 So, quiz one. Given the following point configuration, first thing it says is find the electrical force between the two charges. Okay, electrical force is K Q1 Q2 over R squared. It's going to be 9 times 10 to the 9th force F for force vector or scalar force vector or scalar. It's a vector. Am I going to put the negative in for this charge or not? No, we decide the direction, although it only asked for the magnitude. I am going to say, oh, by the way, what would the directions be? Are they repellent? Well, are they repelling or attracting each other? Attracting. Okay, so I'm going to put 5 times 10 to the negative 6. There's my micro-cool-ohms. 3 times 10 to the negative 6. There's my micro-cool-ohms divided by, you got to be careful. It looks like the radius is 2.35. Is that right? Squared. 1.5 plus 0.85 is 2.35. That's the total distance between them. 9 times 10 to the 9th. 5 times 10 to the negative 6 times 3 times 10 to the negative 6 divided by 2.35 squared. I type that in right. Looks good. You get 2.4 times 10 to the negative 2. 2.44. Newtons. In terms of part marks, I'd probably give a half mark for that. Half mark for that. One mark for the answer. No, you could also have gone 0.0244. Yes, but make sure you're 2 or 3 sig figs. If you went, oh, wait a minute. Yeah, I'm right. I thought for a minute there, that 4 should be a 5, but no, that 4 would be a 5 and ground it up to there. What else can I do with this same diagram? So one thing I can do with 2-point charges and I can say, hey, find the force between them. Another thing that I can do is I can give you a location somewhere, often halfway between them, but in this case, not halfway between them, where I say to you, find the net electric field or the total electric field. Now, electric field, I'm going to find the electric field from charge 1, which is going to be KQ1 over R1 squared. It's going to be 9 times 10 to the ninth, 5 times 10 to the negative 6. I don't put a negative in for fields either. Forces and fields, forget the signs, divided by the distance to A from charge 1 is 1.5 squared. I'm going to be a bit lazy and I'm just going to go like this. Delete, delete, delete, delete. And then what did I say it was? 1.5 squared, 20,000 N per C. Direction. Which way would a positive charge want to move if it could? Because of this guy, left to right. Then I'm going to find the electric field from charge 2 and that's going to be 9 times 10 to the ninth, 3 times 10 to the negative 6, all over 0.85 squared, 3 times 10 to the negative 6, 0.85 squared. Enter. And I get 37,370 N per C. Direction. Which way would a positive charge want to move if it could? Because of this guy. Also left. So this is left plus left. Am I going to go bigger minus smaller this time? Nope, they're both in the same direction. Final answer is going to be this, plus 20,000. Yes, I could have done that in my head, but some of you would be scared if I didn't show you how to do it on your calculator. And I get 57,370 or 5.74 times 10 to the fourth, nuptons per coulomb left. How would I mark this? I would give you a half mark if I saw that. I would give you a half mark if I saw that. I would give you a half mark for the correct magnitude and a half mark for the correct direction, but if you were missing the units you'd lose a half mark. By the way, what's another way to measure electric field? Not only is it nuptons per coulomb, but what else did we learn last day? It's also volts per meter. I'd take either of those units. What if there was a third charge over here? Oh, you'd find that third electric field and then add or subtract depending on the direction. What if there was a charge at an angle up here? Now that I will not give you as a written. I have seen it occasionally as a nasty multiple choice. Then you had to draw vectors and add them tip to tail. But almost always they made it a nice 90 degree right angle. So it was nice Sokotoa tree. See, find the electric potential at location A. What's another word for electric potential? Voltage. I think they want me to find the voltage at location A. Now the voltage is going to be a combination of the voltage from charge one and the voltage from charge two. Voltage from charge one, which is KQ over R is going to be nine times 10 to the ninth. What was charge one? Oh, voltage scalar or vector. Scalar put the sign in negative five times 10 to the negative six all over 1.5. The voltage at location A from charge one is put a negative right there and delete the squared, right? Negative 30,000 volts direction. Random what? It's a scalar. Then I'm going to find the voltage from charge two, which is going to be KQ2 over R2, which is going to be nine times 10 to the ninth. Positive three times 10 to the negative six all over 0.85. I think all I need to do is delete the squared. I knew I typed in most of that for electric field somewhere along the way, and I get 31,764.7, which I'll write down, 31,764.7 volts. What's the total voltage? Add them up. The voltage at A is plus negative 30,000. 