Test 1



Final Exam

Thursday, December 22, 8:30-10:30, Sci2190

Answer all multiple choice questions by choosing the most appropriate answer. There is no partial credit, and only one answer per questions will count (your first one). Please indicate your answer as a letter in the space provided beside the number of the question.

Equations and references:

Units:

1 m = 100 cm = 1000 mm = 3.28 ft

1 km = 1000 m 1 mi = 1609 m = 1.609 km = 5280 ft

1 yr = 365 d 1 d = 24 h 1 h = 60 min = 3600 s 1 min = 60 s

1 kg = 1000 g 1 atm = 105Pa 1 Hz = 1 1/s = 1 s-1

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Intensity level [pic] Interference [pic]

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Intensity of point source [pic] [pic]

Standing waves on string: Standing waves in open pipe in closed pipe:

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Source moving toward observer [pic]

Source moving away from observer [pic]

Harmonic series: [pic]

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|Middle C Every Good Boy Deserves Fudge F A C E |

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Good Boys Deserve Fudge Always Middle C All Cows Eat Grass

A4 = 440 Hz

|C |

|1 |

|1 |[pic] |[pic] |

| |1.0535 |1.125 |

|d) |e) | |

1. You direct the marching band at the University of Southern North Dakota. During the last game of the season, the temperature in the stadium is -10(C (14(F). How long does it take the music to travel from the band to a spectator sitting 65 m away?

a) 0.20 s

b) 0.19 s

c) 0.18 s

d) 5.01 s

e) 2.6 s

2. The air pressure indicated by the zero line in a graph of a sound wave indicates

a) Zero.

b) Always 1.000 atm.

c) The equilibrium pressure.

d) The final pressure.

e) Close to the maximum pressure.

3. You are watching water waves pass a tide gauge fastened to the end of a pier. At their highest the crests reach a mark labeled 3.8 m, and at the low point of the troughs you can just see the 3.2 m mark. What is the amplitude of the waves?

a) 60 cm

b) 3.2 m

c) 3.8 m

d) 7.0 m

e) 0.3 m

4. A harmonic oscillator experiences zero acceleration while…

a) … at the turning points.

b) … passing the equilibrium position.

c) … moving toward the equilibrium.

d) … moving away from equilibrium.

e) …Never. The acceleration is never zero.

5. The frequency of a pendulum, which fulfills 15 complete oscillations in 20 s is

a) 0.75 Hz

b) 0.05 Hz

c) 1.33 s

d) 15 Hz

e) 20 s

6. A spring with a mass at the bottom is connected to a little wheel, which moves the end of the spring up and down with a variable frequency f. If f is set to a certain value, the mass at the bottom starts to move with increasing amplitude. This is an example of

a) Lack of damping

b) Chladni figure

c) Simple harmonic motion

d) Resonance

e) Interference

7. Which of the following pictures of a vibrating string shows the fifth harmonic?

|a[pic] |b[pic] |c[pic] |d[pic] |e[pic] |

8. For the sound of a certain guitar string, every second harmonic is absent from the spectrum. Where was the string plucked?

a) Close to the end

b) In the center

c) At one third of its length

d) At one quarter of is length

e) Impossible to tell

9. A guitar string with a length of 1.20 m and a mass per length of 0.5 g/m is fixed at both ends under a tension force of 300 N. Calculate the fundamental frequency for this string.

a) 323 Hz

b) 11.2 Hz

c) 626 Hz

d) 10.2 Hz

e) 180 Hz

10. The speed of sound in air depends on the:

a) Wavelength

b) Frequency

c) temperature

d) amplitude

e) all of the above

f) two of the above

11. The number of overtones/harmonics present in a sound gives the:

a) quality of the sound

b) amplitude of the sound

c) threshold of pain of the sound

d) the pitch of the sound.

e) it is not possible to have more than one harmonic in a sound

12. If the length of the air-filled pipe in the figure is 3 m, find the frequency for the harmonic shown:

a) 57 Hz

b) 200 Hz

c) 172 Hz

d) 86 Hz

e) 27 Hz

13. You are standing at one end of a long boat pier. There is an explosion at the other end of the pier. You hear three distinct sound waves from this explosion, arising from sound traveling through the water, through the air and through a steel rail along the pier. In which order did they arrive?

