okay, gang, guess what we're gonna talk about today? begin with m, end with agnetism. try that. magnetism. magnetism. see these paperclips? yeah. i take the paperclips and i dump them out on the book. how come they're on the book and not on the ceiling? gravity. gravity. the gravitational interaction between these paperclips and every molecule in the whole world pulling which way? okay, down, right? there's this earth and these mountains and everything, all pulled down, down, down, down. how about the clouds? are they pulling up a little bit? the ceiling pulling up a little bit? how many say, "oh, there's no gravitational interaction at all with the paperclips and the ceiling"? show of hands. how many say, "there's a gravitational interaction between every pair of masses"? show of hands. yeah, my people, all right. so how come the ceiling-- how come these things aren't moving up to the ceiling?

how many say, "i don't be knowing that, gee, 'cause i suspect they should"? come on, gang, what's winning, down or up? down. why down? bigger. there's a lot more ground down there than there are ceiling up there, so the net force is down. and the whole world is pulling these paperclips down against the book. that's a pretty good force, yeah? watch this. see this little dinky magnet? how big is this compared to the whole world? big or small? the answer begin with a s. small. watch this. now you know why dick tracy used to say, "he who controls magnetism controls the universe." look at the force of this little dinky magnet compared to the size of the world pulling all these clips up. so we can talk about the magnetic force today, gang, the magnetic force. ain't that neat? okay. this is a pretty powerful magnet. here's a pretty weak magnet. this one is suspended on a point,

and it's magnetized. and what do we call it, gang, do you know? begin with c, end with ompass. try it. put it together. compass. compass, excellent. that's a compass. and guess which way it's pointing. north. you know what it's doing? it turns out that the whole world is a great big, begin with m. magnet. magnet. and surrounding that world is a magnetic field and guess what that compass lines up with, begin with m, f, the magnetic field of the earth. and that magnetic field in this room is oriented like this, okay? but what is the source of that magnetism? the source of that magnetism was betrayed years ago, more than 150 years ago by a fellow by the name of hans christian oersted, who was a professor-type teaching-- i believe he was in a high school classroom. and he was showing the students that there's no relationship between magnetism and electricity. the physics books at that time had electricity as one subject and magnetism as another. and oersted was showing there's no relationship between the two. and one of the things he would do

is he would line up the piece of wire like this and put it over a magnet, pass a current through it, and you really don't see anything happening. there's no interaction. a student came up after class, gang, and held it in this direction. okay, watch this one, a current is passed over the wire like this, boom. you see that interaction? it turns out there is an interaction between a current-carrying wire and a magnet. and it turns out-- to make a long story short-- the source of all magnetism is moving electric charges. and when the charges move through the wire, they set up about the wire a magnetic field. and that magnetic field is in concentric loops around the wire. if i pass this wire through a hole in a piece of paper and i put a whole lot of little compasses around the wire and no current goes through, all those compasses would point north. but you know what happen if i put a current through that wire? bam, all the compasses will line up with the field.

and it turns out that field takes the shape of concentric circles above the wire. the further away you get, the weaker they get, but their direction is all that way. so surrounding every current-carrying wire is a magnetic field that takes the direction of the concentric circles. the magnetic field of a bar magnet like this-- have you ever seen magnetic field of these things? if i put this down, put a piece of paper on the top and then put iron filings, you'll see all the iron filings piling up in the middle between the shape of that field. you have photographs of that in your book. so the magnetic field is very strong between these pole pieces and it's also relatively strong about a current-carrying wire. the more current through the wire, the stronger the field. and guess what, gang, if i take that wire and i loop it over like that, guess where the field will be concentrated? how many say, "oh, probably out here somewhere"? show of hands. how many say, "oh, the field would probably get all concentrated right in here, all bunched up in here."