1,764.7, 1.76 times 10 to the third volts. How would I mark this? Yeah. How would I mark this? I would give you a half mark for that. I would give you a half mark for that, and then I would give you one whole mark for adding them together. Now, if you missed the negative, if you told me the answer was 61,764, I'd probably give you 1.5, but I'd be frowning. Yes. Except here's the problem with that. That only works with a constant electric field between parallel plates. The issue here is the voltage and the field are changing every single millimeter that you move. Did you get the same answer? I don't think you did. Say it again. Oh, sorry. We calculated the electric field in part A, so you went electric field times 1.5 plus electric field times 0.85. Actually, that will work in this case. I would accept that. That's the tricky part. You would have to then say, well, the voltage is negative because the charge is negative, and I guess you'd have to introduce it into the field somehow. The answer really is which way is the electric field pointing to the left? If you're traveling this way, which direction are you traveling then? If the field is to the left, you're traveling in a negative direction, your distance should technically be negative. If I really, really want to get fussy, I'm going to say that that's so tough to keep track of. Between point charges, I fall back on point charges. Good question, though. You caught me off guard for a second. I have to think. You caught me even more off guard than... Right. Number two, suppose we have a fixed charge of magnitude Q1, which is negative 8 micro coulombs. How much work would it take to move an electron from an extremely large distance away? Now, when they say an extremely large distance away, what do they really mean? Infinity, but we can't quite get to infinity. So, extremely large distance away to a final location, 0.15 meters removed. What's this question asking us to find? How much work? Now, in grade 11, work is force times distance, but I can't use that. Why not? Because the force is changing every time I move a millimeter, and this only works for a constant force. It was also the area under a force versus distance graph. Have they given me a graph here? Say no. It's also change in potential plus change in kinetic. Are they talking about speeds anywhere in this question? Then we're going to assume start and end at rest. Work is going to be potential energy final minus potential energy initial. Where am I starting for my initial? Because we defined relative to 0 at infinity. You know what? I think for four marks, now I have to make this realization, and I would give marks for seeing that, but for four marks, all I'm going to do is I'm going to find k q1 q2 over r final. It's going to be 9 times 10 to the 9, q1 negative 8 micro coulombs, q2 electron. What's the charge on electron? Did you say negative? I hope you did. Oh, why am I putting the negative in energy? Scalar put the signs in. Negative 1.6 times 10 to the negative 19 coulombs all divided by, and I guess my final radius, my final distance at 0.15. Okay, this isn't too bad. 9 times 10 to the 9 times. What's a negative times a negative? I'm not going to bother typing them. I'll just close. You get 7.68 times 10 to negative 14 joules of work. How would I give up part marks? Well, I'd give out one mark for the answer. I'd probably give you one mark for the equation, one mark if I saw that, and one mark if I saw that, I think. There's four. But if you got the right answer, you get full marks. Number three. Troy, what's number three asking me to find? Okay, now that they've introduced the notion of speed, have they mentioned work at all? Say no. I'm going to use conservation of energy. I'm going to say kinetic energy initial plus potential energy initial equals kinetic energy final plus potential energy final. And the nice thing here, Dylan, is because we're on the subatomic level, really not worried about heat. It's not going to make a difference, or not a significant difference. Why can I do that initially at rest? So this is going to be KQ1, Q2 over R initial equals one half MV final squared plus KQ1, Q2 over R final. I think I'm going to minus this to this side, crunch the numbers, and then I'll get the V squared by itself. So I'm going to write this as KQ1, Q2 all over R initial minus KQ1, Q2 all over R final, that equals a half MV final squared. 9 times 10 to the 9th, is that a plus sign on yours? I think it is, yes. So positive and positive. Oh, everything's going to be positive, which is kind of nice. 5.5 microcoulombs. Proton is 1.6 times 10 to the negative 19, all divided by my initial distance is not 2.5. What's my initial distance? 3.5 minus 9 times 10 to the 9th. 5.5 times 10 to the negative 6. 1.6 times 10 to the negative 19, all divided by R final. Oh, hang on. Is my initial X, am I moving, sorry. My initial is X. I was looking at this going, wait a minute. I think I'm starting at X and not, I'm moving away. So my initial is 1 and my final is going to be 3.5. Is that right? That equals a half MV final squared. 9 times 10 to the 9th times 5.5 times 10 to the negative 6 times 1.6 times 10 to negative 19 divided by 1. I know I don't need to type divided by 1, but I'm going to go second function, enter anyways. So I want that radius there. 7.92 times 7.92 minus. On the provincial, I don't think so. So I'm going to say on a test note in your homework or in a quiz, probably, but oh, I can't imagine you ever being lazy. 2.2629. This equals a half MV final squared. So it's going to be 7.92 times 10 to negative 15 minus that answer. I get 5.657. 5.655. What was it, Mr. Doe? 5.657 times 10 to the negative 15. That equals a half MV final squared. Here we go. The final is going to be, how would I move this one half over? Or times by 2, same as dividing by half. So I'm going to go 2 times 5.657 times 10 to the negative 15. How would I move the mass over? Divide. Hey, what is the mass of, what are we moving? A proton? What is the mass of a proton? Times 10 to negative what, Erin? And then to get the squared square root. This number times 2 divided by 1.67 times 10 to the negative 27. Enter. Square root. And do you get 2.6 times 10 to the 1, 2, 3, 4, 5, 6? People are nodding. Woo-hoo. How would I give up part marks there? Holy smokes, what was it worth? 4. I'd probably go something like this. Half mark for that. Half mark for that. One mark for that. That's up to 2. One mark for the answer. Oh heck, you know what? I'd probably give out one mark for each of those. One mark for that. One mark for that. There's your 4. So what's this quiz out of that I didn't put a total on? So can you go out of 14 and give yourself a nice clear score there? Please, my children. It's out of 14. Let's look at the homework from lesson 6. The homework was, for those of you who were away, one, two, three, four, five, six. And what we said was we can find the voltage between parallel, sorry, the electric field between parallel plates. It was the voltage divided by the distance between the plates. Now I should let you know. Let me see if I can find an example here. Desktop, physics 12, electrostatics, ultimate electrostatics review answers. Show me an example, Mr. Dewey. So if they ever want you to find the electric field or the voltage between the plates, because the equation is so simple, look up for a second. They'll always give you two distances. They'll tell you how far apart the plates are, which is what you want to use, but they'll almost always in the diagram tell you how long the plates are because it lets them make up more wrong multiple choice answers. And that's really the only good reason for doing it. So just don't fall for that. They will always put two distances on your question. The distance between the plates is what affects the strength of the electric field and the voltage. Having said that, any of you want me to go over? Now is your chance to ask? Yeah, number four. Okay, did you get number three? Okay, then I'm pretty sure that electric field is also the force divided by the charge that's from on the equation formula sheet. Yes, that means if I want to find the force that a charge experiences, it's going to be how big that charge is times the electric field that it's in. So if I'm going to do number four, there's how big the charge is 1.25 times 10 to the negative 3 times that answer. Okay? Oh, and is this charge positive or negative? So it will experience the force east. What if it was negative? West because electric field is which way would a positive want to move if it could? That'll be it. Is that okay? You really, this unit almost more than any other, you're going to be rearranging the basic formulas quite often and recognizing, look, each one of these is actually two or three equations in one. This one and then the other one we've done this for is the voltage energy one, last class already. Any other? Then if you haven't already, you want to hand in lesson five and lesson six and now we're going to look at lightning. So recall from last lesson, we defined the electric field between parallel plates and it also apparently does work, a list of between point charges but I'm not sure I would necessarily go that way. We defined it as the change in voltage divided by how big a distance you're traveling through and that explains why you had to have a negative distance on the quiz. Okay? Now an electron or an atom can be ionized which means it loses an electron if it's placed in a sufficiently large electric field. Why? Well, the force holding the electron in, so the force holding the electron in is k q1 q2 over r squared where q1 is the positives in the nucleus and q2 is this lonely little electron. What was the force from an electric field? What did I answer about 15 seconds ago e and d? Remember it's on your formula sheet, find the one that has and rewrite it to get the force by itself. Okay, the force from the field is q, the electron, times the strength of the electric field and if my electric field from an external source is big enough, Zach, this force will be bigger than this force and the electron will ionize. You'll lose an electron and now it's free. If we're talking about air because we said what does it take for a spark to occur? What does it take for electrons to jump a gap to leave the molecules that they're currently in and jump across to a new substance which is a mixture of nitrogen and oxygen plus other trace gases? It takes about three million volts per meter. It takes an electric field of about three million newtons per coulomb or volts per meter to produce ionization. Now that may seem like a lot, but remember when we were looking at charges of micro coulombs we were getting electric fields in the tens of thousands and hundreds of thousands. So an electric field of three million, not that big. In other words, if you're on a dry cold winter day and for example you're separating laundry and you hear that crackling noise as you pull it apart, that means the electric field right then was more than three million. It happens very easily. It's the shock that we get when we walk across a carpet on a cold winter day and then reach for a doorknob. And it's also what's occurring with lightning. If you have an electric field between the cloud and the earth of more than three million and again roughly three million, this other factors that play a role. On a damp day you need a bigger electric field because water is a polar molecule. It can absorb an extra electron very very nicely on its own. On a dry crisp cold winter day, well you guys have noticed that's when things are the most staticky. Any of you ever do a winter out in the prairies? Okay that's the ultimate. And wow this is so, in fact most houses have a humidifier, which we don't really care about here in the lower mainland because we're never wanting more water in the atmosphere. We never have a shortage of water in the atmosphere, but out in the prairies they will. Okay now chemistry, Evan, each of these effects is accompanied by light. That's what we actually call the spark. We notice it because of the light. The light occurs because the ionized electron doesn't remain free. It will quickly fall into orbit around a neighboring atom and when it does this some of its energy goes going to lose some energy, some of its energy is released as a photon. You don't need to know that part. That's just telling you, oh why is there light when there's a spark? That's why. Okay and you guys in chemo 12 you guys look at electron orbits and and the fact that it gives up a photon, right? A little bit or if you haven't I think you do. So lightning. You can think of a flat long cloud like a parallel plate roughly and the bottom of the cloud can get charged. It can get charged to let's say 2.5 times 10 to the 8 volts. How cosmic rays from space as they go through. They're hitting particles all the time and they're moving electrons around and they can separate electrons and so you'll have a separate voltage. You'll have the top of the cloud be positive. The bottom of the cloud be negative. You separated the charges. You generated a voltage. How close does the cloud need to be to the ground for a lightning bolt to occur if the air breaks down ionizes at about 3 million volts per meter? Okay the voltage is equal to sorry the voltage divided by the distance is equal to the electric field and remember I said last day that from now on because we're going to have equations that have v velocity and v voltage in them when I'm talking about voltage I'll almost always put wings on the capital V so you can tell it's a capital V. Let's get the distance by itself. The distance is going to be what voltage I think the d will move up and the e will move down yes voltage divided by electric field. If the clouds are higher than this it's unlikely that lightning will occur. If the clouds are lower than this you don't want to be there. What did we say the voltage was 2.5 times 10 to the 8th. What did we say the electric field was let's see 3 million volts per meter so three one two three one two three what do you get sorry 83.3 meters not that high of course it's very tough for us to tell how high clouds are because we it's one of the toughest distances to judge because we don't know how big clouds are right if you have included by now you figure out how far things are away by measuring with your eyes and your brain believe it or not the angle your eyes form from the top to the bottom looking at it and then saying I know how big it is up close I can do some trig in my head it's actually the tangent function and so I know how far away it is if it's the same size as I'm used to problem is we don't have big clouds are we don't so it's very tough to look up and say oh that's 100 meters away I'm safe or ooh that's 75 meters away I'm not safe and that's assuming your cloud has that voltage I just made that number up at rim but this is how lightning occurs if the clouds were closer than that now the real danger is what if the clouds were at 85 meters what's going to get them closer to the ground just slightly your height your height right and that's why people get hit by lightning we are unfortunately when we stand upright shaped very much like lightning rods yes Miguel there is an advantage to being short Kyle would die long before you did yes so where do you not want to be in the lightning storm bad because you're lowering the distance required for lightning to jump bad because the tree is lowering the distance required and it will then conduct the electricity through the ground and you'll pick up some after effects now probably in all honesty you would survive underneath the tree in that the lightning would almost certainly hit the tree and not you but it'll be much more likely to hit the tree than anywhere else and you'd then get the after effects as it then looked to go to the ground and since you're nearby you're gonna be getting a bunch of current going through you too boats are especially bad because sailboats