# Reflection refraction and light 2010

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• 1.INCLUDING TOTALINTERNAL REFLECTION AND THE CRITICAL ANGLE Light: Reflection & Refraction

2. Law of Reflection

• The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.

3. 4. 5. 6. 7. Diffuse Reflection

• Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway leads to a type of reflection known asdiffuse reflection .

8. 9. 10. Why does a dry road diffuse light, when a wet road specularly reflects. 11. Index of Refraction

• n = c/v
• The larger the index,
• the slower the
• speed of light

12. Index of Refraction 13. Reflection and Refraction at an Interface 14. Refraction:The Bending of Wavefronts 15. 16. Index of refraction 17. 18. 19. Refraction RulesLight twists inward when entering medium of higher index of refraction 20. Refraction Rules Light twists outward when entering medium of lower index of refraction 21. Understanding Refraction Wheels on axle rolls along a smooth sidewalk and onto grass. Which picture path is followed?What happens if the motion is reversed? 22. Understanding Refraction One side of wave front slows down, and the entire train of fronts twists. 23. Illustrating Cart AnalogyRight front wheel slows down before left front Left front wheel slows down before right front 24. Snells (Sahls) Law (a history)

• Ibn Sahl was an Arabian Mathematician and optics engineer associated with the court of Baghdad. In 984 he wrote a treatiseOn Burning Mirrors and Lensesin which he set out his understanding of how curved mirrors and lenses bend and focus light. Ibn Sahl is credited with discovering the law of refraction, usually called Snell's law.
• In 1621, Willebrord Snellius (Snel) derived a mathematically equivalent form, that remained unpublished during his lifetime.

25. Snells Law

• Snell discovered that the ratio between the sine of the incident and refracted angles is equal to the ratio of the incident and refracted velocities.

26. Snells Law continued

• Because the velocity of light is extremely difficult to measure, it is more practical to use the indices of refraction.Due to the fact that the velocity is inversely proportional to the index of refraction, you get
• Or

27. Law of Refraction:Snell's Law Right front wheel slows down first. Snell's Law: n2 sin Q2=n1 sin Q1 28. Snell's Law Example n 1= 1.0 (air)n 2= 1.52 (glass) Q 1= 30 degrees ------------------------ n 2sin Q 2=n 1sin Q 1 1.52 sin Q 2= 1.0 sin 30 sin Q 2= 0.33 Put calculator in Mode Degree Q 2= sin -1(0.33) = 19.3 degrees 29. Rear View Mirror 30. Rear View Mirror Explained 31. Apparent Depth in WaterLight exits into medium (air) of lower index of refraction, and turns left. 32. More Apparent Depth Spear-fishing is made more difficult by the bending of light. To spear the fish in the figure, one must aim at a spot in front of the fish 33. Refraction at Sunset Why does the sun appear to be flattened at sunset? --------------------------------------------------- The sun actually falls below below the horizon, i.e., it "sets", a few seconds before we see it set. 34. A Fish-Eye's View 35. Water on Road Mirage There's no water on the road; why does it appear so? 36. The Oasis Mirage 37. Displacement through a Slab of Glass Entering and exiting rays are displaced from each other, but parallel. 38. Internal Reflection All rays reflect internally, but the top three rays reflect only a small percentage internally; most energy leaves the prism. The fourth and fifth rays are reflected 100 % internally. 39. Internal Reflection 40. Critical angle

• An incident angle at which the refracted angle is 90 o
• Note:This can only happen in a case when light travels from a higher index of refraction to one with a lower index of refraction.

41. ` 42. 43. 44. Critical Angle Calculation What must be Q 1to get Q 2= 90 deg ? Snell's Law:n 1sin Q 1=n 2sin Q 2 =n 2sin 90 sin Q 1 =n 2/ n 1 ------------------------------ Assume water to air:n 1= 1.33n 2= 1.00 q 1 = sin -1(0.752) = 48.8 degrees Q c= critical angle= 48.8 degrees 45. Cone of LightCrictical angle for water = 48.8 degrees Light within the 48.8 degree cone is detected by fish, while nothing in the air outside thatcone can be seen. The only light reaching the fish outside the cone is that light (not shown) which is reflected off the bottom of the pool. 46. Critical Angle of Diamond n = 2.419 Q c= sin -1 (1.00/2.419) = 24.42 degrees 90.00 - 24.42 = 65.58 degrees Light outside of 65.58 degree cone is reflected back inside. Virtually all light entering the top face of the diamond is reflected internally. 47. Total internal reflection

• When incident light is at an angle greater than the critical angle, the light will reflect instead of refract.
• When there is total internal reflection, the light will obey the law of reflection.

48. 49. Optical Fiber 50. 51. Optical Fiber 52. Optical Fibers in Medicine Broncho Scope Arthroscopic SurgeryColonoscope 53. Index of Refraction vs Color v = c/n The speed of blue light is less than the speed of red light. Blue light bends more than red light. 54. The Spectrum of White Light Note that the shorter wavelengths of light are bent more than the longer; blue more than red. 55. 56. Refraction in a Raindrop 57. Forming a Rainbow 58. Rainbow 59. 60. 61. 62. 63. 64. Index Matching