Light Properties

• 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

7.

• 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

• Image is VIRTUAL, UPRIGHT, UNMAGNIFIED

15. Spherical Mirrors - Concave

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

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

• Image is VIRTUAL, UPRIGHT, and MAGNIFIED

C F 17. Spherical Mirrors - Convex

• Image is VIRTUAL, UPRIGHT, and DEMAGNIFIED

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