Ch.15.light
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Light travels in straight lines and can be reflected, refracted, or dispersed. Reflection occurs when light bounces off a surface, such as in mirrors. Refraction is when light changes speed and direction as it passes from one medium to another of different density, such as from air to water. White light can be dispersed by a prism into the colors of the visible spectrum.
![32 of 47 © Boardworks Ltd 2008
1. Place a rectangular glass
block on a sheet of paper and
draw around it.
2. Draw a normal at 90° to the top
surface of the block.
3. Shine light rays, with angles of
incidence [i] of 30°, 60° and 0°,
into the block at the point where
the normal meets the glass
surface. Record the angle of
refraction [r].
4. Repeat the investigation for rays
leaving the glass block.
5. What do the results show?
angle i
Refraction investigation
angle r
Angle of
incidence [i]
Angle of
refraction [r]
30°
60°
0°](https://image.slidesharecdn.com/ch-170213144413/85/Ch-15-light-32-320.jpg)
Ch.15.light
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- 2. 2 of 47 © Boardworks Ltd 2008 • Why do we see lightning before we hear thunder?
- 3. 3 of 47 © Boardworks Ltd 2008 Light and reflection • Describe objects as being luminous, non luminous, opaque, transparent, translucent • Draw ray diagrams to show the relationship between the angle of incident and the reflected ray
- 4. 4 of 47 © Boardworks Ltd 2008 Light carries energy and travels as a wave. What is light? Light waves travel in straight lines. Light travels at a speed of 300,000,000 metres per second, which is much faster than the speed of sound. Light is produced by the Sun, and by objects such as light bulbs and matches.
- 5. 5 of 47 © Boardworks Ltd 2008 An object that gives out light is described as luminous. How does light from a luminous object such as a light bulb reach the eye? How do we see things? Light travels in a straight line directly into the eye. LUMOS! Make a list of 5 objects that are luminous
- 6. 6 of 47 © Boardworks Ltd 2008 How do we see things? An object that does not give out light is non-luminous. How does your eye see a non-luminous object such as a comb? Light hits the comb and some of it is reflected into the eye. Make a list of 5 objects that are non- luminous
- 7. 7 of 47 © Boardworks Ltd 2008 Opaque: no light will pass through Transparent: all or most of the light passes through Translucent: some light passes through
- 8. 8 of 47 © Boardworks Ltd 2008 Light and Shadow https://www.youtube.com/watch? v=xgJdXpN9il4
- 9. 9 of 47 © Boardworks Ltd 2008 How can we change the size of a shadow ? (TRY AT HOME) Equipment : 1. ray box (to produce a strong ray of light). 2. card cut out 3. stand 4. screen at the back (white paper).
- 10. 10 of 47 © Boardworks Ltd 2008 How can we change the size of a shadow ? Method : 1.Use a ray box to produce a strong ray of light. 2.Make a card cut out and put it on a stand. 3.Put a screen at the back (white paper). 4.Measure the distance (from the light source to the cut out) and the height (of the shadow) 5.Keeping the distance from the light to the screen the same, move the cut out. 6. Repeat steps 4 and 5. 7.Record your measurements in a table.
- 11. 11 of 47 © Boardworks Ltd 2008 How can we change the size of a shadow ? Prediction : When the object is ________ (near/ far) to the light source the shadow is ___________ (taller/ shorter). How are you making your test fair ?
- 12. 12 of 47 © Boardworks Ltd 2008 Results table Distance of the object from the light source (cm) Height of shadow (cm) Is the shadow sharp or blurred?
- 13. © Boardworks Ltd 200813 of 47 Reflection
- 14. 14 of 47 © Boardworks Ltd 2008 Objects that reflect light well: Reflective materials Have smooth, shiny surfaces and are usually pale colours. Give clear images because they reflect light regularly. We see things when light bounces off them and enters our eyes. Most things reflect light in all directions. A mirror reflects light evenly. What is a plane mirror? Flat, shiny mirror made of glass – with a thin layer of aluminium or silver on the back
- 15. 15 of 47 © Boardworks Ltd 2008 Reflection at a mirror
- 16. 16 of 47 © Boardworks Ltd 2008 Reflection ray diagram
- 17. 17 of 47 © Boardworks Ltd 2008 Why is there a reflection here? but not here? Write your thoughts on your post it note
- 18. 18 of 47 © Boardworks Ltd 2008 Reflection Lesson Outcomes Say what causes a reflection in a plane (flat) mirror Describe how an image is formed by a plane mirror. Draw complex ray diagrams (level 7) Why are you able to see your reflection in a mirror? Watch the clip, then T.P.S. Video clip Key words: Reflection Angle of incidence Angle of reflection Plane mirror Real image Virtual image Normal line Wave front Watch another clip!
