Deck 14: Sound

Question 1

At a rock concert, if the speakers are placed on the floor instead of higher up on a tower, state if the intensity of the sound you would hear, from the same distance away, is the same or different and why.

Answer 1

Intensity would increase due to reflections off floor.

Question 2

What man-made object exceeded the speed of sound long before the invention of the airplane or the bullet?

Answer 2

A "cracked whip" creates a sonic boom.

Question 3

Which of the following is a false statement?

A) Light travels very much faster than sound.
B) Sound waves are longitudinal pressure waves.
C) The transverse waves on a vibrating string are different from sound waves.
D) "Pitch" (in music) and frequency have approximately the same meaning.
E) Sound can travel through vacuum.

Answer 3

Sound can travel through vacuum.

Question 4

Sound vibrations with frequencies less than 20 Hz are called

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

Question 5

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

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

Question 6

As atmospheric pressure increases, what happens to the velocity of sound? (Assume that all other factors remain constant.)

A) It increases on warm days and decreases on cold days.
B) It increases.
C) It does not change.
D) It decreases.

Question 7

If you were to inhale a few breaths from a helium gas balloon, you would probably experience an amusing change in your voice. You would sound like Donald Duck or Alvin the Chipmunk. What is the cause of this curious high-pitched effect?

A) Low frequencies are absorbed in helium gas, leaving the high frequency components, which result in the high, squeaky sound.
B) The helium causes your vocal cords to tighten and vibrate at a higher frequency.
C) Your voice box is resonating at the second harmonic, rather than at the fundamental frequency.
D) For a given frequency of vibration of your vocal cords, the wavelength of sound is less in helium than it is in air.
E) Sound travels faster in helium than in air at a given temperature.

Question 8

What happens to the velocity of sound in a gas when the absolute temperature of that gas is doubled?

A) It increases to 1.41 times its original value.
B) It quadruples.
C) It doubles.
D) It stays the same.

Question 9

Since the Helium molecule (He) is 2 times as massive as the Hydrogen molecule (H₂), the speed of sound in Hydrogen is ________ the speed in Helium.

A) 1.41 times
B) four times
C) 1/ times
D) two times

Question 10

The decibel level of sound is related to its

A) pitch.
B) velocity.
C) intensity.
D) frequency.
E) wavelength.

Question 11

The intensity of a sound wave is proportional to its

A) decibel level.
B) power.
C) wavelength.
D) Doppler shift.

Question 12

If the intensity of sound changes (increases) by a factor of 100, the decibel level changes by a factor of

A) 1.
B) 10.
C) log 100.
D) 20.
E) 100.

Question 13

When sound passes from air into water

A) its velocity does not change.
B) its frequency does not change.
C) its wavelength does not change.

Question 14

Two coherent sound waves will destructively interfere when the path difference is the wavelength times what?

A) an odd integer
B) an integer
C) half an even integer
D) half an odd integer

Question 15

Two coherent sound waves will constructively interfere when the path difference is the wavelength times what?

A) half an odd integer
B) an integer
C) half an integer
D) an even integer plus 1/2

Question 16

If the phase angle between sound waves from two different point sources is 180°, what kind of interference will occur?

A) constructive
B) either constructive or destructive
C) destructive

Question 17

Consider the standing wave on a guitar string and the sound wave generated by the guitar as a result of this vibration. What do these two waves have in common?

A) They have the same velocity.
B) They have the same wavelength.
C) They have nothing in common.
D) They have the same frequency.

Question 18

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

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

Question 19

An unknown tuning fork is sounded along with a tuning fork whose frequency is 256. Hz and a beat frequency of 3. Hz is heard. What is the frequency of the unknown tuning fork?

A) It must be 256 Hz.
B) It must be 253 Hz.
C) It could be either 253 Hz or 259 Hz; there is no way to tell.
D) It must be 259 Hz.

