14.4 Color and Polarizationpp. 543 - 548

Mr. Richter

Agenda (Today and Tomorrow

Review Homework Introduction to Color Notes:

Color Color and Light Color and Pigment Polarization

Objectives: We Will Be Able To… Recognize how additive colors effect the color of light. Recognize how pigments affect the color of reflected

light. Explain how linearly polarized light is formed and

detected.

Warm-Up:

Leaves are green. What makes them green? That is, why do we perceive them to be green?

Discuss at your table and we will discuss as a class in a few minutes.

Color

Introduction to Color The color of an object appears different

depending on the lighting conditions. Think about what you look like under

a black light. Or some jerk’s sunglasses.

The color of an object depends on which wavelengths of light shine on

the object, and which wavelengths are reflected.

Color

Remember, white (visible) light is a combination or red, orange, yellow, green, blue and violet.

These colors each have different wavelengths red = ~700 nm violet = ~400nm

When light hits an object, some wavelengths are absorbed, and some are reflected.

Color

An object will appear to be the color of the light that it reflects.

Green leaves appear green because they absorb all wavelengths of light except green, which they reflect.

If a red light shines on a green leaf, what color will the leaf appear to be? Black!

Color

Green objects only reflect green light.

When white light shines on green objects (white light contains green), green light is reflected

When red light shines on green objects (red light contains no green), the light is absorbed, and the object appears black.

What color does the leaf appear if green light shines on it? Green, of course!

Color and Light

Color and Light A prism breaks up light into six

(or seven) distinct colors. These beams of light cannot be

further broken up, but they can be put back together.

If we add two colors of pure light together, we can create new colors.

This is not the same as mixing pigments!

Color and Light The three primary colors of

light are red green and blue

When two of these colors combine, they create a secondary color

red + green = yellow red + blue = magenta blue + green = cyan

Color and Light (fun facts)

The human eye can only detect the primary colors of light: red, blue and green. Everything else is a

combination of those colors.

Visual screens like monitors and TVs only have red, blue and green pixels. The brightness of each pixel

contributes to the overall picture color.

Color and Light: Your Turn

A substance is known to reflect green and blue light. What color would it appear to be when it is illuminated

by the following colors of light?1. white light2. blue light3. magenta light4. red light

1) cyan, 2) blue, 3) blue, 4) black

Day 2

Warm-Up

If pure yellow light shines on a magenta t-shirt, what color will the t-shirt appear to an observer?

Yellow light = green + red light Magenta = reflects red + blue Yellow shining on magenta reflects

only red light

Agenda

Warm-Up Upcoming Schedule/Exam Notes:

Color and Pigment Polarization

Upcoming Schedule

Today: Finish 14.4 Tomorrow: Ch. 14 Review Friday: Ch. 14 Test (No Quarterly Exam) Next Week: Refraction!

Color and Pigment

Color and Pigment When colors of light are

mixed, they are additive. Yellow light (red + green)

mixed with blue light all combine to form white light.

When colors of pigment are mixed, the result is different.

Yellow pigment mixed with cyan pigment creates green. Why?

Color and Pigment

When colors of pigment mix, they are subtractive.

Each pigment (like a paint color) only reflects certain colors of light.

The more pigments are mixed, the less light is reflected back.

Color and Pigment

The primary pigment colors are: cyan yellow magenta

Just like a printer cartridge.

All other pigments are formed from combinations of these pigments.

Polarization

Polarization

Light from most sources has electric and magnetic fields that oscillate at all random angles. Vertical, horizontal, , etc.

This light is said to be unpolarized.

Polarization

Light is polarized when the all of the electromagnetic waves are transmitted at the same angle. Everything is aligned.

The vibrations of the electric and magnetic fields are parallel to each other.

Polarization

Light can be polarized in two ways:

Transmission: a polarizer (good word!) allows only waves of a certain angle to pass through. Kind of like a picket fence.

Reflection: most waves of light bouncing off of a surface are polarized parallel to that surface Like glare off of glass or other shiny

objects.

Polarization: Applications

Most light we see that is polarized due to reflection is horizontally polarized. Parallel to snow covered ground,

car hoods, lakes, etc.

Glasses and goggles are polarized vertically to block this glare. Like adding a horizontal picket

fence.

Wrap-Up: Did we meet our objectives?

Recognize how additive colors effect the color of light. Recognize how pigments affect the color of reflected

light. Explain how linearly polarized light is formed.

Homework

p. 548 #1-4 p. 552 #37-39, 41 Chapter 14 Test Friday