Reflection Transmission when end is free to move

Reflection & Transmission when end is free to move, reflected wave is not inverted when end is fixed, reflected wave in inverted General Physics 2 Waves & Sound 1

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

Interference; Principle of Superposition Constructive Interference General Physics 2 Destructive Interference Waves & Sound Partial Destructive Interference 3

Speed of Sound • • Different in different materials v = 331 m/s • • in air at 00 C and at 1 atm temperature dependence • v = (331 +0. 60 T) m/s General Physics 2 Waves & Sound 4

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 General Physics 2 Waves & Sound 5

Intensity General Physics 2 Waves & Sound 6

Human Ear General Physics 2 Waves & Sound 7

Frequency Response of Ear General Physics 2 Waves & Sound 8

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. General Physics 2 Waves & Sound 9

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? General Physics 2 Waves & Sound 10

Tacoma Narrows Bridge • Watch movie General Physics 2 Waves & Sound 11

Sources of Sound: Wind Instruments General Physics 2 Waves & Sound 12

Closed at one end General Physics 2 Waves & Sound 13

Quality of Sound General Physics 2 Waves & Sound 14

Interference & Beats fbeats = f. A - f. B General Physics 2 Waves & Sound 15

Doppler Effect higher frequency lower frequency General Physics 2 Waves & Sound 16

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. General Physics 2 Waves & Sound 17

Doppler Effect • • • v = speed of wave vo = speed of observer vs = speed of source f 0 = emitted frequency f’ = observed frequency General Physics 2 • f’ > f 0 • • s and o approaching f’ < f 0 • s and o receding Waves & Sound 18

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? � General Physics 2 Waves & Sound 19

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? General Physics 2 Waves & Sound 20

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! General Physics 2 Waves & Sound 21

Ultrasound Imaging delay of echo indicates distance to boundary General Physics 2 Waves & Sound color reflects strength of echo 22

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. General Physics 2 Waves & Sound 23

Think-Pair-Share • A single mosquito 5. 0 m from a person makes a sound close to the threshold of human hearing (0 d. B). What will be the sound level of 1000 such mosquitos? General Physics 2 Waves & Sound 24

Interactive Physics • • PHET phet. colorado. edu/sims/wave-on-astring/wave-on-a- string_en. html Create a standing wave Adjust the settings to match your calculations for the harmonics General Physics 2 Waves & Sound 25