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3. Light : What is Light? Light carries energy and travels as a wave.
Light travels at m/s or km/s (much faster than sound).
Light waves travel in straight lines.

4. Light : What materials will light travel through?
 Hold different materials between the lamp and the screen. Use the results table and shading chart on the next slide to estimate the opacity of different materials.

5. What materials let light through?
Shading chart.
100%
2.5 %
75 %
5 %
50 %
10 %
30 %
15 %
25 %
20 % 0%
Opaque objects do not allow light to pass through them - transparent ones do. Translucent materials only let through part of the light.

6. How does light travel?
1) Fill a clear glass trough or empty fish tank with smoke.
2) Shine rays of light through the tank and describe what you see.
 LIGHT WAVES TRAVEL IN STRAIGHT LINES.

7. The light from the object enters our eye.
Seeing objects
How do we see an object?
The light from the object enters our eye.
Do we see all objects in the same way?
There are two ways we see objects…..
We see some objects by reflected light.
We see other objects because they are light sources.

8. Light sources
How do light rays from a light bulb and other light sources reach our eye?
They travel in a straight line directly into our eye.

9. Reflected light
How do light rays from a book and other such (non-luminous) objects reach our eye?
Light from the lamp or another light source strikes the book and some of the light is reflected into our eye.

10. Reflection : Good or Poor?
 Objects which reflect light well have smooth, shiny surfaces and are usually pale colours.
 They give clear images because they reflect the light regularly.
 Mirrors are excellent reflectors.
 Objects which do not reflect light well have rough, matt surfaces and are usually dark colours.
 They give no or diffuse images because they reflect the light irregularly.

11. Reflection : Good or Poor?
Best Reflectors
Red Roses
Yellow Banana
Tarmac Road
White Paper
Blue Car
Polished Black Shoes
Tangerine
Green Leaf
Al foil
Tree Bark
Worst Reflectors
Arrange these items along the arrow:

12. What happens to the light which isn’t reflected?
Some of this light may be absorbed (e.g. as heat).
Some of this may also be transmitted (e.g glass reflects a small amount of light, absorbs some of the rest and allows most of it to pass through.

13. Reflection: Investigating Reflection.
 These activities allow you to investigate the main laws of reflection.
 You should summarise each investigation with a law you have written based on that exercise.
1) Reading in mirrors.
2) How far away is the image?
3) The maths of reflection.
4) Reflecting without mirrors.

14. Reflection: 1. Reading in Mirrors.
 In small groups, take it in turns to read the list of words on the next slide with your back to the screen using a mirror.
 You can only move on to the next word when you read the first word correctly.
 Put your results in a table like this:

15. Reflection : 1. Words Dog Man Ball Bat Bike Ants Park Fins Pink
Litter Sandy Shark
No Cheating

16. Reflection : 1. Results A) Who read the words in the quickest time?
B) Plot a bar chart of you r results like:
C) What was the average time taken in your group?

17. Reflection : 1. Lateral inversion
The way plane mirrors reflect light regularly gives a clear image which is the same size as the object
- but what is different about the image ?
Physics
Physics
 This is called lateral inversion.

18. Place a pin as the object in front of the mirror.
Reflection : 2. How far away is the image? I
1. Fix a plane mirror along the centre of a piece of A4 paper and draw around it.
Place a pin as the object in front of the mirror.
2. Line up a ruler with the image of the pin and draw along the edge of the ruler on the paper. Repeat for 3 more positions of the ruler.
3. Remove the mirror and ruler. Where the lines cross is the image position. What are the distances between the mirror and object and its image?

19. Reflection : 3. The Maths of Reflection
 Fix a plane mirror to a piece of A5 paper and draw around it.
 Draw a normal line (at 90º) through the middle of the mirror outline.
Angle i
 Use a ray box to shine an incident ray at the mirror - plot the incident and reflected rays.
Angle r
 Measure the angles of incidence [i] and reflection [r] and write the answers in the table on the right.
 Repeat for another 5 angles of incidence.

20. Reflection : 4. Reflecting without mirrors
 Mirrors are good reflectors but not perfect - they give 2 reflections.
 We use glass prisms instead of mirrors in good quality binoculars and other instruments.

