Polarization of Light And dispersion of light, too - PowerPoint Presentation

Slide1

Polarization of Light

And dispersion of light, tooSlide2

Dispersion of light

Visible light = full spectrum

wavelengths range from 400 nm to 700 nm

Different wavelengths have ever so slightly different indices of refraction when passing through materials such as glass, plastic, or water (and probably others)

Dispersion

is the effect of these differences on the appearance of refracted light:

https://phet.colorado.edu/sims/html/bending-light/latest/bending-light_en.html

Slide3

Dispersion of Light

Longer wavelengths tend to refract less than the shorter wavelengths, thus resulting in the very familiar rainbow patternSlide4

Rainbow from Airplane

Picture courtesy of Caroline B.

Slide5

What IS Polarization?

First…we have to understand what light is:

http://hyperphysics.phy-astr.gsu.edu/hbase/waves/emwavecon.html

Slide6

Electromagnetic Radiation

Electric fields and magnetic fields vary in strength simultaneously and perpendicularly to each other.

Both

E

and

B

vary following a sinusoidal pattern, resulting in what appears to be a transverse wave…but one that does not require a medium.

Electric and magnetic fields exist in the vacuum of space, so EM waves (light) can travel through space.Slide7

Polarization

Plane Polarization

refers to a wave that is only oscillating in a single fixed plane (i.e. a wave on a string)

Light

normally propagates in all directions:Slide8

Polarized light…

When light passes through a polarizer, The electric field will only oscillate in 1 direction (it’s okay to ignore the magnetic field when talking about polarization…):Slide9

Warm-up

Polarization

1

2

3

a) only case 1

b) only case 2

c) only case 3

d) cases 1 and 3

all

three

cases

none of the cases

If unpolarized light is incident from the left, in which case will some light get through?

Explain your reasoning.Slide10

Question 24.9

Polarization

1

2

3

In cases 1 and 3, light is blocked by the adjacent horizontal and vertical polarizers. However, in case 2, the

intermediate 45° polarizer allows some light to get through

the last vertical polarizer.

a) only case 1

b) only case 2

c) only case 3

d) cases 1 and 3

e) all three cases

If unpolarized light is incident from the left, in which case will some light get through?

Slide11

Polarizers and Analyzers

Polarizer:

A material that has a molecular structure that will only allow one specific orientation of electric field (from the light) to pass through.

Analyzer:

A polarizer that is specifically used to determine if light is polarized (and in what direction)Slide12

Example: LCD displaysSlide13

What’s happening here?Slide14

When light reaches a surface of a transparent or semi-transparent material, much of the light will be able to pass through the boundary and will refract as it passes into the new medium, following Snell’s Law

Some of the light will reflect off the surface, following the law of reflection

Polarization of Reflected LightSlide15

At one particular angle, the reflected light will be fully plane polarized (rather than partially polarized)

The angle of incidence at which this occurs is called the

Brewster’s Angle

The reflected ray and the refracted ray will be perpendicular to each other!

Brewster’s AngleSlide16

and

Brewster’s Angle—

How can it be determined?Slide17

Brewster’s Angle depends on the indices of refraction for the 2 media, and nothing else.

The angle between the angle of refraction and the angle of reflection is

always 90°

at the Brewster’s Angle

Brewster’s Angle—

noteworthy notesSlide18

Most common method of producing polarized light is by using filter

When 2 filters are used in sequence, the first polaroid the light passes through is called the

Polarizer

The second filter the light passes through is called the

Analyzer

Polarizing Filters (Polaroids)Slide19

Exploration lab: Polarization

You will now be determining the relationship between the angle the electric field makes with a polarizer and the intensity of the light that passes through the polarizer

Use the Light Intensity meter and the polarization equipment provided.

Attach the light intensity meter to a ring stand so that it is positioned directly in the center of the polarizer  

Choose one of the polarizing filters to be the "polarizer", and maintain the position of that filter so that "0" is always in the same position.

The other filter will be the analyzer, and you will rotate it every 5° and record the light intensity throughout the entire 360°Slide20

The intensity of the light that passes through two

polaroids

is dependent on the angle measured between their two polarizing axes.

I

0

 the intensity of the light incident upon the analyzer

I  the intensity of the light after passing through the analyzer

q

 the relative angle between the polarizer’s and the analyzer’s axis

Malus

’ Law