The Two-slit Experiment
This web page has the best explanation I know of the two-slit experiment:

http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html

I'll try to show this in today's lecture (2014-05-07). I'm putting it here in case it doesn't work in the lecture theatre (or in case, god forbid, you miss the lecture).

Jason