1. Light Absorption and Reflection
SPH4U

2. Primary Colours
The primary colours of light (the colours the cones of our retinas respond to) are blue, green, and red:

3. Secondary Colours
The secondary colours of light are combinations of two primary colours:

4. Secondary Colours
The secondary colours of light are combinations of two primary colours: blue + red = blue + green = green + red =

5. Secondary Colours
The secondary colours of light are combinations of two primary colours: blue + red = magenta blue + green = green + red =

6. Secondary Colours
The secondary colours of light are combinations of two primary colours: blue + red = magenta blue + green = cyan green + red =

7. Secondary Colours
The secondary colours of light are combinations of two primary colours: blue + red = magenta blue + green = cyan green + red = yellow

8. Secondary Colours
The secondary colours of light are combinations of two primary colours: blue + red = magenta blue + green = cyan green + red = yellow

9. White Light
White light is a combination of all the primary colours (or the full spectrum):

10. Reflection Most objects do not emit visible light but reflect it:
A wave reflecting at a boundary between media.

11. Reflection Most objects do not emit visible light but reflect it:
A wave reflecting at a boundary between media.
Note that a wave reflected at a fixed end will invert.

12. Reflection Most objects do not emit visible light but reflect it:
A wave reflecting at a boundary between media.
A wave reflected at a free end will not invert.

13. Absorption
Some light energy may be absorbed by the particles of the object. Different chemical substances will absorb different colours.

14. Absorption
An object illuminated with white light that absorbs all colours of light will appear black.

15. Absorption
An object illuminated with white light that absorbs blue light will appear ?.

16. Absorption
An object illuminated with white light that absorbs blue light will appear yellow.

17. Absorption
Side note: objects underwater appear blue because other wavelengths are absorbed at shallower depths.

18. Reflection
Light is reflected from a surface such that the angle of incidence equals the angle of reflection:

19. Reflection
Light is reflected from a surface such that the angle of incidence equals the angle of reflection:
Note that these angles are measured from the normal: the line perpendicular to the surface.

20. Regular vs. Diffuse Reflection
If the surface reflecting the light is smooth, parallel incident rays will have parallel reflections (and may form an image). This is regular or specular reflection.

21. Regular vs. Diffuse Reflection
If the surface reflecting the light is rough, the rays reflect in seemingly random directions. This is diffuse reflection.
Note that qi = qr at the point of reflection.

22. Regular vs. Diffuse Reflection
Side note: wet roads are more reflective (and may produce glare) because water fills in rough gaps to produce a smooth surface.

23. Ultraviolet
Another side note: some materials will absorb ultraviolet light and re-radiate the light at a lower energy (longer wavelength). We call these materials fluorescent.
A fluorescent smiley face under an ultraviolet “black light.”

24. More Practice
“Additive and Subtractive Colour Activity” “Angles of Reflection Activity” “Black Light Activity”
Do not point lasers into someone’s eyes or in a direction that could reflect into someone’s eyes.
Limit your exposure to the UV black lights.