2. 1) Recall that the electromagnetic spectrum is a family of waves and give 2 examples 2) Recognise that light travels in straight lines. 3) Explain, in terms of colour absorption and reflection, why an object appears to be a particular colour and why its appearance changes in different coloured light. 4) Explain the effect of coloured filters on light. 5) Demonstrate how white light can be spilt using a prism and use the terms dispersion and spectrum. 6) Label the parts of the human eye and describe their functions 7) Describe how we see ourselves in mirrors (plane and curved). 8) Describe the effect of lenses on light 9) State some uses for concave and convex mirrors 10) State some uses for concave and convex lenses. Objectives

3. What is light? Light is a form of energy that travels in waves. It is part of the family of waves called the electromagnetic spectrum (see powerpoint on electromagnetic spectrum) Light waves are too small to see but different colours of light have different wavelengths. Red light has a longer wavelength than violet light.

4. Wavelength Wavelength is the distance between the crests of two waves. The symbol for wavelength is the Greek symbol, λ

5. Types of Waves Transverse waves- made on a slinky by moving the end of the slinky at right angles. Longitudinal waves- made by pushing the end of the slinky back and forward in the direction of the wave (pulse).

6. Sound travels as a longitudinal wave or vibration. Light travels as a transverse wave like the waves at the beach.

7. A light source is something that produces light e.g.________________________________ A light detector is something that senses light e.g ________________________________ A light reflector is something that reflects light e.g.________________________________ Sources, detectors and reflectors.

8. light bulb candle motion sensor laser sun moon computer screen mirror light meter

9. Experiment: Can light bend? Collect ray box and a piece of rubber tubing for your group. Plug in and switch on the ray box. Close one eye and look through the tubing at the light with your other eye. What do you need to do to the tubing to be able to see the light? What does this tell you about light? Draw a diagram in your Science book to explain this experiment.

10. Light terminology Light rays can be: Absorbed (taken in) by an object Reflected off an object Refracted (pass through an object but change direction) Objects can be: Transparent (let all light pass through) Translucent (let some light pass through) Opaque (let no light through)

11. TransparentOpaque Translucent Allows light to pass through freely. Only a small amount of light is absorbed or reflected. Prevents any light from passing through it. It will only absorb or reflect light. Most light rays pass through, but are scattered in all directions. Different Materials

12. Behaviour of light Light travels at 300 000 kms -1 in space. This is called the speed of light. (the speed of sound is only 340 ms -1 ) Light travels in straight lines A stream of light travelling in the same direction is called a ray.

13. ShadowSolid Object Light travels in a straight line.

14. Light travels in straight lines

15. Rays and Reflection Light rays which are coming in are called incident rays Light rays that have bounced off an object are called reflected rays Incident ray Reflected ray Object surface

16. Specular vs. Diffuse Reflection Applications of Specular and Diffuse Reflection: Countertop surfaces Furniture or car wax Glazed vs, unglazed ceramics Matte vs. Glossy finish on photographs or in paint

17. The Normal The normal is an imaginary line at right angles to the object surface at the point where the incident ray hits the surface Incident ray Object surface normal

18. Drawing and labelling rays off of a plane mirror -

19. Conclusion The angle of incidence always equals the angle of reflection.

20. 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 Using plane mirrors

21. How periscopes work Periscopes prove that light travels in straight lines

22. Plane Mirrors Reflected Images The image formed in a plane mirror is always the ________ size as the object. It is the ________ way up, but the _________ are swapped over. The image is always as far behind the mirror as the object is in front. We say the image is laterally inverted. The image in a plane mirror is virtual because it forms in a place where light does not pass. (Answer) The image formed in a plane mirror is always the same size as the object. It is the right / same way up, but the sides are swapped over.

