1. PHY138 – Waves, Lecture 3 Today’s overview
The Wave Model
Speed of Waves on a String
Sinusoidal Waves
Spherical Waves, Plane Waves

2. Reading Assignment
This week’s reading assignment from the text by Knight is: Chapter 20, Sections
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!)

3. Transverse versus Longitudinal

4. Snapshot Graph

5. History Graph

6. A string of beads are connected by a set of tiny springs
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?

7. 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?
STT20.1
(A) (B) (C)

8. Sinusoidal Waves

9. What is the frequency of this traveling wave?
A. 10 Hz
B. 5 Hz
C. 2 Hz
D Hz
E Hz
STT20.3

10. What is the phase difference between the maximum of a wave and the adjacent minimum? (crest to trough) A
B. π /4
C. π /2
D. 3 π /2
E. π
STT20.4

11. Sinusoidal Wave Snapshot Graph
k = 2π/λ is the wave number

12. Sinusoidal Wave History Graph
ω=2π/T is the angular frequency