Announcements 10/27/10
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Prayer
Slinky turn-in
Long list of HW changes/corrections/cancelations for the next month—
make sure you got this email!!
Term projects:
a. Make sure you got emailed feedback from me
b. Make sure you have a score for “Project 1”, via website grade
report
c. Can you change topics? Yes, but you need to send me a new
proposal.
Exam 2 starts tomorrow, goes through next Thursday
a. Covers through tonight’s HW.
b. Anyone need “what’s on exam” handout?
c. Can bring handwritten 3x5 card (both sides). Just one!
Exam review session tonight, 5:30 – 7 pm. Room: C295 (next door)
a. Remember to come with questions: HW problems, worked
problems & concepts from class, demos, labs, Exam 1
problems/multiple choice questions, etc.
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”)
The wave nature of light
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Speed of light…how did each of the people
on the preceding slide measure it?
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What is “waving”?
http://stokes.byu.edu/emwave_flash.html
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Medium?
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
frequencies have
different speeds!
Dispersion!
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Song: Roy G. Biv
blue green
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 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 via 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
ts polar . 
n1 cosq2  n2 cosq1
rp polar. 
n1 cosq2  n2 cosq1
2n1 cosq1
t p polar. 
n1 cosq2  n2 cosq1
2n1 cosq1
n1 cosq1  n2 cosq2
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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”