Physics 198
Exam 2
Fall 2015
21. When a sound wave passes from air into water, what properties of the wave will change?
A)
B)
C)
D)
E)
The frequency f (only)
The wavelength  (only)
The speed of waves v (only)
Both f and 
Both v and 
Solution:
Wave speed must change (different medium).
Frequency does not change (determined by the source).
Now, v  f and since v has changed and f is constant then  must also change.
22. A railroad train is traveling at 30.0 m/s in still air. The frequency of the note emitted by the
train whistle is 262 Hz. What frequency is heard by a passenger on a train moving in the
opposite direction to the first at 18.0 m/s and approaching the first? (Assume that speed of
sound is 343m/s)
A)
B)
C)
D)
E)
262 Hz
272 Hz
292 Hz
302 Hz
322 Hz
Solution:
 v  vL 

General equation: f L  f S 
v

v
S 

The source is moving toward the listener:  decrease, f increase   v s 
The listener is moving toward the source:  decrease, f increase   vL 
 v  vL
f L  f S 
 v  vS

343  18
  262 Hz 
 302 Hz
343

30

23. What is the range of hearing?
A)
B)
C)
D)
E)
1 Hz – 1 KHz
10 Hz – 10 KHz
20 Hz – 20 KHz
40 Hz – 40 KHz
220 Hz – 1200 Hz
Page 1 of 7
Physics 198
Exam 2
Fall 2015
24. Where is the Basilar membrane located?
A)
B)
C)
D)
E)
Positioned inside outer ear
Positioned inside middle ear
Separates middle ear and outer ear
Separates outer ear and middle ear
Positioned inside cochlear
25. Assume that the outer ear canal is a cylindrical pipe 2.50 cm long, closed at one end by the
eardrum. Calculate the resonant frequency of this pipe. (For speed of sound use 343m/s.)
A)
B)
C)
D)
E)
1830 HZ
2840 HZ
3430 Hz
4250 Hz
5158 Hz
Solution:
  4L
f 
v


v
343m / s

 3430 Hz
4 L 4  0.025m
26. Which equation is correct?
A) log( 2000)  3  log 2
B)
C)
D)
E)
log( 2000)  2  log 3
log( 2000)  3 log 2
log( 2000)  2 log 3
log( 2000)  2 log 1000
Solution:
log( 2000)  log (2)  1000  log( 1000)  log( 2)  3  log 2
27. According to Fechner law, as stimuli are increased by multiplication, sensation increases by
A)
B)
C)
D)
E)
Multiplication
Addition (logarithmic scale)
Exponentially (as a power of stimuli)
At low frequencies by multiplication, and at high frequencies by addition
None of the above
Page 2 of 7
Physics 198
Exam 2
Fall 2015
28. If the force applied to a linear system is doubled, what happens with response?
A)
B)
C)
D)
E)
Response is multiplied by log2
Response is doubled
Response is quadrupled
All of the above answers are correct
None of the above answers are correct
29. Suppose that the sound from a speaker is emitted with equal intensity in all directions. If the
sound power, P, emitted from the speaker is 12.57 W, what is the sound intensity, I, in W/m2
at a distance of 2 meters from the speaker? (Hint: note that! 4  12.57 )
A)
B)
C)
D)
E)
1
2
4
¼
½
Solution:
I
P
P
12.57W  1 


  W / m 2
2
2
A 4r
4 2m
4
30. Find the intensity level (in decibels) of a sound if intensity is 2 10 4 W / m 2 .
A)
B)
C)
D)
E)
73dB
75dB
77dB
79dB
83dB
Solution: LI  10dB log
I
2  104W / m2
 10dB log
 10dB log 2  108  83dB
12
2
I0
10 W / m


31. Find the intensity of a sound if intensity level is 70dB.
A) 1.0  10 5 W / m 2
B)
C)
D)
E)
2.0  10 5 W / m 2
1.3  10 4 W / m 2
2.0  10 4 W / m 2
1.0  10 3 W / m 2
Solution: I  I 010 L /10dB  10 12W / m 2 10 70 /10   10 5W / m 2
Page 3 of 7
Physics 198
Exam 2
Fall 2015
32. Suppose that a single violin gives an average sound intensity level of 80 dB at a seat in the
audience. Now suppose that 2 violins play the same piece in the same way. What average
sound intensity level would you expect at the same seat in the audience?
A)
B)
C)
D)
E)
83dB
79dB
77dB
75dB
73dB
Solution:
I  2 I1
LI  10dB log


