Why does 2slit interference depend on wavelength?

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How do 2 waves in a double slit get cut? I know that light spreads in all directions so, when a double slit is infront of a light source, then it only allows light that goes through the slit past the wall. Why do interference patterns depend on the wavelength? Isnt the wave length perpendicular to the orientation of the slit? I would image the interference patters depend on the angle with which the light gets cut, but I don't see conceptually how it depends on the wavelengths. Can someone explain this conceptually?
 

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  • #2
sophiecentaur
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The reason the interference works is that waves of the same wavelength, taking different paths, can add and cancel, depending on where they arrive. Wavelength and the spatial layout of the situation go together to produce an interference pattern.

Interference happens because of the basic properties of waves. The way you are using terms in your question makes me think that you need to start at the very beginning of Wave Theory. I can't tell what stage you are at in your Physics but this link could (don't be offended) be a suitable start. Fire up Google and find a few links about waves and you can then graduate to interference. Hyperphysics (easy to find) is always a good source of concise Physics information but it often requires some extra reading around.
 
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DrGreg
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I can explain it diagramatically:
upload_2016-1-30_17-14-56.png

Image adapted by Dr Greg from File:Two-Slit Experiment Light.svg, public domain.


upload_2016-1-30_17-14-56.png
 
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sophiecentaur
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I can explain it diagramatically:
I have a feeling that the real problem here is understanding the basic way waves work. (i.e. a couple of stages earlier)
Like here:
Isnt the wave length perpendicular to the orientation of the slit?
Translating graphs and diagrams into a feel for what they actually represent can be a problem. That's why I recommended reading around the basics of waves first. Definitions of wavelength, displacement, wave speed etc. are essential for making progress with something as abstract as waves.
 

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