1) yes 2) no 3) it depends on the medium the wave is in Does a longitudinal wave, such as a sound wave, have an amplitude ? low high normalairpressurex

1) yes

2) no

3) it depends on the

medium the wave is in

Does a longitudinal wave,

such as a sound wave,

have an amplitude ?

lowlow

highhigh

normalnormal

airairpressurepressure

xx

AA

1) yes

2) no

3) it depends on the

medium the wave is in

All wave types — transverse,

longitudinal, surface — have

all of these properties:

wavelength, frequency,wavelength, frequency,

amplitude, velocity, periodamplitude, velocity, period

ConcepTest 14.1ConcepTest 14.1 Sound It OutSound It Out

Does a longitudinal wave,

such as a sound wave,

have an amplitude ?

lowlow

highhigh

normalnormal

airairpressurepressure

xx

AA

At a football game, the “wave”

might circulate through the stands

and move around the stadium. In

this wave motion, people stand up

and sit down as the wave passes.

What type of wave would this be

characterized as?

1) polarized wave

2) longitudinal wave

3) lateral wave

4) transverse wave

5) soliton wave

At a football game, the “wave”

might circulate through the stands

and move around the stadium. In

this wave motion, people stand up

and sit down as the wave passes.

What type of wave would this be

characterized as?

1) polarized wave

2) longitudinal wave

3) lateral wave

4) transverse wave

5) soliton wave

The people are moving up and down, and the wave is traveling around the stadium. Thus, the motion of the wave is perpendicular to the oscillation direction of the people, and so this is a transverse wave.

ConcepTest 14.2ConcepTest 14.2 The WaveThe Wave

Follow-up:Follow-up: What type of wave occurs when you toss a pebble in a pond? What type of wave occurs when you toss a pebble in a pond?

Consider a wave on a string moving to the right, as shown below.

What is the direction of the velocity of a particle at the point labeled A ?

1)

2)

3)

4)

5) zero

A

ConcepTest 14.3aConcepTest 14.3a Wave Motion IWave Motion I


What is the direction of the velocity of a particle at the point labeled A ?

1)

2)

3)

4)

5) zero

The velocity of an

oscillating particle

is (momentarilymomentarily) zerozero

at its maximum

displacement.

A

Follow-up:Follow-up: What is the acceleration of the particle at point A? What is the acceleration of the particle at point A?


What is the direction of the velocity of a particle at the point labeled B ?

1)

2)

3)

4)

5) zero

B

ConcepTest 14.3bConcepTest 14.3b Wave Motion IIWave Motion II


What is the direction of the velocity of a particle at the point labeled B ?

1)

2)

3)

4)

5) zero

The wave is moving

to the rightright, so the

particle at B has to

start moving upwardmoving upward

in the next instant of

time.

B

ConcepTest 14.3bConcepTest 14.3b Wave Motion IIWave Motion II

Follow-up:Follow-up: What is the acceleration of the particle at point B? What is the acceleration of the particle at point B?

t

t + t

1) 1 second

2) 2 seconds

3) 4 seconds

4) 8 seconds

5) 16 seconds

A boat is moored in a fixed location, and

waves make it move up and down. If the

spacing between wave crests is 20 m

and the speed of the waves is 5 m/s, how

long does it take the boat to go from the

top of a crest to the bottom of a trough ?

ConcepTest 14.4ConcepTest 14.4 Out to SeaOut to Sea

t

t + t

1) 1 second

2) 2 seconds

3) 4 seconds

4) 8 seconds

5) 16 seconds

A boat is moored in a fixed location, and

waves make it move up and down. If the

spacing between wave crests is 20 m

and the speed of the waves is 5 m/s, how

long does it take the boat to go from the

top of a crest to the bottom of a trough ?

We know that: v = f v = f = = / T, / T, hence T = T = / v / v. If = 20 m = 20 m and v = 5 m/sv = 5 m/s, so T = 4 secsT = 4 secs.

The time to go from a crest to a trough is only T/2T/2 (half ahalf a periodperiod),

so it takes 2 secs2 secs !!

1) 0.3 mm

2) 3 cm

3) 30 cm

4) 300 m

5) 3 km

Microwaves travel with the speed of light,

c = 3 108 m/s. At a frequency of 10

GHz these waves cause the water

molecules in your burrito to vibrate. What

is their wavelength?

