Transcript Polarization of Light

Polarization
of
Light
Presented by Beili Wang
SC 442 Honors class 2001, Dr. Roman Kezerashvili
Objective
Study the polarization of light
2. Study two phenomena of light:
1.
•
•
3.
Absorption
Reflection
Verify Brewster’s law and Malus’s law
Theory
1.
Two properties of light
a. The wave theory of light
The light is a transverse electromagnetic wave
with the vibrating electric and magnetic fields,
which are perpendicular to each other and to
the direction of propagation of light.
b. Polarization
Polarization is a property of transverse wave
related to the directions in which vibration
occur.
Part I. Polarization
(a)
y
(c)
x
y
y
z
(b)
x
z
z
x
(a) Transverse wave on the string polarized in the y-direction
(b) Transverse wave polarized in the z-direction.
(c) The vertical slit passes component polarized in the y-direction
and blocks those in the z-direction acting as a Polaroid.
Polarizer
Axis of Polarizer
Incident
unploarized light
Polarizer
Linearly
polarized light
The light
passes
through a
polarizer
that has the
effect of
polarization.
Analysis for Part I
When light is sent through the polarizers, electric field
components parallel to the polarizing direction is
transmitted; while components perpendicular to the
polarizing direction are absorbed by the polarizers and
disappear.
Crossed Arrow
Target holder
Light source
Holders with polarizer
and analyzer
180
0
Part II. Absorption
I  I 0 cos 
2
Malus’s law
Axis of Polarizer
Direction of axis
of Polarizer on
the left
Polarizer
θ
Analyzer
Axis of Analyzer
Data from Part II
Intensity of the light when both polarizer and analyzer
are removed:
i = 10 w/m^2
Intensity of the light when it passes just through the
polarizer:
i1 = 4 w/m^2
Intensity of the light when it passes through the polarizer
and analyzer:
i2 = 2.5 w/m^2
Ratio of intensities:
Ratio of intensities:
Ratio of intensities:
i1/i = 0.4
i2/i = 0.25
i1/i2 =1.6
Table 1 for Part II
Angle θ, (Cosθ)^2 Intensity of light
Intensity of light
Average
degrees
(clockwise)
(counterclockwise) intensity
0
1.00
10.0
10.0
10.0
10
0.96
9.8
9.6
9.7
20
0.88
9.0
8.6
8.8
30
0.75
7.6
7.2
7.4
40
0.59
6.0
5.6
5.8
50
0.41
4.3
4.0
4.2
60
0.25
2.5
2.3
2.4
70
0.12
1.2
1.0
1.1
80
0.03
0.2
0.2
0.2
90
0.00
0.0
0.0
0.0
Graph for Part II
Average Intensity of Light versus (Cos Brewster's Angle)^2
y = 10.083x - 0.0713
12
Average Intensity
10
8
6
4
2
0
-2
0
0.2
0.4
0.6
0.8
(Cos Brewster's Angle)^2
1
1.2
Part III. Reflection
Unpolarized
Polarized
Incident ray
Reflected ray
Normal line
θB
θB
n2  n1 tan B
Medium 1
90 degree
Medium 2
θ2
Slightly
polarized
Refracted ray
Table 2 for Part III
Acrylic
Cylindrical lens
Glass
Cylindrical lens
Brewster’s angle θB= 57 degree
Index of refraction n1 =1
Index of refraction n2 = 1.50
Stander value for n2 = 1.53
%error = 2%
Brewster’s angle θB= 57 degree
Index of refraction n1 =1
Index of refraction n2 = 1.46
Stander value for n2 = 1.52
%error = 3.95%
Conclusion
In this experiment, we study the
polarization of light by observing the
reflection of the light and the absorption
of the light. Furthermore, we verify
Brewer’s law and Malus’s law for
polarized light.
Questions
or
Comments
Thank You
The End