soundsound physics 102 chapter fourteen amanda hyer
TRANSCRIPT
![Page 1: SoundSound Physics 102 Chapter Fourteen Amanda Hyer](https://reader033.vdocuments.net/reader033/viewer/2022061306/551462ce550346414e8b59e2/html5/thumbnails/1.jpg)
SoundSoundSoundSound
Physics 102Chapter Fourteen
Amanda Hyer
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20 Hz to 20,000 Hz infrasonic ultrasonic
Compressions rarefactions
Audible Frequency Range
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Ultrasonic
infrasonic
20 kHz
20 Hz
Audible
Freq
uen
cy
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Elastic MediaElastic MediaElastic MediaElastic Media Air Helium water rock steel
slow
fast
speed=wavelength x frequency
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Speed of SoundSpeed of SoundSpeed of SoundSpeed of Sound Speed = 331 m/s + 0.6 Tc speed = 343 m/s at 20 °C
d=v x t ~ 1 km in 3 sec or 1 mile in 5 sec
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Classical calculation of Sound SpeedClassical calculation of Sound Speed
v B
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Bulk Modulus for Air
Bulk Modulus for Air
PV nRT
PV PV nRT
PV nRT PV
adiabatic W U
PV 5
2nRT
PV 7
2nRT _ _ And V
5
2nR
T
Pbut
P BV
VBV PV
B52
nRTP
72
nRT
B 1.4P
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PV nRT M
MA
RT
P RTMA
PMA
RT
B 1.4P
PMA
RT
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v B
B 1.4P
PMA
RT
v 1.4RT
MA
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v 1.4RT
MA
1.4 8.314J / K / mole 273K
0.029kg / mole331.0(m / s)
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ExerciseExerciseExerciseExercise How far away is a lightening bolt that is
heard 12.0 sec after the flash is seen? Given: t=12.0 sec and v =1/3 km / sec Wanted: d Solution: Use d= v t d = (1 / 3 km/sec) (12.0 sec)= 4 km
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ReflectionReflectionReflectionReflection
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RefractionRefractionRefractionRefractionThe bending of sound because the speed is different in adjacent regions
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RefractionRefractionRefractionRefraction
sourcefar away
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RefractionRefractionRefractionRefraction
sourcefar away warm
cool
Afternoon
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RefractionRefractionRefractionRefraction
sourcefar away
warm
cool
Late Evening
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Energy in soundEnergy in soundEnergy in soundEnergy in sound High frequencies dissipate faster than low.
loud tuning fork versus soft tuning fork.
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ResonanceResonanceResonanceResonance system that has a natural frequency like a
tight string or a tube (flute)
driven by a tiny oscillating force
Resonce occurs when the frequency of the force matches the natural frequency of the system.
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InterferenceInterference When two waves overlap they form an interference pattern
which can be either a constructive interference or a destructive interference.
+ =
Constructive
+ =
Destructive
Reinforcement Cancellation
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InterferenceInterferenceInterferenceInterferenceConstructive (in Phase)
Destructive (180 ° out of phase)
-2
0
2
0 20
-2
0
2
0 20
-2
0
2
0 20
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InterferenceInterferenceInterferenceInterferenceDestructive (180 ° out of phase)
-2
0
2
0 20
-2
0
2
0 20
-2
0
2
0 20
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BeatsBeatsBeatsBeats When two different frequencies merge beats are heard
The Beat frequency is the difference between the two frequencies.
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BeatsBeatsBeatsBeats
-4
-2
0
2
4
0 10
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ExerciseExerciseExerciseExercise What is the beat frequency when a sound of
256 Hz meets a sound of 260 Hz Given: F1=256 Hz and F2= 260 Hz Wanted: F beats Solution: Use F Beats = Abs(F1 - F2) F Beats = Abs(F1 - F2) = 4 Hz
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ResonanceResonanceResonanceResonance system that has a natural frequency like a
tight string or a tube (flute)
driven by a tiny oscillating force
Resonce occurs when the frequency of the force matches the natural frequency of the system.
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Standing Waves on a Stringf
v
f1 v1
v
2L
f2 v2
vL
2f1
f3 v3
v
23L
3f1
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Open Organ pipeOpen Organ pipe
f v
f1 v1
v
2L
f2 v2
vL
2f1
f3 v3
v
23L
3f1
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Organ Pipe Closed at one endf
v
f1 v1
v
4L
f3 v3
v4
3 L3f1
f5 v3
v4
5 L5f1
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Am and Fm broadcastingAm and Fm broadcasting
AM Amplitude Modulation carrier wave 1040 1040 kHz
FM Frequency Modulation 101 101 M Hz
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Am and Fm broadcastingAm and Fm broadcasting
Radio waves are electromagnetic waves Their speed is 300,000,000 m/s They travel through outer space
Sound is an acoustical wave The speed of sound is 340 m/s They do not travel through outer space
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Am and Fm broadcastingAm and Fm broadcasting
Radio waves are electromagnetic waves Their speed is 300,000,000 m/s They travel through outer space
Sound is an acoustical wave The speed of sound is 340 m/s They do not travel through outer space
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Carrier FrequencyCarrier Frequency
-4
-2
0
2
4
0
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AM broadcastingAM broadcasting
-4
-2
0
2
4
0
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Fm broadcastingFm broadcasting
-4
-2
0
2
4
0