Light and Optics

13. 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?

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

15. 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

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

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

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

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

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

21. 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

22. 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

23. 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

24. 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

26. 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

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

28. 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

29. UV

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

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

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

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

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

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

37. Fireflies

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

40. Some jellyfish

43. Yes there is such a thing! Anglerfish

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

45. Algae in the ocean waves!

48. Textbook Reference: