Light Properties


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Contains most properties of light

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Light Properties

  1. 1. Light <ul><li>Properties of light </li></ul><ul><li>Reflection </li></ul><ul><li>Colours </li></ul>
  2. 2. Part 1 – Properties of Light <ul><li>Light travels in straight lines: </li></ul>Laser
  3. 3. <ul><li>Light travels VERY FAST – around 300,000 kilometres per second. </li></ul>At this speed it can go around the world 8 times in one second.
  4. 4. <ul><li>Light travels much faster than sound. For example: </li></ul><ul><li>Thunder and lightning start at the same time, but we will see the lightning first. </li></ul>2) When a starting pistol is fired we see the smoke first and then hear the bang.
  5. 5. <ul><li>We see things because they reflect light into our eyes: </li></ul>Homework
  6. 6. <ul><li>Luminous and non-luminous objects </li></ul>A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objects Reflectors -The Sun - Lamps - Lights - Lasers - Campfires <ul><li>The Moon </li></ul><ul><li>Mirrors </li></ul><ul><li>People </li></ul><ul><li>Objects </li></ul>
  7. 7. <ul><li>Shadows </li></ul>Shadows are places where light is “blocked”: Rays of light
  8. 8. Out of the Darkness <ul><li>If the light source is small compared to the size of the object, then the shadow will be SHARP </li></ul><ul><li>If the light source is of comparable size to the object, then the shadow will be “fuzzy”. The dark inner region is called the UMBRA; the grey region is called the PENUMBRA. </li></ul>
  9. 9. Properties of Light summary <ul><li>Light travels in straight lines </li></ul><ul><li>Light travels much faster than sound </li></ul><ul><li>We see things because they reflect light into our eyes </li></ul><ul><li>Shadows are formed when light is blocked by an object </li></ul>
  10. 10. Part 2 - Reflection <ul><li>Reflection from a mirror: </li></ul>Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror
  11. 11. <ul><li>The Law of Reflection </li></ul>Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at THE SAME ANGLE it hits it. The same !!!
  12. 12. Clear vs. Diffuse Reflection <ul><li>Smooth, shiny surfaces have a clear reflection: </li></ul>Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions
  13. 13. Using mirrors <ul><li>Two examples: </li></ul>1) A periscope 2) A car headlight
  14. 14. Flat Mirrors <ul><li>Image is VIRTUAL, UPRIGHT, UNMAGNIFIED </li></ul>
  15. 15. Spherical Mirrors - Concave <ul><li>Image is REAL, INVERTED, and DEMAGNIFIED !!! </li></ul>C F
  16. 16. Spherical Mirrors – Concave Object Inside the Focal Point <ul><li>Image is VIRTUAL, UPRIGHT, and MAGNIFIED </li></ul>C F
  17. 17. Spherical Mirrors - Convex <ul><li>Image is VIRTUAL, UPRIGHT, and DEMAGNIFIED </li></ul>C F
  18. 18. Colour <ul><li>White light is not a single colour; it is made up of a mixture of the seven colours of the r a i n b o w . </li></ul>We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops.
  19. 19. The colours of the rainbow: <ul><li>Red </li></ul><ul><li>Orange </li></ul><ul><li>Yellow </li></ul><ul><li>Green </li></ul><ul><li>Blue </li></ul><ul><li>Indigo </li></ul><ul><li>Violet </li></ul>Remember: Roy G. Biv !!!
  20. 20. Light from the Sun <ul><li>The light from the sun contains a grand mixture of electromagnetic waves of varying frequency (i.e. wavelength) </li></ul><ul><li>The spectrum of light is characteristic of the TEMPERATURE of the sun! </li></ul>
  21. 21. Wavelengths of Light <ul><li>Red Light –  nm </li></ul><ul><li>Green Light -  nm </li></ul><ul><li>Blue Light -  nm </li></ul>
  22. 22. Adding colours <ul><li>White light can be split up to make separate colours. These colours can be added together again. </li></ul><ul><li>The primary colours of light are red, blue and green: </li></ul>Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding all three makes white again Adding red and green makes yellow
  23. 23. Seeing colour <ul><li>The colour an object appears depends on the colours of light it reflects. </li></ul>For example, a red book only reflects red light: White light Only red light is reflected Homework
  24. 24. A white hat would reflect all seven colours: A pair of purple pants, in addition to being ugly, would reflect purple light (or red and blue, as purple is made up of red and blue): Purple light White light
  25. 25. Using coloured light <ul><li>If we look at a coloured object in coloured light we see something different. For example, consider the outfit below – I mean, from a physics standpoint, not as a fashion choice: </li></ul>White light Shorts look blue Shirt looks red
  26. 26. <ul><li>In different colours of light this kit would look different: </li></ul>Red light Shirt looks red Shorts look black Blue light Shirt looks black Shorts look blue
  27. 27. Using filters <ul><li>Filters can be used to “block” out different colours of light: </li></ul>Red Filter Magenta Filter