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```Almost There!
Turn in Unit 16 for Grading

Exam-3


Lab reports


Told you about these last time
Assorted small stuff


Working very hard on this but am being careful. I
stopped to put this presentation together but I might
get it done. Or not. Will be reviewed when returned.
All papers will be returned either Monday or at the
final exam. All grades will have been updated.
Clicker Grades

Some time this week via posted file with messed up
PIDs.
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
1
2
3
4
Complete
Induction
5
6
AC
7
8
AC
Quiz?
9
10
11
COMPLE
TE
AC EXPT
12
13 OPTICS
14
15 OPTICS
16
17
18
EXAM #3
(No
Optics)
19
24
25 (LAST LASS) 26
OPTICS
POST TEST
EM Waves
POLARIZATI
ON
Quiz
20 OPTICS
21
22 OPTICS
23
27
28
29
30 FINAL
HPA 119
9:00 AM
4




Light travel’s at a speed c in a vacuum.
In an actual material, it travels a bit slower, at a
velocity of v.
The speed of light depends on the material
through which it is traveling.
DEFINITION – INDEX OF REFRACTION (or
refractive index):
velocityof light in a vacuum
n
1
velocityof light in a transparant medium
6
7
8
Notice
c
v
v  f
n
n
For two
materials
c
c 1 vacuum


f f 

vacuum
n1 
1
vacuum
n2 
2
divide
n1 2

n2 1
9
Huygen’s
Principle
Each point on a wavefront acts
as a secondary source of spherical
waves that progress from the
source at the speed of light (whatever
it may be).
A spherical wave with very large radius,
behaves as a plane wave.
10
Far, far away
11
.
Not there yet!
PHY102
12
The Wave Nature of Light
 The law of refraction is explained by Huygen’s Principle
The little wavelets move slower in
medium 2 than in medium 1. Doing the
tangent shows how the wave fronts bend.
13
Some Geometry



    900
    900

 
14
The Wave Nature of Light
sin 1 v1 c / n1 n2



sin  2 v2 c / n2 n1
n1 sin 1  n2 sin  2
2 v2t v2 c / n2 n1




1 v1t v1 c / n1 n2
ADC   2
BAD  1
v1t
v2t
sin 1 
and sin  2 
AD
AD
If medium 1 is air, then
n1 1 and v1  c and 1  
 n   /n
15
Snell’s Law of Refraction
n1 sin 1  n2 sin  2
Law of Reflection
1   2
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Both Together
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18
nb  na
na Sin critical  nb sin(900 )  nb
nb
Sin critical 
na
At the critical angle and
beyond, only reflection is
possible.
19
Total Reflection – Optical Fiber
20
Waves on a string.
21
dichroism
80%
1% of opposite polarization
22
23
Let’s do some problems if we
have sufficient time….
• No, this is NOT a test!
• Follow the instructions on first
page.
• Do the other problems at home.
```
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