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Anderson Video - Polarization

Professor Anderson
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<font color="#ffffff">Okay, one thing that we need to talk about is this idea of polarization. Okay,</font> <font color="#ffffff">and this is going to come back again later on when we start talking a little</font> <font color="#ffffff">bit more about optics, but when we say polarization what do we mean?</font> <font color="#ffffff">Polarization is the direction of the E field.</font> <font color="#ffffff">Okay, this is just how it's defined. So for instance</font> <font color="#ffffff">if my wave has an E field that's going up and down,</font> <font color="#ffffff">then we say that it has vertical polarization.</font> <font color="#ffffff">Okay, we don't really care about what the B field is doing, it's just defined in</font> <font color="#ffffff">terms of the E field. But if you have a wave</font> <font color="#ffffff">where the E field is in and out of the board</font> <font color="#ffffff">like so,</font> <font color="#ffffff">then this is called horizontal polarization.</font> <font color="#ffffff">Okay, so this -- these are the two polarizations for an electromagnetic</font> <font color="#ffffff">wave, either horizontal or vertical, and things like lasers have a preferred</font> <font color="#ffffff">orientation for their electric field. Okay, they either come out vertical or</font> <font color="#ffffff">horizontal. But things like sunlight have all different polarizations. Okay, they</font> <font color="#ffffff">have a vertical component, they have a horizontal component, and then they have</font> <font color="#ffffff">all the different angles in between. Okay, so incandescent sources like</font> <font color="#ffffff">sunlight, like a light bulb, those will have random polarization, whereas lasers</font> <font color="#ffffff">will have defined polarization. So you're familiar with this because of two things.</font> <font color="#ffffff">One, is you might have sunglasses that are polarized. Okay, and what polarized</font> <font color="#ffffff">sunglasses mean is they block one of these polarizations. It turns out that</font> <font color="#ffffff">the glare off the ocean or the glare off a wet street is dominantly polarized in</font> <font color="#ffffff">one direction and so if you put on your sunglasses to just block that particular</font> <font color="#ffffff">polarization, you essentially cut out the glare. Okay, so when you look at the ocean</font> <font color="#ffffff">you see a bunch of glare, put on your polarized sunglasses, the glare goes away,</font> <font color="#ffffff">and that's because that glare is polarized in one direction, your</font> <font color="#ffffff">polarized sunglasses block it. But this is also used in things like 3D movies.</font> <font color="#ffffff">Okay, 3D movies take advantage of polarization, and basically they use a</font> <font color="#ffffff">different polarizer for each eye.</font> <font color="#ffffff">Okay, so if you go to a 3D movie and you get those glasses, what those glasses are</font> <font color="#ffffff">doing is there's a different polarization on the left eye than on the</font> <font color="#ffffff">right eye, and so when they project it on the screen with a certain polarization</font> <font color="#ffffff">from the lamp, and they use some polarizers to do it, they're creating a</font> <font color="#ffffff">different image for your left eye than your right eye. So now when you put them</font> <font color="#ffffff">back together, it looks like a 3D picture to you.</font>