okay, gang. you go to the zoo, huh? you go to the zoo and you see the peacock. and the peacock spreads its feathers. and as the peacock turns, you noticed that the colors-- the colors of those feathers kinda change a little bit.

or you see a child blowing bubbles, great big bubbles, and the bubbles floating off in the wind, yeah? and you look at the bubbles and you see--wow, what you see? beautiful rainbow colors in the bubbles. you see the spectrum. you see all the colors reflecting from the bubbles. isn't that right? or sometimes you take, like, an abalone shell and you hold up the abalone shell and you see the beautiful colors. we call these iridescent colors, yeah? and you're looking at the shell and then you turn the shell a little bit and--hey, wow, the colors change a little bit. or sometimes on a rainy day, you look at gasoline on a wet street. and you look at the gasoline's splotches and--wow, man. they have beautiful colors. and there are rings of colors too. do you have another-- the rings go all the way around like you got green. the green will continue and come all the way around. it's sort of like a contour map, a microscopic contour map of the different elevations of the gasoline on that wet surface. whenever you have a double reflection like that, oftentimes i should say, when you have a double reflection from two surfaces, these double reflections give you beautiful colors.

we call this interference colors. we talked a little bit about interference before, gang. remember? let's briefly review that interference of waves. consider a wave like this maybe, yeah? now, consider another wave locked right on top of it. same frequency, same step, physically say, same what? phase, okay? right in phase. those two waves will add together to be what? a wave of greater amplitude. greater amplitude, same frequency, okay? no big deal, but how about this? consider a wave and another wave starting maybe here. you know, starting at a different point. that wave is out of phase. if it's half-step out of phase, was he in a 180 degrees out of phase. these two waves are out of phase of one another, 180 degrees. they combine to produce what, gang? ain't that nice? they cancel out, okay. one wave cancels another.

the same thing happens with light. i can show you what i mean with this laser. i'm gonna shine a little laser spot on the wall. i'll put the lights out. you guys see that some-- places there, it's very, very--there's little dark spots--splotches. and some places is very bright? lets talk about that and see what's going on. what happened here now, gang, is the lights coming through piece of glass and the glass is irregular and it's kinda fanning out and making a spot on the wall. but there's bound to be some places with that light comes -- in phase here with maybe another point over here. that they come right in the phase and be extra bright. and right down below it might be light coming in like this and light coming in from another little part of that little lens really there like that. and when those two gang up, guess what they do, gang? begin with co. cancel out. cancel out. and over here, they add up. so over here, you'd have a region that's dark, okay?

and that little dark region is the result of light interfering, okay? destructively. over here, it's light in deferring constructively. so you get those bands or those little splotches because of the light interference. you get the same type thing with gasoline on a wet street. here's some light reflecting off some water, okay? light reflects off the water and your eye is up here and your eye sees the light. let's suppose this is blue light, pure blue light shining down, okay, shinning down on some water and bounces off and gets into your eye. let me ask you a question. what color would the eye see?

blue. it's an easy one. begin with blue. i got b. begin with b, okay? you can see blue. you can see blue, right? but let's suppose it's not shining on the water. let's suppose it's shining on gasoline. now, what color is the eye gonna see? blue. begin with b. blue. blue. it's still gonna be blue because it's reflected and we know that light doesn't change its frequency when it reflects. if you got a blue shirt on, you stand in front of a mirror, what color is the image? blue. how about a red shirt? red. could you do green? you get the idea, okay. light doesn't change frequency when it reflects. but what if this gasoline is floating on a surface of water and it will do that. now, you've got two surfaces. some light is reflecting off like this, but some of that light goes down through and reflects off the water surface. and if it does that in such a way that this distance

puts the reflected wave 180 degrees out of phase or out of phase 1/2 step. then when it gangs up with this one, what's it gonna do, gang? what's the eye gonna see? nothing. nothing. the eye is not gonna see light. the lights cancelled out. you see that? now, how thick this is has to do with the wavelength of light while what work for one thickness won't work for another. and it has to do with whether or not the light changes phase when it hits the different surfaces? i'm not gonna get into that part now. it's footnoted in your text. suffice to say, light from a double reflection might have such a distance-- extra distance that by the time it gets back up here, it's out of phase with the part the reflected from the top. that is destruction interference. the eye gonna see nothing. you're not gonna see this in your local environment. what you will see in your local environment is white light from the sun. the sunlight coming down and hitting the gasoline on a rainy day.

