lesson 2

• Natuurkunde / Scheikunde
• Middelbare school
• havo, vwo
• Leerjaar 2

Light and Colours

Part 2 of 1,1- Primary Colors

When we speak of white light, we are referring to ROYGBIV - the presence of the entire spectrum of visible light. But combining all the frequencies in the visible light spectrum is not the only way of making white light. 

White light can also be produced by combining only three distinct frequencies of light, called primary colors.

Do you know which ones they are???

Seeing colours

• The retina contains…
• Rods - dim light, black & white
• Cones - color

                      - red - absorb red & yellow

                      - green - absorb yellow & green

                      - blue - absorb blue & violet

Rods and Cones in the Retina:

Color addition

Light is perceived as white by humans when all three cone cell types of the eye are simultaneously stimulated by equal amounts of red, green, and blue light. Because the addition of these three colors yields white light, the colors red, green, and blue are termed the primary additive colors. 

Mixing Colors

Primary light colors:

- Red, green, blue

Secondary (additive) colors:

- Cyan, yellow, magenta

These combine to form white light.

Secondary Colors

• 
  
• red + blue = ________
• red + green = _______ 
• blue + green = _______

stare at the dot for 60 seconds

Negative Afterimage - One set of cones gets tired, and the remaining cones produce an image in the complimentary color.

Cyan is composed of blue and green. After staring at cyan for a long time, you have exhausted the blue and green cone cells in your eye. 

Therefore, when you look at white, you see red after staring at cyan.  

WHAT COLOUR IS SEEN IN THE INDICATED AREA?

1. BLUE
2. RED
3. CYAN
4. MAGENTA

WHAT COLOUR IS SEEN IN THE INDICATED AREA?

1. BLUE
2. GREEN
3. CYAN
4. MAGENTA

WHAT COLOUR IS SEEN IN THE INDICATED AREA?

1. RED
2. GREEN
3. CYAN
4. YELLOW

Yellow light shines on a piece of paper that contains red pigment. What color does the paper appear to be?

1. YELLOW
2. RED
3. GREEN
4. BLUE

Red and Green light (i.e., yellow light) is incident on the paper. Red paper contains pigments capable of absorbing both blue and green light (when present). 

In this case, green light is incident upon the paper so the green light gets absorbed. The red light reflects off the paper and it is observed to be red.

HW FOR LESSON 3

- DO EX 9-14 ON PAGE 15

- DO EX 15-18 ON PAGE 17