2 I1
I
I
 10dB  log 1  log 2   10dB log 1  10dB log 2  80dB  3db  83db
I0
I0
I0


33. Compare tension F1 in a violin string tuned to a standard A (440 Hz) with the tension F2 in
the same string tuned to 422 Hz.
A)
B)
C)
D)
F1
F1
F1
F1
F2  2.011
F2  1.853
F2  1.513
F2  1.087
E) F1 F2  0.042
Solution:
v
F

; f 
v


1
F


 F    f  
2
F1 F2   f 1 f 2   440 422  1.087
2
2
34. Which statement is incorrect?
A)
B)
C)
D)
E)
Pitch (as well as loudness) is a subjective characteristic of sound
Pitch increases with sound level for high frequencies
Pitch decreases with sound level for low frequencies
Pitch shows little changes for middle frequencies
Pitch does not changing with sound level
Page 4 of 7
Physics 198
Exam 2
Fall 2015
35. What is virtual pitch?
A)
B)
C)
D)
E)
Second harmonic
Missing fundamental
The lowest frequency in the spectrum
The highest frequency in the spectrum
None of the above
36. Suppose that in the lab you used the SpectraPlus signal generator to produce a tone from a
speaker with significant amplitudes at the following frequencies: 750, 1000, 1250, and 1500
Hz. If you were to listen to this tone, which of the following frequencies would you most
likely guess as the frequency corresponding to the pitch of the tone?
A) 1000 Hz
B) 750 Hz
C) 500 Hz
D) 250 Hz
E) 100 Hz
Solution:
All frequencies (750, 1000, 1250, and 1500 Hz) are multiples of 250 giving the virtual
fundamental 250Hz.
37. The beat frequency between tones with frequencies f1 and f2 is 5.0 Hz. In order to increase
the beat frequency, one must __.
A)
B)
C)
D)
E)
increase f1
increase f2
decrease f1
decrease f2
There is not enough information to choose
Solution:
f beats  f 2  f1 . We do not know f 2  f1 or f 2  f1 .
Page 5 of 7
Physics 198
Exam 2
Fall 2015
38. What are the two most consonant musical intervals?
A)
B)
C)
D)
E)
2:1 octave and 4:3 perfect fourth
2:1 octave and 3:2 perfect fifth
2:1 octave and 5:3 major six
3:2 perfect fifth and 4:3 perfect fourth
3:2 perfect fifth and 5:3 major six
39. What ratio has major third in equal temperament?

A) 21 / 12

4
 21 / 3  1.26
B) 5 : 4  1.25


3
C) 21 / 12  21 / 4  1.19
D) 6 : 5  1.2
E) 3:2=1.5
Solution:

For one semitone the ratio is 21 / 12 . For 4 semitones the ratio 21 / 12

4
 21 / 3  1.26
40. Suppose you strike a 440 Hz tuning fork. What frequency normal mode has the least
dampening? In another words, if you wait a long time which tone will you hear
predominantly (assuming original intensity was about the same)? (Recall Lab 5)
A) 220 Hz
B) 440 Hz
C) 660 HZ
D) 880 Hz
E) One with the much higher frequency (Remember, it was observed at about 2.7 kHz)
Solution:
The fundamental frequency has the least dampening.
Page 6 of 7
Physics 198
Exam 2
Fall 2015
Record Sheet
You may fill in this sheet with your choices, detach it and take it with you after the exam for
comparison with the posted answers
21
E) Both v and 
31
A) 1.0  10 5 watt / m 2
22
D) 302 Hz
32
A) 83dB
23
C) 20 Hz – 20 KHz
33
D) F1 F2  1.087
24
E) Positioned inside
cochlear
34
E) Pitch does not
changing with sound level
25
C) 3430 Hz
35
B) Missing fundamental
26
A) log( 2000)  3  log 2
36
D) 250 Hz
27
B) Addition (logarithmic
scale)
37
E) There is not enough
information to choose
28
B) Response is doubled
38
B) 2:1 octave and
3:2 perfect fifth
29
D) ¼
39
A)
2 
1 / 12 4
30
E) 83dB
 21 / 3  1.26
40
B) 440 Hz
Page 7 of 7