have a lightning rod as their main component we don't worry about it too much here Brandon you gonna make it we don't worry about it too much here out east on the Atlantic especially in Florida if you ever look at sailing blogs you'll hear them talking about how they continually are watching the horizon for thunderheads and if you see thunder clouds you get out of the ocean as fast as you possibly can you don't mess around like you crank your engine doesn't matter how much gas you're wasting you floor it you drop everything we had a day plan to just you don't worry about get out because you're in a big lightning rod there's also all sorts of different i won't call them urban legends but not scientifically proven solution some people will say oh if you trail jumper cables from your mask into the water it'll ground it and it'll go through the jumper cables into the water i've seen some people swear by that i've seen some people say no that's garbage or they'll trail a little wire into the water you know what you know the energy involved in lightning is so off the scale it's ridiculous not worth trying if any of you've been in a prairie lightning storm yeah they're intense in fact i've been told during a very i haven't been in one i've been told during a nasty prairie lightning storm the lightning flashes are frequent enough you can almost read a newspaper at night because the image will stay in your eyes long enough for you to read a line and then there's another lightning flash and the image will stay in your eyes long enough for you to read a line and then there's another lightning flash i i love thunderstorms they don't scare me i they do you and they probably should scare me because of lots of energy but i like it yes oh yeah what why so much lightning on the prairies um would the prairie ground also be a parallel plate mountainous it means we'll see with mountainous areas and that's where we have our lightning is on the mountainous areas that's where it's close enough for the voltage to jump the gap to ionize the air yes yeah yeah yeah yeah and and and ships also especially the old sailing ships would have something called st. Elmo's fire which was actually a static effect because the masks were wood lightning but very very small amounts would be jumping as well yeah so a little bit about lightning there how i can't believe like being inside of it and actually seeing little sparks didn't seem as big as when i saw them in news at 12 it's just huge it looked like a fireworks display coming from the man marcia luffin says it happened in a split second but neither she nor her husband nor their three children knew up to a billion volts of electricity had struck their van as they traveled along the four wandering last night's storm the proof was caught on tape by someone traveling behind them his reaction was wow and he was like i think we were hit by lightning so i'm sure we were hit by lightning and i'm like okay and i said well now i think the car's dead like right away you just i couldn't hear then did anything but you just kind of found the car was just a little bit slower than the 40 i was doing so i'm like it's my fact that one lightning bolt six times hotter than the sun the only damage suffered by the eclan van was to the antenna virgin to the highest part of the car not a coincidence melted off and while it's hard to imagine that no one was actually heard environment canada officials say today no one has ever been killed by a lightning bolt while traveling in their car if i can buy my canada officials tell us the safest place you can be during a lack of a storm is in your car since it immediately grounds the electricity unless in the eclan kids say they'll pay back to their classmates feel like maybe you've got more energy today yeah yeah a little bit of static for your head yeah you need to keep the footage and show it to all your friends yeah yeah any lessons that you learned any safety tips um it's saying to um go somewhere rather because in the lightning bounce it off it has nothing to do with the tires that lightning just jumped several hundred meters believe me it can cover the remaining one foot to the ground despite the tires it's because your cars are a fair day cage and i talked about that earlier i believe and if not i'll talk about it a bit later michelle says the only thing that's really changed today is the fact that husband androids run a police officer's now earn himself the nickname sparky amongst his colleagues they also say the next time they're caught in an electrical storm on the road they'll simply pull over and according to environment Canada that's truly the safest thing you can do in oshawa with the eclan i'm alex pierce in for city polls i'm pretty sure in oshawa figure that's what she said slow motion lightning with a high-speed camera so you can see it doesn't follow a straight path but it's ionizing the air and finding a way to pass electrons through the nitrogen and through the oxygen and you can see the path that it follows this is a very very high speed camera by the way i think there's going to be one more here and so here it is again in slow motion there you saw it suddenly find the grounding follow that path we don't get anything out here resembling the lightning