show of hands. how many not be knowing? okay. well, it turns out, yeah, the field would get all bunched up inside here. and furthermore, if i put a piece of iron through there, guess what the iron will turn into, or guess what the device is called. begin with e, m. electromagnet. and i can kind of show you that over here. here, i have a whole lot of coils or wires. see all those wires, those green coils? it's coiled around, around, around, around, around. when i pass an electric current through here, guess where the field is gonna be concentrated, inside or outside? begin with i. inside. inside. --be concentrated in there. and furthermore, what i'm gonna do is i'm gonna induce the magnetization of this piece of iron core. i can show you that. right now, this does not pick up the clips. why doesn't it pick up the clips? it doesn't pick up the clips because right now, it's not an electromagnet. why is it not an electromagnet? what are the two ingredients you gotta have for electromagnet?

electro, right? i've gotta put some electricity. i gotta put some current through here. and i can do that by simply plugging into a power source here. can you hear that little hum? it turns out this is an alternating current. but let's watch this, gang. it turns into a magnet. guess what kind of magnet? electromagnet, get it? and this electromagnet, guess what? this electromagnet is simply a device that concentrates the magnetic field line in a coil and then you put a piece of iron in there and the iron becomes magnetized by induction. and now it gets-- oh, look at this, a little residual magnetism. that's a fancy word for leftover magnetism, okay? it turns out this is still a little bit magnetized. hey, you wanna screw up a magnet? drop it on the floor a few times, or throw it up against the wall, or put it on a fire. would that be good for a magnet or bad for a magnet? why bad for a magnet? 'cause you're gonna jostle all the alignment out.

you guys be reading about the alignment of the magnetic domains. we don't have time to talk about that today. and all these lectures-- don't we just talk about some of the icing on the cake? and you guys get the cake on the textbook, yeah? but all those domains are all lined up for a permanent magnet, right? that's the difference between this piece of iron, which is not a magnet now, and the piece of iron over here. here, they're all lined up, not all, but many are lined up nice and permanently, okay? this kinda iron, such and such a way. this? no, not until i power it up with electric current. so hence, we have electromagnets, and the name of the game so far is the source of magnetism are moving charges, moving charges. if they move in a wire, then you wrap that wire around, you can concentrate the field lines and you get electromagnet. any questions at this point? lee? which-- how do the moving charges-- or which moving charges cause the magnetism in the natural magnet? in a natural magnet. one, it's a very good point, where are the moving charges,

there's no current. ah, but the iron magnet is made up of what? atoms. atoms. and atoms are made up of what? charges. charges. charges in the nucleus, okay, which don't move very much, okay? and charges, which orbit around, and those of the electrons. those electrons, gang, make up little electric currents. but in most atoms-- and this is in your chapter. in most atoms, you have as many going one way as the other way, it turns out the spin of the electron is even more important. you have as many spins one way as the other way and one effect cancels the other, and so, net effect. but there's one iron-- i mean, there's one atom in the periodic table, which has the-- say a net spin of four. four more spins one way than the other so you get a net effect, and guess what that element is? iron. iron. that's what iron is. and that's why you find iron is said to be ferromagnetic getting into that kind of thing. i wanna show you something that's even more interesting than what would seem.

let's take this magnet. i'm going to put the wire in the magnetic field of this magnet and i'm gonna touch this momentarily so i get a pulse of current. and when i do that, when a current goes through this, will this wire in a sense be a magnet? how about when no current goes through it? it's copper wire. copper is not ferromagnetic. copper--you've all tried when you were a kid to pick up a penny with a magnet. it doesn't work, does it? 'cause the penny is copper, okay? so the only way you're gonna get magnetism with copper is to have, boom, electrons flowing through it. electrons flowing through anything would put-- would set up the magnetic field around anything, yeah? let's see what happens with the magnetic field of the wire and the magnetic field of the magnet, let's see if there's any interaction. what do you suppose? watch this, gang. you see that jump down? see that jump down? let me turn the magnet around.

