Physics 212 Lecture 24, Slide 1

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Physics 212 Lecture 24
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Music

• Who is the Artist?
• Oscar Peterson
• Kenny Barron
• Dave Brubeck
• Thelonius Monk
• Marcus Roberts

Why? I guess Im in a
classic mood.. Most unique piano player?? Check
out the Jazz Biography CD (couldnt find a
picture) great recordings from 40s and 50s
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Things you identified as difficult
how does the Force (like in Star Wars) work?
The stuff about polarization from reflection
and refraction was definitely most
confusing/needs to be covered more in lecture. I
ACTUALLY UNDERSTOOD A PRELECTURE FOR
ONCE!!!!!!!!! I AM SOOOOO HAPPY!!!!!
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More Physics Haiku
Exams, Homework, Labs Quizzes, Lectures, and
Preflights My brain is on fire
Begin the machine Double E's love of
circuits Life integrated
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The speed of light in a medium is slower than in
empty space
vmedium c / nmedium
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Light moving through a medium (say, glass)
Notice Dipoles oscillate perpendicular to the
motion of the light
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Reflection
Another way to see this Light is lazy it
chooses the quickest (shortest) path.
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Refraction
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Think of a day at the beach
What's the fastest path to the ball knowingyou
can run faster than you can swim?
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x1
A
l1
y1
y2
l2
B
x2
Time from A to B t l1/v1 l2/v2
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Refraction
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Refraction
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Intensity
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Total Internal Reflection
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Polarization
Recall dipole vibration is parallel to
polarization
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The frequency must remain constant at the
boundary because both the incident and the
refracted wave must be in phase. The speed
changes, and therefore the wavelength must also.
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A ball sits in the bottom of an otherwise empty
tub at the front of the room.Suppose N people
sit high enough to see the ball (N ).
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A ball sits in the bottom of an otherwise empty
tub at the front of the room.Suppose N people
sit high enough to see the ball (N
). Suppose I fill the tub with water but the
ball doesnt move. Will more or less people see
the ball? A) More people will see the ballB)
Less people will see the ball
??
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Example Refraction at water/air interface

• Divers illusion

Diver sees all of horizon refracted into a 97cone
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Follow Up 3
Consider light incident on two linear polarizers
as shown. Suppose I2 1/8 I0
y
x
60o
I0
I2 1/8 I0
z

• What is the possible polarization of the INPUT
  light?

(A) LCP
(B)
45o
(C) unpolarized
(D) all of above
(E) none of above
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Calculation
A laser beam with a uniform intensity across a
rectangular cross-section (2mm X 4mm) is directed
through a 45-45-90 prism as shown. What must
be the index of the prism if final dimensions of
the beam are 2mm X 2mm?
4mm
2 mm

• Conceptual Analysis
• Refracted light determined by Snells Law
  n1sinq1 n2sinq2
• Strategic Analysis
• GEOMETRY GEOMETRY GEOMETRY
• Use geometric constraints to determine n

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Calculation
A laser beam with a uniform intensity across a
rectangular cross-section (2mm X 4mm) is directed
through a 45-45-90 prism as shown. What must
be the index of the prism if final dimensions of
the beam are 2mm X 2mm?
Interface 2
4mm
2 mm

• Angle of incidence defined relative to normal at
  interface

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Calculation
A laser beam with a uniform intensity across a
rectangular cross-section (2mm X 4mm) is directed
through a 45-45-90 prism as shown. What must
be the index n of the prism if final dimensions
of the beam are 2mm X 2mm?
a
4mm
2 mm
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Calculation
A laser beam with a uniform intensity across a
rectangular cross-section (2mm X 4mm) is directed
through a 45-45-90 prism as shown. What must
be the index n of the prism if final dimensions
of the beam are 2mm X 2mm?
a
b
4mm
2 mm

• We need to use geometry to find sina (then we
  can determine n)

• Find L, the hypotenuse of the triangle (red
  line)

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Calculation
A laser beam with a uniform intensity across a
rectangular cross-section (2mm X 4mm) is directed
through a 45-45-90 prism as shown. What must
be the index n of the prism if final dimensions
of the beam are 2mm X 2mm?
a
b
4mm
2 mm
We can find a from b
Find side x of triangle (yellow line)
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Calculation
A laser beam with a uniform intensity across a
rectangular cross-section (2mm X 4mm) is directed
through a 45-45-90 prism as shown. What must
be the index n of the prism if final dimensions
of the beam are 2mm X 2mm?
a
b
4mm
2 mm