© 2010 Pearson Education, Inc. Slide Traveling Waves and Sound

© 2010 Pearson Education, Inc. Figure 15.3

© 2010 Pearson Education, Inc. Capillary waves in water Surface tension (not gravity)

© 2010 Pearson Education, Inc. Slide 15-3

© 2010 Pearson Education, Inc. The Wave

© 2010 Pearson Education, Inc. Slide 15-4

© 2010 Pearson Education, Inc. Slide 15-5

© 2010 Pearson Education, Inc. Types of Waves A transverse wave A longitudinal wave Slide 15-12

© 2010 Pearson Education, Inc. A transverse wave A longitudinal wave Sound waves in fluids are always longitudinal waves, never transverse waves. Sound waves in solids can be either type. Why?

© 2010 Pearson Education, Inc.

Waves on Strings and in Air Slide 15-13

© 2010 Pearson Education, Inc. A particular species of spider spins a web with silk threads of density 1300 kg/m 3 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

© 2010 Pearson Education, Inc. Snapshot Graphs Slide A snapshot graph shows a wave at a given instant in time. The diagram shows the wave as a function of space, x, in this case, at different times, t.

© 2010 Pearson Education, Inc. Constructing a History Graph A “history” graph shows the displacements in a wave as it has changed over time. The diagram shows the displacement at a particular location, x, of a wave that passes by as a function of time, t.

© 2010 Pearson Education, Inc. Reading Quiz 1.Which of the following is a longitudinal wave? A.sound wave B.water wave C.light wave Slide 15-6

© 2010 Pearson Education, Inc. Answer 1.Which of the following is a longitudinal wave? A.sound wave B.water wave C.light wave Slide 15-7

© 2010 Pearson Education, Inc. Reading Quiz 2.When the particles of a medium move with simple harmonic motion, this means the wave is A.a sound wave B.a sinusoidal wave C.a standing wave D.a harmonic wave E.a transverse wave Slide 15-8

© 2010 Pearson Education, Inc. Answer 2.When the particles of a medium move with simple harmonic motion, this means the wave is A.a sound wave B.a sinusoidal wave C.a standing wave D.a harmonic wave E.a transverse wave Slide 15-9

© 2010 Pearson Education, Inc. Sinusoidal Waves

© 2010 Pearson Education, Inc. 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 10 8 m/s. (Light speed varies with medium too.) Slide 15-32

© 2010 Pearson Education, Inc. The Doppler Effect Slide 15-33

© 2010 Pearson Education, Inc. Doppler shifts for moving source, fixed observer Observed frequency of a wave of speed v emitted from a source approaching at speed v s Observed frequency of a wave of speed v emitted from a source receding at speed v s

© 2010 Pearson Education, Inc. Doppler Effect for Fixed Source - Moving Observer

© 2010 Pearson Education, Inc. Energy and Intensity

© 2010 Pearson Education, Inc. The Decibel Scale Sound intensity level is measured in decibels. Slide Sound intensity is calculated from the base 10 logarithm of the ratio of the sound intensity in watts/m 2 to the intensity at the threshold of hearing, 1/trillionth of a watt/m 2

© 2010 Pearson Education, Inc. Figure 15.17

© 2010 Pearson Education, Inc. Reading Quiz 3.We measure the sound intensity level in units of A.watts B.joules C.candelas D.decibels E.hertz Slide 15-10

© 2010 Pearson Education, Inc. Answer 3.We measure the sound intensity level in units of A.watts B.joules C.candelas D.decibels E.hertz Slide 15-11

© 2010 Pearson Education, Inc.

Figure 15.6

© 2010 Pearson Education, Inc. Figure 15.7

© 2010 Pearson Education, Inc. Figure 15.9a

© 2010 Pearson Education, Inc. Figure 15.9b

© 2010 Pearson Education, Inc. Checking Understanding For this sinusoidal wave: 1.What is the amplitude? A.0.5 m B.1 m C.2 m D.4 m Slide 15-23

© 2010 Pearson Education, Inc. Answer For this sinusoidal wave: 1.What is the amplitude? A.0.5 m B.1 m C.2 m D.4 m Slide 15-24

© 2010 Pearson Education, Inc. Checking Understanding For this sinusoidal wave: 2.What is the wavelength? A.0.5 m B.1 m C.2 m D.4 m Slide 15-25

© 2010 Pearson Education, Inc. Answer For this sinusoidal wave: 2.What is the wavelength? A.0.5 m B.1 m C.2 m D.4 m Slide 15-26

© 2010 Pearson Education, Inc. Checking Understanding For this sinusoidal wave: 3.What is the frequency? A.50 Hz B.100 Hz C.200 Hz D.400 Hz Slide 15-27

© 2010 Pearson Education, Inc. Answer For this sinusoidal wave: 3.What is the frequency? A.50 Hz B.100 Hz C.200 Hz D.400 Hz Slide 15-28

© 2010 Pearson Education, Inc. Figure 15.10a

© 2010 Pearson Education, Inc. Figure 15.11

© 2010 Pearson Education, Inc. Summary Slide 15-40

© 2010 Pearson Education, Inc. Summary Slide 15-41

© 2010 Pearson Education, Inc. 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? Example Problems Slide 15-29

© 2010 Pearson Education, Inc. If you are standing 2.0 m from a lamp that is emitting 100 W of infrared and visible light, what is the intensity of 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 100 watt stereo with the volume cranked up all the way. How far away could you detect the sound from the stereo? Example Problems Slide 15-37

© 2010 Pearson Education, Inc. You are working in a shop where the noise level is a constant 90dB. A.Your eardrum has a diameter of approximately 8.4 mm. How much power is being received by one of your eardrums? B.This level of noise is damaging over a long time, so you use earplugs that are rated to reduce the sound intensity level by 26 dB, a typical rating. What is the power received by one eardrum now? Example Problem Slide 15-38

© 2010 Pearson Education, Inc. Additional Example Problems 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? Slide 15-44

© 2010 Pearson Education, Inc. Additional Example Problems 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? Slide 15-44

© 2010 Pearson Education, Inc. Additional Example Problems 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 15-44