Deck 13: Sound

Question 1

How far away is a lightning bolt if it takes 20 s for the sound of the associated thunder to reach the observer?

A) 1 mile
B) 4 miles
C) 3 miles
D) 15 miles

Answer 1

4 miles

Question 2

Material 1 has Young's modulus and density , and material 2 has Young's modulus and density . If is 30% more than and is 30% less than , which material has the higher speed of sound and how much higher is it?

A) Material 1 has a speed of sound more than 35% higher than material 2.
B) Material 1 has a speed of sound 30% higher than material 2.
C) Material 2 has a speed of sound more than 80% higher than material 1.
D) Material 2 has a speed of sound 30% higher than material 1.

Answer 2

Material 1 has a speed of sound more than 35% higher than material 2.

Question 3

Which of the following ranges corresponds to the shortest wavelengths?

A) infrasonic
B) audible
C) ultrasonic
D) All have the same wavelengths.

Answer 3

ultrasonic

Question 4

Material 1 has Young's modulus and density , material 2 has Young's modulus and density , and material 3 has Young's modulus and density . If and if , which material has the highest speed of sound?

A) material 1
B) material 2
C) material 3
D) They could all have equal speeds of sound.

Question 5

When a sine wave is used to represent a sound wave, the crest corresponds to:

A) rarefaction.
B) condensation.
C) a point where molecules vibrate at a right angle to the direction of wave travel.
D) a region of low elasticity.

Question 6

Which of the following best describes a sound level of intensity 10^-6 W/m²?

A) extremely loud
B) about that of a power mower
C) normal conversation
D) like a whisper

Question 7

When a sound wave moves through a medium such as air, the motion of the molecules of the medium is in what direction (with respect to the motion of the sound wave)?

A) perpendicular
B) parallel
C) anti-parallel (in opposite direction)
D) Both choices B and C are valid.

Question 8

The density of a certain solid is 7.2 *10³ kg/m³, and its Young's modulus is 8.0 * 10¹⁰ N/m². What is the speed of sound in this material?

A) 1.1 * 10⁷ m/s
B) 5900 m/s
C) 3700 m/s
D) 3300 m/s

Question 9

A sound wave in air has a frequency of 515 Hz and a wavelength of 0.68 m. What is the air temperature?

A) -18°C
B) 32°C
C) 15°C
D) 27°C

Question 10

Consider a vibrating guitar string that makes a sound wave that moves through the air. As the string moves up and down, the air molecules that are a certain horizontal distance from the string will move:

A) up and down.
B) toward and away from the guitar string.
C) back and forth along the direction of the length of the string.
D) in circles around the guitar string.

Question 11

The speed of sound in air is a function of which one of the following?

A) wavelength
B) frequency
C) temperature
D) amplitude

Question 12

What is the intensity level of a sound with intensity of 5.0 *10^-11 W/m²? (I₀ = 10^-12 W/m²)

A) 74 dB
B) 54 dB
C) 17 dB
D) 27 dB

Question 13

Doubling the power output from a speaker emitting a single frequency will result in what increase in loudness?

A) 0.33 dB
B) 3.0 dB
C) 4.8 dB
D) 9.0 dB

Question 14

The frequency separating audible waves and ultrasonic waves is considered to be 20 kHz. What wavelength in air at room temperature is associated with this frequency? (Assume the speed of sound to be 340 m/s.)

A) 0.59 cm
B) 1.7 cm
C) 34 cm
D) 55 cm

Question 15

Comparing the speed of sound in liquids, gases, and solids, the speed of sound is usually lowest in _____ and highest in _____.

A) solids, liquids
B) gases, liquids
C) liquids, solids
D) gases, solids

Question 16

How far away is a lightning strike if you hear the thunderclap 2.00 s after you see the lightning bolt strike? (v_sound = 340 m/s, v_light = 3 *10⁸ m/s)

A) 113 m
B) 340 m
C) 680 m
D) 1020 m

Question 17

The speed of sound at 0 $\degree$ C is 331 m/s. What is the speed of sound at 32 $\degree$ C? (0 $\degree$ C = 273 K)

A) 346 m/s
B) 356 m/s
C) 343 m/s
D) 350 m/s

Question 18

A chamber that can be filled with different gases has placed in it a source of sound that in air produces a frequency of 200 Hz and a microphone to pick up the sound for frequency analysis. First the chamber is filled with helium (speed of sound 1000 m/s at room conditions), then the helium is replaced with oxygen (speed of sound 330 m/s at room conditions), and then finally the helium is replaced with carbon dioxide (speed of sound 269 m/s at room conditions). In which gas is the highest frequency of sound found by the microphone during this experiment?

