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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.

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
v1t
v2t
sin 1 
and sin  2 
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
16
Both Together
17
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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