jumps up. [laughter] did you see that? i'm gonna do it one more time. watch. wow, jumped up. so one way, it jumps up, and the other way-- put it this way-- it jumps down. i wonder if that jumping motion could be harnessed. how many people say, "well, no. there's probably no practical application of that"? wires will move and magnets, big deal, right? is it a big deal? it's a very, very big deal, because guess what this underlies, gang, electric what? beginning with m, end with otors. try it. motors. motors, honey. electric motors be working on such principle, okay? and dig this, whenever you see any electric motor, realize-- you know, sometimes we see things and we're so overwhelmed with the complexities,

we don't know what the nitty-gritty is. realize the nitty-gritty of an electric motor is simply a current-carrying wire, foom, being deflected in a magnetic field, period. that's it. motors operate that way, okay? now, let's suppose i take this wire and i put it like this through there, okay? i'm not gonna take the trouble to do that right now. but if i put it like that, then the currents go in this way in one wire, but doesn't that go the opposite way on the other wire? i wanna have you use your mind here. what's gonna happen to this thing if i pass current through it now? one side will jump up, and the other side will-- down. which is gonna produce a-- twist. --twist. do you see it's gonna twist? and the more current flowing through it, the more it will-- twist. --twist.

and guess what we have here, gang. can you see down below here, i have a magnet and i have a copper coil inside? i don't know if you can see that, gang. you've got a magnet here, a permanent magnet, and a copper coil inside. and when current goes in that coil, it comes this way, it comes this way in one loop and this way on the other, one part is pushed up and the other part is pushed down. and the whole contraption is attached to this needle. and when the little coil twists, guess what the needle does. it also twists 'cause they're connected. and the more current that flows through it, the more it's gonna twist. does that make sense? now you know how a meter works. a meter is simply what? it's simply a coil wire-- here i've got a coil with one loop-- in the magnetic field. when the current flows through it, part of the coil is gonna be pushed down, part of it is gonna-- hey, hey, hey, it makes sense, doesn't it? the fact this wire will jump up one way and the other way jump down leads you right

into seeing the connection with how a meter works. we got that? can we take it a step further? how many of you say, "no, no. that's enough. that's enough. information overload." no, come on. we can go further. what would happen if when i put a current here, how would it twist, this way or this way? it depends on which way the current flows. and if i put a strong current in, it'll twist a lot-- little current a little, okay? but can i make this thing rotate around and just keep rotating and rotating and rotating? no, i can't do that. you know why? 'cause there's no way that i know here to change the direction of the current as you do it. but if i get this thing-- so, hey, look at this, gang. if i get this--so, when it makes a twist and boom, it's full scale deflection, okay? and then the current turns around and goes the other way, then it will twist again, and then again, and then again, and again. i'd get a motor, and that's what a motor does. a motor reverses the direction of current in the coil every half turn.

and that's what-- here, we have it right here. there's a motor here. what we have here, a little bit more complicated. see, i have the electromagnet down here, electromagnet, and up here is my magnet, okay? so i get a magnetic field in here, all right? now, what i'm gonna do is i have a coil of wire here. see this coil of wire? if i get current flowing through that coil of wire, maybe up here the current's going this way in the magnetic field, okay? so it gets blown down, maybe. but over here, the current's going this way, it gets thrown up, so it, boom, it twists. but up here, it would stop. but what if i change the direction of the current? so here now, it overshoots a little bit and this gets pulled down, this gets pulled up, bam, bam, bam, bam, bam. if i change the direction with every half turn, i can change a meter movement into a motor movement. and i do that with this little device here called a commutator. i'm not gonna take the time to get into the detail of it. but there's a little split ring there so the current may be feeding in here

now goes to this particular way, and when it turns one half way, then it slips over to this other electrode and goes there, bam, bam, bam. suffice to say, every half turn, the current will change direction in the coil. when that happens, the forces on the coil change direction, and guess what gonna happen, gang? now nobody here really gonna get excited about this. but could you put yourself about 150 years ago and then be thinking about this thing? and then someone shows you something like this, you'll see why people were excited. what i'm gonna do now, gang, is i'm simply gonna attach this electromagnet to the battery because i wanna have some-- i wanna have current in the coil to make that a magnet. and when i do that, then i'm gonna pass current through this coil.

