WALT: about colour

1. WALT: about colour

2. Activity Lack of colour Imagine you could only see in black and white. What are the possible implications this could have on your life? Would it rule out any careers for you? What dangers could there be?

3. Colour : splitting white light up • Shine a ray of bright white light at a prism, as shown above, and move the prism until colours appear.

4. Explanation What happens? Why? The white light ray is split into a spectrum of colours. This is known as DISPERSION. The different colours of light have different wavelengths. Different wavelengths are refracted different amounts. Which colour is refracted the most? RichardOfYorkGaveBattleInVain Red light is refracted least. How do you remember the order of the colours? Violet light is refracted the most.

5. Dispersion • Each of the colours [ROYGBIV] has a slightly different waveform - what is different? They each have a different wavelength [].

6. Dispersion Red light is refracted least because it has a long wavelength. Violet light is refracted the most because it has the shortest wavelength. Because the different colours of light have different wavelengths they are bent (refracted) by different amounts. But which colour do you think is bent the most?

8. Subtractive Colour – Paints and Dyes

9. Additive Colours - Light

10. Newton’s disc

11. Practical – Explore Colour • Shine light from the ray box through a colour filter on to different coloured objects and record the colour they appear. • Record results in a table.

13. Seeing colours How do we see objects like a book? We see objects by light striking an object and then reflecting into our eye. How do we see colour? Why does a red dress look red? Why does a green apple look green?

14. The snooker ball absorbs all the colours of the spectrum EXCEPT red, so red light is reflected into our eye. The snooker ball appears red. Red objects Why does a red snooker ball look red in white light? Remember white light is made of a spectrum of colours.

15. The snooker ball absorbs all the colours of the spectrum EXCEPT green, green light is reflected into our eye. The snooker ball appears green. Green objects Why does a green snooker ball look green in white light?

16. Black objects Why does a black snooker ball look black in white light? The snooker ball absorbs all the colours of the spectrum. NO light is reflected into our eye. The snooker ball appears black.

17. The snooker ball doesn’t absorb any of the colours of the spectrum. The whole spectrum of light is reflected into our eye. The snooker ball appears white. White objects Why does a white snooker ball look white in white light?

18. The ball absorbs all the colours of the spectrum EXCEPT red and blue, red and blue light is reflected into our eye. The ball appears to be magenta, a mixture of red and blue light. Magenta objects Why does a magenta ball look magenta in white light?

19. Look at the clothes below. What colour light is reflected by these clothes?

20. What colours are absorbed by this frog’s skin? What colours are reflected into your eyes? This part of the skin absorbs all the colours of the spectrum but reflects red light. This part of the skin absorbs all the colours of the spectrum and none are reflected.

21. Filters Filters let certain colours of light pass through, but absorb all other colours. Using different coloured filters placed in front of your eye, look around the classroom and see what effect they have on your vision. filter Object

22. … apart from red light … apart from blue light … apart from green light Red, blue and green filters Red filters absorb all colours…. Blue filters absorb all colours…. Green filters absorb all colours….

23. Magenta, cyan and yellow filters Magenta filters absorb all colours…. … apart from red and blue light Cyan filters absorb all colours…. … apart from blue and green light Yellow filters absorb all colours…. … apart from red and green light

25. But why do colours look different in different coloured light? Lets start with the example of a red ball in red light. The red light shines on the ball. The red ball reflects red light and so appears red.

26. What about the red ball in green light? The green light shines on the ball. The red ball only reflects red light so it absorbs the green light and reflects nothing. Because it doesn’t reflect any type of light it appears black. The green ball only reflects green light so it absorbs the red light and reflects nothing. Therefore it appears black. So what colour does a green ball appear in blue light?

27. But what if the filter you are using lets through more than one type of light. For example what will our red ball look like in magenta light. The magenta light shines on the ball. Remember that magenta is a mixture of blue and red light The ball reflects only red light. Therefore it absorbs the blue light and reflects the red light. It will appear to be red.

28. Over the next two slides you will be shown the same girl as in the previous example. However, she will be standing in a different coloured light each time. The colour of this light is written at the top of the slide. Your task is to drag the correct shirt and trousers onto the girl to represent what those clothes would look like in this coloured light.

31. Complete the table below by adding in the colour that each object would appear to be in the conditions listed. red black black blue green black red and black

32. Actvity Flag colours For the flag shown, draw what it will look like in: a) Red light b) Green light c) Blue light

33. Multiple Choice Questions

34. The Sun A star Traffic lights A book Which of the following is not a light source? 

35. Your hand Jupiter Light bulb The Moon Which of the following is not seen by reflected light? 

36. Air Water Glass Lead Which of the following is the most dense? 

37. Reflection Refraction Diffraction Total internal reflection When light changes direction as it moves from one medium to another we call this effect what? 

38. It continues with no change of direction It bends towards the normal It bends away from the normal It stops If a ray of light moves from a more dense medium to a less dense medium at an angle to the normal what happens? 

39. Blue Indigo Yellow Red Which colour has the longest wavelength? 

40. Red Orange Yellow Green Which colour below is refracted (bent) the least by a glass prism? 

41. Red Blue Cyan Green Which of the following is not a primary colour? 

42. Red and cyan Red and yellow Red and blue Blue and violet Which two primary colours make magenta? 

43. Red Red and blue Blue Black If white light passed through a magenta filter and then a blue filter, what colour would emerge? 

44. Red Green Blue Black What colour would a red dress look in cyan light? 