Anderson Video - Single-Slit Diffraction

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