that they get out east on on muggy summer days like in the ontario and in the us we don't get anything like that here all depends if you're inside a car if you're in a faraday cage you're just fine uh there was one more i wanted to go with this was an unusual phenomenon so a photographer snapped this you managed to catch i suspect this is several different bolts not one circular bolt but our eyes are treating that as a circle because we don't realize it had several different bolts but interesting picture and i have more but i think later no i have uh airline getting hit by lightning no not the web page i got a different one oh there it is yeah i couldn't see that now that happens far more often than you think because what are planes made out of a lovely conducting material what are they shaped like sideways lightning parallel plates somewhat and they can roughly half the distance so the lightning if it can get to the plane and then charge the plane up and then jump to the ground so it's a way for it to somehow maybe get there easier happens very very often but because planes are solid metal they also act like a faraday cage they can handle an awful lot of lightning no problem in fact i'm willing to bet if you've flown more than two or three times you've been hit by lightning without realizing it and you guys have learned the old counting trick right five seconds to a mile yeah about two and a half miles sorry what oh most large skyscrapers have lightning rods built in oh yeah because they get hit all the time and so they have a nice very very conducting path that the lightning will follow down to the ground safely so that won't hit any of the civilians absolutely so ian recall that if the field is known we can find the force as follows f equals qe your question was a lovely segue okay rearranging that little equation there so what does that mean here's another question i like this question i like this question i like this question i like this question it says find the acceleration of an electron placed between metal plates that are separated by 2.5 centimeters and charged to 275 volts which way does this electron want to move up or down convince me up most definitely up okay let's see the electron is going to experience a force and that force is given by the size of the charge 1.6 times 10 to 19 times the electric field but what's another equation for force what was our first equation for force ma really what we're saying is this ma equals qe and i'm going to drop the vectors because we already decided up so if i want to get the acceleration it's going to be the charge times the electric field divided by the mass of the electron do i know the charge on an electron 1.6 times 10 to negative 19 negative yeah we're doing vectors acceleration so dips a negative do i know the mass of the electron that's also on your sheet is it not it's 9.11 i remember that 31 do i know the electric field no oh wait a minute this is parallel plates the electric field is the voltage divided by the distance from yesterday what's the change in voltage here 275 divided by what's the separation distance between the plates and don't say 2.5 it's not 0.25 0.025 can someone crunch that what's the electric field sorry 11,000 even and i don't worry about sig figs that's my not my final answer i'm going to plug this in over here the acceleration is going to be what was the charge on an electron 1.6 times 10 to the negative 19 what was the electric field 11,000 divided by what was the mass 9.11 times 10 to the negative 31 find yourself a huge a huge acceleration crunch it vector or scalar acceleration vectors forget the signs i decided the direction up right what you get it's it's big oh per second squared yes very large electron well yeah because we don't our eyes don't see electrons move they seem to be instant they're not but as far as we're concerned they are in a very famous experiment to measure the charge on the electron how the heck did they get that 1.6 times 10 to negative 19 well milik and a scientist he used parallel metal plates to hold in place a charged oil drop and he knew the mass of that oil drop very very very accurately the oil drop remained in place because gravity pulled it down the electric field pushed it out and he was carefully able to tune the electric field and the voltage because we can be very accurate with our voltage that's very easy to do with the electric circuitry and it even was in the 1900s already and he was able then to crunch the numbers and figure out what q had to be so the charged oil drop is at rest due to balanced gravity and electrical forces first of all what's the sign of the charge on the oil drop does this have to be negative or positive why are you right if it was positive which way would it want to move because of the electric field down which way does it want to move because of gravity down i'd have unbalanced forces so i know it's negative a negative b read a balanced force equation gravity equals electric force let's assume they did this experiment on the earth which means i don't need to use cosmic gravity i can use good old mg am i going to use for force k q 1 q 2 over r squared are there two charges in this question nope what's my other expression for force than my friend okay