1. Light
Properties of light
Reflection
Colours

2. Part 1 – Properties of Light
Light travels in straight lines:
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 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.

5. We see things because they reflect light into our eyes:
Homework

6. 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

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: Mirror Normal
Incident ray
Reflected ray
Angle of incidence
Angle of reflection
Mirror

11. Angle of incidence = Angle of reflection
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 a clear reflection:
Rough, dull surfaces have a diffuse reflection.
Diffuse reflection is when light is scattered in different directions

13. Using mirrors
Two examples:
2) A car headlight
1) A periscope

14. Flat Mirrors
Image is VIRTUAL, UPRIGHT, UNMAGNIFIED

15. Spherical Mirrors - ConcaveF
Image is REAL, INVERTED, and DEMAGNIFIED !!!

16. Spherical Mirrors – Concave Object Inside the Focal Point
Image is VIRTUAL, UPRIGHT, and MAGNIFIED

17. Spherical Mirrors - ConvexF
Image is VIRTUAL, UPRIGHT, and DEMAGNIFIED

18. Colour
White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow.
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 – l = 680 nm Green Light - l = 500 nm
Blue Light - l = 470 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 red and green makes yellow
Adding all three makes white again

23. Only red light is reflected
Seeing colour
The colour an object appears depends on the colours of light it reflects.
For example, a red book only reflects red light:
Homework
White
light
Only red light is reflected

24. (or red and blue, as purple is made up of red and blue):
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
A white hat would reflect all seven colours:
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:
Shirt looks red
White
light
Shorts look blue

26. In different colours of light this kit would look different:
Red
light
Shirt looks red
Shorts look black
Shirt looks black
Blue
light
Shorts look blue

27. Using filters Red Filter
Filters can be used to “block” out different colours of light:
Red Filter
Magenta Filter