okay, guys, thank you. we're talking about electricity and magnetism. remember that time i took the rubber rod and i charged it up, okay? well, pretend this is the rubber rod charged up. and now i shake it through space.

when i shake it back and forth, is that not an electric current, charged in motion? what surrounds an electric current? begin with mf. - magnetic field. - magnetic field. how many say, "oh, that magnetic field is probably very, very steady"? how many of you know the magnetic field changing? what's a changing magnetic field induce? begin with ef. electric field. electric fields. what's a changing electric field induce? begin with mf. magnetic field. how many are starting to catch on? what does this changing magnetic field induce? begin with ef. electric fields. what does the changing electric field induce? begin with an mf. magnetic field. how many are getting the idea? okay. it turns out these waves will regenerate one another. so if you have a shaking charge, honey, you get electromagnetic waves throughout space. where the electric field makes the magnetic-- the electric, magnetic-- at the speed of light-- that's what light is. that's what light is. light is electromagnetic wave generated from a shaking charge. if i take this stick and i put it in the water, and i shake it back and forth, won't i disturb the water? won't water waves travel out? you can understand that.

but what i'm saying is you take a charged object. well, just take a charge, shake it back and forth and guess what you generate, gang. begin with a w. - waves. - waves. and these waves are electric and magnetic fields, so guess what kind of wave. electromagnetic. electromagnetic wave. that's right. and that's what we're gonna talk about now. electromagnetic waves and the very, very small part of the electromagnetic waves. you get the whole spectrum of waves. let's start way down with the radio waves, really long, long waves. and the radio and the frequency will get a little higher, a little higher. and pretty soon, those waves-- for example, your radio antennas downtown are shaking waves up and down like a few millions times per second. that's your fm waves. a few thousand times per second, that's your am waves. but if you shook the electrons in your radio antenna up and down like a million, billion cycles per second, honey, the waves that are generated are gonna activate what? begin with ey and get the e on the end of it. eye. your eye, that's right. [laughs] remember we had the tuning forks that time and hit one tuning fork and made the other one ring?

well, in your eye, you got tuning forks there too, and guess what frequency they ring at, gang? million, billion cycles per second. million, billion hertz and that's light. and light, when that light comes in your eye, it make--that sight. would you like a profound statement for a party sometime? sure. when you want to say something, and everyone will say, "wow, heavy, man, heavy." [laughs] would you like that? would you like to hear one? yes. here it is. you probably will want to put this in your notes. here it is. light is the only thing one can see. [laughs] ooh. you saw a lot of substance to that, huh? would you like another one? yeah. just as good? sound is the only thing that one can hear. ooh. you have people following you after that. they'd say, "hey, this guy's-- dude is heavy," okay. you get the idea. anyway, we get all these waves, gang,

and a little narrow, narrow, narrow band of those waves, starting off with the low frequencies that look to the eye to be a color. guess what the color be for the lowest frequency? begin with an r end with a d. try it. red. excellent. red. and then let's shake it a little bit more and guess what the frequency is. orange. orange. okay, some people. shake it a little bit more. what color are you gonna get? yellow. a little more. green. more. blue. more. violet. more. indigo, black. violet. violet. you can't be seeing. you can't be seeing it, okay? that's not light anymore. we call it beyond the light. we don't say beyond. some would say, "what is beyond the violet?" we don't say beyond the violet. what do we say, gang? ultra. ultraviolet, okay. and those waves you don't see. and many even go further still, higher frequencies like x-rays. when x-rays were discovered, it wasn't known what they were. so guess what they call them? no, not y, not z, but what? x.

and it turned out, lo and behold, x-rays are high frequency electromagnetic radiation. and then beyond the x-rays, you get what's called gamma rays. but there's a whole smish-smash of waves, okay? less than 1% we can see, and we call that light. here, gang, i have a prism, all right. this is a prism brought in by roger, okay? this is a roger prism, all right? and this prism will also take the light and bend it into a rainbow. later, we're gonna take some white light shining in here, and, boom, you're gonna see on the other side, what? begin with r and with b. - rainbow. - a rainbow. and that rainbow is another word for spectral-- spectrum of colors, yeah? and this will give us spectrum of colors too. it turns out it will give a spectrum of colors because it turns out different colors of light will travel at different speeds-- right. --through this material or any material. did you guys know the speed of light is less in glass and water than it is in air? and how come the light slows down

when it gets to the glass or when it gets to the water or anything? and here's another thing. this used to bother me years ago. if the light slows down when it gets in the glass, how's it speed up when it comes out the other side? it seemed if you want to get light to slow down, get it on a piece of glass plates and at the end, you can just catch it in a bucket. that keep dribbling down, yeah? but how does the light speed up again? how does light get through glass? let me give you a little scenario of something like how that works. light is a throbbing spark of electromagnetic energy, huh? and that throbbing spark of electromagnetic energy has a certain frequency, at a certain frequency at which it throbs, yeah. and when that, whoom, hits into a piece of glass, that glass got any atoms in there? how many say, "oh, no, the glass probably don't have any atoms"? come on, the glass got atoms. and what's the atom have around its nucleus? begin with e. - electrons. - electrons. and guess what those electrons will do when that electromagnetic energy hits it like this. hit, boom, they'll start moving the same way. they'll be set into vibration, okay?

