Deck 16: Sound

Question 1

What determines the "pitch" of a musical note?

A)amplitude
B)wavelength
C)frequency
D)phase
E)intensity

Answer 1

frequency

Question 2

The loudness of a sound is related to the amplitude squared of the wave.

Answer 2

True

Question 3

The fundamental frequency of a stringed instrument corresponds to a wavelength equal to one-half the length of the string.

Answer 3

False

Question 4

Sound vibrations with frequencies greater than 20,000 Hz are called

A)infrasonics.
B)ultrasonics.
C)supersonics.
D)infrared.
E)megasonics.

Question 5

In a resonating pipe which is open at one end and closed at the other, there

A)are displacement nodes at each end.
B)are displacement antinodes at each end.
C)is a displacement node at the open end and a displacement antinode at the closed end.
D)is a displacement node at the closed end and a displacement antinode at the open end.
E)none of the above

Question 6

Seven seconds after a brilliant flash of lightning, thunder shakes the house. How far was the lightning strike from the house?

A)Much closer than one kilometer
B)About one kilometer away
C)About two kilometers away
D)Much farther away than two kilometers
E)It is impossible to predict.

Question 7

Explain how the pulse-echo technique works for medical imaging.

Question 8

What determines "loudness" of a musical note?

A)frequency
B)wavelength
C)velocity
D)phase
E)amplitude

Question 9

Sound travels as a transverse wave in air and other materials.

Question 10

Explain how sonar is used to locate underwater objects.

Question 11

The wavelengths corresponding to the harmonics of an organ pipe that is open at one end and closed at the other can be found by saying that the length of the pipe must be equal to

A)an odd number of quarter-wavelengths.
B)an odd number of third-wavelengths.
C)an odd number of half-wavelengths.
D)an integer number of half-wavelengths.
E)an integer number of wavelengths.

Question 12

Sound vibrations with frequencies less than 20 Hz are called

A)infrasonics.
B)ultrasonics.
C)supersonics.
D)infrared.
E)megasonics.

Question 13

In western movies you often see a person putting his ear against the rails in the train tracks to find out if a train is approaching. Why would this give him advance knowledge of the approach of a train?

Question 14

Shock waves and a sonic boom occur when an object moves faster than the speed of sound.

Question 15

The fundamental frequency of an open tube corresponds to a wavelength equal to one-half of the length of the tube.

Question 16

Sound intensity is defined as

A)the loudness of a sound.
B)the sound energy passing through a unit of area.
C)the sound power per unit time.
D)the sound power per unit volume.
E)the sound energy passing through a unit of area per unit time.

Question 17

An open pipe of length L is resonating at its fundamental frequency. Which statement is correct?

A)The wavelength is 2L and there is a displacement node at the pipe's midpoint.
B)The wavelength is 2L and there is a displacement antinode at the pipe's midpoint.
C)The wavelength is L and there is a displacement node at the pipe's midpoint.
D)The wavelength is L and there is a displacement antinode at the pipe's midpoint.
E)The wavelength is 3L/2 and there are two displacement antinodes located inside the pipe.

Question 18

The pitch of a sound is determined by the frequency; the higher the frequency, the higher the pitch.

Question 19

If two sounds are at slightly different frequencies, beats can be heard at a frequency equal to the difference in frequency of the two sources.

Question 20

In a resonating pipe which is open at both ends, there

A)are displacement nodes at each end.
B)are displacement antinodes at each end.
C)is a displacement node at one end and a displacement antinode at the other end.
D)all of the above are possible
E)none of the above

Question 21

In order to produce beats, the two sound waves should have

A)the same amplitude.
B)slightly different amplitudes.
C)the same frequency.
D)slightly different frequencies.

Question 22

A factory siren indicating the end of a shift has a frequency of 90.0 Hz.
(a) What frequency is perceived by the occupant of a car traveling towards the factory at 25 m/s?
(b) What frequency is perceived by the occupant of a car traveling away from the factory at 30 m/s?

Question 23

A sound source approaches a stationary observer. The frequency heard by the observer is

A)higher than the source.
B)lower than the source.
C)the same as that of the source.
D)equal to zero.
E)impossible to predict.

Question 24

A sound source departs from a stationary observer. The frequency heard by the observer is

A)higher than the source.
B)lower than the source.
C)the same as that of the source.
D)equal to zero.
E)impossible to predict.

Question 25

A sound source emits 30.0 W of sound power spread equally in all directions. What is the sound intensity level 30.0 m from the source?

