1. WHAT IS LIGHT?
INTRODUCTION

2. What does optics mean?
Physical
properties of
light

3. How can white light allow us to see objects with so much colour
How can white light allow us to see objects with so much colour? Why is the sky blue?

4. Reasons: White light contains all of the colours of the rainbow.
The sky is blue because the particles like water vapour in the air reflect the colour blue and absorb all the other colours found in white light

5. How is Light Produced?
Atoms within the materials must absorb some form of energy.
after absorbing energy, the atoms are considered to be in an excited state.
Then, almost immediately, the excited atoms release the energy often in the form of light.

6. Sources of Light

7. 1) Natural Sources of Light

8. SUN!
most important natural source of light

9. Other Stars

10. Lightning

11. Fires

12. Bioluminescence ability of organisms to produce light
90 % of all sea creatures can
in very deep water no light reaches
use light to see prey
scare predators
camouflage
some produce their own
some contain bacteria that produce light

13. angler fish
long spine with a bulb
used as a lure to attract prey

14. Jellyfish
use light to attract fish into their tentacles

15. Flashlight fish
use light to help to keep in a school

16. Fireflies
attract mates by chemical reactions

17. 2) Artificial Light

18. Incandescent Light produced by metals at very high temperatures
bulbs contain a filament or thin wire (tungsten)
uses electricity to heat up
filament emits light as a way to release some energy as a glow

19. Fluorescent Light bulb such as gas such as mercury vapour
mercury vapour is exposed to electricity which emits UV light
bulb is coated with a white powder called phosphor
phosphor glows after exposed to UV radiation

20. Compact Fluorescent Bulbs
even though compact fluorescent lights are more efficient than incandescent light bulbs, still 80% of energy is converted into heat

21. Phosphorescent Light ability to store energy from radiation
different from fluorescent since phosphor needs UV light
phosphorescent materials glow in the dark for some time after being energized by light
glow in the dark will fade but can re-energize with a light source

22. Chemiluminescence
light produced from chemical reactions (no heat or temperature change)
“cool light”
bioluminescence are also forms
ex. luminol used in forensics: glows when it reacts to iron in blood
ex. glow sticks

23. How Glow Sticks Work

24. Triboluminescence light producing from friction
rubbing crystals together
quartz used in rattles in Aboriginal people flashes light
breaking crystals or rubbing diamonds

25. Electric Discharge
produce light using electric current through air or another gas
halogen gases used often
ex. carbon-arc involves passing a current through the air between 2 rods

26. The Nature of Light
Light is the only form of energy that can travel like a wave through empty space and through some materials.
Light waves are called electromagnetic waves. Similar to water waves, light waves involve the movement of energy from one point to another. These waves are invisible and can travel through a vacuum. (This means they do not require particles of matter in order to move.) The waves travel at 3 x 108 m/s (the speed of light).
A wavelength is the distance from one crest (or trough) to the next.

27. The Electromagnetic Spectrum
The electromagnetic spectrum is a diagram that illustrates the range, or spectrum, of electromagnetic waves, in order of wavelength or frequency.
The frequency of a wave represents the number of crests (or troughs) that pass a given point in one second.