Light

1. Light • Properties of light • Reflection • Colours

2. Laser 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 • The Moon • Mirrors • People • Objects -The Sun - Lamps - Lights - Lasers - Campfires

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

8. Out of the Darkness • If the light source is small compared to the size of the object, then the shadow will be SHARP • If the light source is of comparable size to the object, then the shadow will be “fuzzy”. The dark inner region is called the UMBRA; the grey region is called the PENUMBRA.

9. 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

10. 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

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

12. Flat Mirrors • Image is VIRTUAL, UPRIGHT, UNMAGNIFIED

13. 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.

14. The colours of the rainbow: • Red • Orange • Yellow • Green • Blue • Indigo • Violet Remember: VIBGYOR!!!

15. 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

16. 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

17. A pair of purple pants, in addition to being ugly, would reflect purple light (or red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colours: White light

18. Using coloured light • If we look at a coloured object in coloured light we see something different. For example, consider the outfit below – I mean, from a physics standpoint, not as a fashion choice: Shirt looks red White light Shorts look blue

19. 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

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