now, what's a vibrating electron do? oscillating. did we talk about that before? what's a vibrating electron do? what does it emit? oscillates. an electromagnetic wave. so that light will be captured by the atom. and them, boom, the atom will vibrate. and, foom, send out its own light wave. that catches the next atom. when that light wave hits that atom, what's that atom do? how many say, "oh, it probably don't vibrate"? come on, it vibrates, too, all right? so, boom, it's absorbed. now, what's the vibrating atom do? boom, spit, burp, bam, bam, bam--it cascades, when it gets to the end. here's your piece of glass like this, yeah. here's your first atom just sitting like that. here comes a wave--choo, choo-- okay, hoop, i spit. next atom, boom, okay, boom. hit, boom. here's the atom right on the edge over here. whip, boom. this one, hit, boom, and then foom, free space. how fast did it throw it out? free space. you know what the speed of the light was in between atoms?

300,000 kilometers per second, the speed of light that you get in a vacuum. 'cause guess--we think of a vacuum as void, right? take a piece of glass, take a piece of water, what's in between the atoms? how many say airspace? no, no, no, no, no. no airspace. what's in between there, gang? begin with a v end with oid. try it. - void. - a void. and guess how fast that light wave go or that light particle or that light goes in between atoms? the same as it goes outside. how come light slows down when it goes through? i wonder there could be maybe a time delay between being absorbed and spitting it out. if there is a time delay, wouldn't that, in effect, slow down the light getting through? hmm? let's suppose i have, like, a little toy soldier that can walk like this. and the toy soldier walks at only one speed, only capable of one speed, okay? let's suppose that toy soldier walks over and touches another one, choo, choo, choo, choo

and the other one starts walking, choo, choo, stops. choo, choo, choo, choo. see what i'm saying? the toy soldier that comes out the end here is not the toy soldier that went in. you see that? a little time delay. if there's a lot of interactions, does that mean a lot of time delays? that means a color of light that would interact a lot will probably move slower than a color of light that doesn't interact so much. does that make sense? and guess what color of light interacts a lot with glass. violet or red? violet. blue. you don't be knowing that yet. let me tell you something. the resonant frequency of the electrons in there are like ultraviolet. and when ultraviolet light comes in, and hand, when that sets that electron in the move and, it is really moving

so much it bangs into everything else. and the energy degenerates into? begin with a h end with a t. try it. - heat. - heat. and all that ultraviolet light gonna do, honey, is heat up that glass, because it's hitting that resonance. the resonance, the vibration is too much. so the resonant won't get through. but what's below that ultraviolet? begin with a v. violet. and that violet is close to the resonance. and the vibrations aren't enough-- degenerated the heat, but enough to interact here, here, here, here, here, here, all the way. and by time you--violet light is gonna take a long time to get through. red is way, way, way down underneath. you could, kind of, look at it like this, most of your atoms won't even do a darn thing when red comes by. so red just, vroom, skates right out by and only interacts here and there. guess which color should get through fastest? red. you see it's red? and a term we're gonna learn later on that when the different speeds will bend different amounts. and that's why this and rainbows you see above you,

display the colors that we see. it has to do with different colors bending. and we know why they bend differently, because they got different speeds in the medium, different average speeds. the sun beats down, emits light. why does the sun emit light? honey, those electrons in that sun are shaking like crazy. all kinds of frequencies, okay? and so what you get is you get all kinds of frequencies of light coming down to us. and if we made a graph of the frequencies of light versus the brightness, we'd get something like this. we'd get something like this. over here, you can't even see, that's the infrared. over here, you can't see, that's the ultraviolet. but it turns out that right in here, that's the frequency of light that most of--that is emitted mostly by the sun. and that's right in the middle of our color spectrum.

