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Wave Nature of Light

Wave Nature of Light. Diffraction. Diffraction is the bending of a wave around a barrier or through an opening into the shadow region. Diffraction. The amount of diffraction depends on the size of the barrier or opening compared to the wavelength of the wave.

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Wave Nature of Light

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  1. Wave Natureof Light

  2. Diffraction • Diffraction is the bending of a wave around a barrier or through an opening into the shadow region.

  3. Diffraction • The amount of diffraction depends on the size of the barrier or opening compared to the wavelength of the wave. • Longer wavelengths exhibit more diffraction. • Owl hoots around trees • Water waves around small boats • Light waves diffract for very small openings – on the order of 1 wavelength

  4. Diffraction Applet • This applet shows the diffraction of waves by a narrow opening. • The waves bend into the shadow region.

  5. Breakwater Diffraction • Water waves diffract around barriers which have constructed as breakwaters.

  6. Small Island Diffraction

  7. Huygens’ Principle • According to Huygens’ principle, each of the two slits in Young’s experiment acts as a point source of light waves. Christiaan Huygens (1629-1695)

  8. Ripple Tank Waves • The crests of water waves act as converging lenses for the light shining from above. • On the screen, the crests are bright, and the troughs are dark.

  9. Ripple Tank Waves

  10. Ripple Tank Waves

  11. Diffraction Slit Width Variation

  12. Diffraction Pattern - Fingers • Make a narrow opening between two fingers and look through the opening at a light. You will see thin fringes resembling hairs. These are nodes or dark fringes.

  13. Diffraction – Slit Width

  14. Razor Blade & Penny Diffraction

  15. Poisson’s Spot Explained

  16. Diffraction Links • http://www.cfd-solutions.co.uk/waves.htm • http://www.spacesciencegroup.nsula.edu/lessons/defaultie.asp?Theme=waves&PageName=diffraction • http://lectureonline.cl.msu.edu/~mmp/kap13/cd372.htm • http://www.glenbrook.k12.il.us/gbssci/phys/Class/waves/u10l3b.html • http://www.coastal.udel.edu/ngs/waves.html

  17. Interference • When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location. This is called the principle of superposition. Constructive Interference Antinode Destructive Interference Node

  18. Double Source Interference • When 2 periodic circular patterns interfere, a pattern of constructive and destructive interference emerges. • “Lines” connecting nodes are called nodal lines • “Lines” connecting antinodes are called antinodal lines

  19. Double Source Nodal Lines

  20. Ripple Tank Waves The diffraction due to the two narrow openings results in a pattern of nodal and antinodal lines similar to that of a double source interference pattern.

  21. N A N A A Ripple Tank Waves Antinodal Lines Nodal Lines

  22. Inserting a Screen d A N A N A A N

  23. Double Source Interference • When 2 periodic circular patterns interfere, a pattern of constructive and destructive interference emerges. • “Lines” connecting nodes are called nodal lines • “Lines” connecting antinodes are called antinodal lines

  24. Double Source Applets

  25. Thomas Young • Scientist • Physician • Renaissance Man • Interference • Elastic Behavior of Solids • Kinetic Energy • Work and Energy Connection 1773 - 1829

  26. Double Slit Interference

  27. Light Interference Interference is most noticeable when light is: • Monochromatic -- This means light with a specific wavelength. • Coherent. This means the phase difference between the light waves remains constant over time. Laser light is monochromatic and coherent. Light from incandescent lamps is incoherent.

  28. Coherent & Incoherent Light

  29. Incoherent Light • Atoms emit radiation. For example the "excited" neon atoms in a neon sign emit light. Normally, atoms radiate their light in random directions at random times. The result is incoherent light.

  30. Young’s Double Slit Applets

  31. Young’s Double Slit Layout

  32. Wavelength Comparisons

  33. Interference - Wavelength

  34. Reflections at Boundaries Fast Medium to Slow Medium Slow Medium to Fast Medium Fixed End Reflection 180o phase change Free End Reflection No phase change

  35. Thin Film Interference

  36. Thin Film Interference • Phase change of ray 1 • Phase change of ray 2 • In terms of wavelength in vacuum

  37. Thin Film Interference • difference in phase shifts of the two rays. • Destructive Interference • Constructive Interference

  38. Air Wedge Interference

  39. Air Wedge Interference

  40. Newton’s Rings

  41. Air Wedge Interference Constructive Interference Destructive Interference Fringe Spacing

  42. Iridescence

  43. Iridescence

  44. Iridescence

  45. Soap Film Interference • This soap film varies in thickness and produces a rainbow of colors. • The top part is so thin it looks black. • All colors destructively interfere there.

  46. Sample 6 • A soap bubble is illuminated by a combination of red light (λ = 692 nm) and blue light (λ = 519 nm). • What minimum thickness of the soap bubble film will result in blue light being not reflected?

  47. Parallax Apparent change in position of object due to shift in position of observer

  48. Camera 1 – Camera 2

  49. Binocular Vision • Two Eyes • Camera 1 – Camera 2 • One of the reasons that we can perceive depth. • Our brain uses the two images (one from each eye) to judge the distance to an object. • Subconscious use of parallax

  50. 3D Circle

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