# Announcements 10/28/11 Prayer Exam 2 going on…

```Announcements 10/28/11
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Prayer
Exam 2 going on…
Speed
Bump
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What is a “wave front”?
a. The crest of the wave, repeated every l
b. The complex phase of a wave
c. The first part of the wave to reach an object
d. The reflection of a wave off of a surface
e. The students at the football game who start
“The Wave”
Law of reflection illustrated
Credit: next several slides from Dr. Durfee
Law of reflection illustrated
Law of reflection illustrated
Law of reflection illustrated
Law of reflection illustrated
Law of reflection illustrated
Snell’s Law illustrated
Snell’s Law illustrated
Snell’s Law illustrated
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What do we call the phenomena which
makes fiber optics possible?
a. Brewster’s Law
b. Equivalence Theorem
c. Fermat’s Principle
d. Superluminal Energy Transport
e. Total Internal Reflection
Demo
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Stokes computer demo: (5:00)
http://stokes.byu.edu/refract_script_flash.html
Total Internal Reflection
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TIR: the equation
Demos
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Blackboard optics
TIR in water soluble oil
Laser captured in stream of water
Fiber Optics
Thought question
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If you have a -0.3 dB change, the final
intensity is what fraction of the initial
a. 78%
b. 83%
c. 88%
d. 93%
e. 98%
-0.3 dB  93.3%
-0.2 dB  95.5%
-0.1 dB  97.7%
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When we think of all the points on a wave
front as little sources of secondary waves in
order to calculate what the wave front will
look like after propagating some distance, we
are using the idea known as...
a. the Equivalence theorem
b. Huygen’s Principle
c. Fermat’s Principle
d. Newton’s first law of optics
e. the Wavelet theorem
Huygen’s Principle
Image credit: Wikipedia
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Each wavefront serves as source of spherical waves
HW 26-5 (extra credit):
a. “Stare at the picture until you can visualize that the green lines
tangent to the circles connect matching wavefronts.”
b. Construct an accurate picture like this for a specific situation,
show graphically that it gives you Snell’s law
Huygen’s Principle, cont.
Image credit: Wikipedia
http://en.wikipedia.org/wiki/
Double-slit_experiment
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A wave hits the two slits
Each slit (infinitely narrow) becomes source of spherical
waves
The waves from those two sources interfere with each
other
Spherical Waves
Credit: the next few slides are from Dr. Durfee
Huygen’s Construction of a Spherical Wave
Huygen’s Construction of a Plane Wave
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