Basics of Waves Review

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Questions #1-#14
Questions #15-#26
Questions #27-#38

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1. A single disturbance that moves from point to point through a medium is called a ___.

a. period

b. periodic wave

c. wavelength

d. pulse


Answer: D

A wave is a continuous and repeating disturbance of a medium and a pulse is a single disturbance.



 

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What is a Wave?
 

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2. If the particles of the medium are vibrating to and fro in the same direction of energy transport, then the wave is a ____ wave.

a. longitudinal

b. sound

c. standing

d. transverse


Answer: A

In longitudinal waves, particles of the medium vibrate to and from in a direction parallel to the direction of energy transport. If energy is transmitted along a medium from the east end to the west end, then particles of the medium would vibrate eastward and westward

A sound wave is a longitudinal wave but not the answer since a wave which exhibits this characteristic is not necessarily a sound wave.



 

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Categories of Waves
 

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3. When the particles of a medium are vibrating at right angles to the direction of energy transport, then the wave is a ____ wave.

a. longitudinal

b. sound

c. standing

d. transverse


Answer: D

In transverse waves, particles of the medium vibrate to and from in a direction perpendicular to the direction of energy transport.



 

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Categories of Waves
 

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4. A transverse wave is traveling through a medium. See diagram below. The particles of the medium are vibrating _____.

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 from in a direction perpendicular to the direction of energy transport. In this case, that would be parallel to the line AD.


 

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Categories of Waves
 

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5. If the energy in a longitudinal wave travels from south to north, the particles of the medium would be vibrating _____.

a. from north to south, only

b. both north and south

c. from east to west, only

d. 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.



 

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Categories of Wave
 

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6. As a pulse travels though a uniform medium, the speed of the pulse ____.

a. decreases

b. increases

c. remains the same


 

Answer: C

The speed of a wave or a pulse depends upon the properties of the medium. If the medium is uniform or unchanging, then the speed is constant.


 

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The Speed of a Wave
 

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

a. amplitude of the sound wave

b. intensity of the sound

c. loudness of the sound

d. properties of the medium

e. pitch of the sound

 

Answer: D

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


 

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The Speed of a Wave
 

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

a. decrease

b. increase

c. remain 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.


 

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The Wave Equation
 

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9. 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.


 

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The Speed of a Wave
 

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10. What is the amplitude of the wave in the diagram below?

a. 0.03 m.

b. 0.04 m.

c. 0.05 m.

d. 0.06 m.


Answer: A

The amplitude of a wave is measured from rest to crest or from rest to trough; but not from crest to trough. Thus, take the 0.06 m measurement and "halve it" to get the answer.


 

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The Anatomy of a Wave
 

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11. The wavelength of the wave in the diagram above (Question #10) is ____ m.

a. 0.030

b. 0.040

c. 0.060

d. 0.080


Answer: D

The wavelength of a wave is measured as the distance between any two corresponding points on adjacent waves, which would mean from a crest to the next adjacent crest. Thus, the distance from point b to point d is the wavelength - 0.08 m



 

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The Anatomy of a Wave
 

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12. A wave X meters long passes through a medium with a speed of Y meters per second. The frequency of the wave could be expressed as

a. Y/X cycles/sec.

b. X/Y cycles/sec.

c. XY cycles/sec.

d. (X + Y) cycles/sec.


Answer: A

Let d = wavelength. Since d*f = v, f = v/d.


 

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The Wave Equation
 

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Consider the following diagram for Questions #13-#14.

13. How many complete waves are shown in the diagram?

a. 1

b. 2

c. 3

d. 1.5


Answer: D

From point A to point E is one full wave cycle. After point E, the wave begins to repeat itself, but only for one-half of a cycle. Thus, there are 1.5 waves shown in the diagram.

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14. If the distance from point A to point B in the diagram is 60 cm, then the wavelength is ____.

a. 20 cm.

b. 40 cm.

c. 60 cm.

d. 90 cm.


Answer: B

From point A to point E is one full wave cycle. This distance represents two-thirds of the 60 cm from A to G. Thus, the wavelength is (2/3)*60 cm = 40 cm.


 

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The Anatomy of a Wave
 

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15. The number of cycles of a periodic wave occurring per unit time is defined as a wave's ____.

a. wavelength.

b. period.

c. amplitude.

d. frequency.


Answer: D

This is a basic definition which you should know and be able to apply.