- 19. 19 of 47 © Boardworks Ltd 2008 Complete the ray diagrams to show where the image would appear in the plane mirror
- 20. 20 of 47 © Boardworks Ltd 2008 How is reflection useful in every day life? Try to come up with some examples by discussing with your partner!
- 21. 21 of 47 © Boardworks Ltd 2008 Reflection can be very useful. High-visibility strips are very reflective and make sure that this cyclist gets noticed when there is little light. Using reflection The two plane mirrors must be positioned at 45° from the vertical. Light is reflected at right angles from the top mirror onto the bottom mirror and into the eye of the viewer. How does a periscope use reflection?
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- 25. 25 of 47 © Boardworks Ltd 2008 Reflection: summary
- 26. 26 of 47 © Boardworks Ltd 2008 Reflection: true or false?
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- 28. 28 of 47 © Boardworks Ltd 2008 • What is refraction? • Why does refraction happen? • What happens when light hits a glass block at an angle? • What can you say about the refracted ray compared to the incident ray when light travels through air in to a glass block at an angle?
- 29. 29 of 47 © Boardworks Ltd 2008 glass air The speed of light depends on the material through which the light is travelling. Why is light refracted? When light enters a different material (e.g. from air into glass), the speed of light changes. This causes the light to bend or refract. The speed of light is affected by the density of the material through which it is travelling. When light enters a more dense medium (from air into glass), its speed decreases and this is why refraction occurs.
- 30. 30 of 47 © Boardworks Ltd 2008 What would happen if the light ray hit the glass block at an angle?
- 31. 31 of 47 © Boardworks Ltd 2008 Investigation in to what happens when light passes through air and then glass
- 32. 32 of 47 © Boardworks Ltd 2008 1. Place a rectangular glass block on a sheet of paper and draw around it. 2. Draw a normal at 90° to the top surface of the block. 3. Shine light rays, with angles of incidence [i] of 30°, 60° and 0°, into the block at the point where the normal meets the glass surface. Record the angle of refraction [r]. 4. Repeat the investigation for rays leaving the glass block. 5. What do the results show? angle i Refraction investigation angle r Angle of incidence [i] Angle of refraction [r] 30° 60° 0°
- 33. 33 of 47 © Boardworks Ltd 2008 Complete sheet 1
- 34. 34 of 47 © Boardworks Ltd 2008 Refraction through a glass block: Wave slows down and bends towards the normal due to entering a more dense medium Wave speeds up and bends away from the normal due to entering a less dense medium Wave slows down but is not bent, due to entering along the normal
- 35. 35 of 47 © Boardworks Ltd 2008 Refraction at the air-glass boundary
- 36. 36 of 47 © Boardworks Ltd 2008 Refraction in a glass block
- 37. 37 of 47 © Boardworks Ltd 2008 What happens during refraction?
- 38. 38 of 47 © Boardworks Ltd 2008 Draw the diagram in your book adding angles for the incident ray and the ray that comes out of the block!
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- 40. 40 of 47 © Boardworks Ltd 2008 Refraction causes visual effects such as this ruler appearing to be bent. Effects of refraction This happens because light from the part of the ruler in the water is refracted as it travels from the water into the air. Light rays from the stone are refracted as they leave the water. The brain assumes that these rays have travelled in straight lines and is fooled into forming an image where it thinks the image How does refraction make this stone look closer to the surface of the water than it really is? light rays came from. actual location
- 41. 41 of 47 © Boardworks Ltd 2008 The Archer fish is a predator that shoots jets of water at insects near the surface of the water, e.g. on a leaf. The Archer fish allows for the refraction of light at the surface of the water when aiming at its 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 watch: Effects of refraction – the Archer fish Light is refracted when it passes through air in to water (but not as much as when it passes through air in to glass).
- 42. 42 of 47 © Boardworks Ltd 2008 Refraction summary
- 43. 43 of 47 © Boardworks Ltd 2008 Refraction – true or false?