23. Concave mirrors (Shaped like a cave) Concave mirrors cause rays to CONVERGE (come together) and meet at a focal point called the focus. The focal length is the distance from the focus to the mirrors reflecting surface

24. Concave Mirror

25. Solar cookers A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize food or drink. Many solar cookers presently in use are relatively inexpensive, low-tech devices, although some are as powerful or as expensive as traditional stoves, [1] and advanced, large-scale solar cookers can cook for hundreds of people. [2] Because they use no fuel and cost nothing to operate, many not for profit organizations are promoting their use worldwide in order to help reduce fuel costs and air pollution, and to slow down the deforestation and desertification caused by gathering firewood for cooking. Solar cooking is a form of outdoor cooking and is often used in situations where minimal fuel consumption is important, or the danger of accidental fires is high, and the health and environmental consequences of alternatives are severe. [3]pasteurizelow-tech [1] [2]deforestationdesertificationoutdoor cooking [3] Cooking sausages on a solar cooker

26. Parabolic solar cookers can reach high temperatures over 400°C (750°F) and can be used to fry, grill, steam and bake. SolSource solar stove is an example of a high temperature parabolic cooker.SolSource

27. Optical (visible light) telescopes Optical telescopes use a concave mirror or a convex lens to collect light from distant objects. The greater the size of the mirror or lens: - the more light is collected - the more the image can be magnified - the brighter the image seen - the more detail seen in the image produced. The Mount Palomar telescope in California, with an objective mirror of 5m (200 inches), was for many years the world’s largest telescope

28. Convex mirrors Convex mirrors cause rays to DIVERGE. The focal point is behind the mirror and virtual.

29. Images in a convex mirror Convex mirrorClose upFar away Small/large Upside down/right way up

30. Light rays onto a covex mirror

31. Uses of Convex Mirrors

32. Lenses There are two different types of lenses. Converging/biconvex Diverging/ Biconcave

33. Below you can see the effect these lenses have on light. ---- Concave lensConvex lens Light bends as it goes through the lenses

34. Measuring the focal length of a lens ---- Focal length is the distance between the middle of the lens and the focal point

35. Uses of lenses Binoculars Glasses Camera Telescope Magnifying glass Projectors

36. How do glasses correct vision. Contact lenses work in same way as glasses. However the lens is not glass, but a type of breathable plastic and it sits on your cornea.

37. The Eye

38. Parts of the eye and their functions Cornea – thin clear covering over the front of the eye. Pupil – hole in the centre of the iris, it changes size in bright light and dull light Iris – coloured part of the eye, makes the pupil bigger or smaller Lens – focuses light onto the retina Retina – cells at the back of the eye that can detect light Optic nerve – carries message from the retina cells to the brain.

39. Parts of the eye and their functions Cornea – thin clear covering over the front of the eye. Pupil – hole in the centre of the iris, it changes size in bright light and dull light Iris – coloured part of the eye, makes the pupil bigger or smaller Lens – focuses light onto the retina Retina – cells at the back of the eye that can detect light Optic nerve – carries message from the retina cells to the brain.

40. The lens in the eye is a convex lens. Convex lenses are thicker at the middle. Rays of light that pass through the lens are brought closer together (they converge). A convex lens is a converging lens. When parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus. The distance between the principal focus and the centre of the lens is called the focal length.

41. In the eye the convex lens turns the image upside down. The brain turns it back up the right way, so we do not trip over things. An experiment was done where a special pair of glasses was designed that turned everything a person saw upside down. After a few days of wearing these glasses the brain automatically corrects what it sees. Remarkably when you take the glasses off everything you then see is upside down. It then takes the brain a few days to turn it back up the right way!

42. How we see things!

43. Splitting white light - When white light passes through a prism it is DISPERSED – this means it splits into separate colours. We see the 7 colours of the SPECTRUM when this happens. Red light bends the least (it has the longest wavelength). Violet light bends the most (it has the shortest wavelength).

44. The colours of the spectrum - ROYGBIV Red Orange Yellow Green Blue Indigo Violet

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

46. Newton’s disc animation

47. You see a non-luminous object when light hits the object and is then reflected into your eyes. So how do we see different colours? Why does a red dress look red? Why does a green apple look green? How do you see non-luminous objects such as a book? Seeing colours

48. Primary colours animation

49. Colours are made by mixing other colours of light. There are three primary colours of light used to make all other colours. What are these colours? red green blue The three primary colours of light are red, green and blue. magenta Primary and secondary colours The colours made by mixing two primary colours are called the secondary colours – magenta, yellow and cyan.

50. Which primary colours?

51. Why does a red snooker ball look red in white light? White light is made up of a spectrum of colours. The snooker ball absorbs all the colours of the spectrum except red. Only red light is reflected into your eye, so the snooker ball appears red. Seeing red

52. Why does a green snooker ball look green in white light? Seeing green The snooker ball absorbs all the colours of the spectrum except green. Only green light is reflected into your eye, so the snooker ball appears green.

