 So, here's the tutorial. First of all, for those who aren't here, I forgot to hit record at the very, very beginning, and I apologize. But I told the people that are here, questions that I like from the review, find out who was at the tutorial and ask them which questions that I said I like, and you'll have a very good idea of what you're going to see on the written section. I'll also try and repeat myself during this tutorial. Now let's begin. Yes. Is there a using principle physics question on the test? Yes, one. Yeah, one on the written, and then one multiple choice kind of conceptual one where I give you one of the many, many, many equations that we've dealt with, and I say something like, if you tripled the charge and doubled the radius, what would happen to the blah, blah, blah, blah, blah? Okay, something along those lines. We've done those before. Oh, it's seven times stronger. No, it's five times weaker. We know it's three times stronger. We've done those before. I'm trying to be very, very vague on purpose, but something like that, certainly. Okay. Electric field diagrams I've already said. Are there any from the review that you would like me to go over? This is your chance to ask. Savannah, what number? Number, I'm sorry, 20? 28 or 20? Okay, sorry. I'm looking into, I found a wireless adapter for my projector. The problem with sitting here is the fan goes right there. Whenever it talks in this area, it's coming through the fan turbulence, and that's why I can't hear also in that area. So I think I'll be able to wander the room next year and teach from wherever I want to. That'll be way cool. Yes, I'm doing an F12 tutorial then, but you can certainly come in still. Number, 20. Great question. I think I like this question. Certainly part A. I did say I like this question. Okay. Savannah, what do they want me to find? Seems to me that I can't use force times distance because what would be happening to the force as I'm moving closer and closer changing? So I have to use my other definition. We said that work was the change in potential and the change in kinetic. But have they mentioned speeds here at all? Let's assume it end and begin at rest. Okay. And Savannah, what's changing anything? Now, energy, scalar or vector? Am I putting in the signs, the pluses and minuses or not? Yes, scalars, signs. And we said this. It's K, Q1, Q2 all over our final, there's my final potential, minus K, Q1, Q2 over our initial. Now an electron is negative and this charge is negative. So when I go negative times negative, you know what I'm going to get over here? Positive. So if you wanted to, you could skip typing that part in on your calculator. It's really, really up to you. Okay. Had you got this far already? Okay. So I'm just going to show you my answer key just for this part because I suspect you're wondering probably about part B and part C. So I carefully plugged in the numbers. Initial, final distance was one meter. You got the initial distance is 1.5 meters, not 0.5 meters, 1.5 meters away. And I got 7.2 times 10 to negative 15 minus 4.8 times 10 to negative 15. I got how much work? 2.4 times 10 to negative 15 joules. Okay. I think what you're wondering about is part B. So let's look at part B. What is the potential difference between point X and point Y? You remember what I said for the answer? It was 2.5 times 2.4 times 10 to negative 15 joules. What is the potential difference between point X and point Y? Well, that's going to be the voltage. What mathematical operation does difference suggest? Yeah. I'm going to subtract the two voltages. Okay. It's going to be K big cube over R final minus K big cube over R initial. Now, right about now, I'm also thinking, no, wait a minute, they made this two marks. Is there another way that I could figure out the voltage? Because that's a lot of typing for two marks. So I paused here. The first time I wrote this and I went, hey, wait a minute. We just figured out the work. We just figured out the change in potential energy. Didn't we also say that the change in potential energy was equal to, right? That's not blatantly on your formula sheet. I think it's in disguise. I think voltage is described as energy per Coulomb. Is that, I think, something like that? Yeah. So I quickly rewrote it. Now here's why that's nice. Do I know how much work? Yeah. Do I know the little tiny charge that we're moving? Oh, this is going to be way nicer. Let's see if that gets us there. Apparently, the potential difference is going to be 2.4 times 10 to the negative 15 divided by 1.6 times 10 to the negative 19. Now, although voltage is a scalar, what I've sort of said is when I'm using the QV equation, I don't put in the negatives and positives. And I can't give you a great explanation as to why, except I know you just don't. Hey, let's see if that works. It'd be great if it did. 2.4 times 10 to the negative 15 divided by 1.6 times 10 to the negative 19. 