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The students should understand Young’s double-slit interference as given by s = λD/d where s is the separation of fringes, d is the separation of the slits, and D is the distance from the slits to the screen


Here are experiments our science specialists have selected to support this IB* topic.


Experiment #19 from Advanced Physics with Vernier — Beyond Mechanics

In this experiment, you will

  • Compare and contrast features of the patterns produced on a screen when light from a laser passes through either one or two slits.
  • Discern which features of the pattern arise from the interaction of the light with the single slit and which arise from the double slits.
  • Use the principle of superposition to explain how waves from two sources could interfere constructively or destructively.
  • Use a diagrammatic explanation of how path length differences for light passing through the two slits give rise to bright and dark fringes in the pattern.
  • From experimental parameters, predict the spacing between bright (or dark) fringes in the pattern.
  • Collect intensity vs. position data to test your predictions.

Educational Standard
International Baccalaureate (IB) 2025
C Wave behaviour
C.3 Wave phenomena
Standard level and higher level

* The IB Diploma Program is an official program of the International Baccalaureate Organization (IBO) which authorizes schools to offer it. The material available here has been developed independently of the IBO and is not endorsed by it.