1. Light
In this unit:
Properties of light
Reflection
Colors
Refraction

2. Light travels VERY FAST – around 300,000 kilometers per second.
(that’s 670,000 mph)
At this speed it can go around the world 8 times in one second.

3. Speed of Light
Light is so fast, physicists measure light with ‘light years’.
A light year is the distance that light travels in one year.
Our nearest spiral galaxy is Andromeda. It is 2.5 million light years away

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 the object reflects light into our eyes:
Homework

6. Color
White (visible) light is not a single color; it is made up of a mixture of the seven colors 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.

7. The colors of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
Violet
ROY G BIV

8. Only red light is reflected
Seeing Color
An object looks a certain color because it reflects that color light to our eyes and absorbs all other colors.
For example, a red book only reflects red light:
Homework
White
light
Only red light is reflected

9. The Color White
An object appears white because it reflects all colors from white light:
White
light
White
light

10. The Color Black Black can be thought of as a lack of color.
A black object absorbs all white light and reflects no color at all

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

12. There are two types of objects when dealing with light
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
Luminous objects
Reflectors

13. Reflection Reflection from a mirror: Mirror Normal Angle of incidence
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 the same 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. Adding colors
White light can be split up to make separate colors. These colours can be added together again.
The primary colors 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

18. A white hat would reflect all seven colors:
A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colors:
White
light

19. Using colored light
If we look at a colored object in coloured light we see something different. For example, consider a football kit:
Shirt looks red
White
light
Shorts look blue

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

21. Some further examples:
Object
Color of light
Color object seems to be
Red socks
Red
Blue
Black
Green
Blue teddy
Green camel
Magenta book
Homework

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

23. Investigating filters
Color of filter
Colors that could be “seen”
Red
Green
Blue
Cyan
Magenta
Yellow

24. Words – speed up, water, air, bent
Refraction
Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this:
In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______.
Words – speed up, water, air, bent

27. Red
Blue
Green
White
Yellow
Cyan
Magenta