15,000 volts. First of all, it looks like such a nice answer. Such a voltage answer, because a lot of our voltages were in the thousands. Is it 15,000? Is that the answer it says at the back? All right, Mr. Dewick, you got your answer key right there. Shut up. Okay, fine. So the first time that I did this, I did it the long way, and that's still on my answer key, but I just thought of that today going, wait a minute, for two marks, that's way too much work. I did get 15,000. Now, I wrote plus or minus 15,000 volts. The reason is it depends which direction you're traveling. Are you going from Y or going to X? It just said between X and Y. It didn't say moving from X to Y. No, a lot of them take plus or minus. Is there a part C? No? Okay. That is your question, okay? So I actually gave you a better way, I think, to do that. I might change. Well, no, I'm not going to change my answer key because that works just fine, but this is nice because I got the same answer. What did I get 15,000 volts? I get the same answer two different ways. To me, that second one is a little more elegant. Yeah, sure. Number seven, yo. Yeah, would you like to see the numbers? Q1 is the electron. That's the little tiny one that I'm moving. Q2 is the big charge. No? Oh, the top parts are yeah. Yeah, so on my calculator, I would type this in first. You have a graphing calculator, right? I did that, and then I just went second function, enter. I put the drop the minus down, and I just changed the one to 1.5. Same thing as we did in the last unit in the gravitational homework, assuming you did the homework. Those graphing calculators are so handy. In this unit and the previous unit, because those are about the longest equations you'll be typing in all year. It just saves you time. Sorry, Pat, number seven? Got you. Did I already say I like number seven or not? I did. So those you are listening to this tutorial, apparently I really like number seven. Oh, absolutely. Lutely. So those you are listening to this tutorial, here is a question you're going to see on your test. I'm going to give you two points and a location either somewhere between the two points or maybe over here, and I'm going to ask you to find either the electric field or the electric potential or both. No, potential difference is one charge, not two charges. So, Pat, you asked this question. What's another word for electric potential? Voltage, not energy. Repeat that again for those you are listening at home. Voltage, not energy. So, voltage. Point charges. Can you go to your formula sheet and can you figure out what the voltage for point charges is for me, Pat? So I think we're going to have the voltage from charge one is going to be Q1R1. It's going to be nine times ten to the ninth. Seven point five times ten to the negative six. Voltage, I put in the sign, so positive all over. What's its distance from P, so don't say point two, sorry, point three five. There's a common mistake kids would make. They would just plug in the numbers, right? And when you do that, you get one point nine three times ten to the fifth, well, nineteen thousand three hundred. Okay. The voltage from charge two is going to be KQ2 over R2. It's going to be nine times ten to the ninth. Pat, voltage, scalar or vector? I heard both answers convince me. By the way, I can't remember if I did this with your class. I thought of this later on. If you look at the formula sheet, the block are you Pat, block C? I did this last day with either block B or block C. I can't remember which ones. We noticed that if you look at the formula sheet, all of the vectors are in a row and all of the scalars are in the same row. If you're looking for yet one more way to keep that, and I think you all do know that energy is a scalar. You've got that one down, Pat, since physics 11. So signs here, no signs here. We decide by either using like charges, repel or by which way would a positive charge want to move that could for electric field. Here, it kind of depends but usually not. Usually no signs. So back to my question, Pat, voltage, scalar or vector? What do I just show you an easy way to remember on your formula sheet if you can move your calculator and look at your formula sheet? Yeah. So voltage, scalar or vector? Scalar, put the negative in. You're going to be doing better tomorrow though, right? I hope so too. Okay, and you've given them directions and they don't have any. They do have negative and positive but not directions. You get negative, what you get is a magnitude. The total voltage, the electric potential, what they're really saying is the total voltage. Now this is not the potential difference. Potential difference is between two locations, final minus initial. Here, they've given us one location. They want the total voltage. When I say total, what mathematical operation does that imply? Adding. So if you add them up, where do I get for an answer? Oh, you can even see in my notes here. I wrote, not energy, voltage. 