Chapter 14 Sound AP Physics B Lecture Notes. 14-01 Producing a Sound Wave 14-02 Characteristics of...
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Transcript of Chapter 14 Sound AP Physics B Lecture Notes. 14-01 Producing a Sound Wave 14-02 Characteristics of...
Chapter 14Sound
AP Physics BLecture Notes
14-01 Producing a Sound Wave
14-02 Characteristics of Sound Waves
14-03 The Speed of Sound
14-05 Spherical and Plane Waves
14-06 The Doppler Effect
14-07 Interference of Sound Waves
14-08 Standing Waves
Sound
Sections
14-10 Standing Waves in Air Columns
14-11 Beats
Producing a Sound Wave
Characteristics of Sound
Loudness: related to intensity of the sound wave Pitch: related to frequency Audible range: about 20 Hz to 20,000 Hz Ultrasound: above 20,000 Hz Infrasound: below 20 Hz
Loudness: related to intensity of the sound wave Pitch: related to frequency Audible range: about 20 Hz to 20,000 Hz Ultrasound: above 20,000 Hz Infrasound: below 20 Hz
Phy 2054 Lecture Notes 12
Characteristics of Sound Waves
Chapter 14 Sound
The pitch of a musical note is characterized by the sound’s
(A) amplitude
(B) frequency
(C) wavelength
(D) speed
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 depends somewhat on temperature, especially for gases.
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 depends somewhat on temperature, especially for gases.
The Speed of Sound
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.
The Speed of Sound
Speed of a wave on a string.
LmF
v T
Speed of sound in a fluid.
v
Speed of sound in a solid.
Y
v
K273
Tm/s 331v
Speed of sound in air is temperature dependent.
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.
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
2 (D)
2 (C)
(B)
2 )A(
Spherical and Plane Waves
The intensity of sound from a point source diminishes with distance:
2r
1I
2rπ4
PI
Phy 2054 Lecture Notes 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?
2I
(D) I 4 (C) 2I (B) 4I
)A(
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
"I love hearing that lonesome wail of the train whistle as themagnitude of the frequency of the wave changes due to theDoppler effect."
Phy 2054 Lecture Notes 12
The Doppler Effect
The Doppler Effect
The Doppler Effect for two stationary observers
The Doppler effect occurs when a source of sound is moving with respect to an observer.
Stationary truck
Moving truck
Longer wavelengthLower frequency
Shorter wavelengthHigher frequency
Phy 2054 Lecture Notes 12
The Doppler Effect
Doppler Effect
is experienced whenever there is relative motion between the sound source and an observer.
Observer SourceObserver Source
Observer SourceObserver Source
s
oso vv
vvff
Phy 2054 Lecture Notes 12
The Doppler Effect
Observer Source
Observer Source
s
oso vv
vvff
v
vvff oso
v
vvff oso
s
oso vv
vvff
s
so vvv
ff
s
so vvv
ff
Stationary Source
HigherFrequency
Stationary Observer
HigherFrequency
Phy 2054 Lecture Notes 12
The Doppler Effect
Observer Source
Observer Source
Stationary Source
LowerFrequency
Stationary Observer
LowerFrequency
s
oso vv
vvff
v
vvff oso
v
vvff oso
s
oso vv
vvff
s
so vvv
ff
s
so vvv
ff
Phy 2054 Lecture Notes 12
The Doppler Effect
s
oso vv
vvff
v
vvff oso
s
so vvv
ff
v
vvff oso
s
so vvv
ff
Observer Source
Observer Source
Observer Source
Observer Source
Phy 2054 Lecture Notes 12
The Doppler Effect
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.
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?
Phy 2054 Lecture Notes 12
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?
Phy 2054 Lecture Notes 12
The Doppler Effect (Problem)
Interference of Sound Waves
Sound waves interfere in the same way that other waves do in space.
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
The vibrations are transmitted to the air and then to our ears.
The vibration may be started by:
plucking
striking
bowing
blowing
Musical instruments produce sounds in various ways –
vibrating strings
vibrating membranes
vibrating metal or wood shapes
vibrating air columns
The vibrations are transmitted to the air and then to our ears.
The vibration may be started by:
plucking
striking
bowing
blowing
Phy 2054 Lecture Notes 12
Standing Waves
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 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.
Phy 2054 Lecture Notes 12
Standing Waves
Standing Waves
... 3, 2, 1,n L2
nvfn
First Harmonic - Fundamental
121 λL
L2v
f 1
Second Harmonic
2λL Lv
f 2 L2v2
Third Harmonic
323 λL
L2v3
f 3
λv
f λfv
Phy 2054 Lecture Notes 12
Standing Waves
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.
A tube open at both ends has displacement antinodes, at the ends.
First Harmonic - Fundamental
121 λL
L2v
f 1
... 3, 2, 1,n L2
nvfn
L
Second Harmonic
2λL Lv
f 2 L2v2
Third Harmonic
323 λL
L2v3
f 3
Phy 2054 Lecture Notes 12
Standing Waves in Air Columns
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
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?
Phy 2054 Lecture Notes 12
Standing Waves in Air Columns (Problem)
A tube closed at one end has a displacement node at the closed end.
L First Harmonic - Fundamental
141 λL
L4v
f 1
Third Harmonic
343 λL
L4v3
f 3
Fifth Harmonic
545 λL
L4v5
f 5
... 5, 3, 1,n L4
nvfn
Phy 2054 Lecture Notes 12
Standing Waves in Air Columns
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
Standing Waves in Air Columns
Beats
Beat Frequency
21beat fff
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.
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.