Light Waves Notes

1. Light Waves Notes

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

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. Thunder and lightning start at the same time, but we will see the lightning first. • Light travels much faster than sound. For example: • 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. A luminous object is one that produces light. • A non-luminous object is one that reflects light. • Luminous and non-luminous objects • Luminous objects • Reflectors Sun Stars Light Bulb (when on) Firefly Mirror Moon Person Desk Paper

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

8. Angle of incidence = Angle of reflection • The Law 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: Clear • Rough, dull surfaces have a ______ reflection. • Diffuse reflection is when light is scattered in different directions Diffuse

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

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 red and green makes yellow • Adding all three makes white again

14. Homework 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 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

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

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

18. Homework Some further examples: blue black black black green red blue black

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

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

21. Investigating filters • red • green • blue • Blue, green, cyan • Red, blue, magenta • Red, green, yellow

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

23. Refraction • Speed up • 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 • bent

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

25. Sound – The basics • vibrate • 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. • High frequency • fast • high • Low frequency • low • slow

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

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

28. Conclusion: • The pitchor 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