What is the essence of waviness? The Wave Model. Waves: examples. Particles. Wave. 1. Ripples on a pond. Think of a leaf, or a cork on the water

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1 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 Wave Particles Waves: examples 1. Ripples on a pond Continuous, nonlocalized, collective discrete, localized, individual Think of a leaf, or a cork on the water 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 2. Slinky this leaf (or water) bobs up and down, but the disturbance, i. e. the ripples, moves to the edge of the pond. the disturbance, red-dot moves back and forth, but the wave moves from one end to the other. 3 A wave transfers energy, but no material or substance from the source. 4

2 Waves: examples Waves on a string 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 motion of wave at speed v Wave speed: v = T s /µ T s = tension, µ = linear density = mass/length Does v depend on size of the wave? up/down 5 6 Wave speed, wavelength, time period and frequency t Two types of wave motion: transverse and longitudinal Transverse waves: the disturbance is perpendicular to the direction of the wave. Examples? 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 7 Longitudinal waves: the disturbance is parallel to the wave. slinky 8 Sound wave, speed = 1100ft/s (approx)

3 Electromagnetic spectrum Chapter 20. Reading Quizzes 9 10 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. 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

4 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. 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 A wave front diagram shows 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. 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

5 The waves analyzed in this chapter are 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. 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 Sine-function: mathematical representation of a wave Sinusoidal Waves are periodic both in time and space E( x) Amplitude ϕ = 0 E 0 Amplitude Phase (initial) E( x) E0 sin 2 π x = + ϕ λ Distribution of waves in space at different time λ 2λ 3λ x Source of the Wave v Time x 19 20

6 Phase difference Waves in Two and Three Dimensions Phase = Phase difference: 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 Amplitude 2 Sound intensity level: 23 24

7 Doppler Effect Doppler Effect EXAMPLE How fast are the police traveling? QUESTION: EXAMPLE How fast are the police traveling? 27 28

8 EXAMPLE How fast are the police traveling? Chapter 20. Summary Slides General Principles General Principles 31 32

9 Important Concepts Important Concepts Applications Applications 35 36

10 Applications Chapter 20. Multiple-Choice Questions 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. 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

11 What is the frequency of this traveling wave? 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 A. 0.1 Hz B. 0.2 Hz C. 2 Hz D. 5 Hz E. 10 Hz What is the phase difference between the crest of a wave and the adjacent trough? 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 A. 0 B. π C. π /4 D. π /2 E. 3 π /

12 A light wave travels through three transparent materials of equal thickness. Rank in order, from the largest to smallest, the indices of refraction n 1, n 2, and n 3. A light wave travels through three transparent materials of equal thickness. Rank in order, from the largest to smallest, the indices of refraction n 1, n 2, and n 3. A. n 1 > n 2 > n 3 B. n 2 > n 1 > n 3 C. n 3 > n 1 > n 2 D. n 3 > n 2 > n 1 A. n 1 > n 2 > n 3 B. n 2 > n 1 > n 3 C. n 3 > n 1 > n 2 D. n 3 > n 2 > n 1 E. n = n = n E. n = n 2 = n 3 46 Amy and Zack are both listening to the source of sound waves that is moving to the right. Compare the frequencies each hears. Amy and Zack are both listening to the source of sound waves that is moving to the right. Compare the frequencies each hears. A. f Amy > f Zack B. f Amy < f Zack C. f Amy = f Zack A. f Amy > f Zack B. f Amy < f Zack C. f Amy = f Zack 47 48