and what's it gonna do, yes? and then, put on here like that, now i got current going on there and current going through there and i should get a-- you know how sometime when you shave and you got to get the thing started a little bit, hey? look at that. what do we see there, huh? how many people are bored? would your great-grandfathers and grandmothers be bored about such thing? would they? they would say, hey, because of this-- do you suppose this had any difference in the way the world works? gang, it really did. if it weren't for things like this, these devices, you know, people's teeth would be all green. you know when you see your friend, you smile. and one of the things that's nice is a nice sparkly teeth, right? without one of these things here, everyone would have green, scummy teeth. you know why? because there'd be no such thing as an electric toothbrush. [laughter] yeah. yeah.

you see people rather healthy today? people are rather healthy. you know how people would be if they didn't have motors like this? we'd be emaciated, we'd be undernourished because there'd be no electric can openers, there'd be no way to open the cans of food. [laughter] okay? you hear what i'm saying, okay? you see people their clothes how lint-free? if it weren't for devices like this, you'd have no little lint machine to take the lint off. the world would be different without this electric motor. this electric motor adds to the quality of life. will you agree, huh? think about the electric motor every time you see someone with clean--a nice clean smile, all right? yeah. really changes things. questions, lee? if the current didn't alternate, would the motor keep spinning? if the current didn't alternate, it would just turn to one point and stop. but would it go a little beyond than be-- it might shoot-- oh, it's supposed to go something like this, lee-- and finally set up. just like maybe putting a compass in a magnetic field and seeing it-- and finally settle off, okay?

but it's got to reverse to foom, go the other way. isn't that nice? and there's a little simple device that'll do that. so what we've talked about so far, gang, is how we can begin with magnetism and electricity and get motion, okay? with those two things, we can get motion. but before i go further, i think there's another question. how come--one's charging it to one way and one was charging to the other way, how come it doesn't cancel out and just get to stop? well, bear in mind now, let's look at this. i don't know if i'm answering your question, but let's suppose the current's going through this way. this side is being pulled up, this side is being pulled down. oh, okay. so it twists. now, when it gets to here, boom, the current changes, okay? 'cause i've just gone from a little space to here. oop, the current goes the other way now. how this happens would take a little detail for you to look at, and i'm not gonna explain it too much. i used to explain this in the board, it takes 10 minutes and then you forget anyway. suffice to say, this little thing called a commutator

will reverse the direction of the current. and when it does, then what pulled it up will now pull it down and foom, foom, foom, foom, foom in a way, way, way it go. see? so there's not a cancellation, there's a reversing of direction and a continual rotation. what determines the speed of it? the speed-- what determines the speed is the strength of the current or the strength of the magnetic field, see? the stronger the magnetic field, then the greater the interaction. the more the current in here, the greater the interaction. so if you'll increase either, you'll increase the speed at which this thing goes. 'cause a small force will pull it up a little bit. a big force, boom, snap it up quickly, see? and bam, bam, bam, bigger force will make it go faster, faster, faster. most motors are designed to rotate so that-- at 60 times per second, 60 rotations per second, okay? that's 60 hertz, 60-hert motor. that's what we have in this country. in europe, they have like 50 hertz motors, but there's a particular frequency at which the motors are designed to rotate.

okay, gang, i'm gonna shift gears a little bit. if from electricity you can get magnetism, the question was raised a little over 150 years ago, can you go from magnetism and get electricity? --the answer is no, there's no way to do that. does that bother you a little bit? yeah. come on, gang. is there a way to-- is nature symmetric? yes. how many--oh, no, nature will go from here to there but that doesn't mean it will go from here to there. hey, how about it? come on, think. check your neighbor. can you go from magnetism and get electricity? okay, gang, how many of you be saying, "yeah, it's probably so that you can go from magnetism and make electricity." show of hands. well, almost--oh, okay. all right. okay. all right. all right. we're all together, yeah? okay, all right. let's see how that was done in 1831.

this was done by a couple of physicists about the same time in history. one was michael faraday, a scottish guy in england and the other was joseph henry, an american type in vermont in the 13 colonies. and they both at the same time found the same effect. and here's what they discovered. they had meters similar to this at that time, but they didn't know how to get electricity. well, they get electricity from batteries. a fellow by the name of volta, alessandro volta, italian type, made batteries. and that was kind of nice. everyone's excited about electricity. and then michahael faraday and joseph henry discovered the following, no batteries. battery's over there, gang. no batteries, no tricks. magnet, wire, meter. watch this.

