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 What is the essence of waviness? 1 2 The Wave Model Waves: examples Particles 1. Ripples on a pond … Wave Continuous, nonlocalized, collective discrete, localized, individual Think of a leaf, or a cork on the water … … this leaf (or water) “bobs” up and down, What is a wave? but the disturbance, i. e. the ripples, … a disturbance that moves through a medium (or vacuum). moves to the edge of the pond. Types of waves: 2. Slinky … 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 the disturbance, red-dot moves back and forth…, but the wave moves from one end to the other. 3 4 A wave transfers energy, but no material or substance from the source.
Waves: examples Waves on a string 3. Cornfield… Wave speed: v = √ √ √ T s / µ √ µ µ µ 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. T s = tension, µ µ µ µ = linear density 4. Waves on a string or a rope- example of one dimensional waves = mass/length motion of wave at speed v Does v depend on size of the wave? up/down 5 6 Wave speed, wavelength, time period and frequency Two types of wave motion: transverse and longitudinal Transverse waves: … the disturbance is perpendicular to the direction of the wave. Examples? t Longitudinal waves: …the disturbance is parallel to the wave. 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 slinky 7 8 Sound wave, speed = 1100ft/s (approx)
Electromagnetic spectrum Chapter 20. Reading Quizzes 9 10 A graph showing wave displacement A graph showing wave displacement versus position at a specific instant of versus position at a specific instant of time is called a time is called a A. snapshot graph. A. snapshot graph. B. history graph. B. history graph. C. bar graph. C. bar graph. D. line graph. D. line graph. E. composite graph. E. composite graph. 11 12
A graph showing wave displacement A graph showing wave displacement versus time at a specific point in space versus time at a specific point in space is called a is called a A. snapshot graph. A. snapshot graph. B. history graph. B. history graph. C. bar graph. C. bar graph. D. line graph. D. line graph. E. composite graph. E. composite graph. 13 14 A wave front diagram shows A wave front diagram shows A. the wavelengths of a wave. A. the wavelengths of a wave. B. the crests of a wave. B. the crests of a wave. C. how the wave looks as it moves C. how the wave looks as it moves toward you. toward you. D. the forces acting on a string that’s D. the forces acting on a string that’s under tension. under tension. E. Wave front diagrams were not E. Wave front diagrams were not discussed in this chapter. discussed in this chapter. 15 16
The waves analyzed in this chapter are The waves analyzed in this chapter are A. string waves. A. string waves. B. sound and light waves. B. sound and light waves. C. sound and water waves. C. sound and water waves. D. string, sound, and light waves. D. string, sound, and light waves. E. string, water, sound, and light waves. E. string, water, sound, and light waves. 17 18 Sine-function: mathematical representation of a wave Sinusoidal Waves are periodic both in time and space Phase (initial) Amplitude E x ( ) Distribution of waves in � � � � � � � � x = = = = π π π π + + + + ϕ ϕ ϕ ϕ � � � � � � � � E x ( ) E sin 2 space at different time 0 � � λ λ λ λ � � � � � � E Amplitude 0 ϕ = ϕ ϕ ϕ = = = 0 λ λ λ λ 2 λ λ λ λ 3 λ λ λ λ x v Source of the Wave Time x 19 20
Phase difference Waves in Two and Three Dimensions Phase = Phase difference: 21 22 Power and Intensity Doppler Effect: observed frequency shift due to motion Power (P) = the rate of energy transfer from the source (J/sec) Intensity = P/area = Power-to-area ratio ∝ Amplitude2 ∝ ∝ ∝ Sound intensity level: 23 24
Doppler Effect … Doppler Effect … 25 26 EXAMPLE 20.11 How fast are EXAMPLE 20.11 How fast are the police traveling? the police traveling? QUESTION: 27 28
EXAMPLE 20.11 How fast are the police traveling? Chapter 20. Summary Slides Chapter 20. Summary Slides 29 30 General Principles General Principles 31 32
Important Concepts Important Concepts 33 34 Applications Applications 35 36
Applications Chapter 20. Multiple- -Choice Choice Chapter 20. Multiple Questions Questions 37 38 Which of the following actions would make Which of the following actions would make a pulse travel faster down a stretched a pulse travel faster down a stretched string? string? A. Use a heavier string of the same length, A. Use a heavier string of the same length, under the same tension. under the same tension. B. Use a lighter string of the same length, B. Use a lighter string of the same length, under the same tension. under the same tension. C. Move your hand up and down more C. Move your hand up and down more quickly as you generate the pulse. quickly as you generate the pulse. D. Move your hand up and down a larger D. Move your hand up and down a larger distance as you generate the pulse. distance as you generate the pulse. E. Use a longer string of the same thickness, E. Use a longer string of the same thickness, density, and tension. density, and tension. 39 40
What is the What is the frequency of this frequency of this traveling wave? traveling wave? A. 0.1 Hz A. 0.1 Hz B. 0.2 Hz B. 0.2 Hz C. 2 Hz C. 2 Hz D. 5 Hz D. 5 Hz E. 10 Hz E. 10 Hz 41 42 What is the phase difference between What is the phase difference between the crest of a wave and the adjacent the crest of a wave and the adjacent trough? trough? A. 0 A. 0 B. � B. � C. � /4 C. � /4 D. � /2 D. � /2 E. 3 � /2 E. 3 � /2 43 44
A light wave travels through three A light wave travels through three transparent materials of equal thickness. transparent materials of equal thickness. Rank in order, from the largest to smallest, Rank in order, from the largest to smallest, the indices of refraction n 1 , n 2 , and n 3 . the indices of refraction n 1 , n 2 , and n 3 . A. n 1 > n 2 > n 3 A. n 1 > n 2 > n 3 B. n 2 > n 1 > n 3 B. n 2 > n 1 > n 3 C. n 3 > n 1 > n 2 C. n 3 > n 1 > n 2 D. n 3 > n 2 > n 1 D. n 3 > n 2 > n 1 E. n 1 = n 2 = n 3 E. n 1 = n 2 = n 3 45 46 Amy and Zack are both listening to the Amy and Zack are both listening to the source of sound waves that is moving to source of sound waves that is moving to the right. Compare the frequencies each the right. Compare the frequencies each hears. hears. A. f Amy > f Zack A. f Amy > f Zack B. f Amy < f Zack B. f Amy < f Zack C. f Amy = f Zack C. f Amy = f Zack 47 48
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