4.3 times 10 to the fourth, 193,000 plus negative 150,000. 4.3 times 10 to the fourth volts. You see the slight difference between potential total and potential difference to locations and voltage, which is sort of both. Any others? Yeah. Oh, I was just in there. Okay. By the way, those who did the rewrite on circular motion, I emailed the scores out last night at about 1040. Did better. Everyone did better but one person. Some people did quite better. One person got perfect on the rewrite. 18. Did I say I like number 18? Okay. I might. I didn't give you everyone. Okay. I do like number 18 sort of on the multiple choice. I'm going to give you charges that aren't in a nice line with each other. Probably not. Not probably. Definitely not as I've written. Okay. What are they asking me to find a number 18 Savannah? Scalar or vector? That's actually way easier. You see, if this was a vector, if they were wanting, for example, electric field, which is fair game as the multiple choice question, I'd have to add them tip to tail and do some trig Pythagoras. By the way, for electric field or for forces, we'll always keep them nice 90 degree angles. But they only want the electric potential. This question here, because voltage is a scalar, it's exactly the same as the one we just did with power. I'm going to go the voltage from charge one. I'm going to go the voltage from charge two and then the total is going to be the voltage from charge one plus the voltage from charge two. That's the beauty of voltage being a scalar is it doesn't care whether that charge is there or right there mathematically because it's a scalar, same diff. Okay. Not for electric field vector, not for force vector, but for energy and for voltage. Yep. Does that make sense? I'll show you my quick work just in case. So they want the total voltage, voltage one plus voltage two, who cares about direction? Voltage is a scalar. Both were positive, so I did put the positives in because scalar positive, but didn't make a difference because positive times positive is positive. If they put a negative there, Savannah, I would have had just like in the last question, one negative voltage, I would have ended up with a smaller answer. That's fine. That's why voltage is so nice. It's a tricky concept, but mathematically, it's nice. No trig, no nothing. Just conceptually, it's tricky. And yeah, potential, potential difference, voltage, what do they do? I can't change the vocabulary. Yep. Did I say I liked 12? I did. Go so those. Oh, okay. What are we finding then, Dylan? Electric field, vector or scalar? And can you think of a nice easy way I can tell by looking at my formula sheet, Pat? How do you know? Top row, okay? Because also, what's the first thing in the top row? You know forces of vector. I'm hoping you got that memorized this year, right? Because it's 11, right? And in the, pardon me? Well, just humor me. And in the bottom row, what's the first thing? Energy. I'm hoping you got energy as a scalar. So now you got, the middle one is the weird ones for plates and things, so we don't quite freak out as much. Okay. Here's something to do this. This is sending out an electric field as is this. So I'm going to find the electric field from charge one. I'm going to find the electric field from charge two. And then I'm going to add them vectorially because they do have direction. What is the equation for electric field from a point charge? So hints. Point charge, you're looking probably for a Q in the equation, right? And whenever we're talking about point charges, what other letter always appears in the equation? Have you noticed? Okay? Yeah, R. So find something that's got a Q and R. And what's the symbol for electric field? Do you reform the sheet in front of you? Okay. I'll give you a hint also because it's a vector. You should be looking top row. So E1 is going to be KQ1 over R1 squared. 9 times 10 to the ninth, 7.5 times 10 to the negative 6, 0.2 squared. Times 10 to the ninth times 7.5 times 10 to the negative 6 divided by 0.2 squared. And I get 1, 6, 8, 7, 500. Is that big? No, electric fields were in the thousands and tens of thousands and hundreds of thousands. Okay. And that's a pretty good size charge. Let me make sure I type this in right though. That looks 7.5 to the negative 6. So 1, 6, 8, 7, 500. 