you've all noticed that. you notice that? it's gotta be a rainy day that the gasoline gives you the color. why? 'cause the gasoline gotta float on water to give you two surfaces to make reflection from, yeah? okay? now, when white light hits for this particular thickness, the blue is gone. you check with your neighbor and see if your neighbor knows. if the blue is gone from the white reflecting, what color is the eye gonna see? go. what's it gonna be, gang? - green. - something. how many say a yellow or an orange or something like that? yeah, yeah the complementary color of that shade of blue, yeah? we talked about this. we talked about the blue sky, remember? the blue sky scatters off blue. so given enough sky for the light to get through

by the time light gets to you and all the blue is scattered, what do you get left, gang? you get the complementary color. okay? sorta like the orange or the yellow, yeah? so when you take one color out of white light, what you see is the complement, huh? in the same way, the water absorbs the red and so what do we see the red? we see the-- and what do we see the water? we see the water of cyan, the complementary color. same type thing here. now, if you understand that, you can see this. let's suppose the light is coming down. the same thickness of gasoline now, but the light is coming down on a more grazing angle and bounces to your eye. you could do that by taking your eye and say, "hey, i see it sort of a yellow." and you got on like this and all of a sudden, oh, it changes to a different color. and some say, how come it changes? and you say, what is-- no reason for that. it's different angles, different colors. maybe that's--come on. why does it change, gang? the apparent thickness would be greater. wouldn't it? yes. if you're coming in at an angle like this, isn't that a thicker path than this one here? huh? huh? it's like a worm crawling through a book. the worm crawls from the book, from here to here and says,

"hey, pretty short book." now, you hold the book like this and the worm crawls through, as it--"my gosh, an encyclopedia," okay? you get a different apparent thickness for the way you hold it, yeah? and the same thing would happen with light and so light coming in like this. you would cancel a longer wave or a shorter wave? neighbor? through a longer path, would you cancel a longer one or a shorter one? - a longer one. - longer one. so let me ask you a question, gang. let's suppose you happened to cancel out the yellow. and where you're seeing, honey, you ain't seeing the white light, you seeing the white and the yellow ain't there anymore. the yellow have been cancelled. what color your eyes see? check it. what's the neighbor say? if you cancel the yellow, the eye gonna see what? blue. blue? can you see it's blue? get it? magenta.

this saturday night, when you take your bath, use some soap. in fact, splurge. use bubble bath. get a whole lot of bubbles in your bathtub. now, you're taking your bath and your light up above, there's an incandescent lamp, white light, okay? white light shining down on the bubbles. take a look at those bubbles closely. guess what, gang? the highlights ain't white. the highlights are all different... - colors. - hue. how many have noticed that already? how many people have taken baths year after year after year and never looked at the bubbles? look at the bubbles on saturday night, and see if you don't be seeing the bubbles got different colors. and your friends say, "how come the different colors?" and you say, "that's an example of?" physics. begin with i. interference. interference. interference, that's right. you got a bubble like this, maybe you got the white light up above, okay? okay. and the white light coming down--

here's your eye right here. light come down, hit the bubble, bounced to your eye, yeah? but some of that light bounces from the bottom surface and goes to your eyes. - is that right? - right. aren't there two surfaces to that thin bubble in the way that thing filled? two surfaces. part bounces from the top surface, part from the bottom. hey, what if that extra distance going down through is such that it will cancel out one of the frequencies over here? then, honey, that eye ain't gonna get it. now, if you got white coming down, there's no cancellation. you're gonna see white. but if one color is canceled, you're not gonna see white. let's suppose the color that's canceled happens to be red. then the eye will see what color for that particular bubble? you guys know your color rules? no. you gotta know what the complementary color of red is. we take all the red away, what do you got? green. you get that green cyan. you got that cyan, the greenish-blue.

