1. Light and Sound

2. 1. Light travels in straight lines:
Properties of Light
1. Light travels in straight lines:
Laser

3. 2. Diffuse reflection by surfaces - light bounces off rougher surfaces in all directions

4. Definition
Light: a form of radiant energy (the energy that allows you to see objects)

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

6. FYI: 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.

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

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

9. Reflection Reflection from a mirror: Mirror Normal Angle of incidence
Incident ray
Reflected ray
Angle of incidence
Angle of reflection
Mirror

10. 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 !!!

11. FYI: 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

12. Colour
White light 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.

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

14. 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

15. Refraction
Refraction is when waves speed up or slow down due to travelling in a different medium. 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 bent, causing the pen to look odd. The two mediums in this example are water and air.

17. Sound – The basics We hear things when they vibrate.
If something vibrates with a high frequency (vibrates very quickly) we say it has a high pitch.
If something vibrates with a low frequency (vibrates slowly) we say it has a low pitch.
The lowest frequency I could hear was…

18. Other sound effects… Like light, sound can be…
Reflected – sound reflections are called echos.
Refracted – this is why you might sound strange if you try talking underwater