Light & Colour


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Light & Colour

  1. 1. Welcome Back Term 3 and Term 4
  2. 2. Administrative Stuff <ul><li>Hand up Science Holiday Assignment now or the next time I will see you </li></ul><ul><li>Hand up Science File now or the next time I will see you </li></ul><ul><li>Textbook Volume 2 </li></ul><ul><ul><li>But don’t throw away your Volume 1 because you will still need to learn the 2 chapters in Volume 1 for final year exams </li></ul></ul>
  3. 3. Chapters that will be covered in Term 3 <ul><li>Light and Colour </li></ul><ul><li>Introducing Electricity </li></ul><ul><li>Household Electricity </li></ul><ul><li>Force and Pressure </li></ul>
  4. 4. Chapters that will be covered in Term 4 <ul><li>Forces at Work </li></ul>
  5. 5. Light and Colour <ul><li>State the speed of light </li></ul><ul><li>Define luminous and non luminous object </li></ul><ul><li>State that light travels in a straight line </li></ul><ul><li>Angle of incidence = angle of reflection </li></ul><ul><li>Distinguished between regular and diffused light </li></ul><ul><li>Define reflection </li></ul><ul><li>State characteristics of image in a plane mirror </li></ul><ul><li>State the uses of plane and curved mirror </li></ul>
  6. 6. Light and Colour <ul><li>Define refraction and its effects </li></ul><ul><li>Describe the dispersion of white light by prism </li></ul><ul><li>Describe how rainbow is formed </li></ul>
  7. 7. Introducing Electricity <ul><li>To draw and circuit diagram with variety of electrical component </li></ul><ul><li>Explain the meaning of current, voltage, resistance and to state their units </li></ul><ul><li>Recognize the resistance of circuit can be varied by arranging resistors in series and in parallel </li></ul><ul><li>Explain how heating, magnetic and chemical will affects of an electric current and its applications </li></ul><ul><li>Importance of electricity </li></ul>
  8. 8. Household Electricity <ul><li>Explain what is meant by power and its unit </li></ul><ul><li>Solve problems in the cost of using electrical appliances </li></ul><ul><li>Discuss on reducing electrical energy waste </li></ul><ul><li>State electrical hazards and precautionary measures </li></ul><ul><li>To appreciate the need of Singapore which has no natural resources of her own to conserve energy </li></ul>
  9. 9. Force and Pressure <ul><li>Define force as push or pull </li></ul><ul><li>List different types of forces </li></ul><ul><li>Effects of forces </li></ul><ul><li>Newton as the unit of force </li></ul><ul><li>Define pressure </li></ul><ul><li>Application pressure </li></ul><ul><li>Simple calculations in pressure </li></ul>
  10. 10. Do worksheet on the introduction of light and colour Unscramble the words
  11. 11. E3: Light and Colour Textbook pg 34
  12. 12. Objectives <ul><li>At the end of this lesson you should be able to: </li></ul><ul><ul><li>State the speed of light </li></ul></ul><ul><ul><li>Define luminous and non-luminous objects </li></ul></ul><ul><ul><li>Give examples of luminous and non-luminous objects </li></ul></ul>
  13. 13. Introduction to Light Short videoclip
  14. 14. Speed of light <ul><li>Light travels at about 300000 kilometres per second </li></ul><ul><li>Takes about 8 minutes to reach Earth </li></ul><ul><li>Light travel faster than sound </li></ul>
  15. 15. Calculating Speed <ul><li>Can you remember the formula? </li></ul><ul><li>Speed = Distance/Time </li></ul>
  16. 16. Try inquiry time pg 35 (10 minutes) <ul><li>All the questions </li></ul>
  17. 17. What is light? <ul><li>Form of energy </li></ul><ul><li>Enable us to see things around us </li></ul><ul><li>Use by plants to make food </li></ul>
  18. 18. How does light travel? <ul><li>Light travels in straight lines </li></ul><ul><li>Watch short clip on how light travel. </li></ul>
  19. 19. How does light travel? <ul><li>Light travels in straight lines </li></ul><ul><li>Watch short clip on how light travel. </li></ul><ul><li>Thin line of light is called ray </li></ul><ul><li>A stream of light is called a beam </li></ul>
  20. 20. What are the sources of light? <ul><li>Luminous object </li></ul><ul><ul><li>Sun </li></ul></ul><ul><ul><li>Stars </li></ul></ul><ul><ul><li>Lamps </li></ul></ul><ul><ul><li>Fires </li></ul></ul>
