PHY138 – Waves, Lecture 3
Today’s overview
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The Wave Model
Speed of Waves on a String
Sinusoidal Waves
Spherical Waves, Plane Waves
Reading Assignment
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This week’s reading assignment from the
text by Knight is: Chapter 20, Sections 20.120.7
There is also an article on Medical
Ultrasound available on the web-page for
Wednesday’s Lecture (Waves Lecture 4).
Suggested Chapter 20 Exercises and
Problems for Practice: 1, 25, 35, 39, 53, 69,
71, 79, 82 (79 is funny!)
Last time: 14.8 Externally Driven
Oscillations
Resonance!
Transverse versus Longitudinal
Snapshot Graph
History Graph
A string of beads are connected by a set of tiny springs. At
the instant the clock starts (t=0), 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?
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)
Sinusoidal Waves
Quiz 2
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
Quiz 3
What is the phase difference between
the maximum of a wave and the
adjacent minimum? (crest to trough)
A.
0
B. π /4
C. π /2
D. 3 π /2
E.
π
Sinusoidal Wave Snapshot Graph
k = 2π/λ is the wave number
Sinusoidal Wave History Graph
ω=2π/T is the angular frequency