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Sound Pitch Loudness Sound Intensity Level Doppler Effect

Sound Pitch Loudness Sound Intensity Level Doppler Effect. Physics Mrs. Coyle. Sound. Sound is a longitudinal mechanical wave. Compressions(High Pressure) Rarefactions(Low Pressure). Speed of Sound. Depends on the medium.

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Sound Pitch Loudness Sound Intensity Level Doppler Effect

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  1. Sound Pitch Loudness Sound Intensity Level Doppler Effect Physics Mrs. Coyle

  2. Sound • Sound is a longitudinal mechanical wave. • Compressions(High Pressure) • Rarefactions(Low Pressure)

  3. Speed of Sound • Depends on the medium. • The more elastic the medium the faster sound will travel through it.  • Speed in metals>speed in water>speed in air • Sound can’t travel through vacuum.

  4. Speed of Sound in Air v = 331 + 0.6 T ( in meters/sec) • T is the temperature in 0C. • In higher humidity, sound will travel faster.

  5. Properties of Sound • Reflection (Echo) • Refraction • Interference • Diffraction

  6. Pitch: the frequency of a sound wave. • Musical notes have a given pitch. • The note C has a frequency of 327Hz. • When two notes differ by a ratio of 2:1 they are one octave apart. • What would be the next higher C? (Ans:654Hz)

  7. Bow (Shock) Waves When the speed of a moving sound source is greater than the speed of the wave, a pressure ridge builds similar to the wave created by the bow of a ship. physlet animation

  8. Sonic Boom • When the pressure ridge of a bow wave of a jet passes over an observer on the ground, the observer experiences a sonic boom.

  9. Doppler Effect • The change in a wave's perceived frequency due to the motion of either the sound source or the observer.  • It is applicable to any type of wave. • Austrian physicist Christian Doppler (1803-1853). train sound clip Simulations • physlet animation • http://www.walter-fendt.de/ph14e/dopplereff.htm

  10. The Doppler Effect http://www.physicsclassroom.com/Class/sound/u11l3b.cfm

  11. Doppler Effect Detected Frequency, (fD) fD = f (v±vo) v±vs f : frequency of source v : speed of sound vo : speed of observer (+)when observer moving towards source vs: speed of source (-)when source is moving towards observer

  12. Example 1 An ambulance is approaching a stationary observer. The siren of the ambulance emits a frequency of 480Hz and the speed of the ambulance is 50km/h(=13.88m/s). What frequency will the stationary observer hear when the ambulance is approaching? Assume T=20oC.Answer: fd = 500Hz

  13. Sound Intensity (I) I = (Power transmitted by the Wave)/Area • Threshold of human hearing: Io =1 x 10-12 Watts/m2 • Threshold of Pain: IP= 1 Watts/m2

  14. Sound (Intensity) Level • A measure of our perception of the loudness of the sound. • Unit: decibel(dB)

  15. Sound (Intensity) Level, (decibel) b= 10 log I , unit for b is dB (decibel) I0 The decibel compares the sound intensity (I), to Io (1 x 10-12 Watts/m2) , the threshold of human hearing. Remember: log(10x )= x

  16. Examples of Sound Intensity Levels • jet plane taking off 140 dB • air raid siren 125 dB • threshold of pain 120 dB • loud rock music 115 dB • ear damage starts 85 dB • busy traffic 70 dB • normal conversation 60 dB • quiet library 40 dB • soft whisper 20 dB • threshold of human hearing 0 dB

  17. Example 2 • What is the sound level (decibel) of a sound of 10-4 W/m2 intensity ? • Answer: 80dB

  18. Example 3 • How many times louder is a quiet library sound (40 dB) compared to a soft whisper (20 dB)? • Hint 1: Property of logs: log(A/B) = logA –logBHint 2: Take the difference in dB and then find (I2 /I1) • Answer: (I2 /I1 )= 100/1

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