because we start down here with red, orange, yellow, green, blue and violet. and guess what's right in the middle, gang? begin with a g, end with a een. try it. green. excellent. all right, all right. green. it's green. green is right in the middle. it turns out a yellow green. a yellow green is what most of the sun emits mostly. it's like a chartreuse. when i was a teenager, honeys, i had a chartreuse convertible. you could see that thing 15 miles down the road, okay? and you know why you could see it so well? because most of the light from the sun is that color, and guess what we have evolved to see best of all? take a guess. - yellow green. - yellow green. we used to call it chartreuse. is that what why they paint fire trucks that color these days? did you notice that, paul? what are the new fire trucks? they used to be red. what are the new ones? - yellow green. - yellow green. and why they be yellow green, honey, huh? why? because you want to see those things coming down the road.

and so they find you and said, "hey, let's paint them a color that human beings can see the most." and, yeah. do you notice the color of your street lights? what color they'd be, gang? - yellow. - yellow. a little greenish, a little yellow greenish, mostly yellow, right? why the streetlights yellow? they used to be incandescent lamps that used to glow white. now, they're making them yellow. one strong reason it has to do with, guess what we can see most? yellow and green. let's suppose you got a hundred-watt lamp, and it's white. and you're saying that a lot of this is coming out, and a lot of this too, right? so you're spreading it along all of that, right? let's suppose you got a hundred-watts only of this. how about your eye, honey? you're gonna see more light, because it's hitting right where you can see best. now, those yellow lamps aren't very good for your complexion and that sort of thing, all right? but when you're driving at nighttime you're not into that. you're into what's on the road. you really want to maximize seeing. and, hence, that's one strong reason

for the yellow-green lamps. and the yellow-green fire trucks. but, suffice to say, we could break this up into three regions. that's what happens in your eye. the low frequencies average out to be red. the high frequencies average out to be blue. guess what the middle frequencies average out to be. irish, what is that? now, try it. - green. - green. very good. when you're looking at your television set at home, gang, you've only got three colors of phosphorous that give you all that spectrum of color. and what are those colors, gang? - red, green and-- - red, green and? - blue. - yay. and i can, kind of, show you that over here with this light box. do you want to be seeing such thing? let's try this. can we--ted? all right, gang, what color is that? beginning with a b. blue. how many don't even need a hint? [laughs] hey, but you guys are calling that blue, right? can we be sure that everyone is seeing that color?

didn't you used to wonder that when you were a kid? when daddy said, "that's blue." and you wondered your sister called it blue, too, didn't she? but how do you know that she wasn't looking at this, and she learned to call that blue? do you ever wonder about that? do we all see the same, mm? do we all taste the same? do we all smell the same? do we all feel the same? differences, individual differences, huh? and how would you know? -- and look at what we got here, gang. red, green, blue, all together give what? begin with a w. - white. - white. and isn't that nice? isn't that nice? because now what you're doing is the low frequency part of the spectrum, right here, banging into your eye, the middle part of the spectrum, whip-boom, banging you right in the eye and the high part of the spectrum, whoop, and it all averages out to be the light isn't that neat? there's another thing, too, that's kind of neat. notice that the blue and the green mix together to give bluish green.

isn't that wild, huh? isn't that wild, huh? wild. and notice that the red and the blue mix together to give a bluish red. isn't that wild? wild. no, that's not really wild. you would expect that. but how about this, the red and the green, where they overlap, they give yellow. wow. hc. why should they give yellow? now, you mix red and green paint. you get, like, brown, okay? [laughter] but that's color by subtraction. read the chapter on that. here we have light on top of light. and red and green hitting your eye at the same time, gonna give you what? - yellow. - yellow. why? --primary--between the two. that's right. yellow is right between the two. and these are gonna average out to be that, okay? isn't that nice? isn't that neat, gang? anyway, yellow--it's-- oh, look at this. we talked about three colors, red, green and blue adding to give white. is there such a thing as two colors adding together

to give white? answer end with a p. yup. nope. no. try it. nope. nope. no, not a pe. just a p. - yup. - yup. yup. okay. it turns out two colors can give white. can anyone tell me what color mixed with blue will give white? - yellow. - yellow. do you see it? yeah. how many can't reason this? well, the yellow is the red and the green, huh? okay. well, let me ask this, what color--red and what color will equal white? cyan. - bluish green. - cyan. this color here, greenish blue. we don't call it greenish blue. we call it, what? begin with a c. - cyan. - cyan. that's right. and how about this, magenta, we call it. magenta and what give white? green. green. that's right. here's an interesting thing. can you do algebra? white take away red equals what? three. [laughs]

white take away red... cyan. gives cyan. shall i do that again? yeah. there's your white. now, i'm gonna take the red away from it. watch where my finger is. i'll take the red away. whoops. [laughter] and what's it turned into? cyan. cyan. did you ever wonder why the sea water is a cyan color? it's green and blue. how many people have never wondered that? "so, well, it's cyan--" no, no, no, no, there's a reason why it had to be a cyan. can we have the lights please, ted? sure. -- it turns out that seawater, any kind of water, absorbs, like mad, infrared. in fact, if you take an infrared light and shine it on water, it'll heat up very, very quickly. and it also absorbs a lot of red. so when the sunlight comes down, all the colors, yeah, hits the water. guess what color gets absorbed more than any other. red. no. no, not green. okay.