21. Reflection : 4. Reflecting without mirrors
 Shine rays of light into a prism as shown in the ray diagrams below.
 Copy and complete the ray diagrams using a ruler and pencil.
 Don’t forget to include arrows on your rays!

22. Using plane mirrors
By positioning two plane mirrors at 45° to each other at either end of a tube we can make a _________.
periscope
Periscopes are used in _________.
submarines

23. Reflection : Summary You should now know that :
 Pale and shiny surfaces are good reflectors, dark and rough surfaces are not.
 The image in a plane mirror is laterally inverted.
 The image is the same distance behind the mirror as the object is in front.
 The image in a plane mirror is the same size as the object.
 angle of incidence = angle of reflection
¡ = r

24. Refraction

25. Refraction : Bending light
 The speed of light waves depends on the material they are travelling through.
 If the light waves enter a different material [e.g. from glass into air] the speed changes.
 This causes the light to bend [or refract].
Air = Fastest
Glass = slower
Diamond = slowest
Glass

26. Refraction - at the air-glass boundary

27. Refraction : Investigating Refraction
1. Place a rectangular glass block on a sheet of paper and draw around it.
Angle i
2. Draw a normal line [90º] along the top surface of the block.
Angle r
Shine rays of light with incident [i] angles of 30º, 60º and 0º into the block, making sure they all hit where the normal line crosses the glass surface].
Measure angle “r” each time and record your answers .

28. Refraction : What happened?
 Put your answers into the table below:
 Write 2 ‘rules’ to describe:
a) what happens to the ray as it enters the glass.
b) what happens to the ray as it re-enters the air.

29. Air to Glass: angle of incidence > angle of refraction I > r
As the light ray moved from air into glass it moved towards the normal.
If light rays move from a less dense medium (air) to a more dense medium (glass) they ‘bend’ towards the normal.

30. Glass to Air angle of incidence < angle of refraction i < r
As the light ray moved from glass into air it moved away from the normal.
If light rays move from a more dense medium (glass) to a less dense medium (air) they ‘bend’ away from the normal.
If the surface the light ray is incident upon is parallel to the surface it emerges from than the emergent ray makes the same angle with the normal as the incident ray.
(If the two surfaces of the block are parallel, then the ray at the start is parallel to the ray at the end).

31. Angle of incidence = 0°
When the angle of incidence is 0 the light ray is not deviated from its path.
Un-deviated light ray

32. Refraction in a rectangular block

33. Revision tip Remember the word: TAGAGA Towards (normal) Air Glass
Away (from normal)

34. Fast and slow In the water.
If you were running along a beach and then ran into the water when would you be moving slower, in the water or on the beach?
In a similar way as light moves from one medium to another of different density the speed of light changes.
Do you think light moves faster or slower in a more dense medium?
In the water.
Light moves slower through a more dense medium.

35. The speed of light
Light travels at km/s in a vacuum.
As it enters denser media the speed of light decreases.
Looking at the chart, which do you think is denser, Perspex or water?
Perspex must be denser because light travels more slowly through Perspex than water.

36. Why does light change direction as it enters a material?
Imagine a car driving from the road into a muddy field.
In the muddy field it slows down as there is more friction.
If it enters the field at an angle then the front tyres hit the mud at different times.
Tyre one hits the mud first and will move more slowly than tyre two.This causes the car to turn towards the normal.
When the car leaves the mud for the road, tyre one hits the road before tyre two and this causes the car to turn away from the normal.
Tyre Tyre2
Road
Mud

37. No change in direction
If the car approached the muddy field at an angle of incidence of 0° then both front tyres would hit the mud at the same time.
The tyres would have the same speed relative to each other so the direction of the car would not change, it would just slow down.

38. Same for light
When light hits a medium at an angle to the n_____ the light ‘bends’ in a similar way to that described for the car in a muddy field. Part of the light ray s____ d___ before the rest and this causes the change of d______.
If the light enters a new medium along the normal (i = 0) then it does not ‘bend’ because all of the light ray slows down at the s___ t___.
ormal
ame ime
lows own
irection

39. Refraction : Effects of Refraction
 Many visual effects are caused by refraction.
 This ruler appears bent because the light from one end of the ruler has been diffracted, but light from the other end has travelled in a straight line.
 Would the ruler appear more or less bent if the water was replaced with glass?

