1. Lesson 2

2. Review - Energy in a Wave A wave is a disturbance that transfers energy from one point to another without transferring matter. In a water wave, energy passes through water from one point to another as the wave rises and falls. This movement of energy allows the wave to do work.

3. Properties of Waves

4. The Electromagnetic Spectrum

5. The Wave Model of Light The white light separates into the colours of the rainbow, including red, orange, yellow, green, blue, and violet (ROY G BV). The range of different colours of light is called the visible spectrum. These waves lengths are detected by the eye.

7. Additive Colour Theory of Light The additive colour theory of light states that white light is composed of different colours (wavelengths) of light. It is possible to produce white light by combining only three colours.

8. In the retina of the eye, there are three colour detectors called cones. One is sensitive to red light, one to blue, and one to green. Our eyes combine signals from each one of these cones to construct all of the other colours. When our eyes receive light that contains only red, blue and green light, we see it as white.

9. Additive Colour Theory of Light These three colours of light are known as primary colours.

10. Additive Colour Theory of Light If you mix correct amounts of all three primary colours of light, you will make white light. If you mix only two of the primary colours together, you will make a secondary colour. The secondary colours of light for red, green, and blue are magenta, yellow, and cyan.

11. Demonstration with computer program

13. Subtractive Colour Theory of Light When a light wave strikes an object Some wavelengths of light reflect, which means that they bounce off the object. Other wavelengths are absorbed by the object. The colour you see when you look at an object depends on the wavelengths that are reflected R G B

14. The colour of a Rose According to the subtractive colour theory of light, coloured matter selectively absorbs different colours or wavelengths of light. A red object has particles of pigment that absorb the other two primary light colours blue and green, and reflects red light.

15. A yellow rose on the other absorbs blue light and reflects both red and green light. An objects colour is determined by what colours it absorbs and which it reflects. Remember white light contains Red, Green and Blue light. R G B

16. Subtractive Colour Theory of Light According to the subtractive colour theory of light, coloured matter selectively absorbs different colours or wavelengths of light. The colours that are absorbed are “subtracted” from the reflected light that is seen by the eye. A black object absorbs all colours A White object reflects all colours. A blue object reflects blue and absorbs all other colours.

17. Subtractive Colour Theory of Light The primary and secondary colours of light for the subtractive theory are opposite to the colours of the additive theory Cyan, magenta, and yellow are the primary subtractive colours, while red, green, and blue are the secondary subtractive colours.

18. Subtractive Colour Theory of Light If a colour is absorbed, it will not make it to your eye. You only see the reflected colours. Paint and pigment manufacturers mix all three of the primary subtractive colours in varying degrees to make any range of colours reflect from a surface.

19. Primary pigments Yellow M agentaCyan Black

20. Demonstration with computer program

21. Filters also work by using the subtractive theory Filters contain pigments. As light is transmitted through the filter, these pigments absorb some light colours but not all. Example: A blue filter absorbs red and green light, and transmits blue light.

22. Filters and Subtractive Theory What light colours would a cyan filter absorb and transmit?

23. Demonstration with computer program

24. Colour Printing The theory of subtractive colours is applied in many situations, including colour photography and colour printing. Example: Colour printers use three primary colours, yellow, cyan and magenta. By combining these colours as well as black these printers can produce over 1 million colours Demonstration with computer program

25. Colour Theory Lab