# Sound and Music Review

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### Part B: Multiple Choice

10. What type of wave is produced when the particles of the medium are vibrating to and fro in the same direction of wave propagation?

 a. longitudinal wave. b. sound wave. c. standing wave. d. transverse wave.

 Answer: A This is the definition of a longitudinal wave. A longitudinal wave is a wave in which particles of the medium vibrate to and fro in a direction parallel to the direction of energy transport.

Categories of Waves

11. When the particles of a medium are vibrating at right angles to the direction of energy transport, the type of wave is described as a _____ wave.

 a. longitudinal b. sound c. standing d. transverse

 Answer: D This is the definition of a transverse wave. A transverse wave is a wave in which particles of the medium vibrate to and fro in a direction perpendicular to the direction of energy transport.

Categories of Waves

12. A transverse wave is traveling through a medium. See diagram below. The particles of the medium are moving.

 a. parallel to the line joining AD. b. along the line joining CI. c. perpendicular to the line joining AD. d. at various angles to the line CI. e. along the curve CAEJGBI.

 Answer: A In transverse waves, particles of the medium vibrate to and fro in a direction perpendicular to the direction of energy transport. In this case, that would be parallel to the line AD.

Categories of Waves

13. If the energy in a longitudinal wave travels from south to north, the particles of the medium ____.

 a. move from north to south, only. b. vibrate both north and south. c. move from east to west, only. d. vibrate both east and west.
 Answer: B In longitudinal waves, particles of the medium vibrate to and from in a direction parallel to the direction of energy transport. If the particles only moved north and not back south, then the particles would be permanently displaced from their rest position; this is not wavelike.

Categories of Waves

14. The main factor which effects the speed of a sound wave is the ____.

 a. amplitude of the sound wave b. intensity of the sound wave c. loudness of the sound wave d. properties of the medium e. pitch of the sound wave

 Answer: D The speed of a wave is dependent upon the properties of the medium and not the properties of the wave.

The Speed of a Wave

15.  As a wave travels into a medium in which its speed increases, its wavelength ____.

 a. decreases b. increases c. remains the same
 Answer: B As a wave crosses a boundary into a new medium, its speed and wavelength change while its frequency remains the same. If the speed increases, then the wavelength must increase as well in order to maintain the same frequency.

The Wave Equation

16. As a wave passes across a boundary into a new medium, which characteristic of the wave would NOT change?

 a. speed b. frequency c. wavelength

 Answer: B As a wave crosses a boundary into a new medium, its speed and wavelength change while its frequency remains the same. This is true of all waves as they pass from one medium to another medium.

The Speed of a Wave

17. The ____ is defined as the number of cycles of a periodic wave occurring per unit time.

 a. wavelength b. period c. amplitude d. frequency
 Answer: D This is a basic definition which you should know and be able to apply.

Frequency and Period of a Wave

18. Many wave properties are dependent upon other wave properties. Yet, one wave property is independent of all other wave properties. Which one of the following properties of a wave is independent of all the others?

 a. wavelength b. frequency c. period d. velocity
 Answer: D The speed (or velocity) of a wave is dependent upon the properties of the medium through which it moves, not upon the properties of the wave itself.

The Speed of a Wave

19. Consider the motion of waves in a wire. Waves will travel fastest in a ____ wire.

 a. tight and heavy b. tight and light c. loose and heavy d. loose and light
 Answer: B The speed of a wave in a wire is given by the equation v = SQRT (Ftens/mu) where Ftens is the tension of the wire and a measure of how tight it is pulled and mu is the linear density of the wire and a measure of how light it is on a per meter basis. Tighter wires allow for faster speeds. Light wires allow for faster speeds.

Frequency and Period of a Wave

20. TRUE or FALSE:

The SI unit for frequency is hertz.

 a. True b. False
 Answer: A Know this like the back of your hand (assuming you know the back of your hand well).

Frequency and Period of a Wave

21. TRUE or FALSE:

Doubling the frequency of a sound source doubles the speed of the sound waves which it produces.

 a. True b. False
 Answer: B Don't be fooled. Wave speed may equal frequency*wavelength. Yet doubling the frequency only halves the wavelength; wave speed remains the same. To change the wave speed, the medium would have to be changed.

The Wave Equation

22. A sound wave has a wavelength of 3.0 m. The distance between the center of a compression and the center of the next adjacent refraction is ____.

 a. 0.75 m. b. 1.5 m. c. 3.0 m. d. 6.0 m. e. impossible to calculate without knowing frequency.
 Answer: B The wavelength of a wave is measured as the distance between any two corresponding points on adjacent wave. For a sound wave, that would be from compression to the next adjacent compression. If that distance is 3.0 meters, then the distance from compression to the next adjacent rarefaction is 1.5 m.

