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Chapter 20: Traveling Waves
20.1 The wave model
20.2 One-dimensional waves
20.3 Sinusoidal waves
20.4 Waves in 2- & 3-dimensions
20.5 Sound and Light Waves
20.6 Power and Intensity
20.7 Doppler Effect
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What is the essence of waviness?
3
The Wave Model
What is a wave?
… a disturbance that moves through a medium (or vacuum).
Types of waves:
1. Mechanical waves: water waves and sound waves
2. Electromagnetic waves: light waves including radio waves, x-rays, etc
3. Matter waves: electrons and atoms show wave-like characteristics
Wave
Continuous, nonlocalized, collective
Particles
discrete, localized, individual
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Waves: examples
1. Ripples on a pond …
Think of a leaf, or a cork on the water …
… this leaf (or water) “bobs” up and down,
but the disturbance, i. e. the ripples,
moves to the edge of the pond.
2. Slinky …
the disturbance, red-dot moves back and forth…,
but the wave moves from one end to the other.
A wave transfers energy, but no material or substance from the source.
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Waves: examples
3. Cornfield…
As the wind blows across the field, observe one stalk ...the disturbance,
ear of corn, moves side to side, but the wave across the field.
4. Waves on a string or a rope- example of one dimensional waves
up/down
motion of wave at speed v
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Waves on a string
Wave speed: v = √√√√Ts/µµµµ
Ts = tension,
µµµµ = linear density
= mass/length
Does v depend on size of the wave?
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Wave speed, wavelength, time period and frequency
t
Wavelength = distance from one crest to the next
Frequency (f) = number of cycles (ups and downs) per second
Period = time for one complete cycle (up-down-up) = 1/f
Amplitude = Height of a crest
Speed (v) = wavelength/period
= frequency x wavelength 8
Two types of wave motion: transverse and longitudinal
Transverse waves: … the disturbance is perpendicular to the
direction of the wave. Examples?
Longitudinal waves: …the disturbance is parallel to the wave.
slinky Sound wave, speed = 1100ft/s (approx)
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Electromagnetic spectrum
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Chapter 20. Reading Quizzes
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A graph showing wave displacement versus position at a specific instant of time is called a
A. snapshot graph.
B. history graph.
C. bar graph.
D. line graph.
E. composite graph.
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A graph showing wave displacement versus position at a specific instant of time is called a
A. snapshot graph.
B. history graph.
C. bar graph.
D. line graph.
E. composite graph.
13
A graph showing wave displacement versus time at a specific point in space is called a
A. snapshot graph.
B. history graph.
C. bar graph.
D. line graph.
E. composite graph.
14
A graph showing wave displacement versus time at a specific point in space is called a
A. snapshot graph.
B. history graph.
C. bar graph.
D. line graph.
E. composite graph.
15
A wave front diagram shows
A. the wavelengths of a wave.
B. the crests of a wave.
C. how the wave looks as it moves
toward you.
D. the forces acting on a string that’s
under tension.
E. Wave front diagrams were not
discussed in this chapter.
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A wave front diagram shows
A. the wavelengths of a wave.
B. the crests of a wave.
C. how the wave looks as it moves
toward you.
D. the forces acting on a string that’s
under tension.
E. Wave front diagrams were not
discussed in this chapter.
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The waves analyzed in this chapter are
A. string waves.
B. sound and light waves.
C. sound and water waves.
D. string, sound, and light waves.
E. string, water, sound, and light waves.
18
The waves analyzed in this chapter are
A. string waves.
B. sound and light waves.
C. sound and water waves.
D. string, sound, and light waves.
E. string, water, sound, and light waves.
19
Sine-function: mathematical representation of a wave
x
0( ) sin 2
xE x E π ϕπ ϕπ ϕπ ϕ
λλλλ
= += += += +
λλλλ 2λλλλ 3λλλλ
( )E x
0EAmplitude
Amplitude Phase (initial)
0ϕϕϕϕ ====
20
Sinusoidal Waves are periodic both in time and space
Source of
the WaveTime
Distribution of waves in
space at different time
x
v
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Phase difference
Phase =
Phase difference:
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Waves in Two and Three Dimensions
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Power and Intensity
Power (P) = the rate of energy transfer
from the source (J/sec)
Intensity = P/area = Power-to-area ratio
∝∝∝∝ Amplitude2
Sound intensity level:
24
Doppler Effect: observed frequency shift due to motion
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Doppler Effect …
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Doppler Effect …
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EXAMPLE 20.11 How fast are the police traveling?
QUESTION:
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EXAMPLE 20.11 How fast are the police traveling?
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EXAMPLE 20.11 How fast are the police traveling?
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Chapter 20. Summary SlidesChapter 20. Summary Slides
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General Principles
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General Principles
33
Important Concepts
34
Important Concepts
35
Applications
36
Applications
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Applications
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Chapter 20. MultipleChapter 20. Multiple--Choice Choice
QuestionsQuestions
39
Which of the following actions would make a pulse travel faster down a stretched string?
A. Use a heavier string of the same length, under the same tension.
B. Use a lighter string of the same length, under the same tension.
C. Move your hand up and down more quickly as you generate the pulse.
D. Move your hand up and down a larger distance as you generate the pulse.
E. Use a longer string of the same thickness, density, and tension.
40
Which of the following actions would make a pulse travel faster down a stretched string?
A. Use a heavier string of the same length, under the same tension.
B. Use a lighter string of the same length, under the same tension.
C. Move your hand up and down more quickly as you generate the pulse.
D. Move your hand up and down a larger distance as you generate the pulse.
E. Use a longer string of the same thickness, density, and tension.
41
What is the
frequency of this
traveling wave?
A. 0.1 Hz
B. 0.2 Hz
C. 2 Hz
D. 5 Hz
E. 10 Hz
42
A. 0.1 Hz
B. 0.2 Hz
C. 2 Hz
D. 5 Hz
E. 10 Hz
What is the
frequency of this
traveling wave?
43
What is the phase difference between the crest of a wave and the adjacent trough?
A. 0
B. π
C. π /4
D. π /2
E. 3 π /2
44
What is the phase difference between the crest of a wave and the adjacent trough?
A. 0
B. π
C. π /4
D. π /2
E. 3 π /2
45
A light wave travels through three transparent materials of equal thickness. Rank in order, from the largest to smallest, the indices of refraction n1, n2, and n3.
A. n1 > n2 > n3
B. n2 > n1 > n3
C. n3 > n1 > n2
D. n3 > n2 > n1
E. n1 = n2 = n3 46
A light wave travels through three transparent materials of equal thickness. Rank in order, from the largest to smallest, the indices of refraction n1, n2, and n3.
A. n1 > n2 > n3
B. n2 > n1 > n3
C. n3 > n1 > n2
D. n3 > n2 > n1
E. n1 = n2 = n3
47
Amy and Zack are both listening to the source of sound waves that is moving to the right. Compare the frequencies each hears.
A. fAmy > fZack
B. fAmy < fZack
C. fAmy = fZack
48
Amy and Zack are both listening to the source of sound waves that is moving to the right. Compare the frequencies each hears.
A. fAmy > fZack
B. fAmy < fZack
C. fAmy = fZack