2. Reflection and Refraction

3. 1.REFLECTION Most objects we see reflect light.

4. 2.PRINCIPLE OF LEAST TIME Fermat's principle: Light travels in straight lines and will take the path of least time.

5. Fermat says take this path.

6. 3.LAW OF REFLECTION Using Fermat's principle one can show the law of reflection. A B 1 2 3 4 5 Mirror

7. The law of reflection states that the angle of incidence (  i ) equals the angle of reflection (  r ). This is true for specular reflection. (Specular reflection is “mirror-like” reflection.)

8. Included in the law of reflection is the fact that the incident ray, the normal, and the reflected ray all lie in the same plane. Normal Specular Reflecting Surface Incident Ray Reflected Ray ii rr

9. Demo - Candle Burning Under Water Video - Candle Burning Under Water Video - Water Wave Reflections Demo – Mirror Track Tracing

10. Plane Mirror Ray Diagramming Plane Mirror

11. Ray Diagramming Plane Mirror

12. Plane Mirrors Using ray diagramming one finds that the image is 1.Upright 2.Same size as the object 3.Virtual.

13. Diffuse Reflection Video - Diffuse ReflectionVideo - Diffuse Reflection If successive elevations of a surface are no more than /8 apart, then the surface is said to be polished at that wavelength. Most objects are seen by diffuse reflection.

14. Diffuse Reflection Magnification of a surface Colored lines are for the purpose of distinguishing reflected rays from incident rays.

15. Video - Terminator IIVideo - Terminator II Something that is barely polished for red light would not be polished for blue light. Consider microwave satellite dishes. They are polished for microwaves but not for visible. The metal screen in a microwave oven serves what purpose?

16. Reflection from Curved Surfaces (Concave shown here) The law of specular reflection is still obeyed. Principal axis Reflecting Surface Ray Diagramming f

17. Reflection from Curved Surfaces (Concave shown here) The law of specular reflection is still obeyed. Principal axis Reflecting Surface Ray Diagramming f

18. Demo - Coin MirageDemo - Coin Mirage Demo – Deep Concave MirrorDemo – Deep Concave Mirror Demo - Make-up Mirror ImagesDemo - Make-up Mirror Images Concave mirrors can produce real inverted images that are magnified, diminished, or the same size as the object. Concave mirrors can produce virtual upright images that are magnified.

19. More on Mirrors Convex mirrors always produce a diminished, upright, virtual image. Question - Why is it hard to see at night after or during a rain?Question - Why is it hard to see at night after or during a rain? Demo - Convex MirrorDemo - Convex Mirror Demo - Two Perpendicular MirrorsDemo - Two Perpendicular Mirrors Demo - Three Perpendicular MirrorsDemo - Three Perpendicular Mirrors

20. 4.REFRACTION Fermat's principle can also explain refraction (remember the beach). Refraction of light is the bending of light as it passes obliquely from one medium to another. It is due to the different speeds of light in the two different media.

21. Index of Refraction Index of refraction of a material equals the speed of light in a vacuum divided by the speed of light in the material.

22. Demo - Twinkling with Laser Slide - Twinkling Cartoon

23. Video - Water Wave RefractionsVideo - Water Wave Refractions Video - "Broken" Pencil RefractionVideo - "Broken" Pencil Refraction

24. Earth Sun Because of atmospheric refraction, we have lingering, elliptical sunsets.

25. Mirage Warm air Cool air Surface of water?

26. Cool air Looming Warm air

27. 5.CAUSE OF REFRACTION When light passes from one medium to another, its speed changes which in turn causes a bending of the light. Examples: Car running onto shoulder of road Light passing from air into water

28. Air Water ii RR Wave fronts of light

29. This bending produces illusions. Example: Objects in water appear closer and nearer to the surface. Air Water Eye

30. Fish can see everything above the surface of water within a 96 0 cone.

31. 96 0

32. Demo - Disappearing Pyrex

33. Dispersion Different frequencies are bent different amounts which causes a separation of white light into its constituent colors. This is the basic principle behind the operation of a prism. We say that a prism disperses the light. The higher frequencies interact most (slow down the most) and thus are bent the most. Demo - Aquarium PrismDemo - Aquarium Prism

34. Prism Slit White Light Source Dispersion in a Prism

35. Rainbow Rainbow

36. Picture - RainbowPicture - Rainbow Individual drops act as dispersers. The 42 o cone Demo– Rainbow ModelDemo – Rainbow Model A single eye can only see a small range of colors from a single raindrop.

37. Secondary Rainbow Secondary Rainbow Double rainbows are dimmer, higher, and have colors reversed. Link to picture.

38. Green Flash Earth Sun Dispersion occurs causing multiple images of the sun. The last to set would be blue, but most of the blue has been scattered which leaves green.

39. 6.TOTAL INTERNAL REFLECTION Video - Laser Under WaterVideo - Laser Under Water Critical angle is the angle where total internal reflection (TIR) begins. TIR is possible only when light is entering a medium of lesser index of refraction. Binoculars make use of TIR.

40. Flex Cam – Monocular Two Prisms in a Monocular

41. Fiber optic devices make use of TIR. Demo - Laser and Light PipeDemo - Laser and Light Pipe Video - Woman at Edge of PoolVideo - Woman at Edge of Pool Flex Cam – Aquarium & finger dip in waterFlex Cam – Aquarium & finger dip in water

42. 7.LENSES Lenses use refraction to form images. Demo - Fresnel LensDemo - Fresnel Lens

43. Imaging with a Convex Lens sees an image here. Convex Lens f Principal Axis Arrow as Object A ray parallel to the principal axis is bent upon entering the lens. Upon exiting the lens it is bent again and passes through a point called the focal point. A ray passing through the center of the lens is basically undeflected. An eye placed here This arrangement produces an inverted, real, diminished image.

44. Principal axis f Ray Diagramming

45. Principal axis f Ray Diagramming

46. More Imaging With a Convex Lens sees an image here. Convex Lens Principal Axis Arrow as Object A ray parallel to the principal axis is bent upon entering the lens. Upon exiting the lens it is bent again and passes through a point called the focal point. A ray passing through the center of the lens is basically undeflected. An eye placed here This arrangement produces an upright, virtual, magnified image. It is a simple magnifying glass. Farsighted people use lenses similar to these. f

47. f Imaging with a Concave Lens sees an image here. Concave Lens Principal Axis Arrow as Object A ray parallel to the principal axis such that is appears to have come from a point called the focal point. is bent upon entering the lens. Upon exiting the lens it is bent again A ray passing through the center of the lens is basically undeflected. An eye placed here This arrangement produces an upright, virtual, diminished image. Nearsighted people use lenses similar to these.

48. Double Convex Double Concave Plano Convex Plano Concave Convex Meniscus Concave Meniscus Convex lenses are positive converging lenses. Concave lenses are negative diverging lenses.

49. Spherical Aberration Principal axis Cure - Diaphragms or lens combinations 8.LENS DEFECTS

50. Convex Lens Spherical Aberration 8.LENS DEFECTS or lens combinationCure – Diaphragm

51. Convex Lens Chromatic Aberration Cure – Diaphragm or lens combinations (achromatic lens) Demo – Overhead Chromatic Aberration Astigmatism – due to barrel-shaped cornea

52. Chromatic Aberration Cure - Diaphragms or lens combinations (achromatic lenses) Demo - Overhead Chromatic AberrationDemo - Overhead Chromatic Aberration Astigmatism - due to barrel-shaped cornea Principal axis

53. Eyeglasses Picture - FarsightednessPicture - Farsightedness Picture - NearsightednessPicture - Nearsightedness

55. Chapter 28 Review Questions

56. An oar partially immersed in water appears "broken" because of (a) refraction (b) diffraction (c) polarization (d) interference (e) absorption (a) refraction

57. What type of mirror would you use to produce a magnified image of your face? (a) flat (b) concave (c) convex (d) you could use a concave or a convex mirror (b) concave

58. What is (are) the purpose(s) of the wire screen in the door of a microwave oven? (a) to absorb microwaves (b) to allow you to see what's cooking (c) to reflect microwaves (d) all of the above (e) only (b) and (c)

59. A lingering sunset is (a) a looming effect (b) caused by an elliptical (oval) sun (c) due to atmospheric refraction (d) caused by reflections from the upper atmosphere (c) due to atmospheric refraction

60. One way to reduce the problem of spherical aberration in a positive lens is to join a negative lens to it to form a compound lens. (a) True (b) False (a) True

61. When a beam of light emerges at a nonzero angle from water to air, the beam (a) bends away from the normal (b) continues in the same direction (c) bends toward the normal (d) changes frequency (e) slows down (a) bends away from the normal

62. If you wish to take a picture of your image while standing 5 ft in front of a plane mirror, for what distance should you set your camera to provide the sharpest focus? (a) 10 ft (b) 5 ft (c) 2.5 ft (d) it can't be done (a) 10 ft