Sound is a Pressure Wave

23.  Which one of the following factors determines the pitch of a sound?

a. The amplitude of the sound wave

b. The distance of the sound wave from the source

c. The frequency of the sound wave

d. The phase of different parts of the sound wave

e. The speed of the sound wave

 Answer: C The pitch of a sound wave is related to the frequency of the sound wave.

Pitch and Frequency

24. A certain note is produced when a person blows air into an organ pipe. The manner in which one blows on a organ pipe (or any pipe) will effect the characteristics of the sound which is produced. If the person blows slightly harder, the most probable change will be that the sound wave will increase in ____.

 a. amplitude b. frequency c. pitch d. speed e. wavelength
 Answer: A If you put more energy into the wave - i.e., blow harder - then the amplitude of the waves will be greater. Energy and amplitude are related.

Intensity and the Decibel Scale

25. A vibrating object with a frequency of 200 Hz produces sound which travels through air at 360 m/s. The number of meters separating the adjacent compressions in the sound wave is ____.

 a. 0.900. b. 1.80. c. 3.60. d. 7.20. e. 200.
 Answer: B Let w=wavelength; then v = w*f. In this problem, it is given that v=360 m/s and f = 200 Hz. Substitution and algebra yields w = v/f = 1.8 m. The question asks for the wavelength - i.e., the distance between adjacent compressions.

The Anatomy of a Wave | The Wave Equation

26. Consider the diagram below of several circular waves created at various times and locations. The diagram illustrates ____.

 a. interference b. diffraction c. the Doppler effect. d. polarization
 Answer: C The Doppler effect or Doppler shift occurs when a source of waves is moving with respect to an observer. The observer observes a different frequency of waves than that emitted by the source. This is due to the fact that the waves are compressed together into less space in the direction in which the source is heading.

The Doppler Effect

27. In the diagram above, a person positioned at point A would perceive __________ frequency as the person positioned at point B.

 a. a higher b. a lower c. the same
 Answer: A The Doppler effect or Doppler shift occurs when a source of waves is moving with respect to an observer. The observer observes a different frequency of waves than that emitted by the source. If the source and observer are approaching, then the observed frequency is higher than the emitted frequency. If the source and observer are moving away from each other, the observer observes a lower frequency than the emitted frequency.

The Doppler Effect

28. A girl moves away from a source of sound at a constant speed. Compared to the frequency of the sound wave produced by the source, the frequency of the sound wave heard by the girl is ____.

 a. lower. b. higher. c. the same.
 Answer: A The Doppler effect or Doppler shift occurs when a source of waves is moving with respect to an observer. The observer observes a different frequency of waves than that emitted by the source. If the source and observer are moving away, then the observed frequency is lower than the emitted frequency.

The Doppler Effect and Shock Waves

29. An earth-based receiver is detecting electromagnetic waves from a source in outer space. If the frequency of the waves are observed to be increasing, then the distance between the source and the earth is probably ____.

 a. decreasing. b. increasing. c. remaining the same.
 Answer: A The Doppler effect or Doppler shift occurs when a source of waves is moving with respect to an observer. The observer observes a different frequency of waves than that emitted by the source. If the source and observer are approaching, then the observed frequency is higher than the emitted frequency. If the source and observer are approaching, then the distance between them is decreasing.

The Doppler Effect and Shock Waves

30. As two or more waves pass simultaneously through the same region, ____ can occur.

 a. refraction b. diffraction c. interference d. reflection
 Answer: C Interference is the meeting of two or more waves when passing along the same medium - a basic definition which you should know and be able to apply.

Interference of Waves

31. TRUE pr FALSE:

If two crests meet while passing through the same medium, then constructive interference occurs.

 a. True b. False
 Answer: A Yes! Or when a trough meets a trough or whenever two waves displaced in the same direction - both up or both down - meet.

Interference of Waves

32. A node is a point along a medium where there is always ____.

 a. a double crest b. a double trough c. constructive interference d. destructive interference e. a double rarefaction.
 Answer: D A node is a point along the medium of no displacement. The point is not displaced because destructive interference occurs at this point.

Nodes and Anti-nodes

33. TRUE or FALSE:

It is possible that one vibrating object can set another object into vibration if the natural frequencies of the two objects are the same.

 a. True b. False
 Answer: A Yes! This is known as resonance. Resonance occurs when a vibrating object forces another object into vibration at the same natural frequency. A basic definition of a commonly discussed phenomenon.