1, 6, 8, 7, 500. What are the units for electric field doing? You can find out from the formula sheet by looking at the middle of the top row. See the middle equation in the top row? What does it say? Read it to me. E stands for electric field equals what? Okay. Don't read me the letters. Read me the units. What's F measured in? What's Q measured in? Oh, you're telling me it's Newton's per coulomb. Do you see how that's hidden in there? Okay. Direction. We ignore this charge temporarily. We say if we were a tiny positive, positive, positive test charge right there, which way would we want to move if we could because of that guy? East, right, whatever you want to call it. I usually go right and left, unless I put a compass on the question. Okay. Second one. It's going to be 9 times 10 to the 9. Charge to electric field, scalar or vector. So sign or not. Yeah, Pat. This isn't here. Okay. To find electric field, we use what we called the fancy word was the principle of superposition and what that really meant is pretend the second charge isn't there. Just look at the first charge. It would be pushing to the right. Okay. Because your test charge is always a positive, but a really, really small one. How small, so small it doesn't have its own electric field because that would change the question. It's imaginary. All over 0.2 squared. Nice thing Dylan on my calculator. I can just go a second function entered. Was it 2.5? It was, wasn't it? Yeah. 562,500. Again, Pat, pretending this charge isn't there temporarily, sitting right here based on that charge, which way would a positive charge want to move it could? Oh. Oh, by the way, the units are new. These are in the same direction. So you know what Dylan? I'll just add them together. If they were in opposite directions, bigger minus smaller and the bigger direction is the winner. Okay. And on the multiple choice, I wouldn't feel bad having a point there, having one charge here. So you have to the right and up, and then you would have to add them tip to tail and do some lovely trig to get the final electric field. That's a great multiple choice fair game question, but it'll always be a nice right angle Pythagoras trig. So it's not going to be sin log cosine log. Okay. There are a couple like that in the review. You're looking terrified. It tells me how far in the review you've gotten so far. Anyways, we're not done yet. Let me finish this question off. It's going to be 1, 6, 8, 7, 500 plus 5, 6, 2, 500 plus 1, 6, 8, 7, 500. The total electric field here is 2.25 times 10 to the 1, 2, 3, 4, 5, 6 units Dylan. And I'm not done because it didn't say, what does it say in brackets here? It was want me to find and oh, which direction? Now asking your question. What was your question? I think so. Oh, that's your final answer is right there. What number was that? 12? There you go. Okay. There's a very, very, very, very, very, very, very, very, very good chance that you'll see that in the future. Okay. 27. Ooh, someone's actually done the homework. Number seven. Number 12. You're number three, Mr. do it. Number 27, I like. I don't know yet if I like, I like, I mean, I'm just happy to see somebody ask that part. Let's see. Ah, good question. This is very, this is a nice build to the one that Dylan just asked. Dylan had them in a nice straight line. Are these ones in a nice straight line with each other? So this is going to be a little trig. Oh, but you notice it didn't ask for the direction. It just wants the, so we don't have to find theta. Okay. I've seen them do one or the other. Rarely have I seen them do both on the provincial. In fact, often what I've seen them do is if they, if they want to do a direction thing, they'll just make it rough. They'll have four arrows to pick from and say which arrow best matches the direction. One arrow would go that way, one that way, one that way, and one that way. Okay. That would, that, that I've seen them do. Make this a little smaller. There we go. Okay. Temporarily ignore that charge. What direction is this electric field exerting right there? Down. Temporarily ignore this charge. We're going to end up adding those two together tip to tail. And we're going to have something like this. That plus that. And then the resultant will be right there. And I'll use Pythagoras. Okay. What will the numbers be? The number for this one is going to be k q1 over r1 squared. The number for this one is going to be k q2 over r2 squared. The nice thing is, I think in this question here, it's a, oh, sorry. This question's a little bit tougher even. You know why? They didn't give me this charge here. What did they give me instead? They gave me this side. They've told me the electric field. How big is the electric field when I add them tip to tail? They've told me. How big is my net electric field? 