1 GHz = 1 Gigahertz = 109 cycles/sec

H

H

O

ConcepTest 14.5ConcepTest 14.5 Lunch TimeLunch Time

We know vwave = /T = f

so = v/f =

= 3= 31010-2-2 mm = 3 = 3 cmcm

3108 m/s

10109 Hz

1) 0.3 mm

2) 3 cm

3) 30 cm

4) 300 m

5) 3 km

Microwaves travel with the speed of light,

c = 3 108 m/s. At a frequency of 10

GHz these waves cause the water

molecules in your burrito to vibrate. What

is their wavelength?

1 GHz = 1 Gigahertz = 109 cycles/sec

H

H

O

A wave pulse can be sent down a

rope by jerking sharply on the free

end. If the tension of the rope is

increased, how will that affect the

speed of the wave?

1) speed increases

2) speed does not change

3) speed decreases

A wave pulse can be sent down a

rope by jerking sharply on the free

end. If the tension of the rope is

increased, how will that affect the

speed of the wave?

1) speed increases


3) speed decreases

The wave speed depends on the square root of the tension, so if the tension increases, then the wave speed will also increase.

ConcepTest 14.6aConcepTest 14.6a Wave Speed IWave Speed I

A wave pulse is sent down a rope of

a certain thickness and a certain

tension. A second rope made of the

same material is twice as thick, but

is held at the same tension. How will

the wave speed in the second rope

compare to that of the first?

1) speed increases


3) speed decreases

A wave pulse is sent down a rope of

a certain thickness and a certain

tension. A second rope made of the

same material is twice as thick, but

is held at the same tension. How will

the wave speed in the second rope

compare to that of the first?

1) speed increases


3) speed decreases

The wave speed goes inversely as the square root of the mass per unit length, which is a measure of the inertia of the rope. So in a thicker (more massive) rope at the same tension, the wave speed will decrease.

ConcepTest 14.6bConcepTest 14.6b Wave Speed IIWave Speed II

A length of rope L and mass M hangs

from a ceiling. If the bottom of the

rope is jerked sharply, a wave pulse

will travel up the rope. As the wave

travels upward, what happens to its

speed? Keep in mind that the rope is

not massless.

1) speed increases


3) speed decreases

A length of rope L and mass M hangs

from a ceiling. If the bottom of the

rope is jerked sharply, a wave pulse

will travel up the rope. As the wave

travels upward, what happens to its

speed? Keep in mind that the rope is

not massless.

1) speed increases


3) speed decreases

The tension in the rope is not constant in the case of a massive rope! The tension increases as you move up higher along the rope, because that part of the rope has to support all of the mass below it! Since the tension increases as you go up, so does the wave speed.

ConcepTest 14.6cConcepTest 14.6c Wave Speed IIIWave Speed III

1) the frequency f

2) the wavelength

3) the speed of the wave

4) both f and

5) both vwave and

When a sound wave passes

from air into water, what

properties of the wave will

change?

ConcepTest 14.7aConcepTest 14.7a Sound Bite I

1) the frequency f

2) the wavelength

3) the speed of the wave

4) both f and

5) both vwave and

When a sound wave passes

from air into water, what

properties of the wave will

change?

Wave speed must change (different medium).Wave speed must change (different medium).

Frequency does not change (determined by the source).

Now, vv = f = f and since vv has changed and ff is constant

then must also changemust also change.

Follow-up:Follow-up: Does the wave speed increase or decrease in water? Does the wave speed increase or decrease in water?

If you fill your lungs with

helium and then try

talking, you sound like

Donald Duck. What

conclusion can you

reach about the speed

of sound in helium?

1) speed of sound is less in helium

2) speed of sound is the same in helium

3) speed of sound is greater in helium

4) this effect has nothing to do with the speed in helium

If you fill your lungs with

helium and then try

talking, you sound like

Donald Duck. What

conclusion can you

reach about the speed

of sound in helium?

1) speed of sound is less in helium

2) speed of sound is the same in helium

3) speed of sound is greater in helium

4) this effect has nothing to do with the speed in helium

The higher pitch implies a higher frequency. In turn, since v = f, this means that the speed of the wave has increased (as long as the wavelength, determined by the length of the vocal chords, remains constant).

ConcepTest 14.8cConcepTest 14.8c Speed of Sound III

Follow-up:Follow-up: Why is the speed of sound greater in helium than in air? Why is the speed of sound greater in helium than in air?

You stand a certain distance away from a speaker and you hear a certain intensity of sound. If you double your distance from the speaker, what happens to the sound intensity at your new position?

1) drops to 1/2 its original value




5) does not change at all

ConcepTest 14.10aConcepTest 14.10a Sound Intensity I

You stand a certain distance away from a speaker and you hear a certain intensity of sound. If you double your distance from the speaker, what happens to the sound intensity at your new position?





5) does not change at all

For a source of a given power P, the intensity is given

by I = P/4r2. So if the distance doublesdistance doubles, the intensity

must decrease to one-quarterdecrease to one-quarter its original value.

ConcepTest 14.10aConcepTest 14.10a Sound Intensity I

Follow-up:Follow-up: What distance would reduce the intensity by a factor of 100? What distance would reduce the intensity by a factor of 100?

(1) the long pipe

(2) the short pipe

(3) both have the same frequency

(4) depends on the speed of sound in the pipe

You have a long pipe

and a short pipe.

Which one has the

higher frequency?

A shorter pipeshorter pipe means that the standing wave in

the pipe would have a shorter wavelengthshorter wavelength. Since

the wave speed remains the same, the frequency frequency

has to be higherhas to be higher in the short pipe.

(1) the long pipe

(2) the short pipe

(3) both have the same frequency

(4) depends on the speed of sound in the pipe

You have a long pipe

and a short pipe.

Which one has the

higher frequency?

ConcepTest 14.12aConcepTest 14.12a Pied Piper I

A wood whistle has a variable length. You just heard the tone from the whistle at maximum length. If the air column is made shorter by moving the end stop, what happens to the frequency?

1) frequency will increase

2) frequency will not change

3) frequency will decrease

A wood whistle has a variable length. You just heard the tone from the whistle at maximum length. If the air column is made shorter by moving the end stop, what happens to the frequency?




A shorter pipeshorter pipe means that the standing wave in the pipe would have a shorter wavelengthshorter wavelength. Since the wave speed remains the same, and since we know that vv = = ff , then we see that the frequency has to increase frequency has to increase when the pipe is made shorter.

ConcepTest 14.12bConcepTest 14.12b Pied Piper II

If you blow across the opening of a partially filled soda bottle, you hear a tone. If you take a big sip of soda and then blow across the opening again, how will the frequency of the tone change?




If you blow across the opening of a partially filled soda bottle, you hear a tone. If you take a big sip of soda and then blow across the opening again, how will the frequency of the tone change?




By drinking some of the soda, you have effectively increased the length of the air column in the bottle. A longer pipelonger pipe means that the standing wave in the bottle would have a longer wavelengthlonger wavelength. Since the wave speed remains the same, and since we know that vv = = ff , then we see that the frequency has to be lowerfrequency has to be lower.

ConcepTest 14.12cConcepTest 14.12c Pied Piper III

Follow-up:Follow-up: Why doesn’t the wave speed change? Why doesn’t the wave speed change?

1) depends on the speed of sound in the pipe

2) you hear the same frequency

3) you hear a higher frequency

4) you hear a lower frequency

You blow into an open pipe

and produce a tone. What

happens to the frequency

of the tone if you close the

end of the pipe and blow

into it again?

In the open pipeopen pipe, 1/2 of a wave1/2 of a wave “fits”

into the pipe, while in the closed pipeclosed pipe,

only 1/4 of a wave1/4 of a wave fits. Because the

wavelength is larger in the closed wavelength is larger in the closed

pipepipe, the frequency will be lowerfrequency will be lower.

1) depends on the speed of sound in the pipe

2) you hear the same frequency

3) you hear a higher frequency

4) you hear a lower frequency

You blow into an open pipe

and produce a tone. What

happens to the frequency

of the tone if you close the

end of the pipe and blow

into it again?

ConcepTest 14.13ConcepTest 14.13 Open and Closed Pipes

Follow-up:Follow-up: What would you have to do What would you have to do to the pipe to increase the frequency?to the pipe to increase the frequency?

When you tune a guitar string, what physical characteristic of the string are you actually changing?

