1. Chapter 14
Sound
AP Physics B
Lecture Notes

2. Sound
Sections
Producing a Sound Wave
Characteristics of Sound Waves
The Speed of Sound
Spherical and Plane Waves
The Doppler Effect
Interference of Sound Waves
Standing Waves
Standing Waves in Air Columns
Beats

3. Producing a Sound Wave

4. Characteristics of Sound Waves Characteristics of Sound
Loudness: related to intensity of the sound wave
Loudness: related to intensity of the sound wave
Pitch: related to frequency
Pitch: related to frequency
Audible range: about 20 Hz to 20,000 Hz
Audible range: about 20 Hz to 20,000 Hz
Ultrasound: above 20,000 Hz
Ultrasound: above 20,000 Hz
Infrasound: below 20 Hz
Infrasound: below 20 Hz
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5. Chapter 14 Sound
The pitch of a musical note is characterized by the sound’s
(A) amplitude
(B) frequency
(C) wavelength
(D) speed

6. The Speed of Sound
Sound can travel through any kind of matter, but not through a vacuum.
Sound can travel through any kind of matter, but not through a vacuum.
The speed of sound is different in different materials; in general, it is slowest in gases, faster in liquids, and fastest in solids.
The speed of sound is different in different materials; in general, it is slowest in gases, faster in liquids, and fastest in solids.
The speed depends somewhat on temperature, especially for gases.
The speed depends somewhat on temperature, especially for gases.

7. Chapter 14 Sound
Which of the following is a true statement?
(A) Sound waves are transverse pressure waves.
(B) Sound waves can not travel through a vacuum.
(C) Sound waves and light waves travel a the same speed.
(D) When the frequency of a sound wave increases its
wavelength also increases.

8. The Speed of Sound
Speed of a wave on a string.
Speed of sound in a fluid.
Speed of sound in a solid.
Speed of sound in air is temperature dependent.

9. Chapter 14 Sound
As the temperature of the air increases, the speed of sound through the air
(A) increases.
(B) decreases.
(C) does not change.
(D) increases if the atmospheric pressure is high.

10. Chapter 14 Sound
Sound of a frequency f travels through air with a wavelength l. If the frequency of the sound is
increased to 2f, its wavelength in air will be

11. Spherical and Plane Waves
The intensity of sound from a point source diminishes
with distance:
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12. Chapter 14 Sound
The intensity of a point source at a distance d from the source is I. The intensity of the sound at a distance 2d from the source?

13. Chapter 14 Sound
The intensity of a sound increases when there is an increase in the sound’s
(A) frequency
(B) wavelength
(C) amplitude
(D) speed

14. The Doppler Effect
"I love hearing that lonesome wail of the train whistle as the
magnitude of the frequency of the wave changes due to the
Doppler effect."
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15. The Doppler Effect
The Doppler Effect for two stationary observers

16. The Doppler Effect
The Doppler effect occurs when a source of sound is moving with respect to an observer.
Stationary truck
Longer wavelength
Lower frequency
Shorter wavelength
Higher frequency
Moving truck
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17. The Doppler Effect is experienced whenever there is
relative motion between the sound
source and an observer.
Doppler
Effect
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18. The Doppler Effect Stationary Source Higher Frequency Stationary
Observer
Higher
Frequency
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19. The Doppler Effect Stationary Source Lower Frequency Stationary
Observer
Lower
Frequency
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20. The Doppler Effect
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21. Chapter 14 Sound
A police car with its siren on departs from a stationary observer. The frequency heard by the observer
(A) is higher than the source.
(B) is lower than the source.
(C) is the same as that of the source.
(D) is equal to zero.

22. The Doppler Effect (problem)
You are standing still. What frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/s
a) toward you?
b) away from you?
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23. The Doppler Effect (Problem)
A bat flies toward a wall at a speed of 5.0 m/s. As it flies, the bat emits an ultrasonic sound wave with a frequency of 30.0 kHz.
What frequency does the bat hear in the reflected wave?
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24. Interference of Sound Waves
Sound waves interfere in the same way that other waves do in space.

25. Sources of Sound: Vibrating Strings and Air Columns
Standing Waves
Sources of Sound: Vibrating Strings and Air Columns
Musical instruments produce sounds in various ways –
vibrating strings
vibrating membranes
vibrating metal or wood shapes
vibrating air columns
Musical instruments produce sounds in various ways –
vibrating strings
vibrating membranes
vibrating metal or wood shapes
vibrating air columns
The vibration may be started by:
plucking
striking
bowing
blowing
The vibration may be started by:
plucking
striking
bowing
blowing
The vibrations are transmitted to the air and then to our ears.
The vibrations are transmitted to the air and then to our ears.
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26. Standing Waves
The strings on a guitar can be effectively shortened by fingering, raising the fundamental pitch.
The strings on a guitar can be effectively shortened by fingering, raising the fundamental pitch.
The pitch of a string of a given length can also be altered by using a string of different density.
The pitch of a string of a given length can also be altered by using a string of different density.
Standing Waves
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27. First Harmonic - Fundamental
Standing Waves
First Harmonic - Fundamental
Second Harmonic
Third Harmonic
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28. Chapter 14 Sound
The standing wave on a vibrating guitar string produces a sound wave in the air. The two waves have
(A) the same wavelength.
(B) the same speed.
(C) the same frequency.
(D) the same amplitude.

29. Standing Waves in Air Columns
A tube open at both ends has displacement antinodes, at the ends. L
First Harmonic - Fundamental
Second Harmonic
Third Harmonic
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30. Chapter 14 Sound
A pipe open at both ends resonates with a fundamental frequency of 150 Hz. Which one of the following frequencies will not resonate in this pipe
(A) 300 Hz
(B) 450 Hz
(C) 500 Hz
(D) 750 Hz

31. Standing Waves in Air Columns (Problem)
A uniform narrow tube 1.8 m long is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. What is the speed of sound in the gas in the tube?
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32. Standing Waves in Air Columns
A tube closed at one end has a displacement node at the closed end. L
First Harmonic - Fundamental
Third Harmonic
Fifth Harmonic
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33. Chapter 14 Sound
A pipe open at one end and closed at the other end. resonates with a fundamental frequency of 150 Hz. Which one of the following frequencies will not
resonate in this pipe
(A) 300 Hz
(B) 450 Hz
(C) 760 Hz
(D) 1050 Hz

34. Standing Waves in Air Columns

35. Beats
Beat Frequency

36. Chapter 12 Sound
The interference of two sound waves can produces a beat frequency if the waves have
(A) the same amplitude.
(B) slightly different amplitudes.
(C) the same frequency.
(D) slightly different frequencies.

37. Chapter 12 Sound
Two pure tones are sounded together and a particular beat frequency is heard. If the frequency of one of the tones is decreased slightly, the beat frequency
(A) will increases.
(B) will decreases.
(C) does not change.
(D) could either increase or decrease.

38. END