• AP Physics 2: Light 1: Light Wave and Huygens’ Principle
  
  http://www.wikiwand.com/en/Diffraction_formalism: Very nice interference and diffraction simulation based on Huygen's principle. 
  
  Professor Lewin on the Dutch pronunciation of Huygens: http://www.youtube.com/watch?v=wENZmBofwSw (Update: MIT indefinitely removes online physics lectures and courses by Walter Lewin for good reasons. However, this video link is to a video segment posted by some other person, so the link still works. I do not condone Lewin's terrible behavior. For your safety, students should not contact Lewin in any way.) 
  
  
• AP Physics 2: Light 2: Young’s Double-Slit Interference Experiment
  
  
  
  
• AP Physics 2: Light 3: Double-Slit Interference Problem
  
  
  
• AP Physics 2: Light 4: Single-Slit Diffraction
  
  
  
• AP Physics 2: Light 5: Single-Slit Diffraction Problem
  
  
  
• AP Physics 2: Light 6: Double-Slit Interference & Single-Slit Diffraction Patterns
  
  
  
• AP Physics 2: Light 7: Diffraction Grating
  
  
  
• AP Physics 2: Light 8: Diffraction Grating Problem
  

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