Chapter 5

Question 1

Sound is

Answer 1

a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid.

Question 2

Acoustics

Answer 2

the study of mechanical waves in gases, liquids and solids including vibration, sound, ultrasound, and infrasound

Question 3

the sound waves are generates by

Answer 3

a sound source, such as the vibrating diaphram of a stereo-speaker.

Question 4

The sound source creates

Answer 4

vibrations in the surrounding medium

Question 5

as the source continues to vibrate the medium the vibrations

Answer 5

propagate away from the source at the speed of sound, thus forming the sound wave

Question 6

at a fixed distance from the source ……………. vary in time

Answer 6

the pressure, velocity and displacement of the medium

Question 7

at an instant in time the

Answer 7

pressure, velocity and displacement vary in space

Question 8

note that the particles of the medium ……………. with the sound wave

Answer 8

do not travel

Question 9

the …………….. of the particles over time does not change

Answer 9

average

Question 10

during propagation waves can be ……………………. by the medium

Answer 10

reflected

refracted

attenuated

Question 11

A relationship between the density and pressure of the medium. This relationship, affected by

Answer 11

temperature, determines the speed of sound within the medium

Question 12

Sound travels most slowly in

Answer 12

gases; it travels faster in liquids; and faster still in solids.

Question 13

Motion of the medium itself. If the medium is moving, this movement may

Answer 13

increase or decrease the absolute speed of the sound wave depending on the direction of the movement.

Question 14

Motion of the medium itself. If the medium is moving, this movement may increase or decrease the absolute speed of the sound wave depending on the direction of the movement. For example, sound moving through wind will have

Answer 14

its speed of propagation increased by the speed of the wind if the sound and wind are moving in the same direction.

Question 15

If the sound and wind are moving in opposite directions, the speed of the sound wave

Answer 15

will be decreased by the speed of the wind.

Question 16

The viscosity of the medium. Medium viscosity determines

Answer 16

rate at which sound is attenuated.

Question 17

The viscosity of the medium. Medium viscosity determines the rate at which sound is attenuated. For many media, such as

Answer 17

air or water, attenuation due to viscosity is negligible.

Question 18

refracted

Answer 18

When sound is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).

Question 19

Sound cannot travel through

Answer 19

a vacuum.

Question 20

Sound is transmitted through

Answer 20

gases, plasma, and liquids as longitudinal waves, also called compression waves.

Question 21

Through solids, however, it can be transmitted as both

Answer 21

longitudinal waves and transverse waves.

Question 22

The energy carried by an oscillating sound wave converts

Answer 22

back and forth between the potential energy and the kinetic energy.

Question 23

Although there are many complexities relating to the transmission of sounds, at the point of reception (i.e. the ears), sound is readily dividable into two simple elements:

Answer 23

pressure and time

Question 24

sound is readily dividable into two simple elements: pressure and time. These fundamental elements form the basis of

Answer 24

all sound waves. They can be used to describe every sound we hear.

Question 25

However, in order to understand the sound more fully, a complex wave is usually separated into its component parts

Answer 25

which are a combination of various sound wave frequencies.

Question 26

Sound waves are often simplified to

Answer 26

a description in terms of sinusoidal plane waves.

Question 27

Sound that is perceptible by humans has frequencies from about

Answer 27

20 Hz to 20,000 Hz

Question 28

In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from

Answer 28

17 m to 17 mm

Question 29

Sometimes speed and direction are combined as

Answer 29

a velocity vector; wavenumber and direction are combined as a wave vector.

Question 30

The speed of sound depends on

Answer 30

medium the waves pass through

Question 31

In fresh water, also at 20 °C, the speed of sound is approximately

Answer 31

1,482 m/s

Question 32

In steel, the speed of sound is about

Answer 32

5,960 m/s

Question 33

The speed of sound depends on

Answer 33

ambient conditions

Question 34

For example, the speed of sound in gases depends on

Answer 34

temperature

Question 35

In 20 °C air at sea level, the speed of sound is approximately

Answer 35

343 m/s using the formula “v = (331 + 0.6 T) m/s”.

Question 36

Note that the effect of the mean flow is

Answer 36

additive

Question 37

Note that the effect of the mean flow is additive. This is a property of

Answer 37

linear waves

Question 38

For linear waves, the phase speed with mean flow is just

Answer 38

the phase speed without the mean flow plus the mean flow itself.