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Sound Waves Flashcards

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1
Q

What is sound?

A

A form of energy produced by vibrating bodies.

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2
Q

What happens when we strike a tuning fork?

A

Its prongs vibrate.

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3
Q

What do these vibrations give rise to?

A

Sound waves.

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4
Q

What does this chapter discuss?

A

The production and transmission of sound

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5
Q

What should students be able to do after completing this chapter?

A

Identify the vibrating sources when sound is produced; Distinguish between (a) noise and music (b) intensity and loudness (c) pitch and frequency as applied to sound; Explain forced vibration and explain how it is used to amplify a sound; Use the relationship ๐‘‰=๐‘“๐œ† in solving numerical problems; Explain and discuss the production of standing waves in stretched strings; Use resonance tube to determine the velocity of sound in air; Classify musical instruments into (a) wind instrument (b) percussion instrument

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6
Q

How is sound produced?

A

By vibrating bodies.

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7
Q

What do the vibrations cause?

A

The surrounding air to vibrate also producing a disturbance of the air.

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8
Q

How does this disturbance travel?

A

Out from the source of vibration in the form of longitudinal waves.

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9
Q

What can vibrate and be a source of sound?

A

Almost any object.

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10
Q

How is the source set into vibration in musical instruments?

A

By striking

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11
Q

What does the tuning fork have?

A

Two steel prongs which vibrate when struck with a hard rubber giving some sound.

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12
Q

What happens during the vibration of the tuning forkโ€™s prongs?

A

They present a hazy appearance due to their rapid to and fro movements.

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13
Q

What happens if the vibrating prongs are dipped into a beaker of water?

A

The water is seen to be violently agitated.

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14
Q

What happens when a small rubber ball suspended by a thread is brought near the vibrating prongs?

A

The ball is seen to be immediately kicked aside.

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15
Q

What is an important aspect of sound transmission?

A

That a material medium is always required for the passage of sound.

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16
Q

What does the experiment demonstrate?

A

That sound cannot travel through a vacuum but requires a transmitting medium.

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17
Q

What does the apparatus consist of?

A

An electric bell covered with a bell jar placed on the plate of a vacuum pump.

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18
Q

What makes the bell toring and produce some sound which is clearly audible?

A

Electrical connections.

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19
Q

What happens as more and more air is pumped out from the bell jar?

A

The sound of the bell becomes fainter and fainter though the clapper is still seen to be striking the bell.

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20
Q

What happens when all the air has been pumped out leaving a vacuum in the bell jar?

A

No sound is heard.

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21
Q

What does the fact that the clapper is still seen to be vibrating even though no sound is heard show?

A

That light waves can travel through a vacuum but sound waves cannot travel through a vacuum.

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22
Q

What happens when air is reintroduced into the bell jar?

A

Sound is again heard.

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23
Q

Why do astronauts on the moon talk to themselves by radio even when they are close together?

A

Because there is little atmosphere to transmit sound on the moon.

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24
Q

How are sound waves propagated through air?

A

By the displacement of air molecules.

