phy2048 lecture32

# phy2048 lecture32 - Chapter 17 Waves-II 171 What Is Physics...

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Unformatted text preview: Chapter 17: Waves--II 171 What Is Physics? 172 Sound Waves 173 The Speed of Sound 174 Traveling Sound Waves 175 Interference 176 Intensity and Sound Level 177 Source of Musical Sound 178 Beats 179 The Doppler Effect 1710 Supersonic Speeds, Shock Waves Chapter 17 Homework 1, 16, 17, 26, 28, 35, 40, 41, 47, 50, 53, 56, 58, 62, 69 Musical Sound Standing Waves String (node-node) 1 = 2 L v f1 = 2L v = T / f1 , 2 f1 , 3 f1 , 4 f1 , ... Pipe, two open ends (antinode-antinode) 1 = 2 L v f1 = 2L f1 , 2 f1 , 3 f1 , 4 f1 , ... Speed of Sound Pipe, one open end (node-antinode) 1 = 4 L f1 = v 4L f1 , _ , 3 f1 , _ , 5 f1 , ... Example Sample Problem 17-6. Cardboard tube with two open ends L = 67.0 cm, v = 343 m/s (a) What frequency do you hear from the tube? (b) What frequency do you hear if you jam your ear against one end of the tube? *Harmonic Analysis Sound Waves Longitudinal waves Frequency 20 Hz ~ 20 kHz hearing range < 20 Hz infrasonic > 20 kHz ultrasonic Pitch Speed Air (20C) Air (0C) Fresh water Steel 343 m/s 331 m/s 1,482 m/s 5,960 m/s Loudness Pressure amplitude Sound intensity Threshold of hearing Interference sin( -t ) sin( -t + 0 ) sin(kL1 - t ) sin( kL2 - t + 0 ) = 2 L + 0 Exactly in phase : = m(2 ) Exactly out of phase : = (m + 1 )(2 ) 2 for m = 0, 1, 2, 3 ... L Path length difference If 0 = 0 Exactly in phase : L = m Exactly out of phase : L = (m + 1 ) 2 for m = 0, 1, 2, 3 ... 2-D Interference Pattern Sample Problem 17-3. S1 and S2 in phase D = 1.5 Beats Two overlapping waves with slightly different frequencies give rise to the phenomenon of beats a periodic variations in the loudness of the resulting sound. s1 (t ) = s m cos 1t s 2 (t ) = s m cos 2t - 2 + 2 s (t ) = 2 s m cos( 1 t ) cos( 1 t) 2 2 f beat = f 2 - f1 ...
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phy2048 lecture32 - Chapter 17 Waves-II 171 What Is Physics...

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