1. 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

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

3. Interference; Principle of Superposition
Partial Destructive Interference
Constructive Interference
Destructive Interference
General Physics 2
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 = ( T) m/s
General Physics 2
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
General Physics 2
Waves & Sound

6. Intensity
General Physics 2
Waves & Sound

7. Human Ear
General Physics 2
Waves & Sound

8. Frequency Response of Ear
General Physics 2
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.
General Physics 2
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?
General Physics 2
Waves & Sound

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

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

13. Closed at one end
General Physics 2
Waves & Sound

14. Quality of Sound
General Physics 2
Waves & Sound

15. Interference & Beats
fbeats = fA - fB
General Physics 2
Waves & Sound

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

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