Post on 22-Feb-2016
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WHAT IS LIGHT?
INTRODUCTION
What does optics mean?
Physical properties
of light
Light and Colour• Why does bright lights seem to make
things more vivid at night?
How can white light allow us to see objects with so much colour?
Why is the sky blue?
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
Sources of Light
1) Natural Sources of Light
SUN!
• most important natural source of light
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
Jellyfish• use light to attract fish into their
tentacles
Flashlight fish• use light to help to keep in a school
Fireflies• attract mates by chemical reactions
2) Artificial Light
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
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
Compact Fluorescent Bulbs• even though compact fluorescent
lights are more efficient than incandescent light bulbs, still 80% of energy is converted into heat
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
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
How Glow Sticks Work
Triboluminescence• light producing from friction• rubbing crystals together• quartz used in rattles in Aboriginal people
flashes light• breaking crystals or rubbing diamonds
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