Resonance

34. An object is vibrating. Then periodic impulses of the same frequency as the natural frequency of the vibrating object impinge upon the vibrating object. The amplitude of vibration is observed to increase. This phenomenon is known as ____.

 a. beats b. fundamental c. interference d. overtone e. resonance
 Answer: E Resonance occurs when a vibrating object forces another object into vibration at the same natural frequency. A basic definition of a commonly discussed phenomenon.

Resonance

35. A Standing wave experiment is performed to determine the speed of waves in a rope. The standing wave pattern shown below is established in the rope. The rope makes 90 complete vibrational cycles in one minute. The speed of the waves is ____ m/s.

 a. 3 b. 6 c. 180 d. 360 e. 540
 Answer: B Ninety vibrations in 60 seconds means a frequency of 1.5 Hz. The diagram shows 1.5 waves in 6-meters of rope; thus, the wavelength is 4 meters. Now use the equation v=f*w to calculate the speed of the wave. Proper substitution yields 6.0 m/s.

The Wave Equation

36. Standing waves are produced in a wire by vibrating one end at a frequency of 100 Hz. The distance between the 2nd and the 5th nodes is 60 cm. The wavelength of the original traveling wave is ____ cm.

 a. 50. b. 40. c. 30. d. 20. e. 15.
 Answer: B The frequency is given as 100 Hz and the wavelength can be found from the other givens. The distance between adjacent nodes is one-half a wavelength; thus the 60-cm distance from 2nd to 5th node is 1.5 wavelengths. For this reason, the wavelength is 40 cm.

Mathematics of Standing Waves

37. Consider the standing wave pattern shown below. A wave generated at the left end of the medium undergoes reflection at the fixed end on the right side of the medium. The number of antinodes in the diagram is

 a. 3.0 b. 5.0 c. 6.0 d. 7.0 e. 12
 Answer: C An antinode is a point on the medium which oscillates from a large + to a large - displacement. Count the number of these points - there are 6 - but do not count them twice.

Nodes and Anti-nodes

38. The standing wave pattern in the diagram above is representative of the ____ harmonic.

 a. third b. fifth c. sixth d. seventh e. twelfth
 Answer: C If there are six antinodes in the standing wave pattern, then it is the sixth harmonic.

Harmonics and Patterns

39. The distance between successive nodes in any standing wave pattern is equivalent to ____ wavelengths.

 a. 1/4 b. 1/2 c. 3/4 d. 1 e. 2.
 Answer: B Draw a standing wave pattern or look at one which is already drawn; note that the nodes are positioned one-half of a wavelength apart. This is true for guitar strings and for both closed-end and open-end resonance tubes.

Nodes and Anti-nodes

40. A vibrating tuning fork is held above an air column, forcing the air into resonance. If the sound waves created by the tuning fork have a wavelength of W, then the length of the air column could NOT be ____.

 a. 1/4 W b. 2/4 W c. 3/4 W d. 5/4 W e. 7/4 W
 Answer: B Review your diagrams for the standing wave patterns in closed end air columns; note that resonance occurs when the length of the air column is 1/4, 3/4, 5/4, 7/4, ... of a wavelength. Because these possible resonant lengths are characterized by an odd-numbered numerator, it is said that closed-end air columns only produce odd harmonics.

Closed-End Air Columns

41. TRUE or FALSE:

A vibrating tuning fork is held above an air column, forcing the air into resonance. The length of the air column is adjusted to obtain various resonances. If the sound waves created by the tuning fork have a wavelength of W, the difference between the successive lengths of the air column at which resonance will occur is 1/2 W.

 a. True b. False
 Answer: A True! Observe the standing wave patterns and the length-wavelength relationships which we have discussed for both open- and closed-end tubes. In each case, resonance occurs at lengths of tubes which are separated by one-half wavelength; e.g., Closed: .25*w, .75*w, 1.25*w, 1.75*w... Open: .5*w, 1.0*w, 1.5*w, 2.0*w, ...

Open-End Air Columns | Closed-End Air Columns

42. TRUE or FALSE:

An organ pipe which is closed at one end will resonate if its length is equal to one-half of the wavelength of the sound in the pipe.

 a. True b. False
 Answer: B It will resonate if the length is equal to the one-fourth (or three-fourths, or five-fourths or ...) the wavelength of the sound wave.

