Light. EM Waves have many uses EM Waves have different frequencies.
Part II Electromagnetic Waves 1. So far 2 We have discussed The nature of EM waves Some of the...
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Transcript of Part II Electromagnetic Waves 1. So far 2 We have discussed The nature of EM waves Some of the...
Part II
Electromagnetic Waves
1
So far
2
We have discussedThe nature of EM wavesSome of the properties of EM waves.
Now we will discussEM waves and optics
MirrorsLensesApplications
3
Reflection & Refraction
4
Reflection
5
Light Reflection
6
Angles of incidence measured from the NORMAL to the mirror.
For reflection – The angle of incidence equals the angle of reflection.
surface normal
sameangleincident ray exit ray
Principle of Least Time
7
A
Btoo longshortest path;equal angles
8 PHY102
Your eye focuses the diverging rays reflected by the mirror.
The light rays appear to come from behind the mirror.
An image is virtual if the light rays from a point on the object are directed as if they diverged from a point on the image, even though the rays do not actually pass through the image point.
Mirror, Mirror, on the wall, how big do you have to be to see it all? The strange world of images.
9
“image” you
“real” you
The speed of light
10
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):1
mediumnt transparaain light ofvelocity
vacuumain light ofvelocity n
Index of Refraction
11
Notice
12
vacuum
f
c
f
cn
fvv
cn
1
For two materials
1
2
2
1
22
11
n
n
divide
n
n
vacuum
vacuum
Huygen’s Principle
13
Each point on a wavefront actsas a secondary source of sphericalwaves that progress from thesource at the speed of light (whateverit may be).
A spherical wave with very large radius,behaves as a plane wave.
14
15 PHY102
.
Not there yet!
16
The Wave Nature of LightThe 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.
Some Geometry
17
0
0
90
90
18
The Wave Nature of Light
ADC2
BAD1
sin1 v1tAD
and sin 2 v2tAD
2
1
1
2
1
2
1
2
1
2
2211
1
2
2
1
2
1
2
1
/
/
sinsin
/
/
sin
sin
n
n
nc
nc
v
v
tv
tv
nn
n
n
nc
nc
v
v
If medium 1 is air, then
n1 1 and v1 c and 1 n /n
Snell’s Law of Refraction
19
2211 sinsin nn Law of Reflection
21
Another ViewOf Reflection(Huygen’s)
20
Both Together
21
22
23
a
bcritical
bbcriticala
ab
n
nSin
nnSinn
nn
)90sin( 0
At the critical angle andbeyond, only reflection is
possible.
Total Reflection – Optical Fiber
24
25
A cross section of a submarine communications cable.1 - Polyethylene2 - Mylar tape3 - Stranded steel wires4 - Aluminium water barrier5 - Polycarbonate6 - Copper or aluminum tube7 - Petroleum jelly8 - Optical fibers
Lengths of 100 KM are possible before amplification is necessary.
Thousands of conversations can be carried on a single fiber.
26
Waves on a string.
dichroism
27
80%
1% of opposite polarization
28
29
30
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Mirage
32
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