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How do you build a double-slit experiment at home?

  1. Mar 21, 2012 #1
    Is it even possible to do so? I used a thick paper sheet with 1x5 mm slits 5mm apart with a normal flashlight (just to do a rough test). I saw what looked like the patches of light with darkness in between, but it was very, very faint.. Is it possible to do an effective model with easy-to-get materials? I live in a developing country, so I can't really get my hands on the things Young used. The most advanced thing I could possible get is a laser pointer as a light.

    I'm sorry if this is in the wrong section, I couldn't find the right section to ask this.
  2. jcsd
  3. Mar 21, 2012 #2
    The slits have to be about the same size as the wavelength of light to give you anything noticeable, which is very small for visible light. You can buy a diffraction grating fairly inexpensively at a hobby shop or science museum gift shop, which is just a film with many very small slits. Look through your diffraction grating at a light bulb turned on and you will see streaks of rainbow off to the side. That is your diffraction/interference pattern. If you want to cut your own slits at mm size, you will have to get a microwave source and receiver, and you will have to cut the slits in metal foil because such frequencies go through paper. This is how they do the experiment in a university lab class.
  4. Mar 21, 2012 #3
    Diffraction gratings can be as cheap as a few bucks.
  5. Mar 21, 2012 #4
    On Feb 5 Millacol88 started a thread to find out how to demonstrate youngs double slits experiment for a school fair.
    If you can find that post you will find some discussion on what to do including photographs of various set ups
  6. Mar 21, 2012 #5
    Take a nice sharp razor blade and slice two slits into cardboard. Just two slashes, as thin as possible and not too far apart. Find a dark room, but where the sun shines in through a small hole like the keyhole in a door or a small hole in the wall. Put your double slit over that, completely covering the aperture such that the only light in the room is from the two slits.

    Finally, let me know if it works :-) I have not tried myself
  7. Mar 21, 2012 #6
    BTW, you can see nice diffraction when you shine a laser pointer grazing onto a CD. The diffraction you see is from the pitch of the spiral information track (that I have tried).
  8. Mar 22, 2012 #7

    Philip Wood

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    If you can get hold of a laser pointer, you've already got much better equipment than Young had. You can make a good pair of Young's slits by gluing two razor blades parallel and with edges separated by half a millimeter or so, on to a microscope slide, and then stretching a thin piece of wire centrally in the gap, gluing it in place at the top and bottom.
    [Be sure you know precautions when using a laser – even a low power one.]
  9. Mar 22, 2012 #8
    You can also try smoking a piece of glass with the soot from a burning candle so that the glass is covered black, and then etching the slits in the soot with two razor blades pressed together.
  10. Mar 22, 2012 #9


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    Using a laser is highly recommended. Otherwise, the diffraction patterns formed by all the different colors will overlap and blur out. Get a cheap laser pointer. To make the slits, you can use a film camera to take a picture of two closely spaced lines. The negative, much reduced in size, should have two clear slits, hopefully submicron in size.
  11. Mar 22, 2012 #10


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    A google search should have plenty of sites that explain how to do this experiment at home.
  12. Mar 22, 2012 #11


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    You can use a CD as a reflective diffraction grating.
  13. Mar 23, 2012 #12
    My favorite way is a clever little trick. Light should diffract the same way around the inverse of a hole as the hole itself, roughly. So I usually ask someone with long hair to give me one of their hairs (~20 micrometers in diameter), and shine a laser pointer at it in darkness. If the hair is taut and you hold it at the right distance, it works great.
  14. Mar 23, 2012 #13
    Excellent idea. I will have to remember that one. It reminds me of the story of the Poisson spot that we recreated in an optics class.
  15. Jul 22, 2012 #14
    Good inkjet or laser transparency film allows you to design any slit grid you want with accuracy of 0.01mm (2400dpi) and it costs about 50 cents a sheet and 2 minutes to print and cut out what you need. You can get a sheet for free at practically any school.

    If you don't have a printer you can use a fine tip marker on transparency with a magnifying glass and ruler to get the distance as small as you can, I did this as a kid and it worked but not as good as a printer did later.

    You can then align 2 sheets with each other and slide a pattern with 1 slit over the pattern with 2 slits to close/open one slit and see/hide the interference pattern; something very important and hard to do with methods involving 3D objects like hair or blades, also probably nicer to look at.

    I tried this with beautiful results and had it working in a few minutes.
  16. Jul 22, 2012 #15


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    Hi njsteele!
    I have tried with laser printed slits, but those failed miserably for me, the laser just went right through the barrier (I tried with very thin barriers, though). Maybe the printer I used was suboptimal? Btw, here's my blog post about double-slit experiments at home (quite recent).
  17. Jul 22, 2012 #16
    Oh my gosh awesome how-to! Thanks for taking so much time to make it.
  18. Jul 22, 2012 #17
    Go out at night, hold the tips of your index finger and thumb lightly together, hold that out in front of you and look through the contact point between the tips at a distant light (street lights are good).
  19. Jul 22, 2012 #18


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    How does that have anything to do with the double slit experiment?
  20. Jul 23, 2012 #19
    ...because it shows an interference pattern; you may just look at it or take a picture.
  21. Jul 23, 2012 #20


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