1. Why does the light do this?

2. Why does the pencil look like this?

4. Answers: Because of “refraction”. Refraction is: “the change in a wave’s direction and speed that is caused by a change in the medium.” remember: 1. The “medium” is the material that the wave travels through. 2. The only thing that can affect the speed of a wave is if there is a change in the medium.

5. Characteristics of Refraction: All types of waves refract: Light waves, sound waves, water waves, etc. Longer wavelengths change direction less. Shorter wavelengths change direction more.

6. The speed of a water wave depends on the depth of the water. This means that water waves will refract (change speed and/or direction) near a shoreline. (This is why near the beach, the top of the wave “falls forward” – it is moving faster than the bottom of the wave!)

7. See how the waves aren’t parallel? Parts of each wave have changed direction due to refraction.

8. These waves changed direction a lot!

9. March 11, 2011 earthquake in Japan

10.  = 700 nm = 400 nm Q: How does a prism cause the colors to separate? A: The longer the wavelength, the less it is affected by refraction. The shorter the wavelength, the more it is affected by refraction.

11. Road Mirages are caused by refraction (the air directly above the road is hotter than the air that is a little higher up, so the light bends as it travels through the layers of air) http://www.youtube.com/watch?v=_M0FcpQWh5E

12. Slow down, Light! Light moving from less dense medium into a more dense medium slows down. – Example: when light goes from Air  Water – Think of a truck on a smooth road suddenly hitting a patch of sand at an angle * First tire to hit slows down * Truck turns because the tires have different amounts of traction. Air Water Incident ray ΘiΘi Refracted ray ΘrΘr

13. Speed up, Light! Light moving from more dense medium into less dense medium speeds up. – Examples: when light goes from Water  Air – Think of a truck on sand suddenly hitting a a smooth road at an angle – First tire to hit speeds up – Truck turns away from normal Water Air Incident ray ΘiΘi Refracted ray ΘrΘr

14. Index of Refraction Ratio of speed of light in a vacuum (3 x 10 8 m/s) to speed of light in a transparent substance is the index of refraction (n). The larger the n, the slower light travels n air = 1 (memorize this!) n = index of refraction (no units) c = speed of light (3 x 10 8 m/s) v = velocity of light in the transparent substance (m/s)

15. Sample Problem Ex: The hardest mineral is diamond, with an index of refraction of 2.42. At what speed does light travel through a diamond? What percentage is this of the speed of light in a vacuum? n = 2.42 c = 3 x 10 8 m/s v = ? In a diamond, light only travels 41% of the “speed of light”

16. Index of Refraction for some common substances Vacuum 1 (by definition) Air1.000277 Ethyl alcohol (ethanol) 1.36 Water 1.33 Diamond 2.42 Cubic zirconia (fake diamonds!) 2.15 to 2.18 Cornea (human) 1.37 to 1.40 Corn Oil 1.47 Crown Glass (pure) 1.50 to 1.54 Flint Glass (pure) 1.60 to 1.62 Pyrex (borosilicate glass) 1.470 Salt 1.52 Sapphire 1.77

17. Critical Angle Critical Angle – the angle of incidence that produces a 90°angle of refraction Air n = 1 Water n = 1.33 ΘcΘc Θ r = 90°

18. Total internal reflection can be seen at the air-water boundary.

19. Total Internal Reflection Occurs when a light ray tries to escape for a dense medium into a less dense medium. If the light ray strikes the surface at an angle GREATER THAN the critical angle then it can’t escape – it is trapped inside the denser material. This is how fiber optics transfer info along glass fiber

20. Total internal reflection: The light waves can’t get out!

21. “Fiber Optic” cables use total internal reflection to transmit data long distances. (Cable TV & Internet)

22. Fiber Optic cables – the light finally escapes at the end of the line.

23. Using Refraction to Create Invisibility http://www.youtube.com/watch?v=BS5BPB4l3Eo http://www.youtube.com/watch?v=KyWgnFm3ebc

24. Mirrors reflect, but lenses refract.

25. The exact shape of a lens, combined with the refraction, is how light can be focused:

26. This type of lens can be used as a magnifying class, or to start fires. The focal point gets very hot because all of the light converges to that point. (In Latin, the word “focus” means “fire place”.)

27. Refraction is how lenses are able to focus images: Light refracts in your eye at two different locations: 1 st at the cornea and 2 nd at the lens.