00:01
Here we're going to look at diffraction, which occurs whenever a wave has to either get into a narrow opening and onto the other side or encounters a small obstacle.
00:16
Usually when you're dealing with light, you are either looking at a slit, or sometimes you can put cells and other very small objects in the way to create the pattern.
00:30
Anyway, the pattern on a far -way screen coming through a single slit, what's actually occurring is the wave breaks up into what are called secondary wavelets.
00:42
They are broken up by the slit, and there's interference between those wavelets.
00:49
So typically the most important parts of the slit are the central portion in which the light comes through strongly, but also the sides, the edges, if you will, are where the secondary wavelets end.
01:08
The pattern you see on the screen is a very bright central maximum, and then there is a very noticeable minimum, and then much dimmer bright spots followed by more dark spots.
01:27
And what's interesting about the pattern equation, so i'll write that down.
01:35
If you have a slit width w, what you have is w times sine of theta, where that theta gives the position of the dark places on the screen.
01:52
Okay, so the angular position of those, that that is equal to m lambda.
01:58
So it looks very much like the interference pattern equation.
02:03
M is called the order, and it starts with one being the first very noticeable dark spot on either side of the bright central region.
02:21
And there's plus or minus one.
02:22
It occurs on both sides, plus or minus one.
02:28
And you may get more than one dark spot noticeable, but.
02:34
They're harder to see as your pattern gets dimmer off to the sides.
02:39
So let's ask the question...