Question 20

The change in the frequency of a wave due to the motion of the source (or observer) is known as

A) the Mach effect.
B) the Bell effect.
C) interference.
D) the Doppler effect.
E) diffraction.

Question 21

The Doppler shift explains

A) the phenomenon of beats.
B) why it is that our hearing is best near 3000 Hz.
C) why a sound grows quieter as we move away from the source.
D) why the siren on a police car changes its pitch as it races past us.
E) how sonar works.

Question 22

If a jet plane were to double its MACH-speed, its half-angle will

A) stay the same.
B) decrease.
C) increase.

Question 23

A trombone or a trumpet can be considered a(n)

A) closed organ pipe.
B) open organ pipe.

Question 24

Only odd harmonics can be produced in a(n) ________ organ pipe.

A) wide
B) closed
C) narrow
D) open

Question 25

After seeing a flash of lightning, if one counts the seconds before hearing the thunder, one can estimate the distance to the flash. How many seconds delay
(a) per mile?
(b) per kilometer?

Question 26

Sound traveling in air at 23.° C enters a cold front where the air temperature is 2.° C. If the sound frequency is 1500. Hz, determine the speed in the warmer air and in the colder air.

Question 27

What is the ratio of the speed of sound in air at 0° C to the speed at 100° C?

Question 28

On a day when the speed of sound in air is 340. m/s, a bat emits a shriek whose echo reaches it 25.0 ms later. How far away was the object that reflected back the sound?

Question 29

What is the ratio of the power levels of two sounds with intensity levels of 40. dB and 70. dB?

Question 30

What is the intensity of a 70. dB sound?

Question 31

The intensity at a distance of 6.0 m from a source is 6 × 10^-10 W/m².
(a) What is the power level emitted by the source?
(b) What is the intensity level in dB?

Question 32

Consider a sound intensity of 16. × 10^-8 W/m².
(a) What is the sound intensity level?
(b) At twice the distance from the source, what would be the intensity level?
(c) At how many times the original distance would the intensity level decrease by 12. db?

Question 33

One cat meowing produces a sound intensity level of 55. db.
(a) What would be the sound intensity level of 2 cats meowing?
(b) ... of 10 cats meowing?
(c) ... of 100 cats meowing?

Question 34

Two adjacent sources each emit a frequency of 800. Hz in air where the velocity of sound is 340. m/s. How much farther back would the first source have to be moved so an observer in front of the sources would hear no sound?

Question 35

What is the beat frequency of two sounds that have equal amplitudes and frequencies of 440. Hz and 444. Hz?

Question 36

Given 4 tuning forks of frequency 446, 440, 443, and 449 Hz, how many different beat frequencies could be produced and what are they?

Question 37

James is listening to the same tone coming from two speakers, one 3.49 m away and the other 3.10 m distant. At his position the two tones destructively interfere.
(a) What is the largest possible wavelength of the tone?
(b) If the air temperature is 30.° C, what is the lowest possible frequency?

Question 38

Estimate by what percent the perceived frequency of speech changes due to a talking person walking away from another person at rest at a speed of 3 m/s.

Question 39

A train moving 30. m/s approaches a station and sounds its whistle and passengers standing at the station hear a pitch of 440. cycles/second. What pitch will be heard when the train is at rest at the station? (assume the air temperature is 20.°C)

Question 40

"Warp one" (the speed of light) is what Mach number at 20.° C?

Question 41

Suppose you hear a car approaching and its horn is heard as a 3037. Hz tone. After passing, you hear 2430. Hz.
(a) What was the Mach number of the car?
(b) What is the speed of sound if the outside temperature is 19.°C?
(c) How fast was the car moving, in meters per second?

Question 42

On a warm 30.°C spring day, you are watching Richard take a buzzer and twirl it horizontally around on the end of a 2.0 meter long string. Why do you hear the buzzer tone vary from 718. Hz to 772. Hz? What is the angular speed?

