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Anderson Video - Optical Instruments- Eyeballs

Professor Anderson
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<font color="#ffffff">Hi guys.</font> <font color="#ffffff">Happy Monday.</font> <font color="#ffffff">How's everybody feeling?</font> <font color="#ffffff">Feeling like we have one week left?</font> <font color="#ffffff">Not even, like three days left.</font> <font color="#ffffff">You guys know your final exams on Thursday, right?</font> <font color="#ffffff">Or what we're calling midterm three.</font> <font color="#ffffff">Okay, good.</font> <font color="#ffffff">We're all in the same place.</font> <font color="#ffffff">So, anybody getting anywhere on the chapter 25 homework?</font> <font color="#ffffff">Anybody aware that we have chapter 25 homework?</font> <font color="#ffffff">Anybody aware that there is homework for the class?</font> <font color="#ffffff">What class are we in here?</font> <font color="#ffffff">What is this?</font> <font color="#ffffff">>> [Inaudible].</font> <font color="#ffffff">>> Yeah. All right, so my first thought was we were going to </font> <font color="#ffffff">largely finish discussing chapter 25 today here in the video lecture.</font> <font color="#ffffff">But my second thought is there's quite a few people that have labs right now, </font> <font color="#ffffff">unable to view the video until later.</font> <font color="#ffffff">So I was thinking we just make the homework for chapter 25 do tomorrow?</font> <font color="#ffffff">So I'm gonna do that right now, okay?</font> <font color="#ffffff">So you got a little bit of a reprieve.</font> <font color="#ffffff">And let's make that chapter 25 homework due tomorrow at 11:59, just like normal.</font> <font color="#ffffff">And then, why don't we take a look at a couple of the problems?</font> <font color="#ffffff">So, let's look at the first misconceptual problem.</font> <font color="#ffffff">And see what it's addressing.</font> <font color="#ffffff">Okay, so this one says, </font> <font color="#ffffff">"If the distance from your eye's lens to the retina is shorter than for a normal eye,</font> <font color="#ffffff">You will struggle to see objects that are far away, colorful, nearby, moving fast."</font> <font color="#ffffff">Okay, so to answer this question we need t o know a little bit more about the eyeball.</font> <font color="#ffffff">And maybe even a little bit more about nearsightedness and farsightedness.</font> <font color="#ffffff">So let's -- let's do that.</font> <font color="#ffffff">We're going to draw the ideal eyeball.</font> <font color="#ffffff">And, remember what the eyeball looks like.</font> <font color="#ffffff">You've got a cornea.</font> <font color="#ffffff">There's a crystalline lens.</font> <font color="#ffffff">On the back is your retina.</font> <font color="#ffffff">You want to form images there.</font> <font color="#ffffff">The ideal eyeball takes parallel rays.</font> <font color="#ffffff">And focuses those parallel rays to a single point on the back of your eyeball.</font> <font color="#ffffff">On the retina. Okay?</font> <font color="#ffffff">This is what the ideal eyeball does.</font> <font color="#ffffff">The relaxed ideal eyeball.</font> <font color="#ffffff">So, when you look at a distant star, it looks like a point.</font> <font color="#ffffff">The rays coming from that star are parallel.</font> <font color="#ffffff">It should all focus down to a single point.</font> <font color="#ffffff">But you, of course, rarely have an ideal eyeball.</font> <font color="#ffffff">A few of you have ideal eyeballs.</font> <font color="#ffffff">But a lot of you are nearsighted.</font> <font color="#ffffff">Nearsighted is, of course, called myopic.</font> <font color="#ffffff">And myopic means that you're not focusing the light quite at the right spot.</font> <font color="#ffffff">So parallel rays coming in, again, will now focus too close.</font> <font color="#ffffff">When they go in, they focus there.</font> <font color="#ffffff">Not on the retina where your photoreceptors are, okay?</font> <font color="#ffffff">Farsighted, which is called hyperopic.</font> <font color="#ffffff">Means that parallel rays coming in -- into the eyeball now focus too far behind the eyeball.</font> <font color="#ffffff">Okay.</font> <font color="#ffffff">This is nearsightedness.</font> <font color="#ffffff">This is farsightedness.</font> <font color="#ffffff">So, when you think about if you're nearsighted or farsighted, </font> <font color="#ffffff">how do you determine that?</font> <font color="#ffffff">Well the first thing you do is you take off your glasses.</font> <font color="#ffffff">And you hold up your book and you put it really close.</font> <font color="#ffffff">If you can read it when you're really close, then you're nearsighted.</font> <font color="#ffffff">If you can't read it when it's really close, then you're farsighted.</font> <font color="#ffffff">Okay and this is obviously where they get the name.</font> <font color="#ffffff">You can see things near or you can see things far.</font> <font color="#ffffff">All right, so how do we deal with this in terms of this question right here?</font> <font color="#ffffff">It says, "If the distance from your eye's lens to the retina is shorter than for a normal eye,</font> <font color="#ffffff">You will struggle to see objects that are (blank)."</font> <font color="#ffffff">Here's our normal eye.</font> <font color="#ffffff">Let's draw it again, but we're going to make the distance from the lens to the retina shorter.</font> <font color="#ffffff">Okay, so now parallel rays that come in</font> <font color="#ffffff">are still going to focus to the same spot as this first picture.</font> <font color="#ffffff">Except, it's now behind the eyeball.</font> <font color="#ffffff">Okay, so this is a shorter eyeball.</font> <font color="#ffffff">Does this look like farsightedness or does this look like nearsightedness?</font> <font color="#ffffff">It looks like farsightedness, right?</font> <font color="#ffffff">It's the same picture that we drew for the farsighted case.</font> <font color="#ffffff">So, if you are farsighted, you can see things far but you struggle to see things close.</font>