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Chapter 23 Ray Optics

Chapter 23 Ray Optics. Why doesn’t this work with real spoons?. Chapter 23. Ray Optics. Topics: The Ray Model of Light Reflection Refraction Image Formation by Refraction Color and Dispersion Thin Lenses: Ray Tracing Thin Lenses: Refraction Theory

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Chapter 23 Ray Optics

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  1. Chapter 23 Ray Optics Why doesn’t this work with real spoons?

  2. Chapter 23. Ray Optics Topics: • The Ray Model of Light • Reflection • Refraction • Image Formation by Refraction • Color and Dispersion • Thin Lenses: Ray Tracing • Thin Lenses: Refraction Theory • Image Formation with Spherical Mirrors

  3. Wave crests When can one consider waves to be like particles following a trajectory? Motion of crests Direction of power flow • Wave model: study solution of Maxwell equations. Most complete classical description. Called physical optics. • Ray model: approximate propagation of light as that of particles following specific paths or “rays”. Called geometric optics. • Quantum optics: Light actually comes in chunks called photons

  4. Wave Picture vs Ray Picture

  5. In the Ray Picture a beam of light is a bundle of parallel traveling rays

  6. Source sends out rays in all directions Pin hole camera (No lens)

  7. A long, thin light bulb illuminates a vertical aperture. Which pattern of light do you see on a viewing screen behind the aperture?

  8. Pin hole camera (No lens) How big and how small can the pin hole be? Spread in rays from same point on object should be smaller than image Diffraction should be negligible Also, a should be big enough to allow enough light to see.

  9. Specular Reflection - reflection from a smooth surface

  10. Diffuse Reflection - reflection from an irregular surface

  11. Angle of Incidence = Angle of Reflection

  12. Why does angle of incidence = angle of reflection? Wave crests Incident ray Incident and Reflected wave crests must match up along surface

  13. geometry also

  14. Two plane mirrors form a right angle. How many images of the ball can you see in the mirrors? 1 2 3 4

  15. Suppose the corner had a third side. How many images? 3 6 7 8

  16. Refraction - path of light bends when going from one medium to another Depends on index of refraction Low index high index

  17. Snell’s Law Remember definition of index of refraction

  18. Why Snell’s Law? Wave crests Incident ray Incident and Transmitted wave crests must match up along surface

  19. For most material n>1 Plasma n<1 On Mastering Physics Homework you are to pretend that plasma does not exist

  20. Tactics: Analyzing refraction

  21. EXAMPLE 23.4 Measuring the index of refraction QUESTION:

  22. EXAMPLE 23.4 Measuring the index of refraction

  23. EXAMPLE 23.4 Measuring the index of refraction

  24. EXAMPLE 23.4 Measuring the index of refraction

  25. EXAMPLE 23.4 Measuring the index of refraction

  26. EXAMPLE 23.4 Measuring the index of refraction

  27. A light ray travels from medium 1 to medium 3 as shown. For these media, • n3 = n1. • n3 > n1. • n3 < n1. • We can’t compare n1 to n3 without knowing n2.

  28. Total Internal Reflection Based on picture, which is bigger? n1 n2 Snell’s Law transmitted Solve for q2 reflected What if Then there is no q2 satisfying SL - no transmission - total reflection Can only happen if wave is incident from high index material, viz. n1 > n2.

  29. Critical angle

  30. Optical fiber

  31. z Fields extend a small distance into region 2 y What happens when q1 >qc ? “Evanescent” layer thickness d as

  32. A light ray traveling in air enters a 30°-60°-90° prism along normal direction to its hypotenuse face, as shown in the figure. The index of refraction of the prism is n =2.1Determine ALL possible outgoing ray directions.

  33. Virtual image formed due to refraction

  34. Approximation for small angles:

  35. Color Different colors are associated with light of different wavelengths. The longest wavelengths are perceived as red light and the shortest as violet light. Table 23.2 is a brief summary of the visible spectrum of light.

  36. Different colors are associated with light of different wavelengths. However, color is a perception, and most of that perception is based on the way our eyes and brain work. For example combinations of light with different wavelengths appear to have colors different from those of the original components. See Chapter 24.3 We will focus n the inherent properties of light, not on the way we perceive it.

  37. Dispersion The slight variation of index of refraction with wavelength is known as dispersion. Shown is the dispersion curves of two common glasses. Notice that n is larger when the wavelength is shorter, thus violet light refracts more than red light.

  38. Examples of dispersive refraction - Rainbow

  39. Rayleigh Scattering l Incident wave small particle -d John William Strutt 3rd Baron Rayleigh Wikimedia commons scattered wave scattered intensity is higher for shorter wavelengths

  40. Lenses

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