1. Reflection and Refraction Physics Mrs. Coyle

2. Reflection When a wave reaches a boundary it is: –Partially reflected (bounces off surface) –Partially transmitted through surface.

3. Law of Reflection Angle of incidence = Angle of reflection

4. Note The angle of incidence is formed between the incident ray and the normal. The angle of reflection is formed between the reflected ray and the normal.

5. Specular Reflection A reflection produced by a smooth surface.

6. Diffuse Reflection Reflection from a rough surface.

7. http://micro.magnet.fsu.edu/primer/java/reflection/specular/specularjavafigure1.jpg

8. Reflection from a Plane Mirror d i =d o h i =h o

9. Type of Image Real or Virtual Enlarged or Reduced Erect or Inverted

10. What is the minimum mirror height required for a person to see their full self in the mirror?

11. Hint: Compare AB to CD A D B C

12. Refraction When a wave crosses a boundary between Medium 1 and Medium 2, the wave changes direction because it changes velocity. Frequency remains constant. Velocity changes as a result of wavelength change. Simulations http://www.walter-fendt.de/ph14e/refraction.htm *******http://www.walter-fendt.de/ph14e/refraction.htm http://www3.interscience.wiley.com:8100/legacy/college/halliday/0471320 005/simulations6e/index.htmwww3.interscience.wiley.com:8100/legacy/college/halliday/0471320 005/simulations6e/index.htm

13. Refraction

14. Example Less Rigid Medium More Rigid Medium Refracted ray bends towards the normal. Incident Ray Refracted Ray

15. Index of Refraction, n n = c / v c : the speed of light in a vacuum, 3 x 10 8 m/sec v : speed of light in the medium. n : medium's index of refraction n>1 (Why?)

16. Indices of Refraction Vacuum1.00 Air1.0003 Water1.33 Ethanol1.36 Crown glass1.52 Quartz1.52 Diamond2.42

17. Note The speed of light has a lower speed in a more optically dense medium.

18. Problem What is the speed of light in quartz? Answer: 1.97 x 10 8 m/s

19. Snell’s Law n 1 sin  1 = n 2 sin  

20. Note When the incident ray travels from a less optically dense medium (low n) to a more optically dense medium (higher n) then the refracted ray bends towards the normal.

21. Problem What is the angle of refraction when a ray from air with an angle of incidence of 25 o is incident to water? Draw the ray diagram. Answer: 18.5 o

22. Total Internal Reflection Can occur when ray goes from higher n to lower n. Above a Critical angle (of incidence) the ray is reflected, not refracted http://www.walter-fendt.de/ph14e/refraction.htm For problems, set the angle of refraction to 90, and solve for critical angle

23. Problem Find the critical angle for a light ray that is incident from water to air. Answer: 48.8 o

24. Dispersion The index of refraction of glass is different for the colors that make up white light because the speed of light is slightly different in glass for each frequency of light. (In vacuum all colors have speed c=3x10 8 m/s.)

25. Problem The index of refraction for crown glass for red light is 1.514. What is the speed of red light in crown glass? Answer: 1.98 x 10 8 m/s

26. Mirage http://www.warren- wilson.edu/~physics/PhysPhotOfWeek/2007PPOW/20070921RoadMirage/IMG_ 1444MirageCrop500.jpg

27. Mirage Total internal reflection occurs because hot air has a lower n, than cold air. http://www.warren- wilson.edu/~physics/PhysPhotOfWeek/2007PPOW/20070921RoadMirage/index.html