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Old 07-01-2002, 12:28 PM
JFMichael JFMichael is offline
Join Date: Apr 2000
Location: Tampa, Florida
Posts: 111
Help me test Thomas Young's Double-Slit Wave Experiment with Household Materials

I want to set up an experiment to show the pattern of dark and light bands of light that are created when photons pass through a double-slitted wall and interfere with each other. I am pretty positive that I won't be able to shoot, much less measure, a single photon to show the freaky nature of quantum physics. How can I create such an experiment with normal, everyday materials that I can find in my house, or at least buy from a normal store? I tried using a flashlight and a piece of paper, but that doesn't seem to work as well as I'd like.
Old 07-01-2002, 01:38 PM
scotth scotth is offline
Join Date: Aug 2001
Location: Dallas, TX
Posts: 1,325
Shooting from the top of my head here, so don't be surprised if there are some mistakes.

First, a good way to make the slits. If you can find a way to bring the edges of two pairs of razor blades together, you can probably make high enough quality slits for this to work at home.

Second, I think you want a monochromatic light source for this to work. (I could be mistaken on this one) A good cheap source would be a good pocket laser pointer. You can split the beam pretty easily by using a glass plate and a front surface mirror. Set the beam up to go straight through the glass into the first slit. Adjust the angle of the glass until roughly 50% of the beam is reflected and 50% passes through. Use the mirror to put the split off beam to the second slit.

Some type of gas arc lamp may work well. (Mercury Vapor or some such). I think if the lamp has multiple emission lines, you will want to use a filter that will only pass one of the lines. I would very surprised if you get it to work with a flashlight or any incandescent light for that matter.

But, like I said, this is from the top of my head. But, hopefully it will get your pointed in the right direction.
Old 07-01-2002, 02:47 PM
Exgineer Exgineer is offline
Join Date: Mar 2002
Location: Albany, NY, USA
Posts: 3,357
Okay, I (sorta) got this to work when I was in high school.

What you need is:

1) a small sheet of cardbord (any type, but corrugated works well);
2) a shoebox (or similar box made of "solid" cardboard, you know what I mean.);
3) a crap-load of duct tape;
4) a well-darkened room(and I mean dark)with one white wall;
5) a brand-new razor blade;
6) a ruler;
7) a standard table lamp.

Discard the lid of the shoebox and seal the remainder of the box with tape along the seams. Using the ruler, find the geometric center of one of the small ends of the box.

Using the razor blade and ruler, cut two parrallel vertical slits about 1/2" to either side of center.

Remove the shade and harp from the lamp, and unscrew the bulb. Cut a hole in the cardboard sheet just big enough to admit the socket, slide the cardboard over the socket, reinstall the bulb, and drop the box over the cardboard. Center the box over the bulb and strap every thing together with tape, making sure (again) to lightproof the seams.

Take the lamp into your dark room and turn it on facing the white wall.

You will have to move it back and forth a bit to see the patterns.
Old 07-01-2002, 04:01 PM
Chronos Chronos is offline
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Join Date: Jan 2000
Location: The Land of Cleves
Posts: 75,177
If you don't have your heart fixed on a transmission experiment, you can get results much more easily with a reflection intereference experiment. You'll need the following:

A laser-- Any sort, so long as the light is visible
A machinist's rule-- Basically, a metal ruler with fine gradations. The smaller the scale, the better. A millimeter or half-millimeter scale seems to work pretty well.
A screen-- A plain white piece of paper works just fine for this
Some sort of structure to hold it all together

What you want to do is to get the laser reflecting off of the scale on the ruler at a very glancing angle-- A few degrees, or so. On your screen, you'll get a very bright zeroth-order spot from plain old reflection, but also spots off to one (or both) sides from interference maxima.
Old 07-01-2002, 10:01 PM
ftg ftg is offline
Join Date: Feb 2001
Location: Not the PNW :-(
Posts: 16,285
What we did way back in the days:

1. Take a glass microscope slide and "smoke it". No, Cheech, put it in the middle of a candle flame to cover one side with smoke.
2. Take two old-style "safety" razor blades and stack them together. Make a pass width-wise on the smoked side of the slide in the middle. This gives you two nice little slits. (Cf. Scotth.)
3. For a "monochromatic" light source, a small incadescent lamp and some red cellophane. (I kid you not.) Keep the cellophane away from the bulb. A good size box with an opening covered by the cellopane helps to keep down stray light. Aim the light thru the slide. (Held in a clamp) And then onto a white background. Darken the room as much as possible.

Now for the real geek factor:
4. Measure: the distance from the slide to the screen. The locations of the light and dark bands on the screen and the width between the two slits. The latter is tricky, we use one of those combo micrometer microscope things. Plug into the formula from your textbook and find the wavelength of your red light. Ta-da city!

Next time on Prof. FtG: Bombarding silver with neutrons to determine decay rates of isotopes using a geiger chamber with nixie tubes! Bring your own dosage badges.
Old 07-01-2002, 11:49 PM
hightechburrito hightechburrito is offline
Join Date: Nov 1999
Location: Campbell CA USA
Posts: 454
Here's an easy way to test it

The main problem with getting light to diffract is that the slit must be of similar width to the wavelength of the light. Good luck making a slit that small.

What I did in school was this: take a cookie sheet (we actually used a similar tray but with a clear bottom, so we could shine light through the waves and focus them on a paper below. But a cookie sheet should do fine.) Anyways, fill the sheet with enough water to be able to send a wave. Then use something (block of wood, plastic, etc.) to make your double slit (or even triple slit, quadruple slit, it all works).

Now take a long piece of wood to send a series of plane waves at the slits. You should be able to see a nifty interference pattern.
Old 07-02-2002, 02:52 AM
bbeaty bbeaty is offline
Join Date: Aug 1999
Location: Seattle WA USA
Posts: 888
Are you sure you don't just want to see some interference fringes? These prove that light is waves. (Much harder to prove that photons exist.)

To see some fringes, go outside at night and look at distant street lights. Now cross your eyes, and those tiny street lights should look like broad disks. (Or if you have any kind of lens, just hold that in front of your eye.)

You are now looking at a beam of light with fairly high spatial coherence. Now move your fingernail in front of your eye, and look at the edge of the fingernail-shadow. Lines! You'll see some parallel lines along the shadow edge. That's a genuine interference pattern.

Incandescent street lights only make one dark line. If you can find some old-fashioned yellow sodium lights, then your fingernail shadow will have lots of parallel fringes.
(((((((((((((((((((((( ( (O) ) ))))))))))))))))))))))
BILL BEATY _ _ _ _ _ _ _ _ billb, _ _ _ SCIENCE HOBBYIST
beaty, _ Seattle, WA USA


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