1. Colour White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops.

2. Adding colours White light can be split up to make separate colours. These colours can be added together again. The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding all three makes white again Adding red and green makes yellow

3. Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

4. A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light White light

5. Using coloured light If we look at a coloured object in coloured light we see something different. For example, consider a football kit: White light Shorts look blue Shirt looks red

6. In different colours of light this kit would look different: Red light Shirt looks red Shorts look black Blue light Shirt looks black Shorts look blue

7. Some further examples: ObjectColour of light Colour object seems to be Red socks Red BlueBlack GreenBlack Blue teddy RedBlack Blue Green Green camel Red Blue Green Magenta book Red Blue Green

8. Using filters Filters can be used to “block” out different colours of light: Red Filter Magenta Filter

9. Investigating filters Colour of filterColours that could be “seen” Red Green Blue Cyan Magenta Yellow

10. Red Magenta White Yellow BlueGreen Cyan

11. Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent

12. Dispersion – different colors refract by different amounts Ex.: glass prism bends blue blue travels the slowest

14. Diagram of the eye Cornea- the protective cover over the the eye The pupil is the hole that lets the light in Iris- this is the color of your eye and expands or contracts to let more or less light in Retina- this is where the image is projected on to the eye. Fovea- is make up of rods and cones to send the image to your brain

15. Optical eye illusion Concentrate on the four dots in the middle of the picture for about 30 seconds. Close your eyes, and tilt your head back. Keep them closed... you will see a circle of light. Continue looking at the circle... what do you see?

17. Explanation… Because this grid is covered with black with white dots in it-your brain is confused and it sees the grid as essentially all black This is why it tries to add black color to the white spots-and this is why the dots dance when your not looking at them

18. Why is the sky blue? Notes: March 8th 2001

19. Something to ponder…? When you look at the sky at night it is black, with the stars and the moon forming points of light on that black background. So why is it that, during the day, the sky does not remain black with the sun acting as another point of light? Why does the daytime sky turn a bright blue and the stars disappear?

20. Light scattering 1. Sun is an extremely bright source of light. 2. We have an atmosphere. Small atoms of oxygen and nitrogen in the atmosphere effect sunlight. Think of ringing bells!

21. Rayleigh scattering Physical phenomenon that causes light to scatter when it passes through particles. Tiny particles bend high frequency light. (oxygen, nitrogen) Large particles bend low frequency light. (methane, sulfur)

22. Blue sky… why not violet? This scattering of the higher frequencies of light illuminates the skies with light on the BIV end of the visible spectrum. Violet is scattered most easily, so why isn’t the sky violet?

23. Sensitivity Our eyes are more sensitive to light with blue frequencies. Three primary color cones in our eye: Blue, green, and red.

24. Why is the sun yellow? The lower frequencies of sunlight (ROY) tend to reach our eyes unscattered as we look directly at the midday sun. Although sunlight is a combo of all colors, yellow is most intense.

25. Appearance of sun Appearance of the sun changes with the time of day. As the path which the light takes through the atmosphere increases ROYGBIV encounters more atmospheric particles, and scatters more light.

26. Sunset During sunset hours, the light passing through our atmosphere to our eyes tends to be concentrated with red and orange frequencies. This is why sunsets have a reddish-orange hue.

27. What effects a sunset? The effect of a red sunset becomes more pronounced if the atmosphere contains more and more sulfur aerosols (industrial pollutant)

28. Blue haze Some mountain ranges are famous for their blue hazes which result from aerosols from the vegetation reacting with ozone to form small particles (200 nm) which scatter blue light.

29. Why are clouds white? Clouds appear white because they consist of water droplets that are many sizes and scatter all wavelengths equally. (Mie scattering)

30. Why is sea water greenish blue? Water absorbs infrared waves (heats water) Absorption of red light by water. What is left is the complement of red, which is cyan. (Greenish blue )

31. Why are sea creatures red? In deep sea water, since there is no red light coming in to be reflected, the lobsters and other sea creatures look black, and through evolution have avoided being eaten by their predators.

32. In Summary The sky is blue because blue from sunlight is scattered in all directions by molecules in the atmosphere. Sunsets are red because all the other color frequencies are filtered out. Water looks greenish blue because water absorbs red light. The color of things depend on what colors are reflected or absorbed by molecules.

34. The Electromagnetic Spectrum c = f c = speed of light f = frequency  = wavelength

35. Luminescence = "light emission not due to heating something” 1.Fluorescence 2. Phosphorescence “delayed fluorescence”

36. Fluorescence Object only glows if shine some light on it The light shining on it may be “invisible”! The light glowing may also be “invisible” But the light glowing will always have a lower energy (i.e. lower frequency, longer wave) Ex: Shine sunlight (contains uv rays) on your clothes fluorescent detergent emits white light

37. Fluorescence doesn’t last! Incoming light excites electrons to a higher energy level, but then they quickly fall back down and release their energy as light

38. Fluorescence used in forensics, drug research, basic chemistry Fly parts Semen on armminerals

39. Blacklights : electron energy in, out is uv light

40. Phosphorescence keeps glowing! Incoming light excites electrons to a higher energy level, but then electron falls only partly to a middle metastable level and more slowly release extra energy as light

41. Phosphorescence lasts in the dark!