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Sound

Sound. Physics 102. Chapter Fourteen. Amanda Hyer. Audible Frequency Range. 20 Hz to 20,000 Hz infrasonic ultrasonic Compressions rarefactions. Ultrasonic. 20 kHz. Frequency. Audible. 20 Hz. infrasonic. Elastic Media. slow. Air Helium water

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Sound

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  1. Sound Physics 102 Chapter Fourteen Amanda Hyer

  2. Audible Frequency Range • 20 Hz to 20,000 Hz • infrasonic ultrasonic • Compressions rarefactions

  3. Ultrasonic 20 kHz Frequency Audible 20 Hz infrasonic

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

  5. 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

  6. Classical calculation of Sound Speed

  7. Bulk Modulus for Air

  8. Exercise • 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

  9. Reflection

  10. Refraction The bending of sound because the speed is different in adjacent regions

  11. Refraction source far away

  12. Refraction cool source far away warm Afternoon

  13. Refraction warm source far away cool Late Evening

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

  15. Resonance • 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.

  16. Interference • When two waves overlap they form an interference pattern which can be either a constructive interference or a destructive interference. Destructive Constructive + = + = Cancellation Reinforcement

  17. Interference Constructive (in Phase) Destructive (180 ° out of phase)

  18. Interference Destructive (180 ° out of phase)

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

  20. Beats

  21. Exercise • 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

  22. Resonance • 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.

  23. Standing Waves on a String

  24. Open Organ pipe

  25. Organ Pipe Closed at one end

  26. Am and Fm broadcasting • AM Amplitude Modulation • carrier wave • 1040 1040 kHz • FM Frequency Modulation • 101 101 M Hz

  27. 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

  28. 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

  29. Carrier Frequency

  30. AM broadcasting

  31. Fm broadcasting

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