PHY138 Waves, Lecture 3 Todays overview

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PHY138 Waves, Lecture 3Todays overview

• The Wave Model
• Speed of Waves on a String
• Sinusoidal Waves
• Spherical Waves, Plane Waves

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Reading Assignment

• This weeks reading assignment from the text by
  Knight is Chapter 20, Sections 20.1-20.7
• There is also an article on Medical Ultrasound
  available on the web-page for Wednesdays Lecture
  (Waves Lecture 4).
• Suggested Chapter 20 Exercises and Problems for
  Practice 1, 25, 35, 39, 53, 69, 71, 79, 82 (79
  is funny!)

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Transverse versus Longitudinal
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Snapshot Graph
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History Graph
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• A string of beads are connected by a set of tiny
  springs. At the instant the clock starts (t0), a
  pulse is moving to the right on the beads and the
  snapshot graph looks like this

Which of the following history graphs tracks the
position for the bead marked with a red arrow as
a function of time?
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The graph at the top is the history graph at x
4 m of a wave traveling to the right at a speed
of 2 m/s. Which is the history graph of this wave
at x 0 m?
(A) (B) (C)
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Sinusoidal Waves
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What is the frequency of this traveling wave?
A. 10 Hz B. 5 Hz C. 2 Hz D. 0.2 Hz E. 0.1
Hz
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What is the phase difference between the maximum
of a wave and the adjacent minimum? (crest to
trough)
A. 0 B. p /4 C. p /2 D. 3 p /2 E.
p
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Sinusoidal Wave Snapshot Graph

• k 2p/? is the wave number

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Sinusoidal Wave History Graph

• ?2p/T is the angular frequency

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