you see anything? no. faraday didn't see anything, either. [laughter] okay. and--but watch this. henry didn't see anything, either, but watch this. did you see something? yeah. again. my goodness. my goodness. there's no battery nearby and guess what we are generating? begin with e, c. electric current. i am generating electric current. and faraday and henry found out that. no batteries, no cells, no lightning, none of that, just the motion of a wire and a magnetic field. so faraday goes to bed and he's really excited about that. and while he's in bed that night, i'm making this up now. while he's in bed that night, he's kind of thinking, "gee, i wonder what would happen if i did it with two wires?"

so he gets up in the middle of the night, takes his candle, goes downstairs, had to do with candle. little did he know that he was gonna get rid of candles, honey. the candle industry was furious later on, okay? 'cause what he did is he went down and he took two wires and guess what happens with two wires, gang? twice as much current. he goes back to bed and he thinks, "i wonder three wires." shall we try it? yeah. didn't sleep the rest of the night, gang. i wonder a million wires. what do you think? a million times as much, okay? this is a remarkable discovery that one can, it turns out, induce voltage by simply moving a wire in and out of a magnetic field. and so faraday's discovery is couched a little differently. today, it's called faraday's law, and what it says is this, a little more complex.

change the magnetic field in the close conducting loop of wire-- they may not be conducting. just change the magnetic field intensity in a closed loop and you will induce a voltage in that loop. now, this loop happens to be a copper wire so the voltage in that produces a current. so look at this, you get a current. change the magnetic field in two loops of that closed copper wire, two loops of that circuit and guess what you get, gang? twice as much voltage. three loops, three, da, da, da, da, da. so that's the rule. all you got to do is change the magnetic field intensity and you will induce a voltage which will produce a current if you're talking about a conductor. ain't that neat? that is really, really nice. now we can produce electricity. see, now all of europe started converting to electricity. they started having lamps and all that stuff and they had all these kids up on the hills going like this, okay?

and these kids are all doing this thing, okay? and one day they say, hey, we're getting tired doing this. see that waterfall coming down? why don't we put this wire on a great big piece of wood and have it rotate, huh? by the waterfall, put a little paddlewheel and we go home and get all electricity. and that's of course-- they started the industrial revolution. i'm making that part up but you get the idea. [laughter] all you got to do is rotate the loops in a magnetic field or just plop in and out of the magnetic field and there's your electricity, faraday's law. got such thing? questions? it seems that the characteristics of electromagnetism and gravitation are similar. if from what i understand, they haven't been able to quite figure out what gravitation is, am i right in thinking that? yeah. yeah. of course, einstein spent most of his life trying to find the unification of all the forces, you know? and they still haven't-- they, meaning the physics type,

still haven't found that magnetism or electromagnetism and gravity have a commonality. that has not been found. if it's there, if it's there. let me say this, though. it seems like there's two different things going on here. when i first learned about this, i thought-- i learned two different phenomenon. one was, if a current flows through a wire, it's deflected. and then a completely different one was that if you take a wire and plunge it out of a magnetic field, you'll induce current. but you know what? they're one and the same. there is a commonality there. let's look at it. if it's true that electrons going through a magnetic field, crisscrossing, will be deflected, then it ought to be true that you can generate electricity by doing this because it's one and the same thing. how fast do the electrons travel in a common circuit compared to the speed of light, fast or slow? slow, about a snail's pace.

did you pick that up in the study of electric currents? the actual drift speed of the electrons is very, very slow. the signal traveling through the wire, that's about the speed of light. so when i have current coming through here, when you saw that deflected out, the electrons did not go racing through at the speed of light through the wire, gang. they're probably going like this. and that motion through there, boom, you had interaction. now, if electrons moving this way are forced up, what would happen if i just take the electrons and force them down or just move them down? they're gonna be forced perpendicular. but this time, guess what's along the perpendicular direction? begin with w. wire, there's a path. so when the electrons are coming down there again deflected, it could go like this, it could go like that, the same thing. they're deflected. this time they shot up before there's nothing to do, but pull the whole wire up too. but if i came in this way, foom, they shoot up, but they go along the wire.