Question 43

An organ pipe open at both ends has a length of 0.800 m. If the velocity of sound in air is 340. m/s, what are the frequencies of the second and third harmonics?

Question 44

The corresponding violin strings on two violins in an orchestra are found to produce a beat frequency of 2. Hz when a frequency of 660. Hz is played. What percentage change in the tension of one of the strings would bring them to the same frequency?

Question 45

The wavelength in air (temperature of 20°C) of a sound wave of frequency 0.50 kHz is

A) 0.68 m.
B) 0.75 m.
C) 2.0 m.
D) 1.5 m.
E) 1.8 m.

Question 46

What is the speed of sound in air at freezing temperature?

A) 650 mph
B) 650 m/s
C) 331 m/s
D) 1100 m/s
E) 331 mph

Question 47

How many times faster does sound travel through iron rails than through air at 20.° C?

A) 12.8
B) 13.6
C) 13.1
D) 13.9
E) 12.2

Question 48

If you hear thunder 5.0 s after seeing a flash of lightning, the distance to the lightning strike is about

A) 1.2 km.
B) 2.2 km.
C) 0.60 km.
D) 1.7 km.
E) 0.90 km.

Question 49

What is the intensity level of a sound with intensity 10^-3 W/m²?

A) 90 dB
B) 79 dB
C) 30 dB
D) 60 dB
E) 96 dB

Question 50

How many decibels correspond to a sound intensity of 7.0 × 10^-7 W/ m²?

A) 69
B) 58
C) 63
D) 75
E) 70

Question 51

How many times more intense is an 80. db sound than a 60. db sound?

A) 100
B) 20
C) 1.33
D) 10
E) 2.0

Question 52

Two violin strings, vibrating at 880. Hz and 876. Hz respectively, will cause a beat frequency of

A) 8. Hz.
B) 878. Hz.
C) 4. Hz.
D) 1.76 kHz.

Question 53

For 440. Hz sound in 20.°C air, which of the following path differences would result in constructive interference?

A) 39. cm
B) 117. cm
C) 156. cm
D) 11. cm

Question 54

A sound source (normal frequency of 1000 Hz) approaches a stationary observer at one-half the speed of sound. The observer hears a frequency of

A) 2000 Hz.
B) 1500 Hz.
C) 500 Hz.
D) 250 Hz.
E) 1414 Hz.

Question 55

An observer approaches a stationary 1000 Hz sound source at twice the speed of sound. The observer hears a frequency of

A) 1500 Hz.
B) 500 Hz.
C) 4000 Hz.
D) 3000 Hz.
E) 2000 Hz.

Question 56

The half angle of the conical shock wave produced by a supersonic aircraft is 60°. What is the Mach number of the aircraft?

A) 1.15
B)

C) 0.87
D) 1.73
E) 2.0

Question 57

A jet flies at a speed of Mach 1.3. What is the half-angle of the conical shock wave formed?

A) 44°
B) 100°
C) 50°
D) 30°
E) 36°

Question 58

Middle C has a frequency of 262. Hz. What is the frequency of C an octave higher?

A) 786. Hz
B) 2.62 kHz
C) 2.10 kHz
D) 270. Hz
E) 0.524 kHz

Question 59

To produce an "A" note (440. Hz) at 20.° C, a saxophone must create how long an effective air column?

A) 59. cm
B) 78. cm
C) 39. cm
D) 20. cm
E) 66. cm

Question 60

The lowest tone to resonate in an open pipe of length L is 400. Hz. What is the frequency of the lowest tone that will resonate in a closed pipe of length 2L?

A) 0.800 kHz
B) 200. Hz
C) 100. Hz
D) 1.60 kHz

Question 61

A closed organ pipe of length 0.750 m is played when the speed of sound in air is 340. m/s. What is the fundamental frequency?

A) 171. Hz
B) 570. Hz
C) 0.113 kHz
D) 0.228 kHz
E) 57.0 Hz