let's try-- let me give you a hint then. begins with r, ends with d. red. yeah, red. good. okay. some people said green. it turns out the red gets absorbed. when the red gets absorbed, is that the stuff that reflects to your eye? no, no. it's been absorbed. you can't absorb then reflect. you take your pick, honey. so if the red gets absorbed, what does the white light become? green and blue. shall i do it again? shall we put the lights off and do it again? yep. and turned-- no, i'm not gonna do it again. [laughter] it turns out to be that cyan color, see? if red plus cyan equal white, your problem is what's white take away red? and that's why the sea water is the color "a". isn't that nice? that's why sea water is that color. different colors of-- different temperatures of waters, different nutrients in the water, then different shades of that cyan, too, right? having a lot to do with different amounts of red being absorbed. so the color you see in things around you are not the colors that are being resonated off. they're the colors that--

that's a leftover of colors being absorbed. you see this green, this cyan shirt here. guess what color is being absorbed by that? begin with a r. red. red, okay? now, where's someone with a-- you see, this red over here, this red shirt? guess what color is being absorbed. begin with a c. cyan. cyan. all right. could you do without the hints? yeah. well, no. okay. you get the idea, yeah? isn't that kind of neat? colors, fascinating. red lamp. what color is the shadow? black. black. why is it black? because there's no light there. is that mysterious no. how many say, "wow, far out man. what a shadow. is this black?" we all see it's black, yeah? all right, now, i'm gonna put on the green lamp. the green lamp, what's the color we're getting on the background? green, yellow.

well, the green is a little closer. but strain your eyes, begin with a "y." yellow. yellow. now, i put my hand, boom. "hey, this was the black shadow before, now it's green. how it turn green?" "there's no reason for that. it just happened to turn green. "i don't know why when the green light hit the black shadow, it turned green." why did it turn green, gang? because the green light's shining on it. but green light is making a shadow too, this one over here, but it ain't black. red. why is it red? because the red light is shining on it. how many say that's mysterious? nobody-- you see that--ain't that neat? now, watch this. would like to see three lamps at one time? wow. i can show you. blue, now what color we get through the screen? white. white. bam. now, the one that was green before in our screen, it ain't green anymore. now, it's greenish-blue. why is this one greenish-blue?

because green and blue light are hitting the black shadow. mystery? all right, now this one over here is not red anymore. it's red now. but the red light is hitting-- and not only the red light hitting, but the blue light is hitting it. so what is it? reddish-blue? is it a mystery why this shadow is reddish-blue? no, because the only lights hitting it are red and blue. magenta, you get? --and look at it over there. what color shadow we're getting in the far left? yellow. why is it yellow? it ought to be black, because of this shadow here. but the green and the red are hitting it. and when red and green hit the black shadow, they mismash to be what? yellow. isn't that nice? there's your yellow, magenta and cyan. these are your complementary colors, gang. red, green and blue, and the complementary colors, yellow, red and cyan. isn't that nice? ain't that nice? do you like it? [applause]

if you get the right shade of blue and orange. let's try this. let's catch that light again, ted. this is sort of like a sky blue. and here's, like, a sunset orange. and these two are complementary. that particular shade of blue and that particular shade of orange give a white, okay? now, let me ask you a question. if i take that blue away from the white, what will the white turn? orange. orange. isn't that neat? look at that. let's try it again, okay? white take away the blue, turns... orange. orange. can you remember that?

how about if it goes the other way, what if i said white take away orange, turns blue. remarkable? well, the effects of that are kind of nice. ted, the lights, please? would you ever be wondering why the sky is blue? how many say, "well, it's probably the reflection of the water." no, now, i go to minnesota. now, i go to kansas. what's the color of the sky in kansas? well, it's usually yellow-green, right? come on, what is it, gang? it's still blue. why is the sky blue? because it's absorbing all the red. a little bit different phenomenon going on here. let me just tell you about it. it turns out that light coming down from the sun-- [makes noise] --showers itself upon the atmospheric molecules. now, we got big ones, we got little ones, we got all sizes up there, okay?

