======Double Slit Experiment with Light======


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**Materials: **{{$demo.materials_description}}\\
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**Safety: **{{$demo.safety_description}}\\
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**Alternative titles:** Light Interference Experiment
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====Summary====                   
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====Procedure====  
  - Set up a coherent light source, such as a laser, pointing at a barrier with two narrow, closely spaced slits.  
  - Place a screen or sensitive detector behind the barrier.  
  - Turn on the laser and observe the pattern of alternating bright and dark fringes that appear, caused by constructive and destructive interference of light waves.  
  - Reduce the light intensity so photons pass through the slits one at a time.  
  - Use a sensitive detector with a long exposure to record the impacts. Initially, single photons appear as random points, but over time the familiar interference pattern emerges.



====Links==== 
Interference Demo: Double Slit - Physics Demos: 
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Simple double slit experiment at home - no81e: 
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📄 Double slit experiment - Anton Paar: [[https://wiki.anton-paar.com/au-en/double-slit-experiment/]]\\


====Variations====
  * Try using different wavelengths of light (red, green, blue lasers) to compare fringe spacing.  
  * Use one slit covered to show the difference between single-slit diffraction and double-slit interference.



====Safety Precautions====
  * Do not look directly into the laser beam; it can damage eyes.  
  * Secure the laser on a stable surface to prevent accidental movement.  
  * Keep reflective surfaces (mirrors, watches, jewelry) away from the beam path to avoid stray reflections.




====Questions to Consider====
  * Why do bright and dark fringes appear on the screen? (Constructive interference produces bright fringes; destructive interference produces dark fringes.)  
  * What happens when photons are sent one at a time? (They arrive as particles, but collectively form a wave-like interference pattern.)  
  * How does this experiment support the idea of wave-particle duality? (Light acts like a wave when passing through slits and like a particle when detected.)  
  * How would changing the wavelength affect the pattern? (Longer wavelengths produce wider spaced fringes; shorter wavelengths make fringes closer together.)