53. Why does a black snooker ball look black in white light? Seeing black The snooker ball absorbs all the colours of the spectrum. No light is reflected into your eye, so the snooker ball appears black.

54. Why does a White snooker ball look in white light? Seeing white The snooker ball does not absorb any of the colours of the spectrum. The whole spectrum of light is reflected into your eye, so the snooker ball appears white.

55. Why does a magenta ball look magenta in white light? Seeing magenta The snooker ball absorbs all the colours of the spectrum except red and blue. Red and blue light are reflected into your eye, so the snooker ball appears magenta.

56. Which colours of light are reflected by these clothes? Which colour is reflected?

57. 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 except red, and so reflects red light. Seeing different colours This part of the skin absorbs all the colours of the spectrum and none are reflected.

58. What colours are absorbed by this flower? What colours are reflected into your eyes? Seeing different colours This part of the flower absorbs all colours except red and green. It reflects red and green light, and so appears yellow. This part of the flower absorbs no colours. It reflects them all and so appears white.

59. 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. object filter Using coloured filters

60. 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. Red, blue and green filters

61. 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. Magenta, cyan and yellow filters

62. Using colour filters

63. Why do colours look different in different coloured light? Consider a red ball in red light. The red light shines on the ball. The red ball reflects the red light and so appears red. Seeing colours in coloured light

64. What colour does a red ball appear in green light? Seeing colours in coloured light The green light shines on the ball. The red ball only reflects red light and so it absorbs the green light. So in green light, this ball does not reflect any light and so appears black.

65. What colour does a green ball appear in blue light? Seeing colours in coloured light The blue light shines on the ball. The green ball only reflects green light and so it absorbs the blue light. So in blue light, this ball does not reflect any light and so appears black.

66. What happens when using a coloured filter which lets through more than one type of light? What will a red ball look like in magenta light? Seeing colours in coloured light The magenta light, which is a mixture of red and blue light, shines on the ball. The red ball only reflects red light and so absorbs the blue light. So in magenta light, this ball reflects the red light and appears red.

67. The next two slides include a girl wearing a t-shirt and trousers. The girl is standing in a different coloured light each time. The colour of this light is written at the top of the slide. The aim of each activity is to decide what colours the girls’ clothes would appear in each type of coloured light. Coloured light activity – instructions

68. Coloured light activity 1

69. Coloured light activity 2

70. How would the colours in this flag appear under these lighting conditions? Flag colours in different coloured light a)red light b)green light c)blue light

71. Object (Colour)Colour FilterAppearance red ballred red ballblue blue bookgreen blue bookmagenta green applecyan green applemagenta red and blue tiered black blue green black red and black What colour does each object appear under the given lighting conditions? What colour does it appear?

72. Rainbows Sunlight is refracted as it enters a raindrop, which causes the different wavelengths of visible light to separate. Longer wavelengths of light (red) are bent the least while shorter wavelengths (violet) are bent the most.refracted Page 137 SW9

73. Anagrams

74. Multiple-choice quiz

75. How and why we see colour http://www.amonline.net.au/colour/colour14.swf 18. Explain, in terms of colour absorption, why an object appears to be a particular colour and why its appearance changes in different coloured light.

76. To demonstrate why objects are certain colours click on the hyperlink below and go to: Seeing colour Reflection and absorption http://www.amonline.net.au/colour/colour14. swf

77. Telescopes A telescope is an instrument designed for the observation of remote objects. The earliest known telescopes are credited to three individuals, Hans Lippershey and Zacharias Janssen, spectacle-makers in Middelburg, and Jacob Metius of Alkmaar "Telescope" (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') was a name invented in 1611 by Galileo Galilei.Hans LippersheyZacharias JanssenJacob MetiusAlkmaarGreekGalileo Galilei There are three types of telescopes Click here to see the telescopes in action

78. Refractor Refracting telescopes gather light with a lens, directing it to the eyepiece.

79. Reflecting telescopes Reflecting telescopes gather light with a mirror, reflecting it before directing it to the eyepiece. The simplest type of reflecting telescope is called a "Newtonian," after Sir Isaac Newton who invented them.

80. Compound Another major class is the Catadioptrics (compound) these systems combine both mirrors and lens elements. One of their main features is a "folding" of the optical system, to fit a long effective focal length into a shorter tube.

81. Pictures from telescopes Spiral GalaxyMars Eagle NebulaSun