and these molecules will scatter off the frequencies of light. it's called scattering. now, what frequencies will be scattered? let me give you an example. let's suppose i have a couple of bells here. here's a little bell, and here's a big bell. when i disturb these things, they're gonna scatter sound off in all directions and what will the sound be, high-pitched or low? let's try the little one right here. [makes noise] do you hear that? now, let's try the big one. [makes noise] [laughs] is that right? no. how many are saying, "no, i got that wrong"? wrong. wrong? okay. you know, that's completely wrong. it turns out the little bell will-- [makes noise] --and the big bell- [makes noise] isn't that true? guess what behaves the same way up in the... sky. sky. the what? molecules. what do you suppose a little tiny, tiny, tiny ones will ring: high frequency or low frequency?

high. high frequency. how about great, big ones? low. low frequency, okay? now, what are the size of the molecules in the sky, large or small? begin with a s. - small. - small. and then nitrogen and oxygen mostly, isn't that true. o2, n2. and when that sunlight comes beating down on those things, it scatters off, light scatters off. and it turns out the color of the sky is the color of all those little bells, all those little optical tuning forks, all those little vibrators. and they're vibrating at mostly, what frequencies, gang? high frequency. how many know what high frequency looks like to the human eye? blue. blue. and higher frequency even violet. let me tell you something, the sky really scatters off more violet than it does blue. but you know what? we're not so good at seeing violet. we're a lot better at seeing blue. so guess what our eyes tell us the color of the sky is? begin with a b. blue. you could have done that without the hint, okay? and it's blue because the tiny, tiny particles

are scattering off the high frequency, so we see a blue sky. okay, interesting enough. now, you look straight up at the sun, straight up above, you see the sun white, yellowish-white, okay? okay, a little bit of filtering coming through, but not very much. how about that sunset, gang? it's sunset, when you look at the sun, it isn't white anymore. how many would say, "well, it's sort of like an orange, "but there's probably no reason for that. it's just characteristic of sunsets and sunups to be orange. how many already see why it is that the sun is kind of orange at sunset? let's take a look. there's the earth there. here, you're out standing right here. here's the sun at noon. somehow, light comes down, hits the air, scatters off to your eye, scatters off to your eye, and you're seeing what? what mostly scattered as blue, so you look up and you see blue all around. but you look directly at the sun, that white light--

[makes noise] --overwhelms, a little bit scattering going on, and you see a white sun, whitish, okay? so at noontime, boom, you see the sun whitish, huh? how about at sunset? what happens at sunset? can we do this next week and do this experimentally? we can do this experimentally. i tell you what? let's just do it right here. here's the atmosphere of the world right here. here's the atmosphere of the world, huh. no. let's do it this way. here's the atmosphere of the world, and here's the sun. now, the sun, red, orange, yellow, green, blue, violet, okay? [makes noise] --swoosh, what do you guys hear? well, let me just do it now. i'll do it again. red, orange, yellow, green, blue, violet-- [makes noise] --what do you got here? blue. white, do you know why, huh? all the frequencies together give you white.

isn't that true? right? so you hear what? what's the color of the sun? begin with a w. white. end with ite. try it. - white. - white. all right, whitish, anyway, all right? white sun, all right? here's our atmosphere down here. the atmosphere, these tuning forks, blue, blue, blue, blue, violet, violet, blue, blue, red, blue, blue, pink, blue, blue, chartreuse, blue, blue, get the idea? what do you think might happen, let's say, i'm gonna ring all these? [makes noise] --what do you guys hear? blue. blue. you all heard blue. that's right. now, there's a little bit of red in there, yeah, a little bit green in it. but mostly what? blue and violet, and you heard blue, yeah? okay, let's try the sunsets. can i have a volunteer? would you stand right here, put your ear right down here, and i'm going to hit these tuning forks. no, right behind, right behind, i want to go out there. i'm gonna hit these tuning forks. this is the sun, 150,000 kilometers away,

and the sunlight gonna come down to the atmosphere- [makes noise] and maydell standing on the ground, and here's the sky between her and the sun, yeah? here we go, gang. we do, by experiment, one of the beauties of science is you do by experiment, huh. you don't just do it all in your head. here we go. [makes noise] oh, oh, first of all, i should say this, you guys get the white again. let me put a reflector here. so all this beam energy goes down here, and this beam energy is gonna scatter off here, all right, okay? [makes noise] what color do you guys hear? blue. do you hear blue? you all get it? good. maydell, what color do you hear? white. yeah, she heard white. why did she hear the white? because she's standing right next to the-- that's right, honey-- some, some, filtering. she could have come right at her. it's a good thing you didn't have your eyes there. [laughter]