A) helium
B) oxygen
C) carbon dioxide
D) They all have the same frequency of sound.

Question 19

A sound wave coming from a tuba has a wavelength of 0.674 m and travels to your ears at a speed of 345 m/s. What is the frequency of the sound you hear?

A) 512 Hz
B) 1/517 Hz
C) 230 Hz
D) 1/230 Hz

Question 20

A series of ocean waves, 2.5 m between crests, move past at 2.0 waves/s. Find their speed.

A) 2.5 m/s
B) 5.0 m/s
C) 8.0 m/s
D) 10 m/s

Question 21

When two sound waves are out of phase by _____, destructive interference will occur.

A) 90°
B) 270°
C) 540°
D) 720°

Question 22

Of the frequencies listed below, to which one is the human ear most sensitive?

A) 33 Hz
B) 330 Hz
C) 3300 Hz
D) 33,000 Hz

Question 23

If the distance between a point sound source and a dB detector is increased by a factor of 10, what will be the reduction in intensity level?

A) 10 dB
B) 16 dB
C) 20 dB
D) 32 dB

Question 24

What sound level change most nearly corresponds to a factor of three change in intensity?

A) 0.5 dB
B) 2 dB
C) 3 dB
D) 5 dB

Question 25

If I₀ = 10 ^{- 12} W/m² is the threshold of hearing, a sound with intensity I₁ = 10 ^{- 10} W/m² will give a certain decibel level. Suppose a new sound has an intensity I₂ = I₁²/I₀. What is the new decibel level?

A) 40
B) 20
C) 10,000
D) It will square the decibel level.

Question 26

A phase difference of 480° corresponds to what wavelength difference?

A) 3 $\lambda$
B) 3 $\lambda$ /2
C) 3 $\lambda$ /4
D) 4 $\lambda$ /3

Question 27

If one-half of the members of a symphony orchestra are absent because of head colds, thus reducing the overall intensity of sound by 50%, what will be the reduction in the decibel level?

A) 5 dB
B) 3 dB
C) 48 dB
D) 1.7 dB

Question 28

If the intensity of a sound is increased by a factor of 1000, how is the decibel level changed? The new decibel level will be:

A) three units greater.
B) ten times greater.
C) thirty times greater.
D) twenty units greater.

Question 29

By what amount does the sound intensity decrease when the distance to the source triples?

A) 9.0 dB
B) 9.5 dB
C) 6.0 dB
D) 3.5 dB

Question 30

The intensity level of sound 30 m from a jet airliner is 120 dB. At what distance from the airplane will the sound intensity level be a tolerable 100 dB? (Assume spherical spreading of sound.)

A) 60 m
B) 90 m
C) 300 m
D) 400 m

Question 31

A source of sound has an intensity and when its sound level is measured at a fixed distance the value found is 70 dB. The source then has its intensity increased to and when its sound level is measured at the same distance the value found is 96 dB. What is the ratio ?

A) 26
B) 400
C) 600
D) 14

Question 32

Two loudspeakers are placed facing each other and driven by the same source at 680 Hz. A listener is positioned between the two speakers on the line separating them, thus creating a constructive interference at the listener's ear. What minimum distance would one of the speakers be moved back away from the listener to produce destructive interference at the listener's ear? (The speed of sound = 340 m/s.)

A) 0.13 m
B) 0.25 m
C) 0.50 m
D) 1.00 m

Question 33

If the air temperature decreases, how does the resonant frequency in a pipe closed at one end change?

A) It increases.
B) It decreases.
C) It doesn't change since one end of the pipe is closed.
D) It doesn't change because resonance is a pressure phenomenon.

Question 34

A very loud train whistle has an acoustic power output of 80 W. If the sound energy spreads out spherically, what is the intensity level in dB at a distance of 100 meters from the train? (I₀ = 10 ^{- 12} W/m²)

A) 78.3 dB
B) 88.0 dB
C) 92.8 dB
D) 95.0 dB

Question 35

The air in a pipe resonates at 150 Hz and 750 Hz, one of these resonances being the fundamental. If the pipe is open at both ends, how many resonances are between the two given ones, and if the pipe is closed at one end, how many resonances are between the two given ones?

A) open: 3; closed: 1
B) open: 1; closed: 3
C) open: 2; closed: 0
D) open: 0; closed: 2

Question 36

What is the intensity of a sound with a measured intensity level of 84 dB? (I₀ = 10^-12 W/m²)

A) 8.4 *10^-3 W/m²
B) 2.5 *10^-4 W/m²
C) 2.5 *10-^-5 W/m²
D) 7.4 *10-^--⁴ W/m²

Question 37

Doubling the distance between sound source and a listener will change the intensity, as detected by the listener, by what factor?