so what i've done is i've produced a current. so this over here produces an electric pressure on there, which we call a voltage. and so a voltage produced in a wire crossing through a magnetic field is not fundamentally different than having electrons go through a wire this way and being popped up the side. mm, it's the same thing. check that part in the book. it's the distinction between the motor effect and the generator effect. they're really one and the same physics. check that out. now over here, we have a generator. it turns out this is a generator too. take the time to do this. well, i'm not gonna take the time to do this, gang, 'cause i got too many ideas to talk about. but with this, what i would now do is i would now hook up the electromagnet and i wouldn't put any hookup with this, the coil, with the battery at all. i'd make that an electromagnet and then i'd hook this up to the galvanometer and turn this,

and guess what you're gonna see over here. it's the same thing as like twisting it in here, okay? you're gonna see current produced, okay? i'm not gonna take the time to do that. i can kinda show you this 'cause it's already hooked up. i think you've seen this before. look at that. i'm lighting up the lamp, okay? now i'm generating electricity to light up the lamp. see if you're sitting next to someone who knows how is it i'm able to generate electricity and light up that lamp by turning the crank. what is going on? okay, gang, how about it? how about it? what is going on? how am i generating electricity over here? what am i doing? what's faraday say you got to do? you have to have a magnet-- i gotta change the magnetic field intensity and some closed loop of wire, yeah? and guess what's inside here, gang? begin with closed loop of-- wire. --wire. and when i take a closed loop of wire and i rotate it, guess what i do to the magnetic field intensity? if i'm holding my arms out like this and it's raining,

and the rain is coming straight down, foom, i threw my arms. i got a lot of rain coming through my arms, yeah? right. how about i turn like that, how much rain coming through? none. none. okay, how about i go like that some, i mean, i can't keep doing it, you see what i'm saying? but i could clip the amount of rain that i'm-- you see what i-- same thing over here. in a magnetic field, you're rotating a loop. you're changing your magnetic field in that loop, honey, you're getting a voltage. and that voltage, light up the lamp. you see that, yeah? i mean, it's just not-- it's just a little gadget here. i want you to see what's going on with it, huh? okay. here's a piece of aluminum. aluminum, does it have magnetic domains in it? answer begin with a n. no. no, very good, okay. no magnetic domains. but watch this piece of aluminum, which is not a magnet now. is this the first time you've seen that? yeah. remember that. do you know how we put things in orbit, no?

the way we put things in orbit is we take a rocket and we-- [grunts] --and it keeps picking up speed and finally goes into orbit, okay? but what are we going to do in the future? well, you can't do it with people inside, gang. but if you wanna get something into orbit, okay, instead of a gradual acceleration where you pick up in speed, they'd be doing this. so, today, remember today is today's the day you first saw that. this is a very, very serious candidate for propelling things from the earth up into orbit. okay, yeah, electromagnetic propulsion. now why did this thing fly out, gang? should i leave that as a question for you? how many would have the next few days completely spoiled by not having that information? why did this thing fly out? why did this all of a sudden become a magnet?

maybe there is no reason for that. maybe it's just one of the strange things about the world. well, let me ask another question. let me go like this. i held it way down here where the magnetic field is strong. let's suppose i just put it there. electromagnetic levitation. how come that thing is levitating? why? this becomes a what when i plug it in? beginning with m. magnet. magnet. and this is levitating, so this must become a-- magnet. it's aluminum, but it's a closed loop aluminum. yeah. oh-- it's a closed loop aluminum in a changing-- starting to get it, starting to get it. let's see, this is a changing magnetic field 'cause it's ac. right. and there's some connection between the changing magnetic field and a closed loop. you guys be getting it? no, i guess there's no connection, or is there? how many know why this thing was levitating?

