Building Young's Double-Slit Interference Experiment? 24
TucsonTed asks: "I am a student teacher, preapring for life as a middle or high school teacher. I'd like to build a working model of Young's Double-Slit experiment to show light's wave behavior. Anyone have info on where I can find some blueprints (size of slits, spacing, etc.?) I don't yet have access to a real lab, so I need the DIY approach. I can use monochromatic light or a laser. If you haven't come across this experiment, and its freakish implications at the quantum level, take a look. You may not sleep tonight." For those interested in the math behind this experiment, you might want to check this site.
A simple solution (Score:3, Insightful)
A quick Google search... (Score:1)
...gave me this [cavendishscience.org].
- Freed
Re:A simple solution (Score:1)
So yeah, that'll work.
simple physics (Score:2, Interesting)
Wave vs particle (Score:2, Informative)
The really interesting part is that the interference pattern persists even down to the point you are shooting single photons through the slits, as long as you can't tell which slit the photon is going through, but once you can tell, the pattern breaks down and you get just a single blur.
That is, it is an interference pattern as long as the photons are 'allowed' to act as waves, as soon as you try to treat them as particles, they behave as particles.
I'm no physicist, so my description may be a little off, and I don't know how they experimentally verified single photons going through the slit... but this is used for an example of the dual-nature of light.
Another interesting thing is that QM states that when an object passes through an opening nearly the size of the object, the object will be deflected through some range of angles, thus with the proper sized opening, even bowling balls are deflected and would create some sort of interference pattern (sorta :) ), given the correct slits and enough runs.
Wave/Particle Duality (Score:3, Informative)
That is, it is an interference pattern as long as the photons are 'allowed' to act as waves, as soon as you try to treat them as particles, they behave as particles.
You are attempting to explain the "Wave/Particle Duality" nature of quanta. A very good explanation is located here [telp.com].
From the sound of the experiment, it looks like they use a "quanta source", rather than a photon source (does such a thing exist? Doesn't sound impossible...) - in such case, an electron gun emitting a very low discharge...
I think that is all correct - of course, I am as far from a quantum physicist as can be - correct me if I am wrong...
Another double-slit fabrication method (Score:3, Funny)
Here's one we did in high school:
Take a piece of smoked glass or painted glass, about 1" high by 2.5" long. Scratch two slits in it with a pin or razor blade. (The instructions at this point in our assignment said "Then take it to the instructor who will tell you that the slits are too far apart. Go back and try again." You will probably need to follow this advice.) Once you get a good double slit, tape over all your failed tries (there will probably be 10 or 15 of them) with black tape.
On another note, igotmyfirstlogon, the description of the original doubleslit experiment is übercool and would probably work better than this.
rollie
I did this today (Score:2, Interesting)
What we used was a laser and a small metal sheet which had two very tiny slits in it. I forget the spacing and the width of the slits, but I have it somewhere in my papers if you still want it. Since it was a simple sheet of metal, I suppose you'd be able to make those slits using an exacto. You don't need to be precise, as it will only create a different kind of pattern.
What is also easy to make is to team people in pairs and have them use the laser to determine who has the thickest hair. Don't tell them if the pattern has to be wider or thinner depending on the width of the hair, let them figure it out by themselves. We had some pretty weird theories going.
A couple ideas... (Score:4, Interesting)
1) Bolt two single-edge razor blades together, use them the draw parallel slits on smoked glass. It would probably not be wise to give middle-school students access to the blades...
2) Bolt two single-edge razors blade-to-blade. One side can be fixed, the other adjusted by a screw. Instant variable size single slits, and you should be able to make this middle-school student safe.
3) Take out your trusty laser printer and print two vertical lines on a sheet of bright white paper. Photograph it with true B&W film (not that new "color process" junk), cut the film with your handly single-edge razor and install it in a 35mm slide holder.
4) Use the same technique to produce other fun patterns. E.g., besides single and double slits, gratings, etc., there's the starburst pattern where you alternate white and black wedges. Each wedge is 1/2 to 5 degrees wide. You *will* see weird printer artifacts, but you can minimize this by explicitly setting both black and white pixels. (Easy with postscript, I don't know about other tools.)
Re:A couple ideas... (Score:1)
Take a piece of glass, like a (cheap) slide for a microscope, and spray black spraypaint on one side. Instead of bolting two blades together, just hold them together; it usually is stable enough. The types of blades where there is no lump of metal on the top are preferable so it doesn't spread apart the grating.
hey, do it the easy way (Score:1)
Another simple demo (Score:2, Informative)
The classic explanation of the double slit and its applications to quantum mechanics can be found in Richard Feynman's Lectures on Physics Vol. III or in Six Easy Pieces or Six Not so Easy Pieces which are outtakes from these lectures. The explanation therein is so beautiful that when pertaining to quantum mechanics the double slit problem is often referred to as the "Feynman Double Slit". Putting this into google will return a number of very useful resources.
As a physics lecturer it is hard to avoid Feynman envy.
Could be wrong (Score:2)
-Peter
Re:Could be wrong (Score:1)
Easy (Score:1)
its easier than you think (Score:2)
Take two normal microscope slides, spray paint them black. One is slit directly in the center, parallel to the short ends. The other is slit with two slits, about 1.5cm apart, where each is an even distance from the center.
Mount them (and you can just use tape for this) in a SMALL shoebox (more the size of kids shoes. actually, a box that holds 500 business cards is about the right size too).
Cut a hole ( 1cm in diameter) in the center of one end of the shoebox and a rectangle (about 2x3 or smaller) out of the other one. put a sheet of newsprint or tracing paper, something really transpearant, to cover the 2x3 rectangle.
Lights dimmed low, hold the small hole up to a candle or a halogen bulb. The light source is important. Florescents and most incandescents won't work. You should see at least something of the effect against the newsprint.
From there, play with moving the two slides forward and back to get the best focus, but the effect should be there to some degree no matter what.
implecations schmimplications, as long as i'm rich (Score:2)
The implecations of light being a wave are nothing, as are the implecations of light being a particle...
Its the fact that it is the two at the same time that's troublesome...
we just did this in my physics course (Score:2)
Worked pretty well, our calculations put the slit at about 0.13 mm