34. Wave Optics

Single Slit Diffraction

Physics34. Wave OpticsSingle Slit Diffraction

All right, let's take a look at number two. Number two is talking about a single slit diffraction problem and it says the following: a single slit diffraction pattern is formed on a distant screen, assuming the angles involved are small, by what factor will the width of the central bright spot on the screen change if the slit width is doubled. So, let's think about this for a second. We've got a hole in a screen, here comes our plane wave, we know that it's going to do this sort of thing but there is also a little bit of interference from the edges and the resultant pattern looks like this. Okay. We have some equations that tell us about the dark spot right there, and that angle of the dark spot relative to the optic axis theta. Now, we might be able to make some sense of this without even looking at those equations. Okay, and the way I think we should try to make sense of this as the following. Let's say I do this experiment again. Okay, but I use a very very small hole in the screen. Okay, the single slit is now small compared to this one. When I draw this diffraction pattern on the screen over here. >> (student speaking) Dr. A? >> Yeah? >> (student speaking) I think your display -- >> Okay, that would be Joe failing to pay attention to what's happening up here. Come on Joe, keep up. Thank you. All right, so when I go through a much smaller hole is that diffraction pattern going to look like this? Is it going to look squished together, or is it gonna look expand it out? What do you guys think? Okay, it's in fact going to expand out even more. Okay, and this is the weird thing about diffraction. Diffraction means if you go through a small hole, you're going to spread out much more. If you go through a big hole, you're going to spread out much less, and so in fact the diffraction pattern is going to do this. Okay, it gets much wider over here.