 

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Frequency and Period of a Wave
 

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16. A periodic and repeating disturbance in a lake creates waves which emanate outward from its source to produce circular wave patterns. If the frequency of the source is 2.00 Hz and the wave speed is 5.00m/s then the distance between adjacent wave crests is ___ meter.

a. 0.200

b. 0.400

c. 1.25

d. 2.50

e. 10.0


Answer: D

Let w=wavelength; then v = w*f. In this problem, it is given that v=5.00 m/s and f = 2.00 Hz. Substitution and algebra yields w = v / f = 2.50 m.


 

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The Anatomy of a Wave | The Wave Equation
 

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17. What is the frequency of a wave that has a speed of 0.4 m/s and a wavelength of 0.020 meter?

a. 10 hertz.

b. 20 hertz.

c. 0.008 hertz.

d. 0.5 hertz.


Answer: B

Let w=wavelength; then v = w*f. In this problem, it is given that v=5 m/s and w = .02 m. Substitution and algebra yields f=v/w=20 Hz.


 

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The Wave Equation
 

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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 of a wave is dependent upon the properties of the medium through which it moves, not upon the properties of the wave itself.


 

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The Speed of a Wave
 

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19. A pendulum makes exactly 40 vibrations in 20.0 s. Its period is ____. (Be cautious of the units.)

a. 0.500 Hz.

b. 0.500 s.

c. 2.00 Hz.

d. 2.00 s.

e. 8.00 x 102 Hz.


Answer: B

The period is the time for one complete cycle. If the pendulum takes 20 seconds for exactly 40 vibrational cycles, then it must take 0.500 second for one cycle.


 

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Frequency and Period of a Wave
 

 

20. A period of 0.005 seconds would be equivalent to a frequency of ____ Hz.

a. 20

b. 50

c. 200

d. 500

e. 2000


Answer: C

The period and the frequency are related by a reciprocal relationship; that is, f = 1/T.


 

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Frequency and Period of a Wave
 

 

21. TRUE or FALSE:

The number of waves generated per second by a source is called the frequency of the source.

a. True

 

b. False

 

Answer: A

This is a basic definition which you should know and be able to apply.


 

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Frequency and Period of a Wave
 

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22. TRUE or FALSE:

The SI unit for frequency is hertz.

a. True

 

b. False

 

Answer: A

Know this like the back of your hand.



 

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Frequency and Period of a Wave
 

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23. TRUE or FALSE:

Doubling the frequency of a wave source (without altering the medium) doubles the speed of the waves.

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.


 

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The Wave Equation
 

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24. If the frequency of a wave is doubled and if the speed remains constant, its wavelength is ____.

a. quartered.

b. halved.

c. unchanged.

d. doubled.


Answer: B

Wave speed equals frequency*wavelength. So doubling the frequency must halve the wavelength in order for wave speed to remain the same.

 

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The Wave Equation
 

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25. Two different ropes with different mass densities are attached to each other. A pulse is introduced into one end of the rop and approaches the boundary as shown at the right. At the boundary, a portion of the energy is transmitted into the new medium and a portion is reflected. Which one of the diagrams below depicts the possible location and orientation of the pulse shortly after the incident pulse reaches the boundary?


 

Answer: C

The speeds in the two media can be deduced by the distance of the pulses from the boundary. In A and E, the speed is shown as fastest on the right, which makes the transmitted medium the less dense. Rule out A and E since a reflected pulse should not invert when moving from more dense to less dens. Rule out B for just the opposite reasons; the wave is moving from less to more dense and should invert upon reflection. Rule out D because the transmitted pulse never inverts. That leaves C as the answer.


 

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Boundary Behavior
 

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26. When a pulse reaches a boundary between two different media, it will be____.

a. reflected, only.

b. transmitted, only.

c. partly reflected and partly transmitted.

d. neither reflected nor transmitted.


Answer: C

This is basic information about the boundary behavior of waves.


 

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Boundary Behavior
 

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27. Diagram P at the right shows a transverse pulse traveling along a dense rope toward its junction with a less dense rope. Which of the diagrams (A, B, C, D, or E) below depicts the ropes at the instant that the reflected pulse again passes through its original position marked X? Consider such features as amplitude and relative speed (i.e., the relative distance of the transmitted and reflected pulses from boundary).