did you ever see one magnet repel another? what did you just see now? you saw one magnet repel another. and why did it fly off when it was way down here? here's a question you can all answer. every one of you guys can answer this. this thing weighs an eighth of an ounce. i'm making that up. an eight of an ounce. what is the strength of the electromagnetic force pushing up on that ring? check your neighbor. what's the answer, gang? eighth of an ounce. an eighth of an ounce. that's old mechanics, right? if there's an eighth of an ounce pulling down and there's something pushing up to be getting equilibrium, that up must equal down and that's an eighth of an ounce. ted bradstrom has some ideas of electromagnetic induction he wants to share with us today. speaking of electromagnetic induction. he's got a nice one here. really simple, really nice. magnet, coil.

so we know when we're moving a magnet through the coil, what's gonna happen? hopefully we get current flowing, okay. it goes through the wire and meets another coil. what happens when you got a current through a coil? magnet. magnet, okay. so we put a compass in the middle of this, and, okay, let's see if we get it. there we go. look at that, gang. look at that. an interaction from here to there. hey. just in case you think we were lying, i'll just move this and you can see how it's moving, right? is the-- nothing moves down there, yeah? no. now watch when he changes the magnetic field in the coil. what happened down here, gang? yeah, all right? okay. you want to know the fun part? you don't have to move the magnet. you can hold the magnet steady-- [laughter] yeah. --and move the coil back and forth. hey, you know what, you know what is a neat, neat application of electromagnetic conduction has just been the last few years, and that's the smart lights.

when you're traveling down the road and you're coming through the traffic light, and the lights change for you. you drive over something, and that something changes the lights. i used to put, like, a piece of rubber tubing out there with compressed air and it would, boom, make a little pulse of air, and that changed the light, but then the rubber would wear out. what they do now is they bury in the road a coil of wire, okay? a coil of wire buried in the road. now through that coil of wire is a magnetic field called the earth, and part of that field is in that earth, all right? now if you could change the magnetic field intensity of the earth through that big coil of wire, what would you induce in that coil? begin with a v. voltage. a voltage. ain't that right? so when your metal car drives-- or when your iron car, a wooden car won't work. when your iron car goes over that coil of wire,

does it not alter a little bit the magnetic field intensity in that loop? the answer begin with a y. yeah. and when it does that, it makes a little tiny electric current, which activates the switch of changes and changes the lights, isn't that neat? so the next time you're driving near traffic lights, look down to see if someone hasn't put down there a couple of coils of wire, 'cause you get two to make sure, huh? check that out. another thing, too, tape recorders. tape recorders. what does a tape recorder do? well, in the tape recorder-- when you speak into a microphone, you get a little plug like ted had, you go back and forth, back and forth. it makes a little vibrating current in wire, right? what if that is passed down to a little electromagnet and you drag by that electromagnet some rusty tape. and the rust is iron oxide. when that iron oxide slides by that magnet there varying strength, you'd get on that tape then varying strength of magnetism.

some as magnetized a lot, some magnetized a little bit. and the little vibrations you're getting on the tape. now you take that tape, bring it to another machine, i wanna tell you the same machine, and drag that tape at the same speed, pass an empty coil of wire, what's gonna happen to the magnetic field intensity in an empty coil of wire when that tape drags by? it's gonna change. it's gonna change, ain't that right? right. and if a piece of tape comes by that's heavily magnetized, boom, you're gonna get a big pulse of current. a little tiny bit, a little tiny-- well, you can get variations. and isn't it amazing that that tape driving by there, the empty coil, the variations in the magnetism set up variations of voltage in that wire, faraday's law, which then goes into driving the speaker. again, the plug going back and forth glued to a what? a paper cone, and the paper cone vibrates the same way, mm, and you get music.

so next time you look at your tape recorder, honey, what's underlying all of that? it's emi, what are talking about? electromagnetic induction. ain't that neat? now i got one question to leave you with-- i got two questions. number one was, how do this thing, foom, fly off? what's the basis of that electromagnetic levitation? and the other question is, is when i crank this generator, it's harder to turn when it's lit up and easier to turn when it's not. right now, i'm turning only against friction. but when i hook it in, it becomes part of the circuit, it really is more difficult to turn. hc, how come? think about that. it's physics, all right? yeah.