  21. 21. What are the sources of light? <ul><li>Most objects are non-luminous </li></ul><ul><ul><li>Moon </li></ul></ul><ul><ul><li>Book </li></ul></ul><ul><ul><li>House </li></ul></ul><ul><ul><li>Trees </li></ul></ul>
  22. 22. Show animation <ul><li>On luminous and non-luminous objects </li></ul>
  23. 23. Summary <ul><li>Calculations on speed of light </li></ul><ul><li>Understand what is light </li></ul><ul><li>Differentiate between luminous and non-luminous objects and give examples </li></ul><ul><li>How light travel </li></ul>
  24. 24. Check Point (page 36) <ul><li>Luminous objects are objects that produce light and non-luminous objects do not give out light. E.g. sun (luminous), moon (non-luminous) </li></ul><ul><li>Light </li></ul><ul><li>Straight line </li></ul>
  25. 25. Do Theory Workbook pg 19-20 <ul><li>All questions now. </li></ul>
  26. 26. Why are we able to see ourselves in a mirror? <ul><li>Look at the mirror – our image </li></ul><ul><li>Image formed when light rays bounce off the mirror and travel into our eyes </li></ul><ul><li>This bouncing of light off mirror is called reflection (definition) </li></ul>
  27. 27. Why are we able to see ourselves in a mirror? <ul><li>Ray of light that strikes a surface = incident ray </li></ul><ul><li>Ray of light that reflected by a surface = reflected ray </li></ul><ul><li>At the point where the incident ray strikes the surface, line is perpendicular to the surface = normal </li></ul>
  28. 28. Why are we able to see ourselves in a mirror? <ul><li>The normal divides the angle between the incident ray and reflected ray </li></ul><ul><li>Angle of incidence = angle between the incident ray and the normal </li></ul><ul><li>Angle of reflected = angle between the reflected ray and the normal </li></ul><ul><li>Angle of incidence = Angle of reflection (Law of reflection) </li></ul>
  29. 29. Characteristics of an image formed by plane mirror <ul><li>Image is at the same distance from the plane mirror as the object </li></ul><ul><li>Image upright </li></ul><ul><li>Image same size </li></ul><ul><li>Image formed is virtual image (image located behind the mirror where light does not actually pass) </li></ul><ul><li>Laterally inverted </li></ul>
  30. 30. Types of reflection <ul><li>Regular reflection </li></ul><ul><li>Diffuse reflection </li></ul>
  31. 31. Regular Reflection <ul><li>Parallel beam of light hit a smooth surface such as plane mirror </li></ul><ul><li>Reflected as parallel beam </li></ul><ul><li>Image is very clear </li></ul>
  32. 32. Regular Reflection <ul><li>Surfaces such as mirrors, polished metal, calm surface of water </li></ul>
  33. 33. Diffused Reflection <ul><li>Reflection off rough surfaces </li></ul><ul><li>Beam strike a rough surface, the rays are reflected in many directions </li></ul>
  34. 34. Diffused Reflection <ul><li>No images or no clear images are formed </li></ul><ul><li>Surfaces such as frosted glass, rough paper and cloth </li></ul>
  35. 35. Do Inquiry Time pg 39 & Checkpoint pg 40 <ul><li>Inquiry </li></ul><ul><ul><li>Window: regular reflection </li></ul></ul><ul><ul><li>White cloud: diffused reflection </li></ul></ul><ul><ul><li>Regular reflection: mirror, shiny metal surface </li></ul></ul><ul><ul><li>Diffused reflection: white board, rough glass </li></ul></ul><ul><li>Checkpoint </li></ul><ul><ul><li>The bouncing of light off the mirror is called reflection </li></ul></ul><ul><ul><li>Angle of incidence is equal to angle of reflection </li></ul></ul><ul><ul><li>Regular and diffused reflection. Regular: from smooth surface, Diffused: from rough surfaces </li></ul></ul>
  36. 36. Today’s Objectives <ul><li>At the end of this lesson, you will be able to: </li></ul><ul><ul><li>Draw the ray diagram (plane mirror) </li></ul></ul><ul><ul><li>State the uses of plane mirrors </li></ul></ul><ul><ul><li>State the uses of curved mirrors </li></ul></ul>
  37. 37. Ray Diagrams Worksheet
