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Reflection & Transmission

Reflection & Transmission. when end is free to move, reflected wave is not inverted. when end is fixed, reflected wave in inverted. Reflection & Transmission. when a wave enters a heavier material, part of the wave is reflected and part is transmitted.

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Reflection & Transmission

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  1. Reflection & Transmission when end is free to move, reflected wave is not inverted when end is fixed, reflected wave in inverted Waves & Sound

  2. Reflection & Transmission when a wave enters a heavier material, part of the wave is reflected and part is transmitted Waves & Sound

  3. Interference; Principle of Superposition PartialDestructiveInterference ConstructiveInterference DestructiveInterference Waves & Sound

  4. Speed of Sound • Different in different materials • v = 331 m/s • in air at 00C and at 1 atm • temperature dependence • v = (331 +0.60 T) m/s Waves & Sound

  5. Decibels • Intensity of sound is measured in decibels • range of 1012 between intensity of quietest and loudest sounds we can hear • ear hears on logarithmic scale • decibel - measure of intensity Waves & Sound

  6. Intensity Waves & Sound

  7. Human Ear Waves & Sound

  8. Frequency Response of Ear Waves & Sound

  9. Sources of sound • String instruments • Strings are fixed at both ends. • sound is amplified by • sounding box • sounding board • Figure out the equation for harmonic wavelengths in terms of L, where L is the length of the unstretched string. Waves & Sound

  10. Pair Problem • A highway overpass was observed to resonate as one full loop when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good? Waves & Sound

  11. Tacoma Narrows Bridge • Watch movie Waves & Sound

  12. Sources of Sound: Wind Instruments Waves & Sound

  13. Closed at one end Waves & Sound

  14. Quality of Sound Waves & Sound

  15. Interference & Beats fbeats = fA - fB Waves & Sound

  16. Doppler Effect higher frequency lower frequency Waves & Sound

  17. Think-Pair-Share • A monitor is blowing a whistle in front of the child. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning. Waves & Sound

  18. Doppler Effect • v = speed of wave • vo = speed of observer • vs = speed of source • f0 = emitted frequency • f’ = observed frequency • f’ > f0 • s and o approaching • f’ < f0 • s and o receding Waves & Sound

  19. Plug & Chug • The predominant frequency of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30.0 m/s (a) toward the fire engine, and (b) away from it? Waves & Sound

  20. Think-Pair-Share • (a) Compare the shift in frequency if a 200-Hz source is moving toward you at 15 m/s, versus you moving toward it at 15 m/s. Are the two frequences exactly the same? Are they close? • (b) Repeat the calculation for 150 m/s. What can you conclude about the asymmetry of the Doppler formula? Waves & Sound

  21. Sonic Boom If an object moves at the speed of sound as in (c), all the sound waves pile up at one point. The result is an immense sound - a sonic boom! Waves & Sound

  22. Ultrasound Imaging color reflects strength of echo delay of echo indicates distance to boundary Waves & Sound

  23. Think-Pair-Share • If the velocity of blood flow in the aorta is normally about 0.32 m/s, what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of 1.54 x 103 m/s. Waves & Sound

  24. Think-Pair-Share • A single mosquito 5.0 m from a person makes a sound close to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mosquitos? Waves & Sound

  25. Interactive Physics • PHET • phet.colorado.edu/sims/wave-on-a-string/wave-on-a- string_en.html • Create a standing wave • Adjust the settings to match your calculations for the harmonics Waves & Sound

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