00:01
Defraction is a phenomenon that involves light striking either an obstacle or an aperture.
00:11
It is usually best observed if your light is coherent and has all the same wavelength.
00:19
If you do an experiment with monochromatic light, say coming from a laser, and a narrow slit, you can project an intensity pattern on a screen, some distance away, and this intensity pattern exhibits bright spots and dark areas.
00:43
What's going on to create the dark and light areas is essentially interference between light that goes through the middle of the slit, as well as light that gets produced in secondary wavelengths as the light interacts with the edges of the aperture or slit.
01:07
So this is interesting.
01:09
It is an edge effect, but the position of the dark spots, so this is destructive interference happening there.
01:22
The equation is given by a sine of theta is equal to m lambda.
01:31
So it looks very similar to an interference type formula, but it gives positions theta on a screen for dark spots or destructive interference.
01:56
It is a symmetric pattern, of course, especially since the slit has two equal edges.
02:07
So in the drawing, a is the slit width.
02:14
Theta is the angular position of a dark spot on the screen as measured with a central axis that goes through the middle of the slit.
02:27
So for example, if we're told that the angular separation between the two first dark spots, suppose we are told that that, we'll call it phi, is equal to 32 degrees, then we know that that theta is just one half of that, or 16 degrees.
02:53
If it is to the first spot, in addition, we know that m, which is the order of the dark band, is equal to one...