  38. 38. What are the steps? <ul><li>Draw the image of the object </li></ul><ul><ul><li>Object distance is equal to image distance </li></ul></ul><ul><li>Pick one extreme on the image of the object and draw the reflected ray which will travel to the eye as it sights at this point. </li></ul><ul><ul><li>Draw a bold line for the reflected ray (from the mirror to the eye) and a dashed line as an extension of this reflected ray; the dashed line extends behind the mirror to the location of the image point </li></ul></ul>
  39. 39. What are the steps? <ul><li>Draw the incident ray for light traveling from the corresponding extreme on the object to the mirror </li></ul><ul><li>Repeat steps 2 and 3 for all other extremities on the object. </li></ul>
  40. 40. Uses of plane mirrors <ul><li>Rear view mirror </li></ul><ul><ul><li>Help driver to see traffic behind the car </li></ul></ul><ul><li>Mirror on the wall </li></ul><ul><ul><li>Makes the room look bigger </li></ul></ul><ul><li>Microscopes </li></ul><ul><li>Periscope (see pg 41) </li></ul><ul><ul><li>Use in a submarine </li></ul></ul>
  41. 41. Types of curved mirrors <ul><li>Convex </li></ul><ul><li>Concave </li></ul><ul><li>Image formed from these types of mirror is different from those formed by plane mirrors </li></ul>
  42. 42. Convex Mirrors <ul><li>Form upright images that are smaller than the object </li></ul><ul><li>Large field of view (allow many things to be seen) </li></ul><ul><li>Uses are: </li></ul><ul><ul><li>Security camera </li></ul></ul><ul><ul><li>Blind corners of roads </li></ul></ul><ul><ul><li>Rear view mirrors in vehicles </li></ul></ul>
  43. 43. Concave Mirrors <ul><li>Form upright magnified images if the object is close to the mirror </li></ul><ul><li>If object is further away, the image is inverted </li></ul><ul><li>Uses are: </li></ul><ul><ul><li>Reflect light into the microscope </li></ul></ul><ul><ul><li>Dentist’s mirror to magnifies image of teeth </li></ul></ul><ul><ul><li>Car headlights </li></ul></ul>
  44. 44. Do checkpoint pg 43 <ul><li>Image is upright </li></ul><ul><li>Image same size as object </li></ul><ul><li>Image is the same distance as the object from the mirror </li></ul><ul><li>Image is laterally inverted </li></ul><ul><li>The rear view mirror </li></ul><ul><li>To make the room look bigger </li></ul><ul><li>Concave (dentist mirror) and convex (for blind corners of roads) </li></ul>
  45. 45. Do summary worksheet <ul><li>Now </li></ul>
  46. 46. Do theory workbook pg 21-23 <ul><li>Qn 1-3 (pg 21) </li></ul><ul><li>Qn 4a, 5 (pg 22) </li></ul><ul><li>Qn 6 (pg 23) </li></ul>
  47. 47. Today’s Objectives <ul><li>At the end of this lesson, you will be able to: </li></ul><ul><ul><li>Define refraction </li></ul></ul><ul><ul><li>State the effects of refraction </li></ul></ul>
  48. 48. What is refraction? <ul><li>Light changes direction when it travels from one transparent material into another </li></ul><ul><li>Eg. From air into water, from water into glass, and also from glass into air </li></ul><ul><li>Refraction of light is the bending of light as it changes its speed when it passes from one transparent medium to another (definition) </li></ul>
  49. 49. Refraction <ul><li>When a ray of light enters a medium at an angle, the speed of light will change. This change in the speed of light is the cause of the bending of light or the change in the direction of light. </li></ul>
  50. 50. Refraction normal normal a d b c glass air Light bends away from normal as it leaves the glass and enters the air. Light bends towards the normal when it travels from air to glass. Refracted ray Reflected ray Emergent ray Incident light ray
  51. 51. What happen in the diagram? <ul><li>From air to glass, </li></ul><ul><ul><li>light entering a denser medium since air is less dense than glass block. </li></ul></ul><ul><ul><li>Speed of light decreases . </li></ul></ul><ul><li>From glass to air, </li></ul><ul><ul><li>Light entering a less dense medium. </li></ul></ul><ul><ul><li>Speed of light increases . </li></ul></ul>
  52. 52. What happen in the diagram? <ul><li>Speed of light in: </li></ul><ul><li>air/ vacuum : 3 x 10 8 m/s (very fast) </li></ul><ul><li>water : 2.26 x 10 8 m/s (fast) </li></ul><ul><li>glass : 1.97 x 10 8 m/s (slow) </li></ul>
  53. 53. Behaviour of light moving to and from different mediums <ul><li>Less dense to denser (Air to glass) </li></ul><ul><li>Speed of light decreases </li></ul><ul><li>Bend towards normal </li></ul>
