2. 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!

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

5. 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?

6. 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!

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

8. 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

9. 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)

10. Light- is a electromagnetic wavelength visible to eyes
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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

12. 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.

13. Angle between Incident ray & Normal = Angle of Reflected ray & Normal
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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)

14. Definitions in terms of light
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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 =

15. Could Greek Archimedes Destroy the Roman Fleet using Mirrors?

16. The Challenge of Light 3rd idea – Ptolemy (Greek) [1st AD]
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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??

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

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

19. The Challenge of Light 4th idea – al-Haytham (Arab) [1000 AD]
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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!

20. The Challenge of Light 5th idea – Newton (English)
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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?

21. The Challenge of Light 6th idea – Ole Romer (Danish) [1676]
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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.
km/s
p.181 for picture

22. 4 Basic Properties of Light
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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.

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

24. Homework!!
P.181
1-5

25. Lab Time P
Station B
Station C
Station D
Station E
Station F