Electromagnetic waves and optics

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Electromagnetic waves and optics

  1. 1. Chapter 32 Electromagnetic WavesPowerPoint® Lectures forUniversity Physics, Twelfth Edition – Hugh D. Young and Roger A. FreedmanLectures by James PazunCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  2. 2. Goals for Chapter 32 • To do an overview of Maxwell’s equations and electromagnetic waves • To study sinusoidal electromagnetic waves • To consider the passage of electromagnetic waves through matter • To determine the energy and momentum of electromagnetic waves • To observe wave addition, the formation of a standing electromagnetic waveCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  3. 3. Introduction • If an electric field vector propagates, it generates a magnetic field vector. Or, is it the other way? • The “chicken and the egg” argument of which disturbance causes the other aside, this is often a favorite portion of a first course in physics. Electromagnetic waves, at least in the form of light, are common to many of our daily experiences. Even without vision, you can stand in the sun wearing a dark shirt and perceive electromagnetic waves.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  4. 4. Maxwell’s equations • After Ampere and Faraday came James Clark Maxwell. He penned a set of four equations that draw Gauss, Ampere, and Faraday’s laws together in a comprehensive description of the behavior of electromagnetic waves.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  5. 5. Electromagnetic waves are ubiquitous • If you tried to cite all the places you notice electromagnetic waves in your classroom, you would conclude in a few minutes that they are everywhere.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  6. 6. Electromagnetic waves occur over a wide range • Where wavelength is large, frequency is small. • The range extends from low energy and frequency (radio and television) to high energy and small wavelength (gamma rays).Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  7. 7. The propagation of electromagnetic waves • The wave front moves at speed c, equal to 3.0 × 108 m/s.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  8. 8. Propagation of electromagnetic waves II index of refractionCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  9. 9. The wave equation Electromagnetic wave traveling in the +x directionCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  10. 10. The waveCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  11. 11. The wave T = 1.6 s horizontal axis - time axis λ horizontal axis - position axisCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  12. 12. • A coating of oil on water or a delicate glass prism can create a rainbow. A rainstorm among open patches of daylight can cast a conventional rainbow. Both effects are beautiful and arise from the wavelength dependence of refraction angles. • Eyeglasses or contact lenses both use refraction to correct imperfections in the eyeball’s focus on the retina and allow vision correction.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  13. 13. Reflection and refraction • The figure below illustrates both reflection and refraction at once. The storefront window both shows the passersby their reflections and allows them to see inside.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  14. 14. We will consider specular reflections • A real surface will scatter and reflect light. Diffuse reflection is the rule, not the exception. We will use specular reflection as we used the ray approximation, to make a very difficult problem manageable.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  15. 15. Laws of reflection and refraction • Angle of incidence = angle of reflection. • Snell’s Law of Refraction considers the slowing of light in a medium other than vacuum … the index of refraction.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  16. 16. Why should the ruler appear to be bent? • The difference in index of refraction for air and water causes your eye to be deceived. Your brain follows rays back to the origin they would have had if not bent.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  17. 17. Tabulated indexes of refraction As index of refraction increases, velocity of light in the medium decreasesCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  18. 18. Quiz ¼ sheet of paper1. Write down the relationship of frequency and the wavelength of light in a vacuum.2. If an EM wave or light enters a dielectric, its frequency remains the same. As it enters the material, the electrons in the material vibrate with a driving frequency equal to that of the EM wave but its wavelength would differ.• The speed of light in vacuum is c = 3.0 x 108 m/s, what would be its speed in water if its index of refraction is 1.33?3. Write down the law of reflection and refraction (Snell’s law)4. Knowing Snell’s law and the theory of index of refaction, rank the speed of light through each medium from least to greatest. 50o 5o 15o 15o 15o 5o D C A BCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  19. 19. Quiz (by pair) >:)Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  20. 20. Chapter 35 InterferencePowerPoint® Lectures forUniversity Physics, Twelfth Edition – Hugh D. Young and Roger A. FreedmanLectures by James PazunCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  21. 21. Goals for Chapter 35 • To consider interference and coherent sources • To study two-source interference of light • To determine intensity in interference patterns • To consider interference in thin films • To study the Michelson interferometerCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  22. 22. Introduction• Rainbows in the sky: been there, seen that. A thin-film soap bubble: why should that create a rainbow effect?• This thin film is dispersing white light and revealing a r.o.y.g.b.i.v. spectrum of color.