1) the tension in the string

2) the mass per unit length of the string

3) the composition of the string

4) the overall length of the string

5) the inertia of the string

When you tune a guitar string, what physical characteristic of the string are you actually changing?

1) the tension in the string

2) the mass per unit length of the string

3) the composition of the string

4) the overall length of the string

5) the inertia of the string

By tightening (or loosening) the knobs on the neck of the guitar, you are changing the tensionchanging the tension in the string. This alters the wave speed and therefore alters the frequency of the fundamental standing wave because f = v/2L .

Follow-up:Follow-up: To increase frequency, do you tighten or loosen the strings? To increase frequency, do you tighten or loosen the strings?

Observers A, B and C listen to a

moving source of sound. The

location of the wave fronts of the

moving source with respect to

the observers is shown below.

Which of the following is true?

1) frequency is highest at A

2) frequency is highest at B

3) frequency is highest at C

4) frequency is the same at all

three points

ConcepTest 14.15aConcepTest 14.15a Doppler Effect I

Observers A, B and C listen to a

moving source of sound. The

location of the wave fronts of the

moving source with respect to

the observers is shown below.

Which of the following is true?

1) frequency is highest at A

2) frequency is highest at B

3) frequency is highest at C

4) frequency is the same at all

three points

The number of wave fronts

hitting observer Cobserver C per unit time

is greatest – thus the observed

frequency is highest there.

ConcepTest 14.15aConcepTest 14.15a Doppler Effect I

Follow-up:Follow-up: Where is the frequency lowest? Where is the frequency lowest?

You are heading toward an island in a

speedboat and you see your friend

standing on the shore, at the base of

a cliff. You sound the boat’s horn to

alert your friend of your arrival. If the

horn has a rest frequency of f0, what

frequency does your friend hear ?

1) lower than f0

2) equal to f0

3) higher than f0

You are heading toward an island in a

speedboat and you see your friend

standing on the shore, at the base of

a cliff. You sound the boat’s horn to

alert your friend of your arrival. If the

horn has a rest frequency of f0, what

frequency does your friend hear ?

1) lower than f0

2) equal to f0

3) higher than f0

Due to the approach of the sourceapproach of the source toward the stationary observer, the frequency is shifted higherfrequency is shifted higher. This is the same situation as depicted in the previous question.

ConcepTest 14.15bConcepTest 14.15b Doppler Effect II

A string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities. When the string is in position b, the instantaneous velocity of points on the string:

a

b

1) is zero everywhere

2) is positive everywhere

3) is negative everywhere

4) depends on the position

along the string

Observe two points:

Just before b

Just after b

Both points change direction before and after b, so at b all points must have zero velocity.

ConcepTest 14.17aConcepTest 14.17a Standing Waves IStanding Waves IA string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities. When the string is in position b, the instantaneous velocity of points on the string:





along the string

a

b

c

A string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities. When the string is in position c, the instantaneous velocity of points on the string:





along the string

When the string is flat, all points are moving through the equilibrium position and are therefore at their maximum velocity. However, the

direction depends on the locationdirection depends on the location of the point. Some points are moving upward rapidly, and some points are moving downward rapidly.

a

b

c

ConcepTest 14.17bConcepTest 14.17b Standing Waves IIStanding Waves IIA string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities. When the string is in position c, the instantaneous velocity of points on the string:





along the string

Pair 1 Pair 2

1) pair 1

2) pair 2

3) same for both pairs

4) impossible to tell by just

looking

The traces below show beats that

occur when two different pairs of

waves interfere. For which case is

the difference in frequency of the

original waves greater?

Pair 1 Pair 2

Recall that the beat frequency is the difference in frequencydifference in frequency

between the two waves: ffbeatbeat = = ff22 – – ff11

Pair 1 has the greater beat frequencygreater beat frequency (more oscillations in same time period), so Pair 1 has the greater frequency differencegreater frequency difference.

1) pair 1

2) pair 2

3) same for both pairs

4) impossible to tell by just

looking

The traces below show beats that

occur when two different pairs of

waves interfere. For which case is

the difference in frequency of the

original waves greater?

ConcepTest 14.18ConcepTest 14.18 Beats

Documents

1) yes 2) no 3) it depends on the medium the wave is in Does a longitudinal wave, such as a sound wave, have an amplitude ? low high normalairpressurex