven at the same frequency, the two strings support the standing waves shown. a)What is the driving frequency? b)What is the mass of the block suspended from String 2? Slide 16-12

11. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Standing Sound Waves Slide 16-13

12. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Physics of Music The Egyptian tomb of Tutankhamun contained many treasures, including two trumpets. These trumpets were simple instruments, consisting of straight tubes with a mouthpiece at one end and a bell at the other. The smaller of the two was 58 cm long, made of silver. This trumpet, like other similar musical instruments, couldn’t make a reasonable sound at the fundamental frequency, but it could produce all of the harmonics. What frequencies could the instrument have produced? Slide 16-14

13. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Two speakers are emitting identical sound waves with a wavelength of 4.0 m. The speakers are 8.0 m apart, directed toward each other, as in the diagram below. At each of the noted points, say whether the interference is constructive, destructive, or something in between. Interference Along a Line Slide 16-16

14. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Interference of Spherical Waves Slide 16-17

15. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Two speakers emit identical sinusoidal waves. The speakers are placed 4.0 m apart. A listener moving along a line in front of the two speakers finds loud and quiet spots as shown below. The grid lines are spaced at 1.0 m. What is the frequency of the sound from the two speakers? Interference of Sound Waves Slide 16-18

16. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Beats Slide 16-19 f beat = |f 1 - f 2 |

17. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Physics of Speech and Hearing Slide 16-15

18. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 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/m 2 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? Checking Understanding Slide 15-29

19. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Additional Clicker Questions Slide 15-30 A snapshot and a history graph for a sinusoidal wave on a string appear as follows: What is the speed of the wave? A.1.5 m/s B.3.0 m/s C.5.0 m/s D.15 m/s

20. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 15-31 A snapshot and a history graph for a sinusoidal wave on a string appear as follows: What is the speed of the wave? B.3.0 m/s Answer

21. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 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 Examples

22. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 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/m 2 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 m 2 array of solar cells with an efficiency of 12%. Above the earth’s atmosphere, where the intensity of sunlight is approximately 1300 W/m 2, 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