Announcements 10/26/11
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Prayer
Slinkies: Please turn-in, and cross your name off of the sign
out list.
Exam 2 starts tomorrow, goes through Tuesday evening
a. Covers through tonight’s HW (HW 24)
b. Like last time, no notes allowed, but I give you
equations
Comment from Chris: when turning in multiple
assignments, staple them separately.
Found a white sweater after review session last night.
Overboard
Reading Quiz
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Which of the following scientists did not attempt to make
a measurement of the speed of light?
a. Einstein
b. Fizeau
c. Galileo
d. Roemer
e. Michelson (OK, this is not the answer, but I felt his
name should be included on the list even though he
wasn’t mentioned in today’s reading, because he
performed the “canonical experiment”)
How did they all attempt to measure it?
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xkcd
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The wave nature of light
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What is “waving”?
http://stokes.byu.edu/emwave_flash.html
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Medium?
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Polarization: quick definition
Reading Quiz
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A beam of light passes through a hole of
diameter d in a metal plate. Under what
condition are we allowed to ignore the
diffraction or “spreading” of the light? (This
is called the ray approximation.)
a. When λ << d
b. When λ ≈ d
c. When λ >> d
lambda = d/10
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Next three slides: image credit to Dr. Durfee
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lambda = d/4
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lambda = d
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Index of Refraction
v = c/n
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Book table
Index of Refraction
Different
wavelengths have
different speeds!
v = lf
linside = lvacuum/n
Different wavelengths (k values)
have different
speeds!
Dispersion!
blue green
Song: Roy G. Biv (start at 0:30)
http://www.youtube.com/watch?v=Gf33ueRXMzQ
red
(l going into material)
Image:
http://en.wikipedia.org/wiki
/Dispersion_(optics)
Thought question
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Which color of light travels fastest in glass?
a. Red
b. Green
c. Blue
d. Same
Absorption
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“Lorentz oscillator model”
“anomalous” index of refraction
index of
refraction
absorption
increasing
frequency
From Peatross & Ware,
textbook for Phys 471
(decreasing l)
Why is blue light slower through glass than red light?
 It’s closer to an absorption region
Index of Refraction
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Light ray at boundary
fast light
(smaller n)
slow light
(larger n)
q1
q2
Snell’s Law
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n1sinq1 = n2sinq2
fast light
(smaller n)
q1
slow light
(larger n)
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q2
Law of Reflection
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qrefl. = q1
Reflections occur
off of any boundary,
not just “mirrors”
fast light
(smaller n)
q1 qrefl.
slow light
(larger n)
q2
When will you have no reflection?
Fresnel Coefficients / Fresnel Equations
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If near perpendicular (1-D problem)
v2  v1 n1  n2
r
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v1  v2 n1  n2
R r
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2v2
2n1
t
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v1  v2 n1  n2
2
T  1 r
2
Look familiar??
For arbitrary angle (these eqns not needed for HW/exam)
n1 cosq1  n2 cosq2
rs polar . 
n1 cosq1  n2 cosq2
2n1 cosq1
ts polar . 
n1 cosq1  n2 cosq2
n1 cosq2  n2 cosq1
rp polar. 
n1 cosq2  n2 cosq1
2n1 cosq1
t p polar. 
n1 cosq2  n2 cosq1
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Thought question
top
bottom
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I send white light into a prism as shown below
(n>1). Will the red part of the “rainbow” be on
the top or the bottom of the outgoing fan of
light?
a. top
b. bottom
Demos
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Reflection/refraction using water-soluble oil
“Blackboard optics”