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Chapter 28

Chapter 28. Reflection and Refraction. HOME. When light falls on the surface of a material, it can be re-emitted without a change in frequency or wavelength. This is reflection. Red Light. . . Red Light.

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Chapter 28

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  1. Chapter 28 Reflection and Refraction HOME

  2. When light falls on the surface of a material, • it can be re-emitted without a change in frequency or wavelength. This is reflection Red Light   Red Light

  3. or it can be absorbed into the material and be dissipated as heat or propagate through the medium, atom by atom or molecule by molecule. This is (refraction) In this case, there is a change in wavelength but no change in frequency. This also means that the wave speed also changes. (It slows down a little)

  4. Red Light Red Light V1 =1f Red Light V2 =2f V1 =1f

  5. Reflection:The return of light rays from a surface in such a way that the angle at which a given ray is returned is equal to the angle at which it strikes the surface. • Refraction:The bending of an oblique ray of light when it passes from one transparent medium to another.

  6. Fermat’s Principle of least times • c. 1650: Pierre de Fermat proposes his principle of least time: • Out of all possible paths that light might take to get from one point to another, it takes the path that requires the shortest (least) time.

  7. Which path does the light ray take from A to B? B A

  8. Answer: It takes the path of least time! The distance from C to B equals the distance from C to B’ B A C Imaginary line – not a light ray. B’

  9. Other Geometrical Consequences Angle of incidence Angle of reflection   Incident ray Reflected ray Angle of incidence equals the angle of reflection.

  10. Diffuse Reflection Incident parallel rays Reflected rays are not parallel Rough surface

  11. Specular Reflection Incident parallel rays Reflected rays are parallel Smooth Surface

  12. Plane Mirrors Image appears to be as far back in the mirror as it is in front of it.

  13. The mirror forms a virtual image Real Object Virtual Image Side view of the mirror

  14. Reflection from curved mirrors

  15. Geometrical Optics of acurved mirror Object f Real inverted Image. Magnification <1

  16. Virtual Noninverted image Magnification >1 f Object

  17. Object Virtual Noninverted image Magnification <1

  18. Parabolic Mirrors Parallel rays converge to a common point Focal Point

  19. Technological Applications: Communications Satellite dishes and Radio Astronomy

  20. Refraction • The bending of light as it passes from one transparent medium to another

  21. I : angle of incidence air i r: angle of refraction Glass, water, etc. Normal r

  22. Index of refraction n = c/v = index of refraction. nair  1.0 nglass  1.5

  23. Snell’s Law or The Law of Refraction nisin(i) = nrsin(r)

  24. Example of Double Refraction Air Air Glass A i r r i B

  25. Prism

  26. Prism II

  27. Convex (Converging) Lens Focal Point

  28. Mirage- Light travels faster through the hot , less dense air. Hot Air

  29. Observer Apparent position of frog Frog

  30. Rainbows 42o Water drops 40o

  31. Total Internal Reflection (TIR) Critical Angle

  32. Total Internal Reflection (T.I.R.) T.I.R. Angle greater than critical angle Critical Angle

  33. As i approaches the critical angle, r approaches 90o Air r Glass i

  34. nisin(c) = nrsin(90o) nisin(c) = nr Sin(c) = nr/ni This allows us to determine the critical angle, c

  35. Lenses Double Convex (Converging) Lens Focal Point Focal Length

  36. Double Concave (Diverging) Lens Focal Point Focal length

  37. R focal length Central Center of Curvature Axis

  38. Real Object Inverted Real Image f f

  39. Noninverted Virtual Image Real Object

  40. Virtual, non-inverted Image f f Real Object

  41. Virtual, non-inverted Image Real Object

  42. End of Chapter 27 HOME

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