iv. optics wavelength decreases frequency increases note: 1 nanometer = 10 -9 meter nature of...
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IV. Optics
Wavelength decreases
Frequency increases
Note: 1 nanometer = 10-9 meter
Nature of light. Spectrum of electromagnetic waves.
A. Geometric optics
2. Reflection
1. Wave front and rays
1 21 2
21
3. Refraction: Snell’s Law
2211 sinsin nn index of refraction:v
cn 1
221 ff 1
2
1
2
2
1
v
v
n
n
rays
wave fronts
Example:
12
23
n1 n2 n3
332211 sinsinsin nnn
1313 If nn
in out
normal to surface
diffuse reflection
23 fromt independen is n
Example:
?
50
33.1
00.1
2
1
2
1
n
n2211 sinsin nn
35
50sin33.1
00.1sinsin
2
12
12
n
n
?
45
52.1
00.1
4
1
32
41
nnn
nn
Example: Equilateral triangle
n=1.52
4433
32
2211
sinsin
60
sinsin
nn
nn
43
32
21
sinsin
60
sinsin
n
n
34
23
12
sinsin
60
sinsin
n
n
3.54
3.32
7.27
4
3
2
4. Total internal reflection
C
n
n
n
n
2
2
11
2
12
11
0
1sinsin0
1sin0900
1n 2
1
1
21
1
21
1
21
22
sin 0
1sinsin0
1sin0900
n
n
n
n
n
n
CC
21 nn 12 nn
2n
Example:
?
00.1
52.1
2
1
C
n
nn
1.41
52.1
11sin
1
2
C
C nn
n
2
1
Example: A ray of light is incident in air on a block of a transparent solid whose index of refraction is n. If n =1.38, what is the largest angle θ1 for which total internal reflection will occur at the vertical face (point A)?
n=1.38
21
32
3
sinsin
90
1sin
n
n
72
95.0138.1sin
11
1sin1cos
90sinsin
1
21
223
23
31
nn
nnn
n
2
1
3A
Example:
α
αα
n
nC
190sin
1sin
n=1.52
49
52.1
11cos
nC
1) Binoculars often use total internal reflection; this gives true 100% reflection, which even the best mirror cannot do.
4a. Applications of total internal reflection
2) Fiber optics. Light will be transmitted along the fiber even if it is not straight. An image can be formed using multiple small fibers.
5. Plane mirror
O I
dodi
O I
do di
Image:virtualerectthe same size
do = di
6. Comments about objects and images created by different optical instruments
(curved mirrors, lenses and their combinations)
This is for planemirrors
Image:real or virtual erect or invertedlager, smaller, or the same size as the object