A)94.2 dB
B)83.2 dB
C)2.65 × 10^-3 dB
D)2.65 × 10^-3 W
E)-25.8 dB

Question 26

Consider an open pipe of length L. What are the wavelengths of the three lowest tones produced by this pipe?

A)4L, 2L, L
B)2L, L, L/2
C)2L, L, 2L/3
D)3L, L, L/3

Question 27

Consider a closed pipe of length L. What are the wavelengths of the three lowest tones produced by this pipe?

A)4L, 2L, L
B)2L, L, L/2
C)2L, L, 2L/3
D)3L, L, L/3
E)4L, 4L/3, 4L/5

Question 28

A pipe of length L closed at one end is resonating at its fundamental frequency. Which statement is correct?

A)The wavelength is 4L and there is a displacement node at the pipe's open end.
B)The wavelength is 4L and there is a displacement antinode at the pipe's open end.
C)The wavelength is 2L and there is a displacement node at the pipe's open end.
D)The wavelength is 2L and there is a displacement antinode at the pipe's open end.
E)The wavelength is L and there is a displacement antinode at the pipe's open end.

Question 29

Two in-phase loudspeakers are placed along a wall and are separated by a distance of 4.00 m. They emit sound with a frequency of 514 Hz. A person is standing away from the wall, in front of one of the loudspeakers.
(a) What is the closest distance from the wall the person can stand and hear constructive interference?
(b) What is the closest distance from the wall the person can stand and hear destructive interference?

Question 30

The reason that you do not observe a Doppler shift when you listen to the car radio while driving is that

A)the source and observer are moving at the same speed.
B)the air inside the car is moving at the same speed as the car.
C)the speed of the car is too slow compared to the speed of sound.
D)the speed of the car is too fast compared to the speed of sound.
E)there is a Doppler shift but we don't notice it.

Question 31

The speed of sound through the ground is about 6.0 km/s while the speed of sound in air is 343 m/s. A very powerful explosion occurs some distance away and you feel the ground vibrate 60 seconds before you hear the sound of the explosion. How far away is the explosion?

A)20 km
B)22 km
C)25 km
D)27 km
E)30 km

Question 32

If two sources of slightly different frequency and different amplitudes create waves at the same time, the resulting superposition of those waves can be described as

A)a wave with an amplitude that varies from zero to an amplitude equal to the sum of individual amplitudes. This variation would occur at a frequency equal to the difference in source frequencies.
B)a standing wave with an amplitude equal to the average of the amplitudes of the individual waves and a frequency equal to the average of individual frequencies.
C)a wave with an amplitude that varies from an amplitude of the difference in individual amplitudes to an amplitude equal to the sum of individual amplitudes. This variation would occur at a frequency equal to the difference in source frequencies.
D)a standing wave with an amplitude equal to the sum of the amplitudes of the individual waves and a frequency equal to the average of individual frequencies.
E)a standing wave with an amplitude equal to the product of the amplitudes of the individual waves and a frequency equal to the sum of individual frequencies.

Question 33

Under what conditions do shock waves occur?

A)The frequency of the waves is the resonant frequency of the system.
B)The amplitude of waves exceeds the critical shock value.
C)When two waves from different sources collide with each other.
D)The wave source is traveling at a speed greater than the wave speed.
E)The period of the waves matches the lifetime of the waves.

Question 34

The lowest tone to resonate in a closed pipe of length L is 200 Hz. Which of the following frequencies will not resonate in that pipe?

A)400 Hz
B)600 Hz
C)1000 Hz
D)1400 Hz
E)1800 Hz

Question 35

You are standing on a sidewalk. There is a car in the distance. The horn on the car sounds. You hear it at a pitch that corresponds to a sound frequency lower than the frequency emitted by the horn. What can you conclude?

A)The wind has a component of its velocity in a direction toward you.
B)The car is moving on a line directly away from your present location.
C)The wind has a component of its velocity in a direction away from you.
D)The car has a component of its velocity in a direction away from you.
E)Either A or C must be true.

Question 36

Two cars are traveling in the same direction and with the same speed along a straight highway. Does either driver hear a different frequency from the other car's horn than they would if the cars were stationary?

A)They both experience a Doppler shift.
B)Only the driver of the front car experiences a Doppler shift.
C)Only the driver of the rear car experiences a Doppler shift.
D)No, because neither driver experiences a Doppler shift.
E)It is impossible to predict.