  54. 54. Behaviour of light moving to and from different mediums <ul><li>Denser to less dense (glass to air) </li></ul><ul><li>Speed of light increases </li></ul><ul><li>Bend away from normal </li></ul>
  55. 55. Some images of refraction
  56. 56. Some images of refraction
  57. 57. Application of Refraction <ul><li>Magnifying glass </li></ul><ul><li>Spectacles </li></ul><ul><li>Microscopes </li></ul><ul><li>Telescopes </li></ul><ul><li>Overhead projectors </li></ul>
  58. 58. Effects of Refraction <ul><li>Cause swimming pool to appear shallower </li></ul><ul><li>Cause straw to appear bend towards the surface of the water </li></ul><ul><li>Causes the letters to appear nearer to the surface of the glass than they actually are </li></ul>
  59. 59. Reflection vs Refraction <ul><li>Reflection </li></ul><ul><li>Incident angle=reflected angle </li></ul><ul><li>Incident ray and reflected ray travel in the same medium </li></ul><ul><li>Incident and reflected ray travel with the same speed </li></ul><ul><li>Refraction </li></ul><ul><li>Incident angle not equal to refracted angle </li></ul><ul><li>Incident and refracted ray travel in different medium </li></ul><ul><li>Incident and refracted ray travel at different speed </li></ul>
  60. 60. Do Checkpoint pg 44 <ul><li>All questions </li></ul>
  61. 61. Today’s Objectives <ul><li>At the end of this lesson, you will be able to: </li></ul><ul><ul><li>Describe how the white light dispersed by prism </li></ul></ul><ul><ul><li>Describe how rainbow is formed </li></ul></ul>
  62. 62. Light dispersion <ul><li>Is also called white light </li></ul><ul><li>Mixture of different colours </li></ul><ul><li>Separate the colours using a prism </li></ul><ul><li>When white light travels through a glass prism, refraction causes the light to split </li></ul><ul><li>The different colour of light travel at different speed into the prism thus it get separated </li></ul><ul><li>Spectrum of white light </li></ul><ul><li>Splitting of white light = dispersion </li></ul>
  63. 63. Spectrum of Light <ul><li>Consists of </li></ul><ul><ul><li>Red </li></ul></ul><ul><ul><li>Orange </li></ul></ul><ul><ul><li>Yellow </li></ul></ul><ul><ul><li>Green </li></ul></ul><ul><ul><li>Blue </li></ul></ul><ul><ul><li>Indigo </li></ul></ul><ul><ul><li>Violet </li></ul></ul><ul><ul><li>How to remember the colours? ROY G BIV </li></ul></ul>
  64. 64. How rainbow is formed? <ul><li>When white light travels through water droplets in the air </li></ul><ul><li>Spectrum of white light disperses into its seven colours </li></ul><ul><li>Rainbow is formed (usually after rainy days) </li></ul>
  65. 65. How to combine the colours of the spectrum? <ul><li>By using a second prism </li></ul><ul><li>See pg 46 </li></ul>
  66. 66. How do we see colours? <ul><li>We see colours that are reflected </li></ul><ul><li>Some lights are absorbed and some are reflected </li></ul><ul><li>Leaves are green because it reflected green colour and absorb the rest of the colours </li></ul><ul><li>Objects appear white, because it reflected all colours and absorb none </li></ul><ul><li>Objects appear black, because that absorb all colours and no light is reflected </li></ul>
  67. 67. <ul><li>Depends on what colour light is reflected into our eyes. </li></ul>How do we see colours? White light red green White light No light is reflected,is black White light
  68. 68. The primary colour lights <ul><li>When Red, Green and blue lights are mixed: </li></ul><ul><li>Red +green=yellow </li></ul><ul><li>Blue+green=cyan </li></ul><ul><li>Red+blue=magenta </li></ul><ul><li>Red+green+blue=white </li></ul>
  69. 69. What happens when red light is shone onto a <ul><li>White object: </li></ul>red The white object reflects any colour lights
  70. 70. When white light falls on a <ul><li>Black object: </li></ul>Black object absorbs all coloured lights.
  71. 71. When red light falls on a <ul><li>Green object: </li></ul>black The green object absorbs all colour lights except green
  72. 72. When blue light falls on a : <ul><li>Red object : </li></ul>black The red object absorbs all colour light except red.
  73. 73. Do checkpoint pg 48 <ul><li>All questions </li></ul>