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  23. 23. Wave fronts from a disturbance • Think back to our first slide on wave motion when the father threw an object into the pool and the boy watched the ripples proceed outward from the disturbance. We can begin our discussion of interference from just such a scenario, a coherent source and the waves from it that can add (constructively or destructively).Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  24. 24. A “snapshot”• The “snapshot” of sinusoidal waves spreading out from two coherent sources.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  25. 25. A “snapshot”• The “snapshot” of sinusoidal waves spreading out from two coherent sources.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  26. 26. Double slit interference of light We consider Monochromatic Single wavelength Best example is laser Coherent Same frequency Definite constant phase relationship (not necessarily in phase)Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  27. 27. Double slit interference of light • Two waves interfering constructively and destructively. • Young did a similar experiment with light.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  28. 28. Double slit interference of light • Two waves interfering constructively and destructively. • Young did a similar experiment with light. L LCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  29. 29. As the waves interfere, they produce fringesCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  30. 30. As the waves interfere, they produce fringes Constructive Interference Destructive Interference m is called the order numberCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  31. 31. As the waves interfere, they produce fringesCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  32. 32. Interference from two slits or two radio stations • In a two-slit interference experiment, the slits are 0.200 mm apart and the screen is at a distance of 1.00 m. The third bright fringe (not counting the central bright fringe straight ahead from the slits) is found to be displaced 9.49 mm from the central fringe. Find the wavelength of light used.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  33. 33. Interference between mechanical and EM wavesCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  34. 34. Thin Film Interference Constructive Interference Destructive InterferenceCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  35. 35. Thin films will interfereCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  36. 36. Quiz. Understanding interferenceCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  37. 37. Chapter 36 DiffractionPowerPoint® Lectures forUniversity Physics, Twelfth Edition – Hugh D. Young and Roger A. FreedmanLectures by James PazunCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  38. 38. Goals for Chapter 36 • Fresnel and Fraunhofer diffraction • Single-slit diffraction • Diffraction gratingsCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  39. 39. Introduction • It’s intuitive that sound can diffract (and travel around corners). Light doesn’t “show its poker hand” so easily. • If you shine light from a point source to a ruler and look at the shadow, you’ll see the edges are … well … not sharp. A close inspection of the indistinct edge will reveal fringes. • This phenomenon may not sound useful yet but stay with us until the end of Chapter 36. This line of thinking has shown the way for advances in DVD technology and applications in holography.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  40. 40. Fresnel and Fraunhofer diffraction • According to geometric optics, a light source shining on an object in front of a screen will cast a sharp shadow. Surprisingly, this does not occur.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  41. 41. Diffraction • If the source and the screen are close to the edge causing the diffraction, the effect is called “near-field” or Fresnel diffraction. If these objects are far apart, so as to allow parallel-ray modeling, the diffraction is called “far- field diffraction” or Fraunhofer diffraction.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  42. 42. Diffraction from a single slitCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  43. 43. Dark fringes in single-slit diffraction • The figure illustrates Fresnel and Fraunhofer outcomes.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  44. 44. Fresnel or Fraunhofer? • Differentiating Fresnel and FraunhoferCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  45. 45. Fraunhofer diffractionCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  46. 46. Fraunhofer diffraction divide source into two equal parts destructive interference divide source into four equal parts divide source into six equ and so on... eight condition for destructive interferenceCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  47. 47. Fraunhofer diffraction condition for destructive interferenceCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  48. 48. Fraunhofer diffraction and an example of analysis • A photograph of a Fraunhofer pattern from a single slit.Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  49. 49. ResolutionCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  50. 50. ResolutionCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  51. 51. Resolution Smaller wavelength means less angle to resolve object Why electron microscopes can see better than optical microscopes. Wavelength of electron is small ~10-10 m Light is ~10-7 mCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
  52. 52. Quiz! 1. Write down the equation for constructive interference for thin films given na < nb < nc given a light of wavelength λ enters the film. let m be the order number na nb t ncCopyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley

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