Download PHYSICS CHAPTER 15 NOTES DIFFRACTION AND

PHYSICS CHAPTER 15 NOTES DIFFRACTION AND POLARIZATION
1.
Interference--the mutual effect of two beams of light that results in a loss of intensity in certain regions (destructive
interference) and a reinforcement of intensity in other regions (constructive interference).
Destructive Interference
Constructive Interference
A
B
A+B
A
B
A+B
2.
Thin Film Wave Interference--the light that is incident on thin films (a soap bubble, oil or gas on a water surface) is
interfered.
a.
The wave that is reflected off of the thin film is inverted. Since the reflected wave is inverted it is shifted out of
phase by 180 degrees.
1.
Since the second medium of this boundary interface has a higher index of refraction it appears to the
incident light ray as a fixed boundary much like the rope inverting when fixed at the wall.
b.
The wave that is refracted and transmitted through the thin film is just bent towards the normal. When the
refracted ray comes to the second boundary if the medium beyond this boundary has a high index of refraction as
compared to the thin film the reflected ray will be inverted or shifted out of phase. If this medium has a lower
index of refraction than the thin film the wave will be reflected with out a change of phase, or inversion.
c.
Maximum constructive interference occurs with thin films if the optical path difference is an odd number of half
wavelengths.
d.
Maximum destructive interference occurs if the optical path difference is a whole number of wavelengths.
Thin Film
3.
Diffraction--is the spreading of light into a region behind an obstruction.
4.
Single-Slit Diffraction--light penetrating a single slit constructively and destructively wave interfere to produce the
principal image along with the first and second order images.
SINGLE SLIT DIFFRACTION
First Order Image Bright
Dark
Monochromatic
Light
q
q
Principal Image
Bright
Dark
First Order Image Bright
5.
Double-Slit Diffraction--light penetrating a double slit constructively and destructively wave interferes to produce the
principal image along with the first and second order images.
DOUBLE OR MULTIPLE
SLIT DIFFRACTION
Monochromatic
Light
Dark
q1
Principal Image
q2
Bright
Dark
First Order Image Bright
Dark
Second Order Image Bright
PHYSICS CHAPTER 15 NOTES DIFFRACTION AND POLARIZATION
POLARIZATION
1.
2.
3.
Plane-Polarized Light--is light in which the oscillations are confined to a single plane that is perpendicular to the line of
propagation.
Polarizer--is the first frame of slots that plane polarize the light.
a.
Light can be plane polarized before it is sent through a fiber optic cable. Since there can be infinite ways to
plane polarize light with the angle of the polarizer and infinite number of messages can be sent with fiber optics.
(Theoretically)
Analyzer--a second frame of slots that can be parallel to the first.
a.
If analyzer is parallel to the first then 100% transmission occurs.
q
Analyzer
Polarizer
4.
Polarization Angle--is a particular angle of incidence at which polarization of the reflected light is complete.
5.
The Direction of Polarization--is dependent upon the electric field component of light.
6.
The Law of Malus--The intensity of I2 of the light transmitted through both a polarizer and an analyzer is found to depend
on the orientation of the second polarizer relative to the first.
cos 2 θ =
I
I
2
W h e r e θ is th e a n g le b e tw e e n th e
1
p r e ffe r r e d d ir e c tio n s o f th e p o la r iz e r a n d a n a ly z e r
7.
Brewster's Angle--The light ray incident obliquely to a surface contains a reflective beam of light polarized parallel to the
plane of the reflecting surface.
tan θ brewster =
n2
n1
Where n2 & n1 are the indices of
refraction of the incident and reflection mediums.
b.
o
If the angle of incidence is such that the reflected and refracted rays are at 90 to one another, the reflected ray
will be completely polarized in the direction perpendicular to the plane of incident and reflected rays. The
corresponding angle of incidence is known as Brewster's Angle. For incidence at the angle other than Brewster's
Angle, the reflected ray is only partially polarized.
q brewster
90
o