Invention Convention! Backdrop summary sheet due TUES after Spring Break At this point, you should be almost DONE everything! You should be reviewing your material and practicing what you are going to say!

Lights & Optics Unit C What is green, has 8 legs and will kill you if it falls from a tree?? A snooker table.

IB Questions What do we know about the nature of light? What technologies have been developed that use light? What principles of light do these technologies show?

Food for Thought…. How are rainbows formed? Why does a road look wet on a hot, dry day? Why is the sun brighter at noon than sunset? We will answer these questions!

Demo Arrows in water By the end of the unit, you should be able to explain why this occurs.

Myths About Light Light is not only a source (light bulb) or an effect (such as a spot of light on a wall) Cats cannot see in the dark What is true about light: It is energy It exists in space

Sources of Light Sources of Light Natural Light Sources Artificial Light Sources Sun Incandescent  (heat causing a filament of metal to glow - visible light)   Electrical energy ---? Thermal energy ---? Visible light energy Candles or Oil Lamps Florescent (ultraviolet light is absorbed by fabric particles, which in turn emit some of the energy as light - glowing) Ultraviolet light ---? Energy absorbed ---? Visible light energy by particles energy Wood (fire) Phosphorescent (light energy is stored and released later as visible light)paint Bioluminescence(light produced by living organisms) firefly light Chemiluminescent (light energy released by chemical reactions)glow sticks Chemiluminescence Movies (Shackwave/Flash)

Light- is a electromagnetic wavelength visible to eyes Copy This Down Our knowledge about light and vision comes from explanations, inventions, and investigations. Human eyes can only see an object if light is emitted or bounces off an object. Since light travels in straight lines there must be a direct path for the light to strike your eyes to make vision possible. Light- is a electromagnetic wavelength visible to eyes

Copy This Down The Challenge of Light Although for centuries we know how to use light to satisfy our needs, we couldn’t explain how light works. Here are some ideas about light: Early Light Ideas 1st idea – Pythagoras (Greek) [6th BC] Human produced straight beams of light from our eyes, when they hit an object they could see it. People actually believed this for many years! Problem – We can not see in the dark.

Angle between Incident ray & Normal = Angle of Reflected ray & Normal Copy This Down The Challenge of Light 2nd idea – Euclid (Greek) Discovered that light travels in straight lines Discovered the Law of Reflection Angle between Incident ray & Normal = Angle of Reflected ray & Normal  (see next slide)

Definitions in terms of light Copy This Down Incident Ray- a ray approaching a surface Reflected Ray- a ray that leaves or reflects a surface at the point of incidence Point of incidence- where an incident ray strikes the surface Normal- an imaginary line drawn perpendicular to the surface at the point of incidence Incident ray angle Reflected ray angle =

Could Greek Archimedes Destroy the Roman Fleet using Mirrors?

The Challenge of Light 3rd idea – Ptolemy (Greek) [1st AD] Copy This Down The Challenge of Light 3rd idea – Ptolemy (Greek) [1st AD] Discovered that light bends as it passes from air to glass. Problem…doesn’t light travel in straight lines??

The REAL Reason… Light travels through air than in fluid more faster I.e. it slows down in different materials, such as glass & water!

The Bending of Light Demo 2 Pencil in: Water Vegetable oil antifreeze Different substances in different densities

The Challenge of Light 4th idea – al-Haytham (Arab) [1000 AD] Copy This Down The Challenge of Light 4th idea – al-Haytham (Arab) [1000 AD] First to accurately describe how vision worked. Light bounces off objects and then travels to the eyes, not what Pythagoras thought!

The Challenge of Light 5th idea – Newton (English) Copy This Down The Challenge of Light 5th idea – Newton (English) By shining a light through a prism he demonstrated that white light is actually a mixture of different colors of light. Any ideas how a rainbow is made then?

The Challenge of Light 6th idea – Ole Romer (Danish) [1676] Copy This Down The Challenge of Light  6th idea – Ole Romer (Danish) [1676] First reasonably accurate measurement of the speed of light. Albert A. Michelson (USA) [1920] Refined Romer’s experiment by using the tops of two mountains. 299 798 km/s p.181 for picture

4 Basic Properties of Light Copy This Down 4 Basic Properties of Light Due to these, and other people, we can conclude 4 principles of light: 1) Light travels in straight lines. 2) Light can be reflected. 3) Light can bend by travelling in different mediums 4) Light is a form of energy.

Video Segments Elements of Physics: Basics of Physics An introduction to light Basics of Physics Refracted Light The Nature of Light

Homework!! P.181 1-5

Lab Time P. 178-179 Station B Station C Station D Station E Station F