WHAT IS LIGHT? INTRODUCTION

What does optics mean? Physical properties of light

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?

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

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.

Sources of Light

1) Natural Sources of Light

SUN! most important natural source of light

Other Stars

Lightning

Fires

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

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

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

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.

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.