Review Today – Waves and Sound 50 Point Quiz Tomorrow (Last assignment of term)

Review Today – Waves and SoundReview Today – Waves and Sound

50 Point Quiz Tomorrow 50 Point Quiz Tomorrow

(Last assignment of term)(Last assignment of term)

1) yes

2) no

3) it depends on the

medium the wave is in

1. Sound It Out1. Sound It Out

Does a longitudinal wave,

such as a sound wave,

have an amplitude ?

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

1. Sound It Out1. Sound It Out

Does a longitudinal wave,

such as a sound wave,

have an amplitude ?

lowlow

highhigh

normalnormal

airairpressurepressure

xx

AA

At a baseball 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

2. The Wave2. The Wave

At a baseball 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.

2. The Wave2. The Wave

3. Lunch Time3. Lunch Time1) 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 (approximately)?

1 GHz = 1 Gigahertz = 109 cycles/sec

H

H

O

3. Lunch Time3. Lunch 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

4. Wave Speed I4. Wave Speed I

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.

4. Wave Speed I4. Wave 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

5. Wave Speed II5. Wave Speed II

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.

5. Wave Speed II5. Wave Speed II

6. Sound Bite

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?

6. Sound Bite

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.

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

7. Speed of Sound

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).

7. Speed of Sound

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

8. 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

The intensity or energy of a sound is proportional to

1/d2. So if the distance doublesdistance doubles, the intensity must

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

8. Sound Intensity I

1) about the same distance

2) about 3 miles

3) about 10 miles

4) about 30 miles

5) about 100 miles

You hear a fire truck with a certain intensity, and you are about 1 mile away. Another person hears the same fire truck with an intensity that is about 10 times less. Roughly how far is the other person from the fire truck?

9. Sound Intensity II

1) about the same distance

2) about 3 miles

3) about 10 miles

4) about 30 miles

5) about 100 miles

You hear a fire truck with a certain intensity, and you are about 1 mile away. Another person hears the same fire truck with an intensity that is about 10 times less. Roughly how far is the other person from the fire truck?

9. Sound Intensity II

Remember that intensity

drops with the inverse inverse

square of the distancesquare of the distance,

so if intensity drops by

a factor of 10, the other

person must be 10

farther away, which is

about a factor of 3.

1) the longer guitar

2) the shorter guitar

3) both have the same frequency

You have a regular size

guitar and a shorter child-

size guitar. Which one has

the higher frequency?

10. Pied Piper I

A shorter guitarshorter guitar means that the standing wave in

the strings would have a shorter wavelengthshorter wavelength.

Since the wave speed remains the same, the

frequency has to be higherfrequency has to be higher in the shorter guitar.

1) the longer guitar

2) the shorter guitar

3) both have the same frequency

You have a regular size

guitar and a shorter child-

size guitar. Which one

has the higher frequency?

10. 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

11. Pied Piper II

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 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.

11. Pied Piper II

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

12. Out of Tune

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.

12. Out of Tune

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

13. 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.

13. Doppler Effect I

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 normal frequency of f, what

frequency does your friend hear?

1) lower than f

2) equal to f

3) higher than f

14. Doppler Effect II

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 normal frequency of f, what

frequency does your friend hear?

1) lower than f

2) equal to f

3) higher than f

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.

14. Doppler Effect II

15. Out to Sea15. Out 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?

15. Out to Sea15. Out 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 !!

Review Today – Waves and Sound 50 Point Quiz Tomorrow (Last assignment of term)

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