# Double slit experiment

What's the simplest way to describe and show the double slit experiment? I have to perform an experiment proving how it all works in my physics class.

• I advise you to do some research and come back with a more specific question. at the moment, this is quite broad. Mar 13, 2015 at 18:10
• A laser pointer shining at a hair will result in a diffraction pattern on a screen... not quite double slit but diffraction, and super easy. Mar 13, 2015 at 19:40

To demonstrate the double slit experiment, you might consider using a thin sewing needle, two razor blades, two binder clamps and a laser pointer, as shown in the photo below. The sewing needle is held in a vertical position by sticking it into a piece of cardboard. The binder clamps hold the razor blades up. The razor blades are brought close to the needle, forming slits on each side of the needle. The razor blades and the needle are approximately coplanar. The green laser pointer shines on the needle. The interference pattern shows up on the wall across the room. You may have to darken the room to see the interference fringes. There is also a lot of diffraction, so you will have two effects to explain.

You can have a pool of water and place a cardboard or a piece of plastic with two slits in the middle. Just create a wave that goes through both slits and the waves should start interfering.

• I did a demo of geometric optics in high school using a wave tank that had a clear bottom. I set it on top of an overhead projector (does anybody make those anymore?) which vividly rendered the waves on the projection screen. Mar 13, 2015 at 19:04
• Truth be known, it wasn't my own idea. I saw it in a science museum first. Don't remember where, but it was long enough ago (1970-something) that it probably doesn't matter anymore. In my version, I bent strips of sheet metal into parabolic and elliptical shapes to emulate mirror optics. In the science museum version, they had convex and concave lens shapes made from thick sheets of clear acrylic. The lenses worked by changing the depth of the water. The surface waves propagate more slowly in the shallower water above the "lens". May 12, 2015 at 13:18
• Well hey in the end you made it yours. That is pretty interesting how you had to apply different concepts to simulate the slit experiment. May 13, 2015 at 5:07

I think that for the demonstration, a laser and double slits are probably the best way to show the interference pattern. First showing with the 1st slit only, and then the 2nd. Finally show with the 2 slits opened.

You probably want to emphasize one of the wonderful aspect of the interference-based experiments, roughly said: "You put light on light, and you get darkness"

For the explanations you can stick to an analogy based on the wave, which is probably the standard stance.

I'm personnaly fond of the explanation provided by Feynman in "Light and Matter": http://en.wikipedia.org/wiki/QED:_The_Strange_Theory_of_Light_and_Matter

I will not redo the argumentation here, but he provides a very "hand-on" explanation, you're basically putting arrows end-to-end, which in fact describe in layman terms what we call "path integrals" and "quantum electrodynamic".

I believe this can be efficiently used to explain the double slit experiment, as well as many optical effects.