1. The blind spot of the human eye results from

a) rods attached to the retina.

b) cones attached to the fovea.

c) a detached retina.

d) the optic nerve attached to the retina.

e) color blindness.

2. Some minerals absorb ultraviolet light and then release lower energy visible light. This process is called

a) fluorescence.

b) atomic resonance.

c) incandescence.

d) phosphorescence.

Fluorescent LampsFluorescent Lamps

• Primary excitation - electron collisions with low pressure mercury vapor, and ultraviolet light is given off

• Secondary excitation - ultraviolet light is absorbed by phosphors and these emit visible light

Phosphorescence Phosphorescence • Phosphorescence - a type of light emission

that is the same as fluorescence except for a delay between excitation and de-excitation.

• Electrons get "stuck" in an excited state and de-excite gradually.

• Demos - glow-in-the-dark objects

Lasers Lasers • Laser

– Light amplification by stimulated emission of radiation

• Lasers produce coherent light.• Coherent light means that all the light waves

have the frequency, phase and direction.• Demo - Laser and chalk dust• Demo - Laser and prism or diffraction grating

Matching QuestionsMatching Questions1. Incandescence a. mercury vapor

light tubes

2. Fluorescence b. glow-in-the-dark

paints and plastics

3. Phosphorescence c. light bulbs

with filaments

Matching QuestionsMatching Questions1. Fluorescent Lamp a. color changes

with temperature

2. Incandescent Bulb b. only one color

of light

3. Laser c. converts ultraviolet light to visible light

Chapter 13Chapter 13

ColorColor

ColorColor• Different wavelengths of light are perceived

as different colors.

• Pure Colors: ROY G. BIV

• White light contains equal amounts of these colors. (ROY G. BIV)

Selective Reflection and Selective Reflection and TransmissionTransmission

• At an interface, light can be...

• absorbed

• reflected

• transmitted

Fill in the Blanks

• Black objects _______ all of the pure colors.

• White objects _______ all of the pure colors.

• Transparent objects _______ all of the pure colors.

absorb

reflect

transmit

Color Filters• Red filters transmit red light and absorb the

other colors, etc.

• Red objects reflect red light and absorb the rest, etc.

• In red light, what color do the red petals and green leaves of rose appear?– Answer: Petal appear _____, leaves

appear to be _____.

Mixing Colored Light Mixing Colored Light Color AdditionColor Addition

• Additive Primary Colors:

• Red

• Green

• Blue

• One can produce any color by varying amplitude and mixture or red, green and blue light.

• Color Addition Example:

– Tiny dots called pixels on Color TV's and Computer Monitors are colored only red, green, or blue.

Mixing Colored Pigments - Mixing Colored Pigments - Color SubtractionColor Subtraction

• Subtractive Primary Colors:

• Yellow

• Magenta

• Cyan

• One can produce any color by varying the amount of yellow, magenta and cyan pigments.

• Color Subtraction Example:

– Newspapers and the new zip-lock sandwich bags use color subtraction.

White

Red

Green

Blue

Yellow

Cyan

Magenta

Primary Colors

Green

Pure Green

Color AdditionPrimary Green

Why is the sky blue?Why is the sky blue?

• Nitrogen and Oxygen in our atmosphere scatter high frequencies of light.

Why are sunsets red?Why are sunsets red?

• Red light is scattered the least by our atmosphere.

• The greatest path of sunlight through the atmosphere is at sunset or sunrise.

Why are clouds white?Why are clouds white?

• The color of light scattered by clusters of water molecules vary with the size of the clusters.

• The size of clusters of water molecules (droplets) vary in clouds.

Why is the ocean Why is the ocean greenish blue?greenish blue?

• Red light is absorbed by the molecules in the water.

Color VisionColor Vision• Colorblindness - about 10% of population

• Red-green is predominant

• Yellow-blue - a few

• Total - some

• Can you read this number????

• Complementary Colors - any two colors that add together to produce white

• e.g. magenta + green = white

Optical Illusions

Animation

After Images and “Conal Fatigue”• The human eye will see complimentary colors

after staring at a color picture.

• Demos:

• Colored Shapes

• Texas Flag

• American Flag

• Rose

• Lincoln

In-Class ExerciseIn-Class Exercise

1. Make a list of the seven forms of light in order of decreasing wavelength.

2. Draw a Color Addition Diagram using overlapping colored spotlights. Label all 7 colors.

3. Draw a Color Subtraction Diagram using overlapping paints. Label all 7 colors.

QuestionQuestion1. If you look at the yellow Sun just before

sunset for a few seconds and then look at a white cloud you see _______ afterimages of the Sun.

a) red

b) green

c) blue

d) cyan

QuestionQuestion2. A mixture of cyan and yellow paints gives

__________ paint.

a) green

b) red

c) black

d) white

e) blue

QuestionQuestion3. Adding red and green light gives us what

color?

a) yellow

b) cyan

c) blue

d) magenta

Suppose that two flashlight beams are shone on a white screen, one through a pane of blue glass and the other through a pane of green glass. What color appears on the screen where the two beams overlap?

a) yellow

b) green

c) cyan

d) magenta

e) red

If a car headlight emitted only yellow light, the normally green grass appears to be

a) green.

b) red.

c) black.

d) white.

e) yellow.

To see an after image of a red, white and blue Texas flag one would first stare at a flag with the complimentary colors

a) yellow, violet, and green.

b) cyan, yellow, and magenta.

c) cyan, black, and yellow.

d) yellow, cyan and green.

The worst thing that you can do for the health of a green-leafed plant is to illuminate it with only

a) red light.

b) green light.

c) blue light.

d) all are equally bad.

e) none of these.

Most of the light that we see has undergone

(a) selective interference

(b) selective transmission

(c) selective reflection

(d) selective refraction

A mixture of magenta and green lights give white light. These two colors are (a) additive primaries

(b) secondary colors

(c) complementary colors

(d) fluorescent colors

(e) interference colors

Mixing yellow paint and magenta paint gives what color?

(a) red

(b) green

(c) blue

(d) cyan

What color would red cloth appear if it were illuminated by cyan light? (a) cyan

(b) red

(c) yellow

(d) green

(e) black

• Glow in the beads

• Black Light

• Laser & Diffraction Grating

• Color Filters and Color Papers