Waves Review - Answers #2 - The Physics Classroom

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Basics of Waves Review

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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.

Useful Web Links

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.

Useful Web Links

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.

Useful Web Links

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 20.0 seconds for exactly 40 vibrational cycles, then it must take 0.500 second for one cycle.

Useful Web Links

Frequency and Period of a Wave

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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.

Useful Web Links

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.

Useful Web Links

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.

Useful Web Links

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.

Useful Web Links

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.

Useful Web Links

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.

Useful Web Links

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.

Useful Web Links

Boundary Behavior

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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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