Chapter 27

1 / 61

# Chapter 27 - PowerPoint PPT Presentation

Chapter 27. C o l o r. 1. SELECTIVE REFLECTION. Most objects "reflect" rather than emit light. The spring model of the atom works well in explaining reflection. Radiations that match the resonant frequencies of the atoms are absorbed.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## Chapter 27

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

### Chapter 27

Color

1. SELECTIVE REFLECTION
• Most objects "reflect" rather than emit light.
• The spring model of the atom works well in explaining reflection.
• Radiations that match the resonant frequencies of the atoms are absorbed.
• Frequencies of the radiations on either side of the resonant frequencies are “reflected.”
Objects can only reflect the light that is in the source illuminating the object.
• Demo – Razorback Football in Cyan Light (Next Slide)
2. SELECTIVE TRANSMISSION
• As light passes through materials some frequencies of light are removed (absorbed) while other frequencies are transmitted.
• The degree of transmission depends on how transparent the material happens to be.
3. MIXINGCOLOREDLIGHT
• All visible frequencies make up white light.
• Example: The sun emits all frequencies and its light is white.
• (Actually it is slightly yellowish to us on Earth, which possibly explains why we are more sensitive to light in the middle of the spectrum.)

RED, GREEN, and BLUE when added also produce white.

• Red, green, and blue are

Through color addition you are able to see a wide range of colors from a color TV or color projector which actually only emit three different colors.

These colors are red, green, and blue.

They are called the additive primaries.

Your vision system “adds” these together to see a single color from a single location illuminated by more than one color.

You even see colors that don’t appear in the continuous emission spectrum of the sun.

Red, green, and blue are used as the additive primaries because this set of three will produce the widest range of colors that you visually experience.

Colors in White Light

White

Red

Green

Blue

You can see that these three add to give white.

Yellow

Note that yellow is the addition of red and green.

Cyan

Magenta

Note that cyan is the addition of green and blue.

Note that magenta is the addition of red and blue.

What you are about to see is what you would get with three partially overlapping spotlights reflecting off a white screen.

Yellow

Yellow

Red

Red

Green

Green

Cyan

Cyan

Magenta

Magenta

Blue

Blue

Complementary Colors
• Any two colors that add to give white are said to be complementary colors.
• Demo - Complementary Colors
4. MIXINGCOLOREDPIGMENTS
• Subtractive primaries - YELLOW, CYAN, and MAGENTA
• Example - Mixing paints, zip-lock sandwich bags, color printing
• Demo - Color Subtraction
Through color subtraction you are able to see a variety of colors from printings, paintings, etc.

If you have ever bought printer inks, you will notice that the ones used to provide a variety of colors in printing are yellow, cyan, and magenta.

They are called the subtractive primaries.

In subtraction, colors are eliminated by the absorption of colors that were in the original illuminating source.

This particular set of three colors, yellow, cyan, and magenta, will produce the widest range of colors that you visually experience.

White

Blue

Yellow

Colors in White Light

You get blue.

Take away yellow and what is left?

White

Cyan

Red

Colors in White Light

You get red.

Take away cyan and what is left?

White

Green

Magenta

Colors in White Light

You get green.

Take away magenta and what is left?

ColorSubtractionCircles

What you are about to see is what you would get with three partially overlapping transparencies on an overhead projector.

Green

Green

Cyan

Cyan

Yellow

Yellow

Blue

Blue

Red

Red

Magenta

Magenta

Slide - Raincoat Closet

It should be noted from the previous that objects that reflect a particular color are themselves good absorbers of the complimentary color of that particular color.
• For examples:
• A red object is a good absorber of cyan and vice versa.
• A blue object is a good absorber of yellow and vice versa.
• A green object is a good absorber of magenta (blues and reds) and vice versa.

Primary Colors

White

Red

Green

Blue

Yellow

Cyan

Magenta

5. WHY THE SKY IS BLUE
• One man’s view.
Just as resonating tuning forks scatter sound, so do particles in our atmosphere scatter light.
N2 and O2 scatter high frequencies which are near natural frequencies of N2 and O2.
• (Natural frequencies are in the UV.)
• This scattering produces the bluish sky.
• The blue end of the spectrum is scattered ten times better that the red end.

Top of Atmosphere

Sun

Blue in this direction

Earth

6. WHY SUNSETS ARE RED

Ten Most Beautiful Sunsets

Sunset

• If the atmosphere becomes thicker or the paths of light through the atmosphere become longer, more of the longer wavelengths of light will be scattered.

Sun

Sun

Earth

Demo - Blue Sky and Red Sunset

• Because of scattering of blue light the sun appears more yellowish at noon than it really is.
7. WHY CLOUDS ARE WHITE
• Droplet size dictates which colors are scattered best.
• Low frequencies scatter from larger particles.
• High frequencies scatter from small particles.
Electrons close to one another in a cluster vibrate together and in step, which results in a greater intensity of scattered light than from the same number of electrons vibrating separately.
• Large drops absorb more and scatter less.
8. WHY WATER IS GREENISH BLUE
• Water quite often looks bluish.
• This is due to reflected “sky light.”
• A white object looks greenish blue when viewed through deep water.
Water is a strong absorber in IR and a little in red.
• Remove some of the red and cyan is left.
• Crabs and other sea creatures appear black in deep water.
9. COLOR VISION ANDCOLOR DEFICIENCY
• Colorblindness (color deficiency) affects

• Red-green is predominant
• Yellow-blue - a few
• Total – some
• Slide – Colorblindness Tests – URL
10. AFTER IMAGES
• Slides - After Images
After images are due to conal fatigue.
• Cones that have been “firing” for a while will not “fire” as well as “rested” cones when all are exposed to white light.

### Chapter 27 Review Questions

A mixture of magenta and green lights give white light. These two colors are

(b) secondary colors

(c) complementary colors

(d) fluorescent colors

(e) interference colors

(a) cyan

(b) red

(c) yellow

(d) green

(e) black

The sky is blue because air molecules in the sky act as tiny

(a) mirrors which reflect only blue light

(b) resonators which scatter blue light

(c) sources of white light

(d) prisms

(e) none of these

When you stare at a red object for a long time without moving your head and eyes and then suddenly look away at a white screen, you will see a image of the object.

(a) red

(b) blue

(c) cyan

(d) green

(e) white