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Light Light 1) Properties of light 2) Reflection 3) Colours

Light Properties

Jan 13, 2015



Amr Hassaan

Contains most properties of light
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  • 1. Light
    • Properties of light
  • Reflection
  • Colours

2. Part 1 Properties of Light

  • Light travels instraightlines:

Laser 3.

  • Light travels VERY FAST around 300,000 kilometres per second.

At this speed it can go around the world 8 times in one second. 4.

  • Light travelsmuch fasterthan 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. 5.

  • We see things because theyreflectlight into our eyes:

Homework 6.

  • Luminous and non-luminous objects

Aluminousobject is one that produces light. Anon-luminousobject 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 8. 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.

9. 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

10. Part 2 - Reflection

  • Reflection from a mirror:

Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror 11.

  • 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 !!! 12. Clear vs. Diffuse Reflection

  • Smooth, shiny surfaces have aclearreflection:

Rough, dull surfaces have adiffusereflection. Diffuse reflectionis when light is scattered in different directions 13. Using mirrors

  • Two examples:

1) A periscope 2) A car headlight 14. Flat Mirrors


15. Spherical Mirrors - Concave

  • Image is REAL, INVERTED, and DEMAGNIFIED !!!

C F 16. Spherical Mirrors Concave Object Inside the Focal Point


C F 17. Spherical Mirrors - Convex


C F 18. Colour

  • White light is not a single colour; it is made up of a mixture of the seven colours of ther 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. 19. The colours of the rainbow:

  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Indigo
  • Violet

Remember: Roy G. Biv !!! 20. 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!

21. Wavelengths of Light

  • Red Light nm
  • Green Light - nm
  • Blue Light - nm

22. 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 23. 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 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. 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 26.

  • 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 27. Using filters

  • Filters can be used to block out different colours of light:

Red Filter Magenta Filter