Answer: E

A, B, and C can be quickly ruled out since it shows the amplitude of the reflected and incident pulse to be the same size. An incident pulse would give up some of its energy to the transmitted pulse at the boundary, thus making the amplitude of the reflected pulse less than that of the incident pulse. Rule out D since it shows the reflected pulse moving faster than the transmitted pulse. This would not happen unless moving from less dense to more dense. This leaves E as the answer.



 

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Boundary Behavior
 

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28. A wave whose speed in a snakey is 4.4 m/s enters a second snakey. The wavelength changes from 2.0 m to 3.0 m. The wave in the second snakey travels at approximately ____.

a. 1.5 m/s.

b. 2.2 m/s.

c. 2.9 m/s.

d. 4.4 m/s.

e. 6.6 m/s.


Answer: E

This is another boundary behavior question with a mathematical slant to it. The frequency of the incident and transmitted waves are always the same. Thus, use f =v/w to find the frequency of the incident wave - 2.2 Hz. The frequency of the transmitted wave is >also 2.2 Hz, the wavelength is 3.0 m, and so the speed is f*w = 6.6 m/s.


 

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Boundary Behavior
 

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29. The diagram at the right shows a disturbance moving through a rope towards the right. If this disturbance meets a similar disturbance moving to the left, then which one of the diagrams below depict a pattern which could NEVER appear in the rope?


Answer: D

WOW! Tough one. Draw a second wave to the right of the wave which is given. Then visually move the wave to the left. Visualize in your mind the shape of the resultant as interference occurs. It will never look like D. If you still don't get it, take a break and watch some TV.


 

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Boundary Behavior
 

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30. A 2.0-meter long rope is hanging vertically from the ceiling and attached to a vibrator. A single pulse is observed to travel to the end of the rope in 0.50 s. What frequency should be used by the vibrator to maintain three whole waves in the rope?

a. 0.75 Hz

b. 1.3 Hz

c. 4.0 Hz

d. 6.0 Hz

e. 8.0 Hz


Answer: D

The given info allows you to determine the speed of the wave: v=d/t=2 m/0.5 s) = 4 m/s. If there are 3 waves in a 2-meter long rope, then each wave is 2/3-meter long. Now find frequency with the equation v=f*w where v=4 m/s and w=0.667 m. Proper algebra yields 6 Hz as the answer.


 

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The Wave Equation
 

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31. 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 exactly 90 complete vibrational cycles in one minute. The speed of the waves is ____ m/s.


a. 3.0

b. 6.0

c. 180

d. 360

e. 540


Answer: B

If there are exactly 90 vibrations in 60.0 seconds, then there is a frequency of 1.5 Hz. The diagram shows 1.5 waves in 6.0-meters of rope; thus, the wavelength is 4.0 meters. Now use the equation v=f*w to calculate the speed of the wave. Proper substitution yields 6.0 m/s.


 

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The Wave Equation
 

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32. 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

b. 5

c. 6

d. 7

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.


 

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Nodes and Anti-nodes
 

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33. A node is a point located along the medium where there is always ___.

a. a double crest

b. 

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.


 

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Nodes and Anti-nodes

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34. TRUE or FALSE:

Constructive interference of waves occurs when two crests meet.

a. True

b. False

Answer: A

Yes! Or when a trough meets a trough or whenever two waves displaced in the same direction (such as both up or both down) meet.


 

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Interference of Waves
 

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35. Which phenomenon is produced when two or more waves passing simultaneously through the same medium meet up with one another?

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.


 

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Interference of Waves
 

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36. Two pulses are traveling in opposite directions along the same medium as shown in the diagram at the right. Which diagram below best depicts the appearance of the medium when each pulse meets in the middle?

 


Answer: D

When a crest is completely overlapped with a trough having the same amplitude, destructive interference occurs. Complete cancellation takes place if they have the same shape and are completely overlapped.


 

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Interference of Waves
 

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37. TRUE or FALSE:

A vibrating object is necessary for the production of sound.

a. True

b. False


Answer: A

Absolutely! If you don't believe it, then think of some sounds - voice, guitar, piano, tuning fork, chalkboard screech, etc. - and consider what the vibrational source is. All sounds have a vibrating object of some kind as their source.


 

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Sound is a Mechanical Wave
 

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38. Which one of the following CANNOT transmit sound?

a. Liquid air

b. Gaseous oxygen

c. Liquid water

d. Solid steel

e. Perfect vacuum

 

Answer: E

Sound is a mechanical wave and as such requires a medium in order to move through space. For this reason, sound cannot move through a vacuum.


 

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Sound is a Mechanical Wave
 

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