Light Properties
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Light Properties



Contains most properties of light

Contains most properties of light



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Light Properties Light Properties Presentation Transcript

  • Light
    • Properties of light
    • Reflection
    • Colours
  • Part 1 – Properties of Light
    • Light travels in straight lines:
    • Light travels VERY FAST – around 300,000 kilometres per second.
    At this speed it can go around the world 8 times in one second.
    • Light travels much faster than sound. For example:
    • Thunder and lightning start at the same time, but we will see the lightning first.
    2) When a starting pistol is fired we see the smoke first and then hear the bang.
    • We see things because they reflect light into our eyes:
    • Luminous and non-luminous objects
    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
    • The Moon
    • Mirrors
    • People
    • Objects
    • Shadows
    Shadows are places where light is “blocked”: Rays of light
  • Out of the Darkness
    • If the light source is small compared to the size of the object, then the shadow will be SHARP
    • 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.
  • Properties of Light summary
    • Light travels in straight lines
    • Light travels much faster than sound
    • We see things because they reflect light into our eyes
    • Shadows are formed when light is blocked by an object
  • Part 2 - Reflection
    • Reflection from a mirror:
    Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror
    • The Law of Reflection
    Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at THE SAME ANGLE it hits it. The same !!!
  • Clear vs. Diffuse Reflection
    • Smooth, shiny surfaces have a clear reflection:
    Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions
  • Using mirrors
    • Two examples:
    1) A periscope 2) A car headlight
  • Flat Mirrors
  • Spherical Mirrors - Concave
    • Image is REAL, INVERTED, and DEMAGNIFIED !!!
    C F
  • Spherical Mirrors – Concave Object Inside the Focal Point
    C F
  • Spherical Mirrors - Convex
    C F
  • Colour
    • 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 .
    We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops.
  • The colours of the rainbow:
    • Red
    • Orange
    • Yellow
    • Green
    • Blue
    • Indigo
    • Violet
    Remember: Roy G. Biv !!!
  • Light from the Sun
    • The light from the sun contains a grand mixture of electromagnetic waves of varying frequency (i.e. wavelength)
    • The spectrum of light is characteristic of the TEMPERATURE of the sun!
  • Wavelengths of Light
    • Red Light –  nm
    • Green Light -  nm
    • Blue Light -  nm
  • Adding colours
    • White light can be split up to make separate colours. These colours can be added together again.
    • The primary colours of light are red, blue and green:
    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
  • Seeing colour
    • The colour an object appears depends on the colours of light it reflects.
    For example, a red book only reflects red light: White light Only red light is reflected Homework
  • 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
  • Using coloured light
    • 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:
    White light Shorts look blue Shirt looks red
    • 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
  • Using filters
    • Filters can be used to “block” out different colours of light:
    Red Filter Magenta Filter