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SoundSoundSoundSound
Physics 102Chapter Fourteen
Amanda Hyer
20 Hz to 20,000 Hz infrasonic ultrasonic
Compressions rarefactions
Audible Frequency Range
Ultrasonic
infrasonic
20 kHz
20 Hz
Audible
Freq
uen
cy
Elastic MediaElastic MediaElastic MediaElastic Media Air Helium water rock steel
slow
fast
speed=wavelength x frequency
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
Classical calculation of Sound SpeedClassical calculation of Sound Speed
v B
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
PV nRT M
MA
RT
P RTMA
PMA
RT
B 1.4P
PMA
RT
v B
B 1.4P
PMA
RT
v 1.4RT
MA
v 1.4RT
MA
1.4 8.314J / K / mole 273K
0.029kg / mole331.0(m / s)
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
ReflectionReflectionReflectionReflection
RefractionRefractionRefractionRefractionThe bending of sound because the speed is different in adjacent regions
RefractionRefractionRefractionRefraction
sourcefar away
RefractionRefractionRefractionRefraction
sourcefar away warm
cool
Afternoon
RefractionRefractionRefractionRefraction
sourcefar away
warm
cool
Late Evening
Energy in soundEnergy in soundEnergy in soundEnergy in sound High frequencies dissipate faster than low.
loud tuning fork versus soft tuning fork.
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.
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
InterferenceInterferenceInterferenceInterferenceConstructive (in Phase)
Destructive (180 ° out of phase)
-2
0
2
0 20
-2
0
2
0 20
-2
0
2
0 20
InterferenceInterferenceInterferenceInterferenceDestructive (180 ° out of phase)
-2
0
2
0 20
-2
0
2
0 20
-2
0
2
0 20
BeatsBeatsBeatsBeats When two different frequencies merge beats are heard
The Beat frequency is the difference between the two frequencies.
BeatsBeatsBeatsBeats
-4
-2
0
2
4
0 10
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
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.
Standing Waves on a Stringf
v
f1 v1
v
2L
f2 v2
vL
2f1
f3 v3
v
23L
3f1
Open Organ pipeOpen Organ pipe
f v
f1 v1
v
2L
f2 v2
vL
2f1
f3 v3
v
23L
3f1
Organ Pipe Closed at one endf
v
f1 v1
v
4L
f3 v3
v4
3 L3f1
f5 v3
v4
5 L5f1
Am and Fm broadcastingAm and Fm broadcasting
AM Amplitude Modulation carrier wave 1040 1040 kHz
FM Frequency Modulation 101 101 M Hz
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
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
Carrier FrequencyCarrier Frequency
-4
-2
0
2
4
0
AM broadcastingAM broadcasting
-4
-2
0
2
4
0
Fm broadcastingFm broadcasting
-4
-2
0
2
4
0
