CHAPTER 12 TEST
(Sound)
Directions: Show work on problems. Choose correct answer when available and place
next to the question number.
Formulas:
f1 / f2 
p1 / p2
f1 / f2  T1 / T2
Beat freq = 1-2
2 = 1 ( v / v  vs )
1/2 = L2/L1
1/2 = d2/d1
Viewed from above, the areas of minimal intensity that are generated by a tuning fork
separate areas of normal intensity into _____ roughly equal sections.
A. 2 B. 8 C. 4 D. 16
Periodic changes in sound intensity that result from the interference between two sound
waves are called
A. beats. B. peaks. C. troughs. D. periods.
Two sound sources produce a pattern of varying sound intensity with a period of 0.8 s.
Their beat frequency is
A. 0.8 Hz. B. 1.3 Hz. C. 1.6 Hz. D. 2.2 Hz.
The beat frequency produced when a source is played against a 315 Hz tone is 3 Hz. The
other tone is
A. 312 Hz. B. 105 Hz. C. 318 Hz. D. A or C.
Two musicians are tuning their instruments. Both play the same note and produce an
audible beat with a frequency of 2 Hz. One adjusts his instrument, and they play again,
producing a beat frequency of 1.5 Hz. They are now
A. more in tune with each other. C. playing in a fundamental mode.
B. less in tune with each other. D. No adjustment was needed.
A 600 Hz test tone from an oscillator and a flute note produces a beat frequency of 11 Hz,
as shown on an oscilloscope screen. A 582 Hz tuning fork produces a beat frequency of 7
Hz when sounded with the flute note. The actual frequency of the flute note is
A. 589 Hz. B. 611 Hz. C. 618 Hz. D. 604 Hz.
In practice, the human ear can only detect beat frequencies of
A. > 9 Hz. B. < 10 Hz. C. < 7 Hz. D. > 5 Hz.
Constructive interference occurs at points where the distance to two identical sound
sources is
A. not equal and differs by an odd number of wavelengths.
B. equal or differs by a whole number of wavelengths.
C. equal or differs by an even number of wavelengths.
D. not equal and differs by an odd number of half wavelengths.
In the above diagram, the beat frequency of the sound wave interference pattern is
A. 2 Hz. B. 4 Hz. C. 1 Hz. D. 5 Hz.
Destructive interference occurs at points where the distance to two identical sound
sources is
A. not equal and differs by an odd number of wavelengths.
B. equal or differs by a whole number of wavelengths.
C. equal or differs by an even number of wavelengths.
D. not equal and differs by an odd number of half wavelengths.
What causes "dead" areas of sound in an auditorium?
A. destructive interference. C. poor reverberation.
B. constructive interference. D. excess reverberation.
If f = frequency, w = wavelength, and v = velocity, what does beat frequency equal?
A. |f1 - f2|
C. |w1 - w2|
B. |f1 + f2|
D. |v1 + v2|
Two strings have the same length and tension. String 1 has a greater diameter than string
2. The frequency relationship between the two strings (f1 and f2) is
A. f1 < f2.
C. f1 > f2.
B. f1 = f2.
D. You cannot tell from the information given.
Two strings (f1 and f2) have the same density, length, and diameter. String 1 is under four
times greater tension than string 2. The freqency relationship between the two strings is
A. f1 = 4f2
C. f1 = 2f2 .
B. f1 = f2.
D. You cannot tell from the information given.
Two strings have the same diameter, length, and tension, but string 1 is made of denser
material than string 2. The frequency relationship between the two strings is
A. f1 < f2.
C. f1 > f2.
B. f1 = f2.
D. You cannot tell from the information given.
Two strings have the same tension and diameter, but string 1 is three times longer than
string 2. String 2 has a density nine times greater than the density of string 1. The
frequency relationship between the two strings is
A. f1 < f2.
C. f1 > f2.
B. f1 = f2.
D. You cannot tell from the information given.
The resonant frequencies of a vibrating string are directly proportional to the ________ of
the tension on the string.
