Announcements 3/4/11
Prayer

Slinky turn-in

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 send me a new proposal.

Exam 2 starts tomorrow, goes through next Sat
a. Covers through tonight’s HW.
b. Can bring handwritten 3x5 card (both sides). Just one!

Exam review session this afternoon, 3:30 - 5 pm, C261
a. Remember to come with questions: HW problems, worked
problems & concepts from class, demos, labs, Exam 1
problems/multiple choice questions, etc.

TA office hours today: 5:00 - 6:30 pm
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Reading Quiz

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

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

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

Book table
Index of Refraction
Different
wavelengths have
different speeds!
v = lf
linside = lvacuum/n
Different
frequencies have
different speeds!
Dispersion!

Song: Roy G. Biv
blue green
red
(l going into material)
Image:
http://en.wikipedia.org/wiki
/Dispersion_(optics)
Thought question

Which color of light travels fastest in glass?
a. Red
b. Green
c. Blue
d. Same
Absorption

“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

Light ray at boundary
fast light
(smaller n)
slow light
(larger n)
q1
q2
Snell’s Law

n1sinq1 = n2sinq2
fast light
(smaller n)
q1
slow light
(larger n)
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q2
Law of Reflection

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

If near perpendicular (1-D problem)
v2  v1 n1  n2
r

v1  v2 n1  n2
R r

2v2
2n1
t

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

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


Reflection/refraction using water-soluble oil
“Blackboard optics”