so the eye over here is gonna see what? greenish-blue, all right? now, you point to the bubble and you say, "hey, that's a greenish-blue bubble right there." right. your friend. your friend looks down. and your friend looks at the same bubble. but for your friend-- this is a different thickness being canceled. maybe this different thickness, maybe what's being canceled here is the yellow. and so your friend sees that light, white minus the yellow, you say, "hey, look at the greenish-blue bubble." and your friend says, "no, it ain't. it's a..." yellow bubble. "blue bubble." so your friends says it's blue, you say it's cyan. who's right? me. what happens in the tub? "i say it's cyan." "i say it's blue." "i say it's cyan." wham, boom--bubble bath. okay, see what's happening? what color you see depends upon what? with everything. what you see depends upon what? do we all see the same thing? no.

huh? depends on your point of view. open up the hood of a car, have the mechanic look at it. now, you look at it. you see the same thing? you see the same thing? no. i remember years ago, a guy was passing around a picture of his girlfriend, says, "hey, you wanna see my girlfriend, man? look at this." takes out this picture, he shows the picture. and we're all looking at-- we're feeling sorry for him, you know? [laughter] and--but to him, to him, he's--"that's my girl." and we're like, "oh, my god, -- pretty." and you start to wonder, do we really all see the same thing, huh? huh? over here, these-- the different bubbles depend upon your point of view, where your head's at, right? what you see depends upon where your head's at. think about it, gang. and you get the different colors. you know these camera lenses? you see these camera lenses. you see that violet hue on the camera lens? ever see that, coated lenses? and they look violet, don't they? do you know why they look violet?

no reason for that. it's just one of those-- no, come on. you know why they look violet? there's a color being canceled. there's a color being deliberately canceled. and the color being deliberately canceled is a color that we're most sensitive to. and if we wanna cut down that reflection in that lens so we don't photographed by film, and we can only do it for one color. we're gonna pick the color that the eye is most sensitive to, that the sun is emitting mostly of. and what is that color, gang? begin with a y, end with mellow. try it. yellow. well, all right then, y-e-l-l-o-w. try it. yellow. good, good. okay, we got it. okay? here's what happens. have these lenses, camera. here's what the problem is. light will be coming in, and come to focus right there, and that's nice 'cause you got your camera film right there, and you want the cam to focus. but some of the light reflects off. it comes out, you don't care. but then comes back in, reflex out, you don't care. and then comes over here. and part does this.

and that comes to focus here. and so what's it gonna do is photograph your film. you don't want that light getting there. you like to get rid of it. there's a way to get rid of light. you can cancel it. so what you do, at least for the yellow part, you can put a thin film there. and that film is one-quarter the wavelength of yellow light. so the light that bounced from here also is ganged up by light that goes here, a quarter, a quarter, a half. and what happens is you'll cancel it out. and so that thin film will cancel all this. it won't happen, and you'll be back to your nice, sharp picture, at least, for the part of the light in the middle of the spectrum. so you, out here--look at the thin--this little thing. if it's canceling yellow on this side, it's canceling yellow on this side 'cause it's the same type of thing. you're getting a double bounce out here. so when you look at that purplish surface, okay, that purplish surface of the lenses, it isn't like they got some purple gunk they put on there. no, no, no. it's very, very clear.

but the thickness is such that it will cancel out the yellow and give you the complementary color, so you see your coded lenses, the nice purplish color. ain't that neat? you like? yeah. yeah. i bet-- gang, we'll talk about polarization. we talked about charged polarization before. we talked about, like, negative, being on one side of a molecule, positive, on another. polarization, in this sense, is altogether different. we're talking about the lineup of waves. if i take a rope and tie it to the wall, and i shake the rope up and down like this, guess which way the wave will vibrate. how many say, "oh, probably like this"? hey, come on, come on. trick question. no, no. if i shake it up and down like that, the rope will vibrate like that. and the vibration is aligned. we don't say aligned. we say it's polarized. if i shake the rope back and forth horizontally, then i'll generate a horizontally polarized wave. okay? you saw the example in the textbook. if i pass these waves through a picket fence,