5,000. Okay. If I crunch this one here, I'll do it really quickly. It's going to be 9 times 10 to the ninth times 4 times 10 to the negative 6 divided by 3 squared, 4,000. Yeah. As a matter of fact, I think it's going to be the 3,4,5 triangle, which we've run into a few times. I think it's going to be 3,000. Okay. So the mystery electric field here is 3,000. That's not what we want is our answer. They don't want the electric field. They want the charge. So here's what I know. 3,000 equals k q2 over r2 squared. They want q2. Angela, how would I get q2 by itself? Times by r2 squared and divide by, okay. I'm also kind of leaning towards, because it looks like they picked these numbers really carefully. Since a 4 was right there and it showed up there, I wouldn't be shocked if B is the answer with a 3 there and a 3, but I don't know. I'd have to crunch the numbers. That would be my panic guess with, Mr. Dewick just said I have 30 seconds left. That would be my intelligent guess that I would try and do in the pinch, right? Is it B? I don't even know. Whatever was that? 27? Yeah, it is B. Okay. Pardon me? Why would I have needed to? Oh, no. You were away for some of this. My bad. Why were you away again? Oh, the key. For vacations, I can't extend test deadlines. It just becomes too awkward for illnesses. Any others? While we're on the topic, look up. Talking about stuff not in nice right angles. Another twist that I've seen is a force where you have a charge here, charge here, charge here. This charge exerts a force down. This charge exerts a force right. What's your overall net force? Add those together, tip to tail. I don't think I've ever seen them ask for magnitude and direction. I've seen them ask for direction or I've seen them ask for magnitude, but never both. But that would be a nice twist as well. You'd need the extra charge here because force requires two charges and two charges. What else have I seen? I mean, 28 is good, but we've done some electric potential ones. I think I said I'd like to number 30 anyways, even though it's a multiple choice, that'd be a good written question too. Again, make sure you can handle an electric field diagram and translate it, something like number 33. Sure. So electric field lines, they're symbols of the electric field, they're representations. The arrows tell you the direction of the electric field. Since electric field always points from positive to negative, that right away tells you that this must be a negative charge because the arrow is pointing towards it. This must be a negative charge. In fact, what we have here are like charges, which is why the electric fields are being repelled from each other. Compare that with electric field between unlike charges. I think I had one earlier near the beginning up right there. This would be the electric field between unlike charges because what you're saying is if a charge, if the force line was right here, it would get pulled towards, it would want to go towards the negative. We decide electric field direction in two ways. Which way would a positive charge want to move if it could? I use that for complicated diagrams or from positive to negative, I use that when there's parallel plates or electric field diagram of that. We also said the number of lines roughly is proportional to the strength of the charge. This charge here has one, two, three, four, five, six lines coming off of it. This has six lines coming onto it. Those two charges are the same polarity, same magnitude. If this charge had 12 lines and this had six lines, I would say this charge is twice as big as that. I don't know what they are, but I know this one twice as big as that. This notion of field lines also didn't become huge and important when we look at magnetic fields. In fact, I think you guys in science in grade nine or ten do the iron shavings around a magnet experiment where you can actually see the field lines quite nicely. That's a nice little experiment. I bought one of those a three-dimensional one that I hope to bring out when we do magnetic fields. We'll play with that. We bought it about three weeks ago, so I don't even know if it works yet. I think it does. Any others? Yeah, 39? That's fine. I'll throw this online. I'll try and find, I'll try and email out this. Well, I may email this out. You guys have watched and written. I didn't do that much today anyway. It's an easier unit. I think I like number 39 a variation on it. I won't say I like this exactly, exactly, but I have some strong affection for the concepts here. I like to think of them as kind of a younger something. What we have here then is this electron has kinetic energy. When it gets here, this is positive. Is it going to speed up or slow down? Since I have changing speed and changing distance, I'm solving this with conservation of energy. Are any of these zero? I think once it totally travels through the voltage, it will have used up all of its potential energy. It will have fallen down to the ground, essentially. It's the same concept except gravity now aside. They want the impact speed. Let's see. We're going to have