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.
 A: 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.

A: 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. 
A: 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.
