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Chapter 15 Sound
Name
------------------
8. I can recognize that sound is a longitudinal wave with pressure variations that are transmitted
detectors.
to
6. SOUNDwaves are actually produced by:
a. radlQ_ ations
vibrating objects
c. soft objects
d. none of these
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Answer: B
7. If my dog Greta is barking at some people walking past our house, 1hear her sound waves because:
a. there is a source, medium, and house
b. there is a source medium and window
c. there is a source, medium, and detector
d. there is a source, medium, and protector
Answer: C
9. I can recognize which wave characteristic
8. Which
a.
b.
c.
d.
most closely relates to pitch and/or loudness.
characteristic is most closely related to loudness?
amplitude
wave ength
frequency
Answer: B
10. I can relate the temperature
9. Sou
of air to the velocity at which sound will travel.
faster in air if the air is:
a. Warmer
b. older
c. Makes no difference
Answer: A
11. I can describe/recognize
what beats are and/or calculate the apparent
beat frequency between two
frequencies.
10. Beats occur when two tuning forks at equal,frequencies
~~
Answer: B
are sounded together.
of two sound waves that are being observed
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Answer: B
12. I can calculate and describe the amount of audible Doppler shift for sound waves.
12. A car is moving to the right at 20m/s, and its horn emits a pitch of 400 Hz. If you are standing and the
car approaches you, what frequency do you hear? (Assume the temperature of the air is 20°e)
ef
a. 425Hz
423Hz
c. 388 Hz
d. 120 Hz
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Answer: A
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13. Because of the Doppler effect. an observer will hear a sound moving away from her as being higher in
pitch.
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Answer: B
13. I can calculate the velocity of sound given the resonance lengths of open/closed
tubes.
14. A tuning fork produces a fundamental resonance w/ a closed tube 8.3 cm long. Assuming room temp is
200 what is the lowest possible frequency of the tuning fork?
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Answer: C
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15. I can describe some of the relationships
sounds that they produce.
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between the components of musical instrument
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15. A string instrument, which has a node at each end of the string, resonates with an whole number of
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quarter wave Iengths. \
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Answer: B
16. I can describe and calculate relationships
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involving loudness and decibels
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16. Compared to a quiet conversation (30dB), a loud conversation (60db) would be
a.
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d. 3000x intensity
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1) Sound vi
ith frequencies less than 20 Hz are called
infrasonics.
B) u raso cs.
C) supersonics.
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Answer: A
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2) Sound vibrations with frequencies gr ater than 20,000 Hz are called
A) infrasonics.
ultrasonics.
supersonics.
0) megasonics.
Answer: B
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Answer: E
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4) Which of the following is a false statement?
A) Sound waves are Ion itudin
ssure waves. ,.~
ound can rave through vacuum.
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C) The transverse waves on a vibrating string are different from sound waves. rlZ.l.I.{f
0) Light travels very much faster than sound.
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E) "Pitch" (in music) and frequency have approximately the same meaning. rr'tu.[t.
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Answer: B
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5) What is the audible range of sound frequencies?
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17) Total co~structive interference occurs when two waves with similar frequency and wavelength
ffiPIetelY
ase.
) are completely in phase.
e-gO de-grees pFiase ifference.
D) have a phase difference of -gO degrees.
5
Answer: B
Diff:/
18) The natural frequencies for a stretched string of length L, and wave speed v, are nv/(2L) where n
equals
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A)0,1,2,3,.
B) 2, 4 6, 8, .
1, 2, 3 ,
D) , 1, , ,.
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E) 1, 3, 4, 5, .
Answer: C
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2) What is the ratio of the speed of sound in air at 00 C to the speed at 1000 C?
Answer: 0.85
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4) The wavelen th in air of a sound wave of frequency 0.50kHz is (Air Temp is 20' C)
( A) 0.68 m.
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C) 2.0 m.
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D)1.5m,
Answer: A
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of sound in air at1reezing temperature?
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B) 650 m s
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8) 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 (Air Temp is 20' C)
(b) per kilometer?
Answer: (b) 3. seconds per km
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11) Sound traveling in air at 23.0 C enters a cold front where the air temperature is 2.oC. If the sound
frequency is 1500. Hz, determine the speed in the warmer air and in the colder air.
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Answer. 345. mIs, 332. mls
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12) If you were to inhale a few breaths from a helium gas balloon, you would pfObablyexperience 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) The helium causes your vocal cords to tighten and vibrate at a higher frequency.
8) For a given frequency of vibration of your vocal cords, the wavelength of sound is less in
helium than it is in air.
C) Your voice box is resonating at the second harmonic, rather than at the fundamental
frequency.
D) Low frequencies are absorbed in helium gas, leaving the high frequency components,
which re It.
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E) Sound travels faster in helium than in air at a given temperature.
Answer:
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13) If you hear thunder 5.0 s after seeing a flash of Iighll1ing, the distance to the lightning strike is
About (Air Temp is 20'C)
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A) 2.2km.
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8) 0.60 km.
C) 1.7km.
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D) 0.90km.
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E) 1.2 km.
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Answer: C
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14) On a day when the speed of sound in air is 340. mIs, a bat emits a shriek whose echo reaches it
25.0 ms later. How far away was the object that reflected back the sound?
