This lecture is about Polarization and polarid, electromagnetic waves, total internal reflection, dispersion and law of refraction, reflection and refraction difference. a brief review of type of waves

1. Electromagnetic Waves
• It consists of mutually perpendicular and oscillating electric and
magnetic fields. The fields always vary sinusoidally. Moreover, the
fields vary with the same frequency and in phase (in step) with
each other.
• The wave is a transverse wave, both electric and magnetic fields
are oscillating perpendicular to the direction in which the wave
travels. The cross product always gives the direction in
which the wave travels.
• Electromagnetic waves can travel through a vacuum or a material
substance.
• All electromagnetic waves move through a vacuum at the same
speed, and the symbol c is used to denote its value. This speed is
called the speed of light in a vacuum and is:
• The magnitudes of the fields at every instant and at any point are
related by
E B×
r r

2. • E and B are generated from one another.

4. Polarization
• A linearly polarized electromagnetic wave is
one in which the oscillation of the electric
field occurs only along one direction, which is
taken to be the direction of polarization.
• Ordinary or unpolarized light wave is one in
which the direction of polarization does not
remain fixed, but fluctuates randomly in time.

5. • Plane Polarized light “A light wave in which electric
vector E are vibrating in only one plane.”
• Plane of Polarization “ A plane containing electric
vector E and direction of propagation.”

6. Poynting Vector
• The rate of energy transport per unit area in EM wave is
described by a vector, called the Poynting vector
• The direction of the Poynting vector of an electromagnetic wave
at any point gives the wave's direction of travel and the direction
of energy transport at that point.
• The magnitude of S is

7. Polaroid or
Polarizing Sheet
• Polaroid is a transparent sheet of plastic consisting of long hydrocarbon
chains. This sheet is greatly stretched in one direction. This lines up the
molecules. Next, the sheet is dipped in a solution containing Iodine. The
iodine attaches to the long hydrocarbon chains and make the free electrons
to move only along the chain but not perpendicular them.
• The sheet transmits only those wave-train components whose electric field
vectors vibrate parallel to this direction and absorbs those that vibrate at
right angles to this direction

8. Polaroid or Polarizing Sheet
• An electric field component parallel to the polarizing direction is passed
(transmitted) by a polarizing sheet; a component perpendicular to it is
absorbed.
• one-half rule: an unpolarized light pass through a polarizing sheet, the
intensity I of the emerging polarized light is
0
1
2
PS S=

9. Geometrical Optics
Although a light wave spreads as it moves
away from its source, we can often
approximate its travel as being in a
straight line. The study of the properties
of light waves under that approximation is
called geometrical optics
•Wave fronts: the surfaces through all
points of the wave that are in the same
phase of motion are called wave fronts.
•Rays: the radial lines pointing outward
from the source and perpendicular to the
wave fronts are called rays. The rays
point in the direction of the velocity of the
wave.

10. Reflection and Refraction

11. The Reflection of Light
Why are we able to see
ourselves from mirror?

12. LAW OF REFLECTION
The incident ray, the reflected ray, and the
normal to the surface all lie in the same plane,
and the angle of reflection θr equals the angle
of incidence θi: r iθ θ=

13. Example
Two plane mirrors are separated by 120°, as the
drawing illustrates. If a ray strikes mirror M1, at a 65°
angle of incidence, at what angle θ does it leave
mirror M2?

14. Law of refraction
A refracted ray lies in the plane
of incidence and has an angle θ2 of
refraction that is related to the
angle of incidence θ1 by:
the symbols n1 and n2 are dimensionless
constant, called the index of refraction
i
i
c
n
v
=

15. Dispersion
The index of refraction n
encountered by light in any
medium except vacuum
depends on the wavelength of
the light. The dependence of n
on wavelength implies that
when a light beam consists of
rays of different wavelengths,
the rays will be refracted at
different angles by a surface;
that is, the light will be spread
out by the refraction. This
spreading of light is called
chromatic dispersion,
•The index of refraction n in the
different materials is different
for the same wave length of
lights.
•The index of refraction n in the
same materials is different for
different wave length of lights.

16. Dispersion

17. Total Internal Reflection