# Behavior of Waves Review

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14. If the distance from point A to point B in the diagram below 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.

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.

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 2.0 Hz and the wave speed is 5.0 m/s then the distance between adjacent wave crests is ___ meter.

 a. 0.20 b. 0.40 c. 1.25 d. 2.5 e. 10

 Answer: D Let w=wavelength; then v = w*f. In this problem, it is given that v=5 m/s and f = 2.0 Hz. Substitution and algebra yields w=v/f=2.5 m.

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 Hz b. 20 Hz c. 0.008 Hz d. 0.50 Hz

 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.

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.

The Speed of a Wave

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19. A pendulum makes 40 vibrations in 20 s. Its period is ____. (Be cautious of the units.)

 a. 0.50 Hz. b. 0.50 s. c. 2.0 Hz. d. 2.0 s. e. 8.0 x 102 Hz.

 Answer: B The period is the time for one complete cycle. If the pendulum takes 20 seconds for 40 vibrational cycles, then it must take 0.5 second for one cycle.

Frequency and Period of a Wave

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20. A period of 0.0050 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.

Frequency and Period of a Wave

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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.

 a. True b. False

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

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

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.

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.

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 rope 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.

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.

Boundary Behavior

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