a) Air, water, steel

b) Air, steel, water

c) Steel, air, water

d) Steel, water, air

e) Water, steel, air

f) Water, air, steel

14. A wave of amplitude A interferes with another wave of the same kind whose frequency is different but whose amplitude is also A. The resulting wave

a) has an amplitude 2A

b) varies in amplitude between 0 and A

c) varies in amplitude between 0 and 2A

d) varies in amplitude between A and 2A

e) none of the above is correct

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

a) 11 cm

b) 39 cm

c) 117 cm

d) 156 cm

16. Two guitar strings are plucked simultaneously and twelve beats are heard in four seconds. One string is vibrating at 370 Hz, and the other is vibrating at

a) 373 Hz

b) 358 Hz

c) 366 Hz

d) 370.3 Hz

e) 382 Hz

17. How far away from a 200-W source will the intensity level reach 1 W/m2?

a) 0.36 m

b) 15.8 m

c) 4.89 m

d) 0.13 m

e) 3.99 m

18. One person talking on a cell phone produces an intensity level of 40 dB. What intensity level is produced by 10 people on cell phones?

a) 30 dB

b) 10 dB

c) 50 dB

d) 41 dB

e) 400 dB

19. A sound wave travels from air into water at normal incidence. What will change due to the increase in speed?

a) The wavelength and frequency will increase.

b) The frequency will increase.

c) The wavelength will increase.

d) Wavelength and frequency will stay the same.

e) Nothing will change.

20. We can understand a person who is not talking directly at us, even outside on a field. This is an example of

a) Reflection

b) Refraction

c) Diffraction

d) Resonance

e) Beats

21. In clear nights, you can hear the train from a greater distance than during the day. This often is an effect of

a) Reflection

b) Diffraction

c) Resonance

d) Beats

e) Refraction

22. The pizza is ready, and you call everybody for dinner. You can be heard in every room of the house. This works due to

a) Reflection

b) Refraction

c) Diffraction

d) Resonance

e) Beats

23. What frequency corresponds to each D5# in the even-tempered scale?

a) 330 Hz

b) 294 Hz

c) 698 Hz

d) 659 Hz

e) 622 Hz

24. If A5 is the third harmonic in a harmonic series, what is the fundamental?

a) D5

b) D4

c) D4#

d) A4

e) E4

25. Find the true statement

a) If the temperature in a room with a piano changes, all strings change their length at the same rate, so the frequencies change also at the same rate. The piano will stay in tune.

b) Human ears distinguish phase differences very well, but can not identify differences in the harmonics of a sound.

c) If the intensity drops to one tenth of its original value, the intensity level is lower by 10 dB.

d) Every waveform can be composed of a series of sine waves which are members of a harmonic series.

e) If you double the distance from a sound source, the intensity level drops to one fourth of its original value.

26. Which one of the following parts of the human ear contains critical bands that are important for the recognition of pure tones?

a) basiliar membrane

b) cochlea

c) ear drum

d) ossicles

e) scala timpani

27. The gap between the vocal cords is called

a) glottis

b) epiglottis

c) pharynx

d) larynx

e) trachea

28. How many semitones are contained in an octave?

a) 16

b) 12

c) 10

d) 8

e) 5

29. Which of the following shows the spectrum of a closed pipe?

|a) |b) |

|[pic] |[pic] |

|c) |d) |

|[pic] |[pic] |

30. The wave length of the second overtone of a string is

a) twice the fundamental wave length

b) half of the fundamental wave length

c) equal to the fundamental wave length

d) three times the fundamental wave length

e) 3/2 of the fundamental wave length

31. A sound wave is transporting…

a) …frequency

b) …energy

c) …air

d) …up and down motion

e) …all of the above

32. Which of the following processes changes the direction of a sound wave abruptly with no change in speed?

a) reflection

b) interference

c) refraction

d) diffraction

e) all of them

33. A motorcycle with a loud high-pitched engine is approaching you from the right at constant speed and passing your position. The sound from the engine is best described by:

a) a low-pitched noise changing to a high-pitch after passing

b) a constant high pitch

c) a high-pitched noise, decreasing in frequency, and then increasing again

d) a high-pitched noise, changing to a low-pitched noise after passing

e) a low-pitched noise, becoming higher, and then lower again

34. Which of the following is a physically correct and complete description of a harmonic series?

a) A harmonic series is a sequence of notes, following the recipe of octave, perfect fifth, perfect fourth, major third…

b) A harmonic series constitutes the sequence of the chromatic semitones contained in an octave.

c) A harmonic series is the overtone series of a particular instrument.

d) A harmonic series is the sequence of harmonics of a particular string.

e) A harmonic series is a sequence of simple oscillations with frequencies that are integral multiples of a fundamental frequency, as in f, 2f, 3f, 4f, …

35. Shown below are cross-sections through an auditorium, constructed for lectures. Considering our criteria of short reverberation time, no echo effect, homogeneity for different positions in the audience etc, which of them might exhibit the best acoustic qualities for the purpose?

|a) |b) |c) |

|[pic] |[pic] |[pic] |

|d) |e) | |

|[pic] |[pic] | |

I wish you happy holidays, and thank you for all your hard work during the last semester.

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