2. Light and Sound In this unit: Properties of light Reflection Colours
Refraction
Properties of sound
Hearing

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

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

5. 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.

6. 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

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

8. 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

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

10. When Light Strikes an Object
Light travels in a straight line.
It will continue moving in a straight line, until it hit something.
Depending on what it hits, light may behave in very different ways.

11. Reflection When light bounces off a surface, it is called reflection.
When light is reflected it travels in a straight line away from the reflecting surface.
Example of Reflection:

12. Part 2 - Reflection Reflection from a mirror: Mirror Normal
Incident ray
Reflected ray
Angle of incidence
Angle of reflection
Mirror

13. 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 !!!

14. 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

15. Absorption
Any time light hits a surface, some of it is absorbed, or taken in.
When light is absorbed into a surface it is transformed from light energy, into heat energy.
That is why on a sunny day it is cooler to wear a white t-shirt, than a black t-shirt; dark surfaces absorb more light than lighter surfaces.

16. Refraction
Some materials transmit light, or allow light to pass through them.
These transparent materials cause light to bend as it is passing through the surface.
When the light bends, it makes things look like they do not match up.

18. 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

19. Let there be light!!!
The normal human retina contains two kinds of light sensitive cells: the rod cells (active only in low light) and the cone cells (active in daylight to see colour).
Three cones
"red" cones (60% of spectrum)
"green" cones (30% of spectrum)
"blue" cones (10%) of spectrum
Colour blindness comes from a reduction complete loss of function of one or more of the different cones.

20. Different Types of Color Blindness
Monochromacy: occurs when two or all three of the cone pigments are missing and color and lightness vision is reduced to one dimension.
Total color blindness
Dichromacy: occurs when only one of the cone pigments is missing and color is reduced to two dimensions.
- 90% of people affected are male
Partial color blindness
red-green
blue-yellow

21. 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.

22. The colours of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
Violet

23. 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

24. 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

25. A white hat would reflect all seven colours:
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 colours:
White
light

26. Additive Primary Colours
Red
Green
Blue
Called this because if you add them, they will produce WHITE light

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

28. In different colours of light it would look different:
Red
light
Shirt looks red
Shorts look black
Shirt looks black
Blue
light
Shorts look blue

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