Physics Chapter 12: Sound

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Questions and Answers

What does an increase of 3 dB in sound level signify?

A significant change in loudness

A halving of intensity

A doubling of intensity (correct)

No change in sound intensity

Which of the following statements about the sensitivity of the ear is true?

The ear's sensitivity is constant across all frequencies.

The ear is less sensitive to lower frequencies.

The ear's sensitivity varies with frequency. (correct)

The ear cannot detect frequencies above 20 kHz.

How do wind instruments produce sound?

By vibrating membranes

By using mechanical hammers

By vibrating strings

By standing waves in a column of air (correct)

What is the role of the cochlea in the inner ear?

It converts vibrational energy to electrical energy. Signup and view all the answers

What factor does NOT affect the intensity of sound in open areas?

Sound reflection from nearby objects Signup and view all the answers

In musical instruments, how can the pitch of a vibrating string be altered?

By using a string of different density Signup and view all the answers

Which part of the ear is responsible for transmitting vibrations to the inner ear?

Hammer, anvil, and stirrup Signup and view all the answers

How does the intensity of sound change as it travels through air?

It diminishes with distance. Signup and view all the answers

What creates the difference in sound quality between a trumpet and a flute?

The presence and strength of overtones Signup and view all the answers

What phenomenon is created when two sound waves of slightly different frequencies interfere with each other?

Beats Signup and view all the answers

Which of the following describes a tube that is closed at one end, in terms of displacement and pressure nodes?

Displacement node at the closed end, pressure antinode at the open end Signup and view all the answers

What happens to the frequency of sound when the source is moving toward an observer?

It increases Signup and view all the answers

How does the intensity of a sound relate to the decibel level?

Decibel level is a logarithmic measure of intensity Signup and view all the answers

What results from a source moving faster than the speed of sound in a medium?

Shock waves are formed Signup and view all the answers

What is the relationship between wavelength and frequency according to the Doppler effect for a source moving away from the observer?

Wavelength increases while frequency decreases Signup and view all the answers

What is the outcome of sound wave interference in time called?

Beats Signup and view all the answers

What is the result when two sound waves of slightly different frequencies interfere with each other?

They produce beats Signup and view all the answers

How does the pitch of a sound relate to its frequency?

Higher frequency results in higher pitch Signup and view all the answers

What defines the timbre of a sound produced by an instrument?

The fundamental tone and harmonics present Signup and view all the answers

In wind instruments, what determines the fundamental frequency of the note produced?

The length of the vibrating column of air Signup and view all the answers

What causes the Doppler effect in sound?

The motion of the sound source or observer Signup and view all the answers

How is sound intensity measured in relation to its loudness?

Loudness depends on both intensity and ear sensitivity Signup and view all the answers

What is the primary purpose of using sonar technology?

To locate objects underwater Signup and view all the answers

Why are ultrasound waves preferred in sonar applications?

They are less likely to be diffracted by obstacles Signup and view all the answers

Study Notes

Chapter 12: Sound

Sound is a longitudinal wave in a medium.
Sound speed varies in different materials (slowest in gases, fastest in solids).
Speed also depends on temperature, especially in gases.
Loudness is related to the logarithm of intensity (measured in decibels).
The human ear can detect sounds from 10^-12 W/m² to 1 W/m².
Sound level (dB) is calculated using the formula β (dB) = 10 log(I/I₀), where I₀ is the threshold of hearing (1.0 x 10^-12 W/m²).
A 3 dB increase in sound level means a doubling in intensity, but a relatively small increase in perceived loudness.
Intensity decreases with distance (I α 1/r²) in open areas.
Intensity of sound in enclosed areas is complicated by reflections and absorption.

Characteristics of Sound

Loudness is related to the intensity of the sound wave.
Pitch is related to frequency.
Audible range: 20 Hz to 20,000 Hz; decreases with age.
Ultrasound: above 20,000 Hz (used in medical imaging and sonar).
Infrasound: below 20 Hz.

Sources of Sound: Vibrating Strings and Air Columns

Musical instruments produce sounds via vibrating strings, membranes, or air columns.
Vibrations initiated by plucking, striking, bowing, or blowing.
The pitch of a guitar string can be altered by shortening it (finger placement).
Other parameters affecting pitch changes include string density.
A piano uses longer, thicker strings for lower pitches.
Wind instruments produce tones through standing waves in air columns, dependent on tube length and whether open or closed. Open tubes have half-wavelengths, closed tubes have quarter-wavelengths.

Sound Interference and Beats

Sound waves interfere in the same way as other waves; superposition holds.
Beats are the result of interference from sounds with slightly different frequencies.
The beat frequency is the difference in frequencies of the interfering waves.

Doppler Effect

The Doppler effect is the apparent change in frequency of sound due to motion of the source or observer.
A source moving toward the observer has an increased frequency and a decreased wavelength; moving away, the opposite occurs (higher wavelength, lower frequency).
The same is true for an observer moving toward or away from the source (different calculation).

Applications

Sonar uses sound waves to locate objects underwater by measuring reflection time.
Ultrasound waves produce images of internal structures (medical imaging).
Similar techniques are used to study the internal structure of the Earth.
Shorter wavelengths are less likely to be diffracted by obstacles, so ultrasound is often used.
Shock waves are similar to bow waves from a boat moving faster than wave speed and are created when the sound source is moving faster than the speed of sound.
Aircraft exceeding sound speed produce two sonic booms (one from the front and one from the tail).

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Description

Explore the fascinating concepts of sound in this chapter. Learn about sound waves, their behavior in different media, and how loudness and pitch are determined. This quiz covers the fundamentals of sound speed, intensity, and the human ear's auditory range.