Ch 15: Traveling Waves and Sound

Question 1

What is a wave?

Answer 1

It is simply energy propagated through or along a medium.

Question 2

The wave speed is determined by the properties of the medium, not by the ________ or ________ of the wave.

Answer 2

amplitude
frequency

Question 3

Is the speed of light always 3 x 10⁸ m/s?

Answer 3

No, this pertains only to a vacuum. In reality it is slower than this, just never faster than that.

Question 4

Does light exist as a transverse or longitudinal wave?

Answer 4

transverse

Question 5

Do sound waves exist as transverse waves or longitudinal waves?

Answer 5

longitudinal

Question 6

Radio waves are a kind of electromagnetic radiation, and thus they move at the speed of _____.

Answer 6

light
In fact, all electromagnetic radiation travels at the speed of light!

Question 7

Which does sound travel faster through? Air or metal?

Answer 7

Metal!
The speed of sound through air is approximately 343 m/s.

Question 8

The velocity of a wave is equal to the _________ divided by the ___.

Answer 8

wavelength (λ)
period (T)

Question 9

When the particles of a medium move with simple harmonic motion, this means that the wave is a…

a. sound wave
b. sinusoidal wave
c. standing wave
d. harmonic wave
e. transverse wave

Answer 9

b. sinusoidal wave

Question 10

The two most important types of earthquake waves are _ waves (transverse) and _ waves (longitudinal).
The P waves are ______, but the S waves are more _________.

Answer 10

S (remember, there are 2 waves in the word ‘transverse’, but no s’s in the word ‘longitudinal’)

P

faster, destructive

Question 11

A wave is not a ________, so we cannot use Newton’s laws on the wave itself, but the medium is made of particles, so we CAN use Newton’s laws to examine how the medium responds to a disturbance.

Answer 11

particle

Question 12

Waves and strings:

Properties that determine speed are string’s ____, length, and _______. The speed depends on the mass-to-length ratio, the linear density of the string:

μ = m/L

Answer 12

mass

tension

Question 13

A string with a greater tension responds more rapidly, so the wave will move at a higher speed. Wave speed ________ with increasing tension. A string with a greater linear density has more _______. It will respond less rapidly, so the wave will move at a lower speed. Wave speed decreases with increasing linear density.

Answer 13

increases

inertia

Question 14

For a wave pulse on a string to travel twice as fast, the string tension must be

A. Increased by a factor of 4.

B. Increased by a factor of 2.

C. Decreased to one half its initial value.

D. Decreased to one fourth its initial value.

E. Not possible. The pulse speed is always the same.

Answer 14

A. Increased by a factor of 4.

This is true because of this equation:

v_string = √(T_string/μ)

Question 15

The speed of sound in air (and other gases) _________ with temperature.

Answer 15

increases

Question 16

At a given temperature, the speed of sound increases as the molecular mass of the gas _______. Thus the speed of sound in room-temperature helium is faster than that in room-temperature air.

Answer 16

decreases

Question 17

True or False??

The speed of sound doesn’t depend on the pressure or the density of the gas.

Answer 17

True

Question 18

The speed of sound in liquids is _______ than in gases, and ______ in solids than in liquids.

Answer 18

faster; faster

Question 19

What is the speed of sound (think ultrasound!) in human tissue?

Answer 19

1540 m/s

Question 20

The speed of sound is lower for _______ molecules and ______ temperatures, so we expect that the speed of sound on Mars, with its cold, carbon-dioxide atmosphere will be lower than on earth.

Answer 20

heavier

colder

Question 21

What is the formula for the displacement of a traveling wave moving to the right with amplitude A, wavelength λ, and period T?

Answer 21

Question 22

What is the range of hearing (in Hz) for humans?

Answer 22

20-20,000 Hz

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Question 23

As the cone of a loudspeaker moves forward, it moves air molecules closer together, creating a region of higher pressure. A half cycle later, the cone moves backward, and pressure decreases. The regions of higher and lower pressures are called __________ and __________, respectively. The former is the crest of the pressure of wave, while the latter is the trough.

Answer 23

compressions

rarefactions

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Question 24

What are ultrasound waves?

Answer 24

High frequency sounds above our range of hearing, used by some animals for echolocation.

Question 25

Increasing the sound intensity by a factor of 10 results in an increase in perceived loudness by a factor of approximately _. Because of this discrepancy, sound intensity level is measured on a logarithmic scale, since the perceived loudness is much less than the actual increase in intensity.

Answer 25

2

Question 26

Sound is a longitudinal pressure wave. Diagrams depicting sound waves show circles emanating from a source; those circles represent ______ or wave fronts. Sound is simply periodic changes in pressure. Each crest is a location of ____ ________.

Answer 26

crests

high pressure

Youtube video:

Question 27

Sound is energy, and a constant frequency means that this sound moves in _____ ______ ______. Each circle (in a diagram of sound being emitted), actually represents a _______ pressure wave or wave front going out in all directions from the sound source.

Answer 27

simple harmonic motion

spherical

Question 28

The doppler effect –

The wavelength of the sound wave which someone hears when a sound source is approaching is (more/less) that the wavelength of the original sound.

Conversely, the frequency is higher when the source is _________ and lower as the source recedes.

Answer 28

less

approaching

(YouTube video, Flipping Physics, “Doppler Effect Demonstrations and Animations”)

Question 29

What is the Doppler effect?

Answer 29

the perceived change in frequency of a sound due to the motion of the sound source or the observer

Question 30

Equations needed to do calculations involving the Doppler effect, and an approaching or receding observer:

Answer 30

Question 31

Equations needed to do calculations involving the Doppler effect, and an approaching or receding source:

Answer 31

Question 32

The Doppler effect also applies to light waves. If a source of light waves is receding from you (as applies to distant galaxies), the wavelength that you detect is ______ than the wavelength emitted by the source. Because the wave length is shifted toward the red end of the visible spectrum, the longer wavelengths of light, this effect is called the ___ _____. Similarly, the light you detect from the source moving toward you is blue shifted to a shorter wavelengths.

Answer 32

longer

red shift

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Question 33

Frequency shift on reflection is observed for all types of waves. Radar units emit pulses of radio waves and observe the reflected waves. The time between the emission of a pulse and its return gives an object’s ________. The change in frequency of the returned pulse gives the object’s _____. This is the principle behind the radar guns used by traffic police, as well as the Doppler radar images you have seen in weather reports.

Answer 33

position

speed

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Question 34

The frequency shift of reflected waves is shown by the equation:

Answer 34

Question 35

What is produced when a sound source moves faster than the waves, which causes waves to overlap?

Answer 35

a shock wave, aka large amplitude wave

Question 36

A source is supersonic if it travels faster than the _____ of _____. A shock wave travels with the source. If a supersonic source passes an observer, the shock wave produces a _____ ____.

Answer 36

speed of sound

sonic boom

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