that that's how you know to fall back to that one by the way i don't have two charges oh no problem you have an electric field uh q oh i don't know the electric field wait a minute what's the electric field between parallel plates it's the change in voltage over how far apart they were so he carefully measured this distance he carefully calibrated the voltage until this was hovering he had measured the mass on a very accurate scale we knew g is 9.8 and that's how you found the 1.6 times 10 to negative 19 a little more complicated than that but not much so a particle of mass that and charge negative three electrons is held suspended what's the voltage required i think it's the same equation here get the v by itself v equals what get the v by itself here anyone get the v by itself here m times g times d divided by q yep the voltage is going to be the mass 2.3 times 10 to the negative 14 times g 9.8 times the distance 0.015 because it's centimeters divided by three electrons technically my friend because this is a scalar i should put a negative here but if this is zero i know this is positive what it's really saying is if you're moving in the direction of the electric field you would have a positive answer if you're moving in the opposite direction they forget it i know it's a positive voltage from the diagram so how many volts don't all rush for your calculators at once what do you get okay sorry 21,000 something anybody else yes Ian what was it give it to me in scientific notation please two point is that rounded off properly i thought you said 21,700 i don't okay so 2.1 times 10 to the fourth volts turn the page yo oh is that not the right answer okay when i say is that right and everyone nods it doesn't help me at all all right mr duke do it yourself 2.3 scientific notation negative 14 times 9.8 times 0.015 divided by i'm gonna have to go brackets here right three times 1.6 scientific notation negative 19 ladies and gentlemen i'm getting 7,043.75 which i agree with i think you forgot the three friend have a seat my friend i don't know what you're standing up for kiddo why no you want to fall asleep you're staying getting sleepy you want to keep it off to stay awake little advice for you ain't gonna do you any good keep dreaming what's your homework one i'm assuming all of you at least once have got a shock from a doorknob so how many volts were you getting kind of curious um two is good three is good six is good eight is good nine is good ignoring you for a second sorry but wait maybe you've noticed in in the old movies when it's time to zap the monster on the table and bring it to life they always use lightning i mean always and why what because lightning is electric it turns things on know exactly what lightning does is left to your imagination because in the end what makes life that's another mystery but interestingly i didn't know this it turns out that what makes lightning is also still a mystery in fact it's kind of a big mystery here's correspondent try to call it it's an elemental force of nature still one of the most mysterious lightning is very difficult to study i think we probably understand better how a star is sported halfway across the galaxy than how lightning propagates six miles up lightning strikes the earth four million times a day and after hundreds of years of scientific scrutiny we still do not understand the essential secret of how it begins inside the storm it's spinning out that's why professors Ken Egg and Richard Sonnenfeld and their team from New Mexico 10 are on a 10 000 foot mountain waiting for lightning to strike we're trying to find something new about thunderstorms and lightning that discovery i think is is worth the risk whatever causes lightning to start has always been hidden inside the clouds so unlocking that process requires waiting for the weather to reach maximum force than launching sensitive instruments into the heart of the storm it's hazardous and frustrating so we're trying to figure out what charges the clouds we think one of the explanations is cosmic rays traveling through the clouds but not sure yet dr martin human is the director of the international center for lightning testing and research in camp landing florida it's the brightest light that we see it's a loud noise that we hear the lightning on earth would be a nuclear weapon explosion but what triggers the release of all that power we know that lightning is a huge electric spark and sparks happen when positive and negative charges build up so much energy they leak through the air to get at each other it can only happen when the negative charge in that ball on the right and the positive charge in that metal rod on the left gets so overwhelmingly strong they cut a path through the air in the middle it's like a positive full pressure and it can't hold on anything that's what most scientists think is happening see the bottoms of thunder head parallel plate right happening inside thunderstorms as ice and water particles collide with each other moving electric charges to opposite ends of a cloud when the charge above when the charge below gets strong enough they leak through the air as a bolt of lightning except for one thing when you actually examine the storm cloud the strength of the positive