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  • Diffraction is the bending of waves around obstacles.
  • Huygen’s Principle: Every point on a wave front acts as a source of wavelets that move forward at the wave speed; the wave front at a latter time is the surface tangent to the wavelets.
  • Diffraction of light from a narrow slit: If the screen is far away, the first dark fringe occurs for an angle theta given by

    Sin (theta) = lambda / W

    where lambda is the wavelength of light, W is the width of the slit, and theta is the angle that the line from the center of the slit to the dark fringe makes with the line from the center of the slit to the central maximum.

  • In general dark fringes occur at angles theta given by

    Sin(theta) = m * lambda / W

    where m = 1, 2, 3,… The bright fringes are situated halfway between the dark ones.


Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Diffraction of Waves 0:18
    • Source of Sound Waves
    • Huygens' Principle
  • Diffraction of Light from Narrow Slit 10:57
    • Light From a Distant Source
    • Pick Any Point
    • Source of Wave Front
    • Waves Traveling Parallel to Each Other
    • Franhofer Diffraction
    • Drawing Perpendicular
    • First Maximum
    • Every Wave Has Interference and Diffraction
  • Width of Central Maximum 32:49
    • Width of Slit is 0.2 mm
    • Monochromatic Light
    • If Angle is << 1
    • If W= 2cms
  • Intensity of Diffraction Patterns 44:21
    • Plotting Intensity Versus Light
  • Resolution 45:35
    • Considering Two Source
    • Two Objects Resolved
    • Rayleigh Principle
  • Diffraction Grating 51:18
    • First Order Max
    • Intensity Shown in Figure
  • Extra Example 1: Slit Diffraction
  • Extra Example 2: Minima in Diffraction Pattern
  • Extra Example 3: Diffraction Grating