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Thread: OT: Double slit experiment

  1. #1
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    Default OT: Double slit experiment

    Has anyone actually tried the double slit experiment? I tried it recently with very basic materials. Black construction paper with both 1 and 2 slits, and a simple LED light source. With one slit, I just see one band of light passing through the slit and projecting onto a wall and with two slits, I see two bands projecting onto the wall... I don't see any interference patterns unless they are simply too faint to see with the naked eye. Maybe my slits were too close to each other or too far away from each other, etc, but I see what you would expect to see with partials. Oh well
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  2. #2
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    I thought it had to be a laser? Otherwise the patterns are too diffuse to see on the wall?

    I did it in high school but I forget the specifics now.

  3. #3
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    Diffraction effects rely on the slit being some lower number of wavelengths wide. So the slit needs to be DARN fine. And any second slit needs to be very close to the first. I can't see doing that with slits in construction paper done with basic scissors.

    I recall back in Physics 12 that we did diffraction labs that used a rig that held two knife edges which we would carefully bring together with a little screw setup. The final slit to see a good clear pattern was not visible to our eyes unless we held the light behind it or held it up to the sun coming in the room when the drapes were pulled back again at the end of the lab.

  4. #4
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    An LED does not have adequate coherence, even if you make high quality slits.

  5. #5
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    Yea, I was just using a LED flashlight and two 2" x 1/8" slits on black construction paper about 1" apart from each other projecting it onto my wall with a distance of about 1 foot from the light source and the construction paper and about 2 feet of distance between the paper and the wall being projected on. I'd really like to think we're inside of a massively complex simulation and one-day we'll figure it all out and be able to interface directly with reality and be able to engineer environments on a universe scale..
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  6. #6
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    You will need a coherent light source like a laser. The slits should be sharp, straight edges. I don't think cutting construction paper will give an edge sharp enough, but razor blades should work for a simple experiment. Try bringing just two razor blades together as a single slit the thickness of a piece of paper apart, with a small laser pointer as a source. You will probable need to have the lights out to see the fringe pattern.

  7. #7
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    We did this experiment in high school physics. If I remember correctly we put black paint on a microscope slide, placed 2 razor blades side by side and drew 2 scratches in the paint. Interference patterns were very clear.

  8. #8
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    Quote Originally Posted by Erich View Post
    We did this experiment in high school physics. If I remember correctly we put black paint on a microscope slide, placed 2 razor blades side by side and drew 2 scratches in the paint. Interference patterns were very clear.
    What did you use as a light source and how far away did you place the light source from the slide and the slide from the target?
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  9. #9
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    I did this as a kid. I remember pulling thin copper wire past its yield limit to get really straight wire to make the two slits. Razor blades for the sides. I'm sure I didn't have access to any single wavelength source, unless maybe I had some kind of neon light, but I still got results. I remember mounting my microscope horizontally to view the interference pattern. All the measurements worked out.
    Richard

  10. #10
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    A friend of mine did it recently. It works. Reality is a hard hard place.

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