maybe the picket fence can filter them out. it turns out, if i have a picket fence where the fence stakes are all vertical, i have vertical openings. and i shake my rope, and it goes right through the opening. it's like the opening weren't there, the shake goes right on through and the wave travels. that's easy to see. it is very conceptual. if i take the rope and shake it sideways however, it can't--the vibration can't get through the fence. and so what the fence does is it blocks it. and so that's a filter. and i have over here such a thing. here's a polarization filter, okay? and that's what this is. this will allow light to vibrate through going only one way, not another way. i don't know what the plane of this is. i can't see. but the-- and let's suppose it's like this. i have microscopic picket fences like that. i have in the back here a piece of white material that would diffuse light, so that when i shine light through it, it won't-- there won't be too much glare. but nevertheless, this is a piece of polaroid filter.

and let me tell you how this came to be. it turns out that non-cubic-shaped crystals, all non-cubic crystals-- say, something like this or like a diamond shape. all non-transparent crystals will pass light in two directions, the two preferred directions. the crystalline structure is, sort of, like an orange grove. have you ever drive by an orange grove to see all this-- you see right down? and you're driving-- right down the cliffs, okay? there are certain preferred paths. well, it turns out, light will go through vibrating like this, and light will go through vibrating like that. and over here, no. you'd only get components here and components here. and it turns out, in most crystals, the vibrations in one direction go through quicker than the vibrations in the other. so there's little time delay. and you get beautiful colors as a result of that. get into that a little bit later. but, for now, there are some crystals that take this one here and cut it right down, and it's absorbed.

this was known at the first part of the century, a lot of people knew that, that they were needle-shaped crystals that would pass light in only one direction, one direction only. a fellow by the name of edwin land knew about that and did something about that. what edwin land did was took all these crystals, this crystalline material, made into, sort of, like a jelly, put it on some cellophane and stretched it. and when he stretched the cellophane, guess what these things here did. what would happen if you held a whole bunch of needles, a whole bunch of needles on a piece of plastic and they point every which way? and you take and you stretch the plastic out. what will the needles do, gang? won't they kinda all line up? that's what land did. and he got them all to line up. and then what he did is he put it down, he'd put another piece of plastic on top, took his wife's iron and ironed it, and cemented those needles to-- and made a million-- more than a million dollars. edwin land patented it. and these are polaroid filters. and that's what they, in a sense,

are 'cause they're made up of molecules in here which are crystal-- little crystal-- the crystals or molecules that are all lined up in one direction and will allow the light to pass through one way. i can kinda show you that with a lamp here and using tools. you can still see the light. these things must be lined up. what's coming through one comes through the other, but let me turn it. what happens right in there, gang? right in there. can you see that the light doesn't come through? or i can hold this like this and just turn this. comes through, comes through, comes through, doesn't come through. not so much, no much and now it's blocked up. ain't that nice? now, hc.

how come? this is easy to see. it requires a knowledge of vectors, the arrows. let's take a look. let's suppose my lamp, my original polaroid, is like that. light coming through. what kind of light can it come through, gang? light hitting it is like this. like this that hits it-- but the only part that comes true is the part vibrating like this. so what comes through is light vibrating like that. when i put the other polaroid in the way, the square piece, what happens if-- well, let's try this first of all. what happens if this and this are lined up? will these vibrations get through there? yeah. is the vector falling right through there? and--how'd it comes? so the light is not cut out.

what happens when i rotate it 90 degrees? okay. is there any component of this along that direction? when we talked about the bowling ball before in the ally, pulling full straight down, a vector straight down and we said this. is there any component 90 degrees to it? and the answer begin with a n. no. same type of thing, see? we got a vector, vertical, there's no component there so nothing gets through. that's what you saw. what's kind of interesting is an angle. let's suppose i put this on an angle. now, this falls on top of there. as you recall, did any light get through? - no. - yeah. some got through. and here's where your vectors come in. this vector here has a component on this direction and a component on this direction. guess which component won't get through. this one or this one? this one.

