Chapter 12Sound

14-01 Producing a Sound Wave14-02 Characteristics of Sound Waves14-03 The Speed of Sound14-05 Spherical and Plane Waves14-06 The Doppler Effect14-07 Interference of Sound Waves14-08 Standing Waves

Sound

Sections

14-10 Standing Waves in Air Columns14-11 Beats

Sound (02 of 38)

Producing a Sound Wave

Sound (03 of 38)

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

Characteristics of Sound Waves

Sound (04 of 38)

Chapter 14 Sound

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The pitch of a musical note is characterized by the sound’s

(A) amplitude

(B) frequency

(C) wavelength

(DE) speed

Sound (05 of 38)

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

Sound (06 of 38)

Chapter 14 Sound

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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.

Sound (07 of 38)

The Speed of Sound

Speed of a wave on a string.L

mFv T

Speed of sound in a fluid.

v

Speed of sound in a solid.

Yv

K273

Tm/s 331v

Speed of sound in air is temperature dependent.

Sound (08 of 38)

Chapter 14 Sound

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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.

Sound (09 of 38)

Chapter 14 Sound

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

2 (D)

2 (C) (B)2 )A(

fv

Sound (10 of 38)

Spherical and Plane Waves

The intensity of sound from a point source diminishes with distance:

2r1I

2rπ4PI

Sound (11 of 38)

Chapter 14 Sound

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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(

Sound (12 of 38)

Chapter 14 Sound

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The intensity of a sound increases when there is an increase in the sound’s

(A) frequency

(B) wavelength

(C) amplitude

(D) speed

Sound (13 of 38)

"I love hearing that lonesome wail of the train whistle as themagnitude of the frequency of the wave changes due to theDoppler effect."

The Doppler Effect

Sound (14 of 38)

The Doppler Effect

The Doppler Effect for two stationary observers

Sound (15 of 38)

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

The Doppler Effect

Sound (16 of 38)

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

The Doppler Effect

Sound (17 of 38)

Observer Source

Observer Source

s

oso vv

vvff

vvvff o

so

vvvff o

so

s

oso vv

vvff

s

so vvvff

s

so vvvff

Stationary Source

HigherFrequency

Stationary Observer

HigherFrequency

The Doppler Effect

Sound (18 of 38)

Observer Source

Observer Source

Stationary Source

LowerFrequency

Stationary Observer

LowerFrequency

s

oso vv

vvff

vvvff o

so

vvvff o

so

s

oso vv

vvff

s

so vvvff

s

so vvvff

The Doppler Effect

Sound (19 of 38)

s

oso vv

vvff

vvvff o

so

s

so vvvff

vvvff o

so

s

so vvvff

Observer Source

Observer Source

Observer Source

Observer Source

The Doppler Effect

Sound (20 of 38)

Chapter 14 Sound

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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.

Sound (21 of 38)

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

Hz 7091

m/s 23m/s 343m/s 343Hz 1550

a) toward you?

Hz 1418

m/s 23m/s 343m/s 343Hz 1550

b) away from you?

The Doppler Effect (problem)

s

oso vv

vvff

s

so vvvff

s

oso vv

vvff

s

so vvvff

Sound (22 of 38)

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?

s

oso vv

vvff

m/s 5m/s 343m/s 5m/s 343Hz 10x 0.3f 4

s

os vv

vvf

Hz 10x 09.3f 4

The Doppler Effect (Problem)

Sound (23 of 38)

Interference of Sound Waves

Sound waves interfere in the same way that other waves do in space.

Sound (24 of 38)

Sources of Sound: Vibrating Strings and Air ColumnsMusical 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

strikingbowingblowing

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

strikingbowingblowing

Standing Waves

Sound (25 of 38)

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.

Standing Waves

Sound (26 of 38)

... 3, 2, 1,n L2

nvfn

First Harmonic - Fundamental

121 λL

L2vf 1

Second Harmonic

2λL Lvf 2

L2v2

Third Harmonic

323 λL L2

v3f 3

λvf λfv

Standing Waves

Sound (27 of 38)

Chapter 14 Sound

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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.

Sound (28 of 38)

A tube open at both ends has displacement antinodes, at the ends.

First Harmonic - Fundamental

121 λL

L2vf 1

... 3, 2, 1,n L2

nvfn

L

Second Harmonic

2λL Lvf 2

L2v2

Third Harmonic

323 λL L2

v3f 3

Standing Waves in Air Columns

Sound (29 of 38)

Chapter 14 Sound

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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

1n nff

Sound (30 of 38)

Hz 55f

Hz 275Hz 330f

1

1

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?

... 3, 2, 1,n L2

nvfn

L2vf1

1Lf2v Hz 55m 80.12 m/s 198

Standing Waves in Air Columns (Problem)

Sound (31 of 38)

A tube closed at one end has a displacement node at the closed end.

L First Harmonic - Fundamental

141 λL

L4vf 1

Third Harmonic

343 λL L4

v3f 3

Fifth Harmonic

545 λL L4

v5f 5

... 5, 3, 1,n L4

nvfn

Standing Waves in Air Columns

Sound (32 of 38)

Chapter 14 Sound

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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) 750 Hz

(D) 1050 Hz

Sound (33 of 38)

Standing Waves in Air Columns

Sound (34 of 38)

Beats

Beat Frequency

21beat fff

Sound (35 of 38)

Chapter 12 Sound

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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.

21beat fff

Sound (36 of 38)

Chapter 12 Sound

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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.

21beat fff

Sound (37 of 38)

The End