and negative charges and the electric field around them isn't nearly enough to create that big spark well the problem is after decades and decades of measurements up in thunderstorms nobody has ever managed to find an electric field anywhere near that big Dr. Joe Dwyer is a professor at florida tech well maybe we're looking for something that doesn't exist maybe there's something wrong with our understanding about how discharges get started in places like thunderstorms so if thunderclouds even great big thunderclouds don't have electric fields big enough to generate the giant spark that lightning actually is where's all that energy coming from well here in florida they have a pretty dramatic way of trying to figure that out they launch rockets with really long wires attached to try to create that express lane to ground that lightning lights so much to get lightning from these clouds to strike where scientists can measure it requires a simple trigger first of all you need to have a propellant if you get this thing up there in a hurry i have to be able to go to 700 yards or so in about two seconds this is is it just copper wire kevlar covered copper wire okay so we load it connected electrically when we're about to fire switches are turned on here manually after that everything is done with air pressure from downstairs big ac 22 is armed three two one fire from 2000 feet up the wire triggers lightning with a path to ground higher than the empire state building and when it strikes over a hundred million bolts that the array of test equipment on the ground okay two four is good go ahead and fire 11 when ready 211 is armed three two one rockets are for the first time allowing physicists to experiment with lightning under repeatable and controllable conditions so that now joe dweyer and other researchers can test an alternate theory of how lightning starts that theory is called one-way breakdown using this model the energy field inside the store cloud that force between positive and negative two weeks to form a bolt of lightning is struck by outside particles first of electric which carry their own energy very high energy and with that added energy you can now get that big spark we went up with an avalanche of electrons moving near the speed of light now this model would work as long as you have one bad electron to start it off so the first the finger that pushes the first domino to get the whole thing started here's where things get really interesting joe dweyer and many other scientists believe that this outside energy force comes not from the clouds or anywhere else on earth for that matter but from cosmic rays tiny subatomic particles ejected from dying stars millions of years ago and billions of miles away but how do you test this theory we have ten of these detectors spread out over the facility right now well it turns out when cosmic particles hit the earth's atmosphere they leave a unique signature in the form of gamma and x-rays if scientists detect these x-rays they'll have the proof they need this is what's called sodium iodide detector there's a piece of crystalline here that will absorb x-rays and gamma rays and these things are not difficult to measure there that's where triggered lightning comes in for the first time the florida research centers rockets allowed dweyer to place his x-ray detectors in lightning's path he made his first series of measurements in 2002 a big negative voltage pulse that means we got a burst of x-rays in the detector yes i actually didn't think we're gonna see x-rays the first plot we brought out there was a nice little pulse that looked just like an x-ray right at the time of the lightning curtain that's that's interesting you know that's probably a coincidence you know what's the chance of that so we looked at the next lightning stroke and there was an even bigger pulse and the next one and the next one and everyone had these pulses that looked exactly like x-rays i think i just about fell out of my chair at that point every single lightning strike wire measured showed the presence of x-rays but ground measurements can't reach high enough to where lightning actually starts for that you need to get instruments right up into the heart of the storm we finally have technology to build these instruments they're small enough and rugged enough to handle the thunderstorm environment like it won't be enough i mean we see that three bursts and we call it quits on one event well that's that's not good enough and it's just going to take a lot of measurements to get in the right spot at the right time the balloon is sucked into the storm trailing its cardinal of instruments launches like these have finally traced x-rays all the way up to where lightning begins and given scientists the strongest evidence yet that lightning spark comes from forces outside the earth itself these cosmic graves may be the link which will connect a dying star thing i like about that is the science there the term esco physics you heard them talk about electric field and voltage and not getting a big enough electric field it seems so far to generate lightning what's going on so we're pretty sure it's cosmic rays that are causing lightning and come on one more if i don't overload my computer right click