1. Light

2. Light In this unit: Light is form of energy Properties of light
Reflection
Colours
Refraction

3. Keywords

4. Light is form of energy Light can do work eg. Crookes radiometer
Light can be converted to other forms of energy e.g. Solar cell, light to electricity.
Other forms of energy can be converted to light e.g. Fire.

5. Part 2 – Properties of Light
Light travels in straight lines:
Laser
The occurance of what is due to light traveling in straight lines?

6. Light travels VERY FAST – around 300,000 kilometres per second.
At this speed it can go around the world 8 times in one second.

7. 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.

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

9. 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

10. Shadows
Shadows are places where light is “blocked”:
Rays of light

11. shadows
A solar eclipse is a spectacular shadow caused when the moon passes between the sun and the earth.
Part of the earth goes completely dark.

12. Properties of Light summary
Light is a form of energy
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

13. Part 3 - Reflection Reflection from a mirror: Mirror Normal
Incident ray
Reflected ray
Angle of incidence
Angle of reflection
Mirror

14. 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 ____ _____ angle it hits it.
The same !!!

15. 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

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

17. Uses of Reflection Periscope Shaving/make-up mirrors
Moving mirrors in lighthouses
Security mirrors in stores, trains and buses.
Reflectors on bicycles, on the road etc.
Mirrors to direct the light in microscopes.

18. Colour
White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. Scientists call this a spectrum
We can demonstrate this by splitting white light with a prism: This is called dispersion
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

20. 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

21. 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

22. Refraction
Refraction is the bending of light as it passes from one medium to another.
Here the pencil looks like it is broken due the refraction.

23. Refraction through a glass block

24. Lenses
A lens is a piece of glass or other transparent material that has at least one curved surface.
Two types
1. Converging (convex) lens, brings the light rays closer together.

25. 2. Diverging (concave) lens, spreads the light rays apart.

26. 2. Diverging (concave) lens, spreads the light rays apart.

27. Uses of Refraction
Lens in cameras, telescopes, microscopes and glasses.
Phorensic analysis of crime evidence.
Colours seen in diamonds or a rainbow.
Extra daylight due refraction of sunlight in our atmosphere.