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25
How do the molecules vibrate?
In a direction parallel to the direction of travel of the waves.
26
What are waves of this nature known as?
Longitudinal waves.
27
What happens when the vibrating prong moves to the right (position B)?
It compresses the air molecules nearest to it.
28
What is produced as this disturbance is transmitted from particle to particle through the air?
A pulse of compression (air pressure above normal) moving outwards from the prong.
29
What happens when the prong moves to the left (position A)?
The pressure on the nearest layer of air is reduced and the air layer expands to the left producing a rarefaction (air pressure below normal).
30
What travels outwards and propagates through the air as a result of these movements?
A series of alternate compressions and rarefactions.
31
What is important to emphasize about the air particles?
That they do not move along with the disturbance.
32
What happens while the air particles vibrate about their mean position?
Their kinetic energy is transferred from one air layer to the next.
33
What is the region of maximum compression called?
A compression or crest.
34
What is the region of minimum compression called?
A rarefaction or trough.
35
What are the crests and troughs separated by?
Half a wavelength.
36
What is wavelength?
The distance between two successive crests or troughs.
37
What is the speed of sound?
The rate at which the compressions and rarefactions move outwards from the source.
38
What is the speed of sound in air at room temperature?
About 340 msโปยน.
39
What does the speed of sound depend on?
The medium through which it travels.
40
In what are the molecules much closer together?
In liquids and solids.
41
In which does sound travel faster
solids
42
What is noise?
Irregular and non-periodic vibrations which are unpleasant to the ear.
43
What is music?
Regular and periodic vibrations which are pleasant to the ear.
44
What is pitch?
The degree of highness or lowness of a tone.
45
What does the pitch of a sound depend on?
The frequency of the source.
46
What is frequency?
The number of complete vibrations per second.
47
What is the unit of frequency?
Hertz (Hz).
48
What is intensity?
The rate at which energy is being transferred per unit area in a sound wave.
49
What is intensity proportional to?
The square of the amplitude of the wave.
50
What is loudness?
The sensation of sound received by the ear.
51
What does loudness depend on?
The intensity of the sound and the sensitivity of the ear.
52
What is the unit of loudness?
Decibel (dB).
53
What is forced vibration?
When a body is set into vibration by the vibrations of another body.
54
What is an example of forced vibration?
If the stem of a vibrating tuning fork is pressed against a table top
55
What is resonance?
A special case of forced vibrations in which a body is set into vibration by another vibrating body of the same frequency.
56
What is an example of resonance?
If two tuning forks of the same frequency are placed side by side and one is set into vibration
57
What are the conditions for resonance to occur?
The two bodies must have the same natural frequency.
58
What is the formula relating velocity
frequency
59
What is the velocity of sound in air?
Approximately 340 m/s.
60
What is an echo?
A sound heard after the reflection from a distant object.
61
What is reverberation?
The persistence of sound in an enclosed space due to multiple reflections.
62
What is an application of echoes?
Echolocation used by bats and sonar used in ships.
63
What is the audible range of frequencies for humans?
Approximately 20 Hz to 20
64
What are infrasonic waves?
Sound waves with frequencies below 20 Hz.
65
What are ultrasonic waves?
Sound waves with frequencies above 20
66
What are some applications of ultrasonic waves?
Cleaning
67
What are standing waves?
Waves that appear to be stationary
68
What are nodes?
Points of zero displacement in a standing wave.
69
What are antinodes?
Points of maximum displacement in a standing wave.
70
What is the fundamental frequency?
The lowest frequency at which a standing wave can occur.
71
What are overtones?
Frequencies higher than the fundamental frequency at which standing waves can occur.
72
What are harmonics?
Overtones that are integer multiples of the fundamental frequency.
73
What is a sonometer?
A device used to study the relationship between the frequency of a vibrating string and its length
74
What is the purpose of the sonometer?
The frequency of the note produced by a plucked string can be studied with a sonometer.
75
What are the main parts of a sonometer?
A hollow sounding-box with a wire stretched along its length. The wire is attached to a peg at G. The other end is passed over a grooved wheel P and kept taut by attaching weights W at its free end. A movable bridge B is used to vary the length of the vibrating part of the wire.
76
What factors affect the frequency of a vibrating string?
The length of the string
77
What is the relationship between frequency and length of a vibrating string?
The frequency is inversely proportional to the length of the vibrating string.
78
What is the relationship between frequency and tension in a vibrating string?
The frequency is directly proportional to the square root of the tension in the string.
79
What is the relationship between frequency and mass per unit length of a vibrating string?
The frequency is inversely proportional to the square root of the mass per unit length of the string.
80
What is the formula for the frequency of a vibrating string?
f = (1/2L) * โˆš(T/m) where f is the frequency
81
What are standing waves?
Waves that appear to be stationary
82
Where are the nodes in a standing wave on a string fixed at both ends?
At the fixed ends.
83
Where are the antinodes in a standing wave?
Points of maximum displacement.
84
What is the fundamental frequency of a vibrating string?
The lowest frequency at which the string can vibrate
85
What are harmonics and overtones?
Harmonics are frequencies that are integer multiples of the fundamental frequency. Overtones are higher frequencies than the fundamental frequency.
86
Describe the first
second
87
What happens to the frequency of a vibrating string as the number of loops increases?
The frequency increases.
88
What is the formula for the frequency of the fundamental note produced by a vibrating string?
f = v / 2L where f is the frequency
89
How are harmonics produced in a stretched string?
By touching the wire lightly at the center or other points to create nodes and antinodes
90
What are overtones?
Frequencies higher than the fundamental frequency.
91
What are harmonics?
Overtones that are integer multiples of the fundamental frequency.
92
How do you distinguish between overtones and harmonics?
Harmonics are always integer multiples of the fundamental frequency
93
What is a resonance tube?
A tube that can be used to determine the velocity of sound in air using the phenomenon of resonance.
94
How is a resonance tube used to determine the velocity of sound in air?
By finding the length of the air column at which resonance occurs with a tuning fork of known frequency
95
What is the end correction in a resonance tube experiment?
A small correction added to the measured length of the air column to account for the fact that the antinode is not exactly at the open end of the tube.
96
What are musical instruments classified into?
Wind instruments
97
Give examples of wind instruments.
Flutes
98
Give examples of percussion instruments.
Drums
99
Give examples of string instruments.
Guitars
100
How is sound produced in wind instruments?
By setting a column of air into vibration.
101
How is the pitch of the sound changed in wind instruments?
By changing the length of the vibrating air column.
102
How is sound produced in percussion instruments?
By striking a surface to cause it to vibrate.
103
How is the pitch of the sound changed in percussion instruments?
By changing the size
104
How is sound produced in string instruments?
By plucking
105
How is the pitch of the sound changed in string instruments?
By changing the length
106
What is the formula for the velocity of a wave?
V = fฮป where V is the velocity
107
What is the relationship between the frequency of a vibrating string and its length?
The frequency is inversely proportional to the length.
108
What is the relationship between the frequency of a vibrating string and the tension in it?
The frequency is directly proportional to the square root of the tension.
109
What is the relationship between the frequency of a vibrating string and its mass per unit length?
The frequency is inversely proportional to the square root of the mass per unit length.
110
What is the formula for the frequency of a vibrating string?
f = (1/2L) * โˆš(T/m) where f is the frequency
111
What are harmonics?
Frequencies that are integer multiples of the fundamental frequency.
112
What are overtones?
Frequencies higher than the fundamental frequency.
113
How do you calculate beat frequency?
The beat frequency is the difference between the frequencies of the two waves: f = fโ‚ - fโ‚‚.
114
What is resonance?
A phenomenon where a body is set into vibration at its natural frequency by another vibrating body of the same frequency.
115
What is the inverse square law in relation to sound intensity?
The intensity of sound is inversely proportional to the square of the distance from the source: E = Eโ‚€ / dยฒ.
116
What is the Doppler effect?
The apparent change in frequency of a sound wave due to the relative motion between the source and the observer.
117
When does the apparent frequency increase in the Doppler effect?
When the source and the observer are moving towards each other.
118
When does the apparent frequency decrease in the Doppler effect?
When the source and the observer are moving away from each other.
119
Give examples of the Doppler effect.
The change in pitch of a siren as it approaches and then moves away from an observer.

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