a half mv initial squared plus now potential energy between parallel plates. That's the middle row. Can you get me the energy by itself in that middle row there, please? That's voltage in electric field. That's not energy. I know it's an E, but there's no P next to it. Don't get E and EP next up, please. In fact, this is the equation that I told you. This is where I write the big V with the wings because this is where I have big V voltage, little V velocity. I know my handwriting, my capital letters don't look very different from a lower case, so I added the wings out of physics prof teaching that trick. Do the masses cancel? No, because there's no mass in here. In fact, I think what I would start to do is I would probably crunch these numbers, get an answer, and then divide by a half m. Which mass? They didn't give me a mass here. They didn't need to. Why? Oh, are you saying that's not my formula sheet? Okay. And they didn't give me a charge here. Why? Electron. They did give me an initial velocity so I can find final velocity. So, Jimmy, let me just go to my answer key then. I'll walk you through the rest of it. My other hint to use energy, you'll notice I drew an arrow pointing to the word speed on the provincial towards the end of the year. I always look for the difference between velocity and speed. If they say the word speed, usually that's deliberate. Usually they want me to take a scalar approach, which is energies. Oh, look at that. I didn't actually crunch the numbers. I divided by one half and by the mass of an electron to get the final squared by itself. But there is my charge on electron. What voltage difference are we traveling through? 250. Again, be prepared for a diagram, or maybe that's 500, and that's 1,000. That's still a voltage increase of 500, so you might have to do a little bit of math. Not always, but sometimes I throw that in. A half m v squared. Please, please, please, please don't forget the squares. And then divide by a half m. That gives you v final squared. Savannah, what do I have to do at the end? Yeah, and here's how I know. Light speed is 3 times 10 to the 8th. Electrons don't go faster than light. Nothing does. 1.2 times 10 to the 7th meter per second. Nice little question. Any others? 26? Oh, cathode ray. Were you here for the cathode ray tube lesson? Were you here for lesson? You missed one day, I thought, didn't you? So the way a cathode ray tube works, the way a cathode ray tube works is you have an accelerating voltage right here. This is really, really, really, really, really negative. This is positive, and you put a very tiny hole right there. What that does is that gets an electron coming out very fast in an almost a straight line. Then you have a deflecting voltage, maybe where this is negative and this is positive. That would deflect the electron downwards because it would want to go towards the positive. Or you could reverse the current, which is what they do in real life on alternating current. They flip the current back and forth. So some electrons will be deflected up. Some electrons will get deflected down. What would cause the greatest deflection? Well, first of all, if I make this voltage here stronger, that would give you a bigger deflection here. And if I make this voltage here weaker, because if this is weaker, it's traveling slower. That means it's between the plates for longer. It'll get deflected more. If this is stronger, it's going through the plates so fast it hardly gets deflected at all. If it's slower, it gets deflected more. Does that make sense? Okay. We're actually going to revisit the cathode ray tube because I actually, initially they ran it with plates, but they really run it with solenoids and magnetic fields. So we'll come back to it two units from now and do it properly. And that's when I'll give you cathode ray tube questions on your test. I don't think that there is a cathode ray tube question on this test. Or if there is, it's only one multiple choice question. I'd go look at the test, but my screen recorder is going and I don't want the people at home to see a copy of the test suddenly. Somewhere Leo's going, oh, I thought he went for sure. Any others? Okay. Work through the review. You'll find no surprises on the written. You'll find two or three curveball surprises on the multiple choice where you'll be, oh, I did this question, but he's making me go backwards. Okay. I knew how to find the force. Now he wants me to figure out the ray, oh, get the r by itself, get the radius by itself. Or, oh, I know how to find the electric field. Now he wants me to find one of the missing charges. Okay. Otherwise, it's a pretty good test. Usually people do, if they keep the equations straight, which is really the only risk, they do pretty good. It's fairly plug-and-tug-ish. Okay. I'm going to hit stop.