A. square B. cube root C. cube D. square root
If the vehicle shown in the above diagram is moving to the right and carries a sound
source, the pitch of that source will sound
A. higher for I, lower for III, and the same for II.
B. lower for I, the same for II, and higher for III.
C. the same for I, lower for II, and higher for III.
D. lower for I, higher for II, and the same for III.
The length of a string is 0.5 m, and it resonates at 900 Hz. After it is shortened to 0.3 m, it
resonates at
A. 270 Hz. B. 300 Hz. C. 1500 Hz. D. 540 Hz.
Two strings, identical except for their densities, resonate at 425 Hz and 850 Hz,
respectively. If the density of the string with the lower frequency is 9.0 x 103 kg/m3, what
is the density of the string with the higher frequency?
A. 36 x 103 kg/m3
C. 6 x 103 kg/m3
B. 3 x 103 kg/m3
D. 2.3 x 103 kg/m3
If the tension on a string is doubled and its length is halved, its new frequency in terms of
f', its original frequency, would be
A. 0.5f'. B. 2.8f'. C. 2f'. D. f.
If the tension and density of a string are both multiplied by 5, the new frequency, in terms
of f', its original frequency, would be
A. f' B. 5f' C. 24f' D. 25f'
If the length and diameter of a string are both reduced by 1/3, the new frequency, in terms
of f', its original frequency, would be
A. 9/4f' B. 2/3f' C. 2/9f' D. 4/3f'
The property of sound waves that determines the perception of volume is
A. amplitude. B. frequency. C. wavelength. D. harmonic structure.
The property of sound waves that determines the perception of pitch is
A. amplitude. B. frequency. C. harmonic structure. D. volume.
In the above diagram, the string vibrates at a fundamental frequency of 440 Hz. If 3 kg
were added to the weight placing tension on the string, the new fundamental frequency of
the string would be
A. 220 Hz. B. 1676 Hz. C. 880 Hz. D. 110 Hz.
Guitarists (and other stringed instrument players) can produce harmonic overtones by
pressing the strings very lightly. To obtain an overtone of 1 octave (that is, twice the
fundamental frequency), a guitarist would need to press lightly ___________ the way
down the string.
A. 1/4 B. 1/2 C. 3/4 D. 5/8
One would expect that two pendulums of length 0.5 m
A. would not resonate at the same frequency.
B. would resonate at the same frequency.
C. could not be made to resonate.
D. You cannot tell from the information given.
Mechanical resonance occurs when a system free to vibrate is driven (oscillated) at
A. less than its natural frequency.
B. more than its natural frequency.
C. one-third its natural frequency.
D. its natural frequency.
Which of the following does NOT affect the resonant frequency of an air column?
A. length B. temperature C. diameter D. ends open or closed
The resonant frequencies of an air column are
A. inversely proportional to temperature.
B. directly proportional to temperature.
C. equal to temperature.
D. not affected by temperature.
Which of the following is NOT a possible resonant wavelength for a cylinder open at
both ends?
A. 3/4L B. 2L C. L D. 3/2L
In the cylinder shown in the above diagram, A = 0.1 m and B = 0.3 m. If the temperature
is 20C, what is the fundamental frequency of the cylinder?
A. 1147 Hz B. 367 Hz C. 437 Hz D. 573 Hz
Which of the following is NOT a possible resonant wavelength for a cylinder closed at
one end?
A. 5/4L B. 5/12L C. 3/4L D. 1/4L
The temperature is 20C. The first resonant length of a cylinder closed at one end is 17
cm. What is the frequency?
A. 437 Hz. B. 257 Hz. C. 506 Hz. D. 2024 Hz.
The temperature is 20C. The first resonant length of a cylinder with both ends open is 26
cm. What is the frequency?
A. 1347 Hz. B. 662 Hz. C. 337 Hz. D. 252 Hz.
The temperature is 20C. The third resonant length of a cylinder with both ends open is
21 cm. What is the frequency?
A. 1092 Hz. B. 546 Hz. C. 1667 Hz. D. 2457 Hz.
How long would a flute have to be to produce a first harmonic of 440 Hz at body
temperature (37C)? Assume a flute is an ideal cylinder that is closed at one end.
