Basics of Waves Review
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Answers to Questions: All || #1-#14 || #15-#26 || #27-#38
15. The number of cycles of a periodic wave occurring per unit time is defined as a wave's ____.
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a. wavelength.
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b. period.
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c. amplitude.
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d. frequency.
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Answer: D
This is a basic definition which you should know and be able to apply.
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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.
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a. 0.200
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b. 0.400
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c. 1.25
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d. 2.50
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e. 10.0
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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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17. What is the frequency of a wave that has a speed of 0.4 m/s and a wavelength of 0.020 meter?
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a. 10 hertz.
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b. 20 hertz.
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c. 0.008 hertz.
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d. 0.5 hertz.
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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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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?
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a. wavelength
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b. frequency
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c. period
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d. velocity
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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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19. A pendulum makes exactly 40 vibrations in 20.0 s. Its period is ____. (Be cautious of the units.)
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a. 0.500 Hz.
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b. 0.500 s.
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c. 2.00 Hz.
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d. 2.00 s.
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e. 8.00 x 102 Hz.
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Answer: B
The period is the time for one complete cycle. If the pendulum takes 20.0 seconds for exactly 40 vibrational cycles, then it must take 0.500 second for one cycle.
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20. A period of 0.005 seconds would be equivalent to a frequency of ____ Hz.
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a. 20
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b. 50
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c. 200
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d. 500
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e. 2000
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Answer: C
The period and the frequency are related by a reciprocal relationship; that is, f = 1/T.
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21. TRUE or FALSE:
The number of waves generated per second by a source is called the frequency of the source.
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Answer: A
This is a basic definition which you should know and be able to apply.
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22. TRUE or FALSE:
The SI unit for frequency is hertz.
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Answer: A
Know this like the back of your hand.
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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.
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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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24. If the frequency of a wave is doubled and if the speed remains constant, its wavelength is ____.
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a. quartered.
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b. halved.
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c. unchanged.
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d. doubled.
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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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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?
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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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26. When a pulse reaches a boundary between two different media, it will be____.
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a. reflected, only.
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b. transmitted, only.
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c. partly reflected and partly transmitted.
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d. neither reflected nor transmitted.
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Answer: C
This is basic information about the boundary behavior of waves.
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Navigate to:
Review Session Home - Topic Listing
Waves - Home || Printable Version || Questions with Links
Answers to Questions: All || #1-#14 || #15-#26 || #27-#38
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