- 44. 44 of 47 © Boardworks Ltd 2008 How the eye works
- 45. 45 of 47 © Boardworks Ltd 2008 Refraction in the eye
- 46. 46 of 47 © Boardworks Ltd 2008 Colours and filters Learning Objectives: Describe how white light becomes a spectrum of colour (5) Explain how a coloured filter works and why certain objects look certain colours in different light (7)
- 47. 47 of 47 © Boardworks Ltd 2008 Passing white light through a prism
- 48. 48 of 47 © Boardworks Ltd 2008 A prism splits a ray of white light into the colours of the rainbow. This process is known as dispersion. The colours that make up white light are called the spectrum. The order of the colours in the spectrum is always the same. Splitting white light Richard Of York Gave Battle In Vain Use this phrase (mnemonic) to remember the order of colours:
- 49. 49 of 47 © Boardworks Ltd 2008 Colours of the spectrum
- 50. 50 of 47 © Boardworks Ltd 2008 Recombining colours
- 51. 51 of 47 © Boardworks Ltd 2008 Newton’s disc animation
- 52. 52 of 47 © Boardworks Ltd 2008 The three primary colours of light (red, green and blue) can be mixed in different amounts to make all other colours. Primary and secondary colours The colours made by mixing two primary colours are called the secondary colours – magenta, yellow and cyan. red green blue magenta
- 53. 53 of 47 © Boardworks Ltd 2008 Mixing coloured light
- 54. 54 of 47 © Boardworks Ltd 2008 Which primary colours?
- 55. 55 of 47 © Boardworks Ltd 2008 How do we see different colours?
- 56. 56 of 47 © Boardworks Ltd 2008 How do we see the different colours in this frog’s skin? Seeing different colours This skin absorbs all colours. No colours are reflected and so it appears black. How do we see the different colours in this flower? This part absorbs all colours except red and green. It reflects red and green light, and so appears yellow. This part absorbs no colours. It reflects all the colours and so appears white. This skin absorbs all colours except red and so is seen as red.
- 57. 57 of 47 © Boardworks Ltd 2008 Colour you see Colour light that is reflected white Black red yellow Green Blue
- 58. 58 of 47 © Boardworks Ltd 2008 Recap on last lesson 1. What do we call the separation of white light and how is it done? (2) 2. Name all 7 colours of the spectrum in order (1) 3. Which is refracted most, red or violet light? (1) 4. Give two ways of making white light again (2) 5. What are the three primary colours? (1) 6. Name the three secondary colours and which primary colours make each one (3)
- 59. 59 of 47 © Boardworks Ltd 2008 A red filter absorbs all colours… A blue filter absorbs all colours… A green filter absorbs all colours... …apart from red light. …apart from blue light. …apart from green light. Using filters of primary colours: watch A filter absorbs some colours of white light and lets other colours through to create coloured light.
- 60. 60 of 47 © Boardworks Ltd 2008 A magenta filter absorbs all colours… A cyan filter absorbs all colours… A yellow filter absorbs all colours... …apart from red and blue. …apart from green and blue. …apart from red and green. Using filters of secondary colours
- 61. 61 of 47 © Boardworks Ltd 2008 Seeing colours in coloured light
- 62. 62 of 47 © Boardworks Ltd 2008 How do we see colours in coloured light?
- 63. 63 of 47 © Boardworks Ltd 2008 Coloured light activity
- 64. 64 of 47 © Boardworks Ltd 2008 What colour does it appear?
- 65. 65 of 47 © Boardworks Ltd 2008 • 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
- 66. 66 of 47 © Boardworks Ltd 2008 Some further examples: Object Colour of light Colour object seems to be Red socks Red Red Blue Black Green Black Blue teddy Red Black Blue Green Green camel Red Blue Green Magenta book Red Blue Green
- 67. 67 of 47 © Boardworks Ltd 2008 Using filters • Filters can be used to “block” out different colours of light: Red Filter Magenta Filter
- 68. 68 of 47 © Boardworks Ltd 2008 Investigating filters Colour of filter Colours that could be “seen” Red Green Blue Cyan Magenta Yellow
- 69. 69 of 47 © Boardworks Ltd 2008 • This little light of mine • I’m going to let it shine • This little light of mine • Shines in straight lines • Let it shine • Let it shine • Let it shine • Let it shine This little light of mine Aka the incident ray This little light of mine Reflected the other way Let it shine Let it shine Let it shine Let it shine
- 70. 70 of 47 © Boardworks Ltd 2008 Red Magenta White Yellow Blue Green Cyan