Closed-End Air Columns

43. A 20-cm long pipe is covered at one end in order to create a closed-end air column. A vibrating tuning fork is held near its open end, forcing the air to vibrate in its first harmonic. The wavelength of the standing wave pattern is ____.

 a. 5 cm. b. 10 cm. c. 20 cm. d. 40 cm. e. 80 cm.
 Answer: E This is a closed-end air column. If you draw the standing wave pattern for the first harmonic, you will notice that the wavelength is four times the length of the air column. Thus take the length of 20 cm and multiply by 4.

Closed-End Air Columns

44. A stretched string vibrates with a fundamental frequency of 100 Hz. The frequency of the second harmonic is ____.

 a. 25 Hz b. 50 Hz c. 100 Hz d. 200 Hz e. 400 Hz
 Answer: D The frequency of the nth harmonic is n times the frequency of the first harmonic where n is an integer. Thus, f2 = 2*f1 = 2*100 Hz = 200 Hz.

Fundamental Frequency and Harmonics

45. A 40-cm long plastic tube is open at both ends and resonating in its first harmonic. The wavelength of the sound which will produce this resonance is ____.

 a. 10 cm. b. 20 cm. c. 40 cm. d. 80 cm. e. 160 cm.
 Answer: D For an open-end air column, the length of the column is 0.5*wavelength. This becomes evident after drawing the standing wave pattern for this harmonic. Then, plug in 40 cm for length and calculate the wavelength.

Open-End Air Columns

46. The diagrams below represent four different standing wave patterns in air columns of the same length. Which of the columns is/are vibrating at its/their fundamental frequency? Include all that apply.

 Answer: CD The fundamental frequency is the lowest possible frequency for that instrument, and thus the longest possible wavelength. For open tubes, there would be anti-nodes on each end and a node in the middle. For closed end tubes, there would be a node on the closed end, an anti-node on the open end, and nothing in the middle. Diagram C is the third harmonic for a closed end tube and diagram D is the second harmonic for an open-end tube.

Open-End Air Columns

47. The diagrams above (Question #46) represent four different standing wave patterns in air columns of equal length. Which of the columns will produce the note having the highest pitch?

 a. A b. B c. C d. D e. All column produce notes having the same pitch
 Answer: D Just look at the wave patterns and notice that the shortest wavelength is in diagram D and so it must have the highest frequency or pitch.

Open-End Air Columns

48. An air column closed at one end filled with air resonates with a 200 Hz tuning fork. The resonant length corresponding to the first harmonic is 42.5 cm. The speed of the sound must be ____.

 a. 85.0 m/s. b. 170 m/s. c. 340 m/s. d. 470 m/s. e. 940 m/s.
 Answer: C Draw the standing wave pattern for the first harmonic of a closed-end tube to assist with the length-wavelength relation. Then, L=0.425 m so w=1.7 m. Since f is given as 200 Hz, the speed can be calculated as f*w or 200 Hz*1.7 m. The speed of sound is 340 m/s.

Closed-End Air Columns

49. TRUE or FALSE:

A violinist plays a note whose fundamental frequency is 220 Hz. The third harmonic of that note is 800 Hz.

 a. True b. False

 Answer: B The frequency of the nth harmonic is n times the frequency of the first harmonic where n is an integer. Thus, f3 = 3*f1 = 3*220 Hz = 660 Hz.

Guitar Strings

50. In order for two sound waves to produce audible beats, it is essential that the two waves have ____.

 a. the same amplitude b. the same frequency c. the same number of overtones d. slightly different amplitudes e. slightly different frequencies
 Answer: E Beats occur whenever two sound sources emit sounds of slightly different frequencies. Perhaps you recall the demonstration in class with the two tuning forks of slightly different frequencies.

Interference and Beats

51. TRUE or FALSE:

Two tuning forks with frequencies of 256 Hz and 258 Hz are sounded at the same time; Beats are observed; 2 beats will be heard in 2 s.

 a. True b. False
 Answer: B Beats occur whenever two sound sources emit sounds of slightly different frequencies. The beat frequency is just the difference in frequency of the two sources. In this case, the beat frequency would be 2.0 Hz, which means that 2 beats would be heard every 1 second or 4 beats every 2 seconds.

Interference and Beats

52. A tuning fork of frequency 384 Hz is sounded at the same time as a guitar string. Beats are observed; 30 beats are heard in 10 s. The frequency of the string in hertz is ____.

 a. 38.4 b. 354 or 414 c. 369 or 399 d. 374 or 394 e. 381 or 387
 Answer: E Beats occur whenever two sound sources emit sounds of slightly different frequencies. The beat frequency is just the difference in frequency of the two sources. In this case, the beat frequency is given as 3.0 Hz, which means that the second source must have a frequency of either 3 Hz above or 3 Hz below the first source - either 381 Hz or 387 Hz.

Interference and Beats