A) 4
B) 2
C) 1/2
D) 1/4

Question 38

A sound intensity of 70 dB is observed at a distance d from the source of sound. What sound intensity would be observed at a distance 2d from the source?

A) 68 dB
B) 67 dB
C) 64 dB
D) 62 dB

Question 39

What is the intensity of sound from a band with a sound level of 120 dB? (I₀ = 10 ^{- 12} W/m²)

A) 1 W/m²
B) 1.2 W/m²
C) 10 W/m²
D) 12 W/m²

Question 40

In the afternoon, the decibel level of a busy freeway is 80 dB with 100 cars passing a given point every minute. Late at night, the traffic flow is only 8 cars per minute. What is the late-night decibel level?

A) 77 dB
B) 74 dB
C) 70 dB
D) 69 dB

Question 41

A train station bell gives off a fundamental tone of 1000 Hz as the train approaches the station at a speed of 20.0 m/s. If the speed of sound in air is 335 m/s, what will be the apparent frequency of the bell to an observer riding the train?

A) 1060 Hz
B) 1070 Hz
C) 943 Hz
D) 940 Hz

Question 42

A buzzer with frequency f₀ is thrown straight upwards. On the buzzer's trip down, what is the frequency behavior heard by an observer below?

A) The frequency heard is still f₀.
B) The frequency is a constant one greater than f_0.
C) The frequency is an increasing one greater than f_0.
D) The frequency is a decreasing on less than f_0.

Question 43

The air in a tube open at both ends is sent into its fundamental resonance. One end of the tube is then closed and the air column is again set into its fundamental resonance. The resonant frequency _____ after the end is closed.

A) halves
B) stays the same
C) doubles
D) increases by a factor of 1.4

Question 44

A flute behaves like a tube open at both ends. If its length is 70.0 cm, and the speed of sound is 340 m/s, what is its fundamental frequency in Hz?

A) 121 Hz
B) 159 Hz
C) 243 Hz
D) 260 Hz

Question 45

If two adjacent frequencies of an organ pipe closed at one end are 500 Hz and 700 Hz, what is the length of the organ pipe? (v_sound = 340 m/s)

A) 0.85 m
B) 1.25 m
C) 1.50 m
D) 1.70 m

Question 46

Two tuning forks sounding together result in a beat frequency of 3 Hz. If the frequency of one of the forks is 512 Hz, what is the frequency of the other?

A) 509 Hz or 515 Hz
B) 105 Hz
C) 518 Hz or 506 Hz
D) 85 Hz

Question 47

A tuning fork is sounded above an adjustable length resonating tube (one end closed), which resonates at a length of 0.250 m and again at 0.750 m. What is the frequency of the fork when the speed of sound is taken to be 340 m/s?

A) 340 Hz
B) 680 Hz
C) 1020 Hz
D) 170 Hz

Question 48

What is the next harmonic frequency over the fundamental for an organ pipe 1.50 m in length, closed at one end? The speed of sound in air is 340 m/s.

A) 227 Hz
B) 170 Hz
C) 113 Hz
D) 56.7 Hz

Question 49

Two vibrating tuning forks, held side by side, will create a beat frequency of what value if the individual frequencies of the two forks are 321 Hz and 326 Hz, respectively?

A) 323.5 Hz
B) 647 Hz
C) 5 Hz
D) 2.5 Hz

Question 50

For a displacement standing wave in an air column in a pipe that is open at both ends, there must be at least:

A) one node and one antinode.
B) two nodes and one antinode.
C) two antinodes and one node.
D) two nodes and two antinodes.

Question 51

When the standing wave pattern in a pipe is NANA, the pipe has which of the following set of properties? (N stands for node, A for antinode.)

A) It is open at both ends.
B) It is closed at both ends.
C) It is open at one end and closed at the other end.
D) Any of the above could be true.

Question 52

Two loudspeakers are placed facing each other and driven by the same source at 680 Hz. A listener is positioned between the two speakers on the line separating them, thus creating a constructive interference at the listener's ear. If one of the speakers is gradually pushed toward the listener, how far must it be moved to repeat the condition of constructive interference at the listener's ear? (The speed of sound = 340 m/s.)

A) 0.13 m
B) 0.25 m
C) 0.50 m
D) 1.00 m

Question 53

A vibrating guitar string emits a tone simultaneously with one from a 500-Hz tuning fork. If a beat frequency of 4 Hz results, what is the frequency of vibration of the string?

A) 2500 Hz
B) 496 Hz
C) 504 Hz
D) Either choice B or C is valid.