A. 10 cm B. 20 cm C. 15 cm D. 25 cm
How long would an organ pipe have to be to produce a 100 Hz tone at 20C? Assume the
pipe is a cylinder that is open at both ends and the tone is first harmonic.
A. 8.10 m B. 24.90 m C. 6.86 m D. 1.71 m
Path length A of the Herschel tube shown in the above diagram is 0.30 m, and the
frequency of the tuning fork is 460 Hz. What path lengths, B, will produce a resonance
(that is, constructive
interference) at the outlet? The temperature is 20C.
A. 4.05 m, 6.30 m, 7.05 m
C. 4.00 m, 8.00 m, 16.00 m
B. 2.50 m, 3.50 m, 8.50 m
D. 2.60 m, 5.30 m, 10.4 m
When an airplane is flying at the speed of sound, wavefronts in front of it pile up. These
wavefronts produce
A. a sound barrier.
C. a fundamental frequency.
B. a doppler effect. D. a wind tunnel.
The area covered by a jet's sonic boom depends on the jet's
A. velocity. B. altitude. C. engine type. D. N-signature.
The apparent pitch emitted from an object accelerating towards an observer
A. rises continously.
C. fall continuously.
B. is constant.
D. lowers and then rises.
If a sound-emitting source is moving towards a stationary observer, the frequency
perceived by the observer will be ________ the actual frequency of the source.
A. lower than
C. lower and then higher than
B. the same as
D. higher than
Stereo systems sound more life-like, in part, because there are two sound sources at the
listener's position. Based on what you know of constructive and destructive interference
and tuning forks, briefly discuss how the listener's position and the speakers' positions
affect sound quality.
The beat frequency produced by sounding a 623 Hz tone and a 599 Hz tone at the same
time is :
The beat frequency produced sounding a 1527 Hz tone and another tone at the same time
is 6.5 Hz. What are the possible frequencies of the second tone?
A tuning fork is dropped by accident. What is one way to detect if it was significantly
damaged?
The tension on a string is initially 210 N, and it resonates at 440 Hz. After the tension is
changed, it resonates at 750 Hz. What is the new tension?
One string with diameter 0.002 m resonates at 540 Hz. A second string, identical except
for its diameter, resonates at 820 Hz. What is the diameter of the second string?
Changing only one variable to control pitch produces unmanageable sizes of strings or
puts impossible amounts of stress on the piano frame. Recall that 7 octaves
implies f'x 27.
Why isn't it practical to manipulate just one variable to control pitch (length, tension,
density, diameter) in building a large instrument, such as a piano, which has slightly over
a 7 octave range?
How does mechanical resonance occur?
Why is mechanical resonance an important design consideration for
machines with oscillating parts?
Briefly explain the Doppler Effect and how its effect on sound is perceived.
What is one possible reason for NOT using sonar to gauge motorists' speed on the
highway?
A car is approaching an observer at the side of the road and blowing its horn. Its velocity
is 120 km/h, and the pitch perceived by the observer is 1205 Hz. The air temperature is 15
C. What is the original pitch?
A locomotive approaches a crossing and sounds its whistle. An observer hears a pitch of
880 Hz. The temperature is 12C. The actual frequency of the source is 870 Hz. What is
the velocity of the train?
Based on your lab observations of interference patterns created by two loudspeakers, what
would you expect the relationship to be between frequency and the number of maximum
and minimum intensity spots between the two loudspeakers?
Based on what you know of tuning forks and destructive and constructive interference,
why do you think there are no tuning forks that have three tines?
Which of the following is NOT a possible source of significant error when measuring
resonant lengths of a closed air column?
A. a different temperature inside the pipe than outside in the lab
B. a different temperature in the tuning fork
C. measuring the pipe length
D. marking the water height for future measure
Which of the following is NOT essential to know in determining the speed of sound using
a tuning fork to create resonance in an air column?
A. the diameter of the tube
B. the length of the tube at resonance
C. the temperature of the air
D. the frequency of the tuning fork