Chapter 35

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Chapter 3536 Interference and the Wave Nature of
Light

• Light as a Wave
• THE PRINCIPLE OF LINEAR SUPERPOSITION
• Young's Double-Slit Experiment
• Diffraction

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What is physics?
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Light as a Wave

• Huygens' principle
• All points on a wavefront serve as point
  sources of spherical secondary wavelets. After a
  time t, the new position of the wavefront will be
  that of a surface tangent to these secondary
  wavelets.

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Constructive Interference

• Condition , m0, 1, 2, 3, .

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Destructive Interference

• Condition , m0, 1, 2, 3,
  .

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Young's Double-Slit Experiment
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Bright fringes
Dark fringes
Where m1, 2, 3,
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Example 1  Youngs Double-Slit Experiment

• Red light (?664 nm in vacuum) is used in
  Youngs experiment with the slits separated by a
  distance d1.20104 m. The screen in Figure is
  located at a distance of L2.75 m from the slits.
  Find the distance y on the screen between the
  central bright fringe and the third-order bright
  fringe.

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Interference from Thin Films
Condition for destructive interference is
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Diffraction
The diffraction is the bending of waves around
obstacles or the edges of an opening
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Diffraction determined by the ratio ?/W
Smaller ? /W, less diffraction
Larger ? /W, more diffraction
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Conditions for dark fringes

• Conditions for dark fringes in single-slit
  diffraction

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Example   Single-Slit Diffraction

• Light passes through a slit and shines on a
  flat screen that is located L0.40 m away (see
  Figure). The width of the slit is W4.0106 m.
  The distance between the middle of the central
  bright fringe and the first dark fringe is y.
  Determine the width 2y of the central bright
  fringe when the wavelength of the light in a
  vacuum is (a) ?690 nm (red) and (b) ?410 nm
  (violet).