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Unformatted text preview: Ch 16: Sound Waves
Focus: Pressure waves 1) Sound Speed: v = B/ v= E/ ( Like v = T / ) B = bulk modulus E = elastic modulus 2) Travelling wave: D = DM sin(k x  t ) PM = 2 v DM f Max pressure change: 3) Decibel Scale dB: Log scale based on a reference intensity: I 0 = 1.00 10 12 W/m 2 Example: I (in dB) = 10 log10 I0 = 20 dB I = 10 10 W/m 2 Ch 16: Sound Waves
P = IA 4) Power Recall: I = intensity in W/m2 and A = area in m2 For spherical wave, A1 = 4 p r12 r1 = distance from small source and similarly for 2 I1 A1 = I 2 A2 5) Vibrating Air Columns length L: node L = 1 / 2 L = 1 / 4
Closed pipenodes at ends Open pipeantinodes in displacement at ends L = 2
Draw Pictures! L = 33 / 4 Ch 16: Sound Waves
6) Beats: D1 = DM sin(2 f1 t ) D 2 = DM sin(2 f 2 t )
Beat frequency:  f1  f 2  D =D1 + D 2 7) Interference: Waves from two spatially separated sources l = distance between successive crests or troughs r1 = distance from source 1 to P P r2 = distance from source 1 to P (Assume sources driven in phase.) Constructive interference:
r1  r2 1 2 (Crests meet crests)
Destructive interference:
r1  r2 = integer = half an odd integer (Crests meet troughs) Ch 16: Sound Waves 8) Doppler Effect: v = sound speed vobs = observer speed vsource = source speed Observed frequency: v obs 1 v f= f v source 1m v f = frequency at the source Frequency increases if source/observer move toward each other (upper signs, numerator, denominator) Frequency decreases if source/observer move away from each other ...
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This note was uploaded on 05/13/2010 for the course PHYSICS 53L taught by Professor Mueller during the Fall '07 term at Duke.
 Fall '07
 Mueller
 Physics

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