Question 54

The term "timbre" refers to which of the following?

A) Any musical instrument made primarily of wood.
B) The quality of sound from instruments due to the mixture of harmonics.
C) Instruments that have valves.
D) An instrument made in France.

Question 55

When I stand halfway between two speakers, with one on my left and one on my right, a musical note from the speakers gives me constructive interference. How far to my left should I move to obtain destructive interference?

A) one-fourth of a wavelength
B) half a wavelength
C) one wavelength
D) one and a half wavelengths

Question 56

What is the lowest frequency that will resonate in an organ pipe 1.00 m in length, closed at one end? The speed of sound in air is 340 m/s.

A) 42.5 Hz
B) 85.0 Hz
C) 170 Hz
D) 680 Hz

Question 57

You stand by the railroad tracks as a train passes by. You hear a 950-Hz frequency when the train approaches, which changes to 820 Hz as it goes away. How fast is the train moving? The speed of sound in air is 340 m/s.

A) 14.0 m/s
B) 20.0 m/s
C) 25.0 m/s
D) 37.8 m/s

Question 58

A 2.00-m long organ pipe is open at one end and closed at the other. Its fundamental tone has wavelength:

A) 8.00 m.
B) 4.00 m.
C) 2.00 m.
D) 1.00 m.

Question 59

A tuning fork is sounded above an adjustable length resonating tube (one end closed), which resonates at a length of 0.250 m and again at 0.750 m. If the tube length were extended further, at what point will the tuning fork again create a resonance condition?

A) 1.75 m
B) 1.50 m
C) 1.25 m
D) 1.00 m

Question 60

What phenomenon results from two tuning forks, side by side, emitting frequencies which differ by only a small amount?

A) resonance
B) interference
C) the Doppler effect
D) beats

Question 61

Two cars, one in front of the other, are traveling down the highway at 25 m/s. The car behind sounds its horn, which has a frequency of 540 Hz. What is the frequency heard by the driver of the lead car? (v_sound = 340 m/s)

A) 463 Hz
B) 540 Hz
C) 579 Hz
D) 500 Hz

Question 62

While standing at a crosswalk, you hear a frequency of 540 Hz from an approaching police car. After the police car passes, its frequency is 480 Hz. What is the speed of the police car? (speed of sound = 340 m/s)

A) 13.1 m/s
B) 17.4 m/s
C) 20.0 m/s
D) 26.2 m/s

Question 63

An airplane flying with a constant speed flies from a warm air mass into a cold air mass. The Mach number (the ratio of the speed of the airplane to the speed of sound) will:

A) increase.
B) decrease.
C) stay the same.
D) become unstable.

Question 64

A sound source of frequency 1000 Hz moves at 40.0 m/s toward a listener who is at rest. What is the apparent frequency heard by the listener? (speed of sound = 340 m/s)

A) 853 Hz
B) 872 Hz
C) 1130 Hz
D) 1170 Hz

Question 65

As a train starts from rest and then accelerates down the track, coming toward me faster and faster, the speed of the sound waves coming toward me will be:

A) slower than the normal speed of sound in air.
B) equal to the normal speed of sound in air.
C) some constant speed faster than the normal speed of sound in air.
D) faster and faster.

Question 66

A 500-Hz whistle is moved toward a listener at a speed of 10.0 m/s. At the same time, the listener moves at a speed of 20.0 m/s in a direction toward the whistle. What is the apparent frequency heard by the listener? (The speed of sound is 340 m/s.)

A) 473 Hz
B) 485 Hz
C) 533 Hz
D) 545 Hz

Question 67

A plane is traveling at Mach 0.980 through air at a temperature of 0 $\degree$ C. What is the plane's speed? (Speed of sound at 0 $\degree$ C is 331 m/s.)

A) 314 m/s
B) 324 m/s
C) 348 m/s
D) Mach number is undefined at 0 $\degree$ C.

Question 68

A bat, flying at 3.00 m/s toward a wall, emits a chirp at 50.0 kHz. If the wall reflects this sound pulse, what is the frequency of the echo received by the bat? (v_sound = 340 m/s)

A) 51.5 kHz
B) 51.2 kHz
C) 40.8 kHz
D) 50.9 kHz

Question 69

The Doppler shift of ultrasonic waves can measure the speed of blood in an artery. If the frequency of the stationary source is 100 kHz and the reflected sound has a Doppler shift of 300 Hz, what is the blood flow speed? (The speed of sound inside the body is 1500 m/s.)

A) 1.0 m/s
B) 1.5 m/s
C) 2.2 m/s
D) 3.3 m/s