Answer: 4.25m
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15) As the temperature of the air increases, what happens to the velocity of sound? (Assume that all
other fa
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• ) It increases.
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reases.
C) It does not change.
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D) It increases when atmospheric pressure is high and decreases when the pressure is low.
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Answer: A
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2) Which of the following is most closely identified with loudness of a musical note?
A) frequency
B) velocity
C) pitch
<['~phase
artlplitud~
Answer: D
Diff:!
4) How many times more intense is an 80. db sound than a 60. db sound?
A)10
B) 20
C) 2.0
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Answer: E
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8) The decibel level of sound is related to its bOJ& - go/~ to IOtl:X/O~t!{)6kJ
A) wavelength.
intenSity)
C) velocity.
D) frequency.
E) pitch.
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Answer: B
Diff: 1
Answer: C
Diff:1
2) 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
must be 259 Hz.
) It cou
er
Hz or 259 Hz; there is no way to te .
3= 2S-(;i-3 ••.
Answer: C
Diff: 2
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3) In order to produce beats, the two sound waves should have
A) slightly different amplitudes.
B) the same frequency.
9J!?:.e same am[2litude.
~ghtly
different frequencle .
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Answer: d
Diff: 1
5) Given 4 tuning forks of frequency 446,440, 443,and 449 Hz, how many different beat frequencies
could be produced and what are they?
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~~;.~er: Three beat frequencies: 3, 6, 9 Hz
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8) If the phase angle between sound waves from two different point sources is 1800, what kind orinterferEJjlce.wilLoccur?
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Q) destru~
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C) either constructive or destructive - I Answer: A
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9) 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 wave~rhave in common?
A) They have the same velocity. Ie d,tt~
B) They have the same wavelength. G4I
~ey ~:~: ~ne same frequency.
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Answer: C
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13) 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 to es is increa(sed?
A) It does not change.
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It could either increase or decrease.
D) It incre
Answer: C
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1) The Doppler shift explains
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A) how sonar works.
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B) why the siren on a police car changes its pitch as it races past us.
C) the phenomenon of beats. ~
D) why a sound grows quieter as we move away from the source./Jo
E) why it is that our hearing is best near 3000 Hz.
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B or A (some sonar uses Doppler shift to find speeds)
4) Middle
A)
B
C)
C has a frequency of 262. Hz, What is the frequency of C an octave higher?
2.10 kHz
78 Hz
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Answer: C
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A) the Bell effect.
~ tbe-Ma~h effect.
the Doppler effecD
D) interference.
E) diffraction.
Answer: C
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7) A sound source (normal frequency of 1000 Hz) approaches a stationary observer at one-half the
speed
observer hears a frequency of (Alriemp is 2Q"C)
A) 2000 Hz.
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C) 250 Hz.
D) 1500 Hz.
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9) A train moving 30. mls 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
~lJJtatiOn?
(The air temperature is20.0 C)
Ans~:
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402. Hz
2) Two
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C) 878. Hz.
D) 1.76kHz.
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A
et can be considered a(n)
open organ pipe.
B) co
organ pipe.
Answer: A
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4) A closed organ pipe has a 5th harmonic frequency of 1230.Hz at 20"C.
(a) What is the length of the organ tube?
(b) What is the 1st harmonic of the pipe?
(c) If one end of the pipe were opened, what would be the 1st harmonic?}.
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7) A sound wave of pure frequency can under certain circumstances cause a gl
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This would be an example of
A
uctive interference.
resona e.
C) destruc Ive interference.
D) overtones.
E) the Doppler effect.
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10) Which of the following properties of a sound wave is most closely ident fied with the "pitch" of a
musical note?
A) amplitude
en th
C) frequency
D p ase
E) intensity
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11) A closed organ pipe of length 0.750m is played when the speed of sound in air is 340. m/s. What
is the fundamental frequency? (open-closed)
A
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D) 57.0 Hz
E) 171. Hz
Answer: B
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Answer: B and A
Diff: 1
Answer: C
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12) Only odd harmonics can be produced in a(n)
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organ pipe.
opel\-d~etI rJ!~
C) open
0) wide
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Answer: A
Oiff: 2
Choose from the following:
(a) meters
(b) radls
(e) seconds
(f) N/m
(c) degrees
(g) glcm
(d) Hertz
(h) mls
13) Beat frequency has which of the units shown above?
Answer: (e) Hertz
Oiff 1
14) What is the beat frequency of two sounds that have equal amplitudes and frequencies of 440. Hz
and 444. Hz?
Answer: 4. Hz
Oiff:2
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12) A car is moving toward you as you stand on a corner in 20.0 C air. The car's horn is designed to
blow at a frequency of 400. Hz tone. How fast is the car moving if the air is steadily blowing 10. ml s
toward you in the same direction that the car is moving?
A) 20. mls
B) 30. mls
C) 28. mls
0) 10. mls
E) 40. mls
Answer: E
Oiff: 2
Difficult
3) Suppose you hear a car approaching and its horn is heard as a 3037. Hz tone. After passing, you
hear 2430. Hz.
(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?
Answer:
(b) 342. mls
(c) 38.0 mls
Oiff:3