Question 37

You drop a stone down a well that is 9.50 m deep. How long is it before you hear the splash? The speed of sound in air is 343 m/s.

A)1.39 s
B)1.40 s
C)1.41 s
D)1.42 s
E)1.43 s

Question 38

Two pure tones are sounded together and a particular beat frequency is heard. What happens to the beat frequency if the frequency of one of the tones is increased?

A)It increases.
B)It decreases.
C)It does not change.
D)It becomes zero.
E)It could either increase or decrease.

Question 39

The lowest tone to resonate in an open pipe of length L is 200 Hz. Which one of the following frequencies will not resonate in the same pipe?

A)400 Hz
B)600 Hz
C)800 Hz
D)900 Hz
E)1000 Hz

Question 40

You drop a stone down a well. You hear the splash 2.23 s later. How deep is the well? The speed of sound in air is 343 m/s.

A)6.96 m
B)20.2 m
C)22.9 m
D)18.8 m
E)20.0 m

Question 41

Two in-phase loudspeakers are some distance apart. They emit sound with a frequency of 1536 Hz. You move between the speakers, along the line joining the them, at a constant speed of 2.8 m/s. What beat frequency do you observe? The speed of sound in the room is 330 m/s.

A)13 Hz
B)431 Hz
C)26 Hz
D)4.7 Hz
E)118 Hz

Question 42

A source emits sound with frequency 1000 Hz. A second source emitting sound simultaneously causes a 4 Hz intensity variation to appear. What are the possible frequencies of the second source?

A)0.004 Hz and 4000 Hz
B)250 Hz and 4000 Hz
C)996 Hz and 4000 Hz
D)0.004 Hz and 250 Hz
E)996 Hz and 1004 Hz

Question 43

A 0.640-m long gas column is open at one end and closed at the other. What is the fundamental resonant frequency of the air column if the speed of sound in the air is 340 m/s?

A)432 Hz
B)198 Hz
C)266 Hz
D)669 Hz
E)133 Hz

Question 44

A 1.50-m long gas column that is open at one end and closed at the other has a fundamental resonant frequency 80.0 Hz. What is the sound speed in this gas?

A)120 m/s
B)53.3 m/s
C)30.0 m/s
D)213 m/s
E)480 m/s

Question 45

If the intensity level of one trombone is 70 dB, what is the intensity level of 76 trombones?

A)146 dB
B)89 dB
C)70 dB
D)76 dB
E)82 dB

Question 46

An air column is being designed so that its second lowest resonant frequency is 440 Hz. The column is open at one end and closed at the other. What length should the column be if the speed of sound in air is 340 m/s?

A)0.386 m
B)0.772 m
C)1.16 m
D)0.193 m
E)0.580 m

Question 47

A 0.640-m long gas column is open at both ends. What is the fundamental resonant frequency of the air column if the speed of sound in the air is 340 m/s?

A)432 Hz
B)266 Hz
C)198 Hz
D)132 Hz
E)669 Hz

Question 48

A 4.0-m long pipe is closed at one end. Find the frequency of the second harmonic. The speed of sound is 340 m/s.

A)170 Hz
B)64 Hz
C)85 Hz
D)21 Hz
E)57 Hz

Question 49

Two microphones, 3.0 m apart, pick up the sound of a source emitting sound at 1024 Hz. The source is moving in a direction parallel to the line joining the microphones. When the source is equidistant from the microphones, the signals picked up by the microphones interfere constructively. At that instant the angle between the right bisector to the line joining the microphones and the line joining the midpoint to the source is 0°. What will the angle be when the two signals again interfere constructively for the first time?The speed of sound is 330 m/s. Assume that the distance to the source of sound is very large compared with the wavelength.

A)15°
B)9.4°
C)12°
D)6.2°
E)19°

Question 50

Sound of frequency 600 Hz is emitted by a point source. The sound can travel along two different paths to reach an observer. What is the minimum non-zero path length difference that results in constructive interference? Assume the speed of sound in air is 340 m/s.

A)28.3 cm
B)1.13 m
C)1.76 m
D)88.2 cm
E)56.7 cm

Question 51

The sound from a single source can reach point O by two different paths. One path has a length 20.0 m and the second path has a length 21.0 m. The sound destructively interferes at point O. What is the minimum frequency of the source if the speed of sound is 340 m/s?

A)340 Hz
B)6800 Hz
C)520 Hz
D)680 Hz
E)170 Hz

Question 52

The third harmonic of an organ pipe of length L open at one end has nodes at the closed end, 2L/5 from the closed end, and 4L/5 from the closed end. The open end is an antinode. What expression describes this wave? Take the speed of sound to be 336 m/s, the length of the pipe to be 2.0 m, and let x be the distance from the closed end.