that won't get through, see? and you guys remember this? you take a little component here, huh? and here's a-- other component here. and this vector here behaves as if it's really this one and this one at the same time. this one doesn't make it, but this one does. and look what, some comes through. this one is not as big as this one. did you notice the light was not as bright so the light is dimmer? but never the less some comes through. and rock this all the way around, this component keeps getting smaller and smaller, smaller and finally shrinks to zero, and whip, boom, nothing gets through. so that's happens to these polaroids. kinda neat, huh? it turns out that when light reflects from surfaces at a grazing angle, the polaroid's component is preferred, you know? if you're like driving and you have a road surface and the light is coming down, hitting, it turns out the light that would make up the glare is polarized in the same plane as the surface.

do you ever take these scaly rocks and go out in a pond and you get flat rocks, you wanna scale on across the surface? if you take the rock and you throw it kinda flat, sort of like this, okay? it will--bounce off, yeah. how about you throw it like this? kinda go down, yeah. light does the same thing. light is coming down like this-- bounce, huh? light is coming like this-- gets absorbed. so that's why you get the glasses. what kind of polaroid glasses would you wear to cut out glare from horizontal surfaces? let me show you three pair. which would you use, gang? this, this or this for driving.

you are a truck driver and you gonna ride along the road, which pair of polaroids? how many say they're all the same? how many say i'd wear these ones here. squint city, honey. what's gonna come through those glasses? polaroids light. you got to drive like this, okay. [laughter] --a cup of coffee, please. okay. occupational you-- no, this is what you get. see. the--yeah. the polaroid glasses that you buy are-- usually like this because most of the glare comes from horizontal surfaces. what if you're a painter all the time? you paint in vertical surfaces then you probably wear glasses like these. i don't where do you get them. okay? but usually the glariest polaroid is horizontal so we cut the horizontal off like that. you're gonna like that, honey, that light came in--it's okay. but--and now what you see is without glare, hmm? do you know what this pair are for? 3ds. 3d movies, used to be popular. used to be 3d movies

where you have two projectors are going one at one time and you've gotta see each scene independently so the polaroids-- one in this way. you got your glasses that way, the other projectors polarizing this way, you got glasses that way. boom. each eye sees an independent view and 3d vision right there. questions on that. question. yeah. polaroid glasses ain't necessarily cut out uv, though, right? no. polaroid--the function of polaroid glasses is to cut out the horizontal component of all light. it turns out all glasses will cut out uv, all glasses. now, what part of the uv? very, very close to the visible part, a lot of glasses will transmit. but the high frequency uv, the kind is dangerous, all glass. and i believe most plastics will cut it out. so anyone that's wearing glasses, you don't have to worry about uv light hitting your glass. any kind of glasses.

have you heard of the blublockers? the blublockers. i haven't heard of the blublockers. a new kind of glass? yeah. supposedly, it cuts back on the little ray side? do you pay more for it? i don't know. i don't have them yet. i mean, there's a lot of things that these glasses will cut out the uv. well, honey, what glasses won't? okay. you know what i'm saying, so-- i got a question for you, gang, something nice, keep you entertained a little bit. see this? okay. i remember the first time i saw what i'm gonna show you now.

a fellow came in my office when i was a graduate student and he had three sheets of polaroid. i've never dealt with three sheets. two is enough, yeah. and he had three sheets. and he says, "hey, hewitt. "if i take this third sheet and i put it in front, will light come through?" i said, "nwh." right? okay. here, how about if i put it in the back, will now they come through? and i said nwh, right? he says, "how about if i put it, like, in between the two, will light come through then?" i said nwh--yeah? there's your light, honey. what's this nwh? can you kinda see that? light is getting trough. that's sandwiched in between. over here no, no, yes. to understand that and explain that, you need to know something about vectors.

you guys, have known about vectors? could you kind of make a little vector diagram showing that how are light does get through? i think you can all do it particularly if you pay attention to your textbook. all right? and can you do that and hand that in next monday? okay. okay. okay, great. all right, physics. catch you later.

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