OPTICS Gr. 8 Science

Lesson 6 – Colour (p. 266 – 280) Teacher Copy

8-2-04 & 8-2-06 Explain, using the additive theory and the subtractive theory, how colours are produced, and identify applications of this theory in daily life.8-2-05 Explain how the human eye detects colour, and how the ability to perceive colour may vary from person to person.

The Source of Colours

Sunlight is white light – which is made from mixing together all the different colours of light.

When white light is refracted into different colours, the pattern (rainbow) is called a

spectrum. For sunlight, the pattern is called the solar spectrum and can be remembered

using: ROYGBIV

OPTICS Gr. 8 Science

How we see colour (p. 270 – 271, 274 - 275)

Watch: https://www.youtube.com/watch?v=l8_fZPHasdo (4 min)

https://www.youtube.com/watch?v=KoUyMuMVJQY (2 min)

We learned in Lesson 3 that when light strikes an object, any combination of the following could happen - the light could be:

o Reflected off the object

o Absorbed by the object

o Transmitted through the object

When white light strikes a blue bottle, the glass absorbs all of the colours except blue. Only the blue light is transmitted or reflected.

Discussion: What is black?

Items appear black when they absorb all of the colours in the light – they do not reflect any light.

OPTICS Gr. 8 Science

The human eye contains two types of nerve cells that respond to light:

Rods

shaped like tiny cylinders

detect the presence of light

do not detect colour

work in low amounts of light

Cones

shaped like cones

work in bright light

detect colour

3 types of cones that each detect a different colour of light

o red , blue and green

Discussion Question:

What is colour blindness?

Answer: Caused by defective cone cells. Do the colour blindness test on p. 275.

OPTICS Gr. 8 Science

Additive Theory (p. 273)

The 3 additive primary colours are: Red, Green and Blue

They are called additive colours because adding all three together will make white light.

The light of 2 additive colours will produce a secondary colour - these are: Yellow, Cyan,

and Magenta.

Application: What two devices use additive theory to produce colours?

Answer: Televisions and computer monitors

Subtractive Theory (p. 276)

The 3 secondary colours (yellow, cyan, and magenta) are called subtractive primary colours

because some portion of white light has been removed in order to produce each colour.

Complementary Colours

When a secondary colour and a primary colour combine to form white light, they are said to

be “complementary.”’

For example, magenta is made up of red and blue – it is missing green. If you add green to magenta, it will produce white light.

OPTICS Gr. 8 Science

Use the colour diagram on the previous page to complete the chart below:

Light Colour Includes Missing (ie. Complementary Colours)

Cyan Blue + Green Red

Magenta Red + Blue Green

Yellow Red + Green Blue

Application:

In order to print in colour, subtractive colour theory is applied. Let’s work through it below. (Use the colour diagrams above to help you.)

1. What happens when we mix magenta and yellow?

Answer:

Magenta (red + blue) + Yellow (red + green) Red (blue + green get absorbed, leaving red)

2. What happens when we mix cyan and magenta?

Answer:Cyan (green + blue) + Magenta (red + blue) Blue (red + green are absorbed, leaving blue)

3. What colours in your printer must mix in order to print green?

Answer: yellow and cyan

OPTICS Gr. 8 Science

Lesson 6 – Colour (p. 266 – 280) Student Copy

8-2-04 & 8-2-06 Explain, using the additive theory and the subtractive theory, how colours are produced, and identify applications of this theory in daily life.8-2-05 Explain how the human eye detects colour, and how the ability to perceive colour may vary from person to person.

The Source of Colours

Sunlight is _____________ light – which is made from mixing together all the different colours of light.

When white light is _________________ into different colours, the pattern (___________)

is called a ______________. For sunlight, the pattern is called the __________ __________

and can be remembered using: _____________________

OPTICS Gr. 8 Science

How we see colour (p. 270 – 271, 274 - 275)

Watch: https://www.youtube.com/watch?v=l8_fZPHasdo (4 min)

https://www.youtube.com/watch?v=l8_fZPHasdo (2 min)

We learned in Lesson 3 that when light strikes an object, any combination of the following could happen - the light could be:

o _____________________ off the object

o _____________________ by the object

o _____________________ through the object

When white light strikes a blue bottle, the glass absorbs all of the colours except blue. Only the blue light is transmitted or reflected.

Discussion: What is black?

___________________________________________________________________________

OPTICS Gr. 8 Science

The human eye contains two types of ___________ cells that respond to light:

___________ shaped like tiny _______________

detect the presence of _____________

do not detect ______________

work in ________ amounts of light

___________

shaped like ______________

work in _______________ light

detect _________________

3 types of cones that each detect a different _____________ of light

o ________ , __________, and __________

Discussion Question:

What is colour blindness?

OPTICS Gr. 8 Science

Additive Theory (p. 273)

The 3 additive _____________ colours are: ______, ___________, and ________

They are called additive colours because adding all three together will make __________

_______________. The light of 2 additive colours will produce a _______________ colour -

these are: _____________, ___________, and _______________

Application: What two devices use additive theory to produce colours?

_____________________________________________________________________________

Subtractive Theory (p. 276)

The 3 secondary colours (____________, __________, and _____________) are called

_______________ primary colours because some portion of white light has been removed

in order to produce each colour.

Complementary Colours

When a secondary colour and a primary colour combine to form __________ light, they are

said to be “___________________.”’

For example, magenta is made up of red and blue – it is missing green. If you add green to magenta, it will produce white light.

OPTICS Gr. 8 Science

Use the colour diagram on the previous page to complete the chart below:

Light Colour Includes Missing (ie. Complementary Colours)

Cyan

Magenta

Yellow

Application:

In order to print in colour, subtractive colour theory is applied. Let’s work through it below. (Use the colour diagrams above to help you.)

1. What happens when we mix magenta and yellow?

2. What happens when we mix cyan and magenta?

3. What colours in your printer must mix in order to print green?