A)A sin[(3.9 m^-1) x] sin[(210 s^-1) t + φ]
B)A cos[(3.9 m^-1) x] sin[(1.3 x 10³ s^-1) t + φ]
C)A cos[(3.9 m^-1) x] cos[(210 s^-1) t + φ]
D)A sin[(3.9 m^-1) x] sin[(1.3 x 10³ s^-1) t + φ]
E)A sin[(0.625 m^-1) x] sin[(4.8 x 10^-3 s^-1) t + φ]

Question 53

A crying baby emits sound with an intensity of 8.0 × 10^-8 W/m². What is the intensity level for a set of quintuplets? The lowest detectable intensity is 1.0 × 10^-12 W/m².

A)79 dB
B)69 dB
C)56 dB
D)49 dB
E)36 dB

Question 54

Two people are talking at a distance of 3.0 m from where you are and you measure the sound intensity as 1.1 × 10^-7 W/m². Another student is 4.0 m away from the talkers. What sound intensity does the other student measure?

A)6.2 × 10^-8 W/m²
B)1.5 × 10^-7 W/m²
C)8.3 × 10^-8 W/m²
D)7.8 × 10^-7 W/m²
E)2.5 × 10^-8 W/m²

Question 55

Two harmonic sound waves reach an observer simultaneously. The observer hears the sound intensity rise and fall with a time of 0.200 s between the maximum intensity and the succeeding minimum intensity. What is the difference in frequency of the two harmonic sound waves?

A)10.0 Hz
B)0.200 Hz
C)5.00 Hz
D)2.50 Hz
E)1.25 Hz

Question 56

The intensity level of a power mower at a distance of 1.0 m is 100 dB. You wake up one morning to find that four of your neighbors are mowing their lawn 20 m from your open bedroom window. What is the intensity level in your bedroom?

A)80 dB
B)104 dB
C)400 dB
D)50 dB
E)40 dB

Question 57

A 200-Hz and a 206-Hz sound are emitted into the same volume of space. What is the frequency of intensity variation?

A)406 Hz
B)41.2 kHz
C)6 Hz
D)1.03 Hz
E)203 Hz

Question 58

Two tuning forks have frequencies of 480 and 520 Hz. What is the beat frequency if both are emitting a sound at the same time?

A)40 Hz
B)20 Hz
C)1000 Hz
D)490 Hz
E)500 Hz

Question 59

One of the harmonics of a column of air open at one end and closed at the other has a frequency of 448 Hz and the next higher harmonic has a frequency of 576 Hz. What is the fundamental frequency of the air column?

A)32 Hz
B)64 Hz
C)88 Hz
D)128 Hz
E)256 Hz

Question 60

The sound level of a person talking at 1.0 m of distance is 60 dB. You are surrounded by five people all talking at the same time. What sound level are you being exposed to?

A)600 dB
B)60 dB
C)74 dB
D)67 dB
E)81 dB

Question 61

You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind and you perceive the frequency as 1470 Hz. You are relieved that he is in pursuit of a different speeder when he continues past you, but now you perceive the frequency as 1400 Hz. What is the frequency of the siren in the police car? The speed of sound in air is 343 m/s.

A)1300 Hz
B)1320 Hz
C)1430 Hz
D)1360 Hz
E)1370 Hz

Question 62

Two in-phase loudspeakers that emit sound with the same frequency are placed along a wall and are separated by a distance of 5.00 m. A person is standing 12.0 m away from the wall, equidistant from the loudspeakers. When the person moves 1.00 m parallel to the wall, she experiences destructive interference for the first time. What is the frequency of the sound? The speed of sound in air is 343 m/s.

A)211 Hz
B)256 Hz
C)422 Hz
D)512 Hz
E)674 Hz

Question 63

A supersonic plane passes overhead at a speed of 500 m/s. If you hear the sonic boom (shock wave) 4.00 s after the plane is directly overhead, at what altitude is the altitude the plane flying? Assume the speed of sound in air is 340 m/s.

A)1.36 km
B)2.16 km
C)1.85 km
D)2.45 km
E)The plane is not flying fast enough to produce a shock wave.

Question 64

A bat emits a sound at a frequency of 30.0 kHz as it approaches a wall. The bat detects beats such that the frequency of the echo is 900 Hz higher than the frequency the bat is emitting. What is the speed of the bat? The speed of sound in air is 340 m/s.

