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Light and Optics

Light and Optics. In this unit: A. What is light? B. What makes light? C. How do mirrors work? D. Can light ever bend? E. How do lenses work? F. What is colour? G . How do our eyes work?. What is light?. A form of energy that is visible (that our human eyes are capable of sensing).

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Light and Optics

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  1. Light and Optics In this unit: A. What is light? B. What makes light? C. How do mirrors work? D. Can light ever bend? E. How do lenses work? F. What is colour? G. How do our eyes work?

  2. What is light? • A form of energy that is visible (that our human eyes are capable of sensing)

  3. Sources of Light What’s the difference between light coming from the Sun and light coming from the Moonor a tree? The Sun produces its own light The moon / tree reflects light

  4. Why can we see these things? Either the object produces light or light is reflected off it!

  5. We see most objects because they reflect light into our eyes: Homework

  6. Objects that make their own light are called:Luminous • Objects that can only reflect light areNon-Luminous

  7. Rays of light Shadows are places where light is “blocked”: Shadows

  8. Light Has Many Sources • Some are natural, some are artificial (devices made by humans – like a flashlight)

  9. LIGHT FROM THE SUN • The sun has "burned" for more than 4.5 billion years • It is huge ball of gas, mostly hydrogen and helium

  10. LIGHT FROM THE SUN • Hydrogen atoms combine to form helium in a “fusion” reaction, which releases lots of energy • Energy reaches Earth as light/heat, that we call sunshine

  11. Sources of Light Incandescence • Light is given off a material because it is very hot. • Not very efficient: most of the energy given off is heat and not light. • Examples: hot burner on a stove, incandescent bulb, lit match, gas lantern

  12. Electric Discharge • Produced by an electric currentpassing through a gas. HEAT is produced • Different gases produce different colours • neon lights, lightning Examples of gases: • neon  red light; • argon  pale purple/blue light

  13. Fluorescence • occurs when an object absorbs UV light and immediately releases the energy as visible light. Examples: • highlighters contain fluorescent dyes • some detergents contain fluorescent dyes to make clothes look brighter • forensic scientists use UV light to detect bodily fluids • UV light used to detect counterfeit money

  14. Fluorescent dye only seen under UV light Fingerprint seen under UV light

  15. Fluorescent Lights • Electricity causes gas inside the light bulb to emit UV light. • The UV light hits phosphor coating on inner surface of tube which causes visible light to be emitted. • More efficient than incandescent lights (less heat produced) and last 5-10X longer

  16. UV

  17. Light-Emitting Diode (LED) • Electric current to flow in only one direction. • No filament • Little heat produced • Very energy efficient

  18. Luminescence • Luminescence: light is generated with NO heat produced • There are several types of luminescence:

  19. Phosphorescence • Materials called “phosphors” absorb ultraviolet light (UV) and emit it back out over several hours • Known as “glow in the dark”

  20. Chemiluminesence • A chemical reaction produces light. • No heat

  21. Triboluminescence • light caused by friction as a result of scratching, crushing, or rubbing certain crystals

  22. Bioluminescence • Light is produced by a chemical reaction inside a living organism • Examples.....

  23. Fireflies

  24. Not stars! Glow worms on the ceiling of a dark cave

  25. Some jellyfish

  26. Yes there is such a thing! Anglerfish

  27. Some algae and bacteria….even some mushrooms!

  28. Algae in the ocean waves!

  29. Textbook Reference:

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