• Learning Objectives :To explain how we see different colors.

• Key Words : absorbed, reflected, transmitted, diffraction

• How do we remember the colors of the rainbow in the correct order.

• R ichard• O f• Y ork• G ained• B attle• I n• V ain

• Why do we see white?

How do color filters work?

Filter

White light

Blue Light passes through

Ray Box

Filter

White light

Red Light passes through

Ray Box

Filter

White light

Indigo Light passes through

Ray Box

Filter

White light

Green Light passes through

Ray Box

Filter

White light

Green Light passes through

Ray Box

Filter

Green light absorbed

No light passes through

Colored filters Colored filters only let their color

through. All the other colors are absorbed within the pigment that makes up the filter. Colored objects work the same way; the pigments that make up the color we see on the object filters out (absorbs the wavelengths) of the other color wavelengths in the visible spectrum.

1. What color(s) will be transmitted by the red filter?

red blue

2. What color will we see on the screen?

Answer : red

screen

Answer : black

3. Why?

Answer : the blue filter absorbs the red light.

1. What color(s) will be transmitted by the green filter?

2. What color will we see on the screen?

Answer : green

Answer : black

3. Why?

Answer : the blue filter absorbs the green light.

green blue screen

1. What color(s) will be transmitted by the yellow filter?

2. What color will we see on the screen?

Answer : green and red

Answer : red

3. Why?

Answer : the red filter absorbs the green light and transmits red light.

yellow red screen

1. What color(s) will be transmitted by the yellow filter?

2. What color will we see on the screen?

Answer : green and red

Answer : green

3. Why?

Answer : the cyan filter absorbs the red light and transmits green light.

yellow cyan screen

If the light from the lamp is white light, made up of all colors. Why do we see it as red?

Only red is reflected

Orange, yellow, green, blue, indigo and violet are absorbed

All the colors are reflected

White pencilWhite pencil

All the colors are absorbed

Black pencilBlack pencil

Filter

White light

Red Light passes through

Ray Box

The pencil is RED so REFLECTS the RED light We see the pencil as RED

In the SAME colored light

Filter

White light Indigo Light

passes through,

We see a black pencil instead of a red one

Ray Box

The pencil is RED so ABSORBS the indigo light. We see the pencil as BLACK because NO colors are reflected the wavelengths are all absorbed instead.

In a DIFFERENT colored light

Red Orange Yellow Green Blue Violet

Indigo?!

MIXING COLORS

Primary Colors of Light are the blue, green, and red

wavelengths

Can you spot something strange?

Demonstration 1 (the prism)

White = Red Orange Yellow green blue indigo violet

Demonstration 2 (mirrors)

Red Blue Green = White

What’s so special about red, green and blue?

Aqueous humor

fills this space

Vitreous Humor fills this space

Retina growing on choroid at the back of the eye

How does it work?Cyan is made up of and light. When you stare at the part of the image the blue and green light sensitive cells become desensitized. After this, when you look at the white screen the all the colors fall on your retina; however, only the cells are stimulated because the and

cells are still inactive. Your brain only sees where the was.

Now explain why yellow forms a blue after Image…

1. American flag

2. Korean flag

3. A pink heart

Now try and work our what colors you would need to create an after image of...

4. The yellow sun

5. Green leaf

6. Blue-green ocean, blue sky and yellow sand

Quick questions

• What are the 3 primary colors? (3 marks)

• What are the three secondary colors? What two primary colors is each made from? (6 marks)

• If you wanted to make a green after image what color would you use in the real image? (1 mark)

Discuss…

• Are there any undiscovered colors?

• Do we all see red the same way? Can we ever know?

• Could the concept of red be fully explained to a person born blind?

Quick REVIEW• Primary colors are red, green and

blue.• Primary colors may be combined

to make white light.

Primary colors of light together form white light. But primary pigments together make black. This is because they absorb all color wavelengths.

Transparent objects transmit color

• Red glass absorbs all colors of light except red, which it transmits.

Opaque objects reflect and absorb light

• This apple reflects red and absorbs all other colors.

Have a Good Day!