1. Light Waves Notes

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: 1)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 objectsReflectors Sun Stars Light Bulb (when on) Firefly Mirror Moon Person Desk Paper

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

8. 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 !!! the same

9. Clear vs. Diffuse Reflection Smooth, shiny surfaces have a _____ reflection: Rough, dull surfaces have a ______ reflection. Diffuse reflection is when light is scattered in different directions Clear Diffuse

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

11. 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.

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

13. 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 all three makes white again Adding red and green makes yellow

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

15. 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 White light

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

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

18. Some further examples: ObjectColour of light Colour object seems to be Red socks Red BlueBlack GreenBlack Blue teddy RedBlack Blue Green Green camel Red Blue Green Magenta book Red Blue Green blue black green red blue black

19. Light & Colour Bill Nye http://www.youtube.com/watch?v=gtgBHsSzCPE

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

21. Investigating filters Colour of filterColours that could be “seen” Red Green Blue Cyan Magenta Yellow red green blue Blue, green, cyan Red, blue, magenta Red, green, yellow

22. Red Magenta White Yellow BlueGreen Cyan (No Color) Primary Colours of Light Black (All colors) Secondary Colours of Light

23. Refraction Refraction is when waves _______ or slow down due to travelling in a different _________. A medium is the area or space that waves will travel through. For example, if you put a pen in a cup of water, the light rays are slowed down by the water and are _____, causing the pen to look odd. ~Two examples on next slide~ medium Speed up bent

24. medium  Due to change in medium, the phase velocity of the wave is changed but its frequency remains constant (the same).

25. Sound – The basics We hear things when they ________. If something vibrates with a ____________ (vibrates very ______) we say it has a _____ pitch. If something vibrates with a ___________ (vibrates ______) we say it has a ____ pitch. vibrate High frequency fast Low frequency slow low high

26. Drawing sounds… This sound wave has a _____ frequency: This sound wave has a ___ _frequency: high High pitch low Low pitch

27. Drawing sounds… This sound wave has a _____ amplitude: high Loud low Quiet

28. Conclusion: The pitch or note of a sound that we hear is determined by its wavelength or its frequency. The shorter the wavelength, the higher the frequency becomes, and the higher the pitch that we hear. The amplitude of a sound wave is the same thing as loudness. The wavelength of a wave is independent of its amplitude [loudness] and inversely proportional to its frequency. Independent— wavelength does not affect loudness. Inversely proportional—high frequency = short wavelength, low frequency = long wavelength