A)20.0 m/s
B)15.0 m/s
C)10.0 m/s
D)30.0 m/s
E)5.0 m/s

Question 65

As you stand by the side of the road, a car approaches you at a constant speed, sounding its horn, and you hear a frequency of 80.0 Hz. After the car goes by, you hear a frequency of 60.0 Hz. What is the speed of the car? Assume that he speed of sound in air is 343 m/s.

A)64 m/s
B)49 m/s
C)16 m/s
D)36 m/s
E)25 m/s

Question 66

Two strings of identical material and radius are stretched with the same tension with their ends fixed, but one string is 8.0 mm longer than the other. Waves on these strings propagate at 420 m/s. The fundamental frequency of the longer string is 528 Hz. What is the beat frequency when each string is vibrating at its fundamental frequency?

A)22 Hz
B)11 Hz
C)16 Hz
D)5.5 Hz
E)27 Hz

Question 67

The siren on a police car emits waves with a frequency f = 500 Hz. You are standing by the side of the road when a police car, sounding its siren, approaches you at 30.0 m/s. What frequency do you hear? The speed of sound is 340 m/s.

A)544 Hz
B)540 Hz
C)548 Hz
D)532 Hz
E)536 Hz

Question 68

You are driving along a highway at 25 m/s when you hear the siren of an emergency vehicle traveling in the opposite direction on the other side of the highway. When the vehicle is approaching you, you hear the frequency of the siren as 2300 Hz, but when it is past you the frequency becomes 1600 Hz. What is the speed of the vehicle? The speed of sound in air is 343 m/s.

A)37 m/s
B)32 m/s
C)30 m/s
D)41 m/s
E)50 m/s

Question 69

You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind and you perceive the frequency as 1370 Hz. You are relieved that he is in pursuit of a different speeder when he continues past you, but now you perceive the frequency as 1330 Hz. What is the speed of the police car? The speed of sound in air is 343 m/s.

A)38.4 m/s
B)30 m/s
C)39.2 m/s
D)40.0 m/s
E)41.7 m/s

Question 70

Two in-phase loudspeakers are placed 6.00 m apart along one wall of a room. They emit sound with a frequency of 512Hz. Starting at the location of one of the loudspeakers, a microphone is moved in a direction perpendicular to the wall until constructive interference is detected for the first time. How far is the microphone from the wall at that point? The speed of sound in air is 330 m/s.

A)0.141 m
B)0.664 m
C)0.203 m
D)0.138 m
E)0.282 m

Question 71

Two in-phase loudspeakers that emit sound with the same frequency are placed along a wall and are separated by a distance of 8.00 m. A person is standing 12.0 m away from the wall, equidistant from the loudspeakers. When the person moves 3.00 m parallel to the wall, she experiences destructive interference for the second time. What is the frequency of the sound? The speed of sound in air is 343 m/s.

A)278 Hz
B)422 Hz
C)452 Hz
D)562 Hz
E)694 Hz

Question 72

A policeman in a stationary car measures the speed of approaching cars by means of an ultrasonic device that emits a sound with a frequency of 41.2 kHz. A car is approaching him at a speed of 33.0 m/s. The wave is reflected by the car and interferes with the emitted sound producing beats. What is the frequency of the beats? The speed of sound in air is 330 m/s.

A)9.2 kHz
B)4.1 kHz
C)4.6 kHz
D)1.2 kHz
E)8.2 kHz

Question 73

A car horn emits a frequency of 400 Hz. A car traveling at 20.0 m/s sounds the horn as it approaches a stationary pedestrian. What frequency does the pedestrian hear? The speed of sound in air is 343 m/s.

A)200 Hz
B)375 Hz
C)400 Hz
D)425 Hz
E)450 Hz

Question 74

A boy on a bicycle approaches a brick wall as he sounds his horn at a frequency 400 Hz. The sound he hears reflected back from the wall is at a frequency 408 Hz. At what is the speed is the boy riding his bicycle toward the wall? Assume the speed of sound in air is 340 m/s.

A)3.68 m/s
B)333 m/s
C)6.67 m/s
D)6.80 m/s
E)3.37 m/s

Question 75

An airplane flying faster than the speed of sound of 340 m/s produces a shock wave with an angle θ₀ = 50°. What is the speed of the plane?

A)490 m/s
B)530 m/s
C)390 m/s
D)440 m/s
E)405 m/s