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SoundSound Physics 102 Chapter 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 Frequency

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Elastic Media Air Helium water rock steel slow fast speed=wavelength x frequency

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Speed 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 Speed

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Bulk Modulus for Air

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ExerciseExercise 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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ReflectionReflection

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RefractionRefraction The bending of sound because the speed is different in adjacent regions

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RefractionRefraction source far away

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RefractionRefraction source far away warm cool Afternoon

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RefractionRefraction source far away warm cool Late Evening

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Energy in sound High frequencies dissipate faster than low. loud tuning fork versus soft tuning fork.

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ResonanceResonance 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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Interference 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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InterferenceInterference Constructive (in Phase) Destructive (180 ° out of phase)

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InterferenceInterference

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BeatsBeats When two different frequencies merge beats are heard The Beat frequency is the difference between the two frequencies.

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BeatsBeats

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ExerciseExercise 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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ResonanceResonance 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 String

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Open Organ pipe

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Organ Pipe Closed at one end

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Am 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 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 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 Frequency

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AM broadcasting

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Fm broadcasting

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