40. Refraction : Apparent Depth
The rays of light from the stone get bent [refracted] as they leave the water.
Your brain assumes they have travelled in straight lines.
Image
Actual location
Your brain forms an image at the place where it thinks the rays have come from - the stone appears to be higher than it really is.

41. The Archer fish
The Archer fish is a predator that shoots jets of water at insects near the surface of the water, say on a leaf.
The Archer fish allows for the refraction of light at the surface of the water when aiming at the prey.
The fish does not aim at the refracted image it sees but at a location where it knows the prey to be.
image of prey
prey location

42. Refraction : Magic coins
Place a coin in the bottom of a bowl and clamp an empty cardboard tube so that it points above the coin.
Gradually add water to the bowl and watch the coin through the tube float up - can you explain this?

43. Refraction : Summary  When light bends this is called refraction.
 Refraction happens because the light changes speed [or velocity].
 When light enters a more dense medium [e.g. glass], it bends towards the normal.
 When light enters a less dense medium [e.g. air], it bends away from the normal.
 If the incident ray hits a surface at 0º, no refraction occurs.
 Remember that the angle of reflection [r] and angle of refraction [r] have the same symbol.
In reflection, I = r
In refraction, I  r

44. Colour

45. Lack of colour Activity 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?
You must give a two minute presentation to the rest of the group on your ideas.

46. 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.
Draw a diagram to show what your observed.

47. Explanation What happens? Why? Which colour is refracted the most?
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?
Richard Of York Gave Battle In Vain
How do you remember the order of the colours?
Red light is refracted least.
Violet light is refracted the most.

48. Colour : splitting white light up

49. Colour : splitting white light up
Until now we have used the title ‘splitting white light up’. However this process has a scientific name.
The splitting of white light into a spectrum of colours is called DISPERSION.
But why does white light get dispersed?

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

51. But which colour do you think is bent the most?
Dispersion
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?
Red light is refracted least because it has a long wavelength.
Violet light is refracted the most because it has the shortest wavelength.

53. Colour : joining the colours back together
Remember how you dispersed white light to give a spectrum of colours?
Now do the opposite to it - you’ll need 2 prisms!
A similar effect can also be seen using a colour wheel [or Newton’s disc].

54. Newton’s disc
Colour in a paper or card circle with the colours of the spectrum.
What do you predict you will see?
What did you observe?
Using string or a pencil spin your disc around.
What does this tell you?

55. Newton’s disc

56. 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?

57. Primary Colours Animation

58. Primary Colours
You can make any colour by mixing three colours. Do you know what they are?
Yellow
The colours labelled in blue text are called SECONDARY COLOURS. They can be made by mixing the primary colours
Green
Red
The colours labelled in white text are the PRIMARY COLOURS.
Cyan
Magenta
Blue

60. Red objects Why does a red snooker ball look red in white light?
Remember white light is made of a spectrum of colours.
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.

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

62. 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.

63. White objects Why does a white snooker ball look white in white light?
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.

64. Why does a magenta ball look magenta in white light?
Magenta objects
Why does a magenta ball look magenta in white light?
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.

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

66. What colours are absorbed by this frog’s skin
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.

67. What colours are absorbed by this flower
What colours are absorbed by this flower? What colours are reflected into your eyes?
This part of the flower absorbs all the colours of the spectrum but reflects yellow (a mixture of red and green) light.
This part of the flower absorbs no colours, it reflects them all.

68. 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

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

70. 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

72. The red light shines on the ball.
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.

73. The green light shines on the ball.
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?

74. 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.

75. 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.

76. Drag and drop activity

77. Drag and drop activity

78. Complete the table below by adding in the colour that each object would appear to be in the conditions listed.
Object (Colour)
Colour Filter
Appearance
red ball
red
blue
blue book
green
magenta
green apple
cyan
red and blue tie
red
black
black
blue
green
black
red and black

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

80. Multiple Choice Questions

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

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

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

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

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

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

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

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

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

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

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