College Physics

acoustic impedance:

antinode:

bow wake:

Doppler effect:

Doppler shift:

Doppler-shifted ultrasound:

fundamental:

harmonics:

hearing:

infrasound:

intensity reflection coefficient:

intensity:

loudness:

node:

note:

overtones:

phon:

pitch:

sonic boom:

sound intensity level:

sound pressure level:

sound:

timbre:

tone:

ultrasound:

Ultrasound is used for nondestructive testing in industry and by the military. Because ultrasound reflects well from any large change in density, it

can reveal cracks and voids in solids, such as aircraft wings, that are too small to be seen with x-rays. For similar reasons, ultrasound is also

good for measuring the thickness of coatings, particularly where there are several layers involved.

Basic research in solid state physics employs ultrasound. Its attenuation is related to a number of physical characteristics, making it a useful

probe. Among these characteristics are structural changes such as those found in liquid crystals, the transition of a material to a superconducting

phase, as well as density and other properties.

These examples of the uses of ultrasound are meant to whet the appetites of the curious, as well as to illustrate the underlying physics of

ultrasound. There are many more applications, as you can easily discover for yourself.

Check Your Understanding

Why is it possible to use ultrasound both to observe a fetus in the womb and also to destroy cancerous tumors in the body?

Solution

Ultrasound can be used medically at different intensities. Lower intensities do not cause damage and are used for medical imaging. Higher

intensities can pulverize and destroy targeted substances in the body, such as tumors.

Glossary

property of medium that makes the propagation of sound waves more difficult

point of maximum displacement

V-shaped disturbance created when the wave source moves faster than the wave propagation speed

an alteration in the observed frequency of a sound due to motion of either the source or the observer

the actual change in frequency due to relative motion of source and observer

a medical technique to detect motion and determine velocity through the Doppler shift of an echo

the lowest-frequency resonance

the term used to refer collectively to the fundamental and its overtones

the perception of sound

sounds below 20 Hz

a measure of the ratio of the intensity of the wave reflected off a boundary between two media relative to the

intensity of the incident wave

the power per unit area carried by a wave

the perception of sound intensity

point of zero displacement

basic unit of music with specific names, combined to generate tunes

all resonant frequencies higher than the fundamental

the numerical unit of loudness

the perception of the frequency of a sound

a constructive interference of sound created by an object moving faster than sound

a unitless quantity telling you the level of the sound relative to a fixed standard

the ratio of the pressure amplitude to a reference pressure

a disturbance of matter that is transmitted from its source outward

number and relative intensity of multiple sound frequencies

number and relative intensity of multiple sound frequencies

sounds above 20,000 Hz

Section Summary

17.1 Sound

• Sound is a disturbance of matter that is transmitted from its source outward.

622 CHAPTER 17 | PHYSICS OF HEARING

This content is available for free at http://cnx.org/content/col11406/1.7