 there's the magic. Number four, I think for number four I'm gonna do kind of a little rough sketch of a circuit as well here so as I read this I said I got a 12 volt cell and I guess it has an internal resistance because they're talking about the terminal voltage and they've told me that the terminal voltage here is 8.8 volts and this battery is 12 volts so if the voltage after we come off the chairlift battery after we go through the internal resistance will bump is 8.8. Madison what must the voltage be that we lose going through there if the chairlift is 12 but we're really only 8.8 high 2.2 yes 3.2 3.2 that's what I said you weren't listening very closely clearly you need to work on your listening skills yeah 3.2 volts clearly one of the things I'm gonna find in this video is just how many mistakes I make in the day and try and cover up we're nearly double digits right now wow I'd say it was nerves but really the kids know it's just normal oh and how much current is going through this resistor well it says that 70 amps of current is going through this whole thing so there is 70 amps of current going through this resistor that okay do you know two then you know four or three in this case because they want the internal resistance so the resistance is going to be this divided by that by the way 70 amps big or small 70 amps large or small yeah large enough to kill you okay five amps large enough to kill you you know what this is great as a short circuit and this battery would probably drain very very fast and get uncomfortably warm and break that okay Madison any others okay what I'm gonna try and do today is get through about half of a lesson of the next unit and the next unit I have to admit is quite a fun one but I'm going to take a risk especially in this class I'm going to hand out a I was gonna say a possible distraction but I saw my guests starting to smile instead of possible distraction definite distraction and trust that you'll be able to deal with it the next unit we're looking at is on magnetism so I've handed out magnets we're gonna see if you can deal with the distraction I have confidence that most of you well some of you if you can okay and today is mostly going to be terminology and what we're really gonna be focusing on today is direction is vectors so lesson one do me a favor and arrange the magnets that I gave you in a nice straight line so that it sort of looks like this bar magnet put them all together okay what do we know about magnets well magnets are dipolar that's the fancy way for saying they have two poles what are the two poles called north and south all magnets have a north pole and the south pole so here's my bar magnet north and south and if you put your magnets in a straight line although you don't know which end is north and which end is south they do behave very much like a single bar magnet and just like in electricity Cody in electricity like charges repelled and unlike charges attracted in magnets like poles repel and opposite poles attract a north repels a north a north attracts a south however unlike electric charges you cannot isolate a magnetic pole we can isolate a charge that we called a negative charge and electron we called one positive charge proton but if you took a magnet and you broke it in half and I'll do a jagged line like this to symbolize that we've taken that bar magnet that was right above that had a north pole right there and the south pole right there you don't get a north only magnet and the south only magnet in fact as soon as you snap the magnet in half this ends up being the south pole of this magnet and this ends up being the north pole of that magnet it's sort of like if you ever a kid and played with earthworms when you pulled the earthworms in half you got two worms here you get two magnets as far as I know we don't know how to isolate a magnetic pole yeah now I did my little rant about action at a distance with Alex and with Malcolm I said oh by the way take your magnet and split it roughly in half the chain and then take one of those halves and rotate it 180 degrees and you should have like poles repelling I think yes now I can't tell you whether it's north north or south south we'll talk about how you could figure that out in a bit but definitely like for it pulls repell unlike poles attract and that's part of what fascinates us as well it's funny as soon as I've said that there's kind of you that have two little finger things that are kind of twirling around each other because you're repelling each other it's fine Victoria what is it that causes them to repel how can they touch each other without touching each other well just like charges had electric field lines Carly magnets send out magnetic field lines they send out an invisible octopus tentacle like series of magnetic field lines hey review time what was the direction for electric field how did we figure out the direction we asked ourselves a question Cody which way would a positive want to move it could so it was just defined that way we said that's already fine here is how we define the direction of a magnetic field the direction of a magnetic field is always always from north to south you'll need to memorize that although Malcolm that's a fairly easy one I think to memorize in that kind of bits from north to south or if you're actually trying to figure out what the specific poles of your magnets are we have a tool called a compass in terms of a compass a compass always points in the direction of the magnetic field a compass always points in the direction of the magnetic field that means a compass always points south say what Mr. Duke a compass always points magnetics out well no mr. Duke I have a compass and it points north it points geographical north many of you don't realize that the poles are named wrong at the bottom of your page right here draw a little circle this is the earth the earth is magnetic I'm gonna draw an imaginary bar magnet inside the earth and I'll tilt it about 23 degrees just like the earth axial tilt as it turns out Madison inside the earth that's the south magnetic pole that's the north magnetic pole despite the fact that that's the geographical north pole up it's the south magnetic pole how do I know because the compass always points in the direction of the magnetic field a compass points from now north to south and my compass points that way that way that way that's something a lot of students don't realize they made me wrong that's what the inside of the earth looks like this your maps look like silly you vote for me as world president someday maybe I'll change it boy that would not make people happy suddenly we were the true south strong and free probably wouldn't go over too well although maybe we'd all feel warmer cuz we lived in the south that would mean birds would fly north for the winter it would mean that me as being left-handed would be a northpaw okay enough little Doppler effect there but he got it what's the symbol for magnetic field well we can't use the letter m because what does m stand for in physics pretty much always mass so maybe we could use a field we could use letter oh where letter f stand for and those are pretty important concepts so thankfully fortunately not all physics is done in English I think the magnetic field letter comes from a word from Latin the letter that we use the symbol that we use for magnetic field is a capital letter B in fact often Cody you'll hear me just call it a B field because B is easier to say than magnetic so when you see the letter B in an equation they're talking about the magnetic field the same way as E stood for electric field and we measure magnetic field it has its own special units magnetic field is measured in Teslas named after a scientist whose last name was Tesla arguably Nicholas Tesla Nikolai Tesla can't remember with Nikolai Nicholas arguably Tesla understood electricity better than anyone before or since certainly better than anyone before and you can make an argument he lived around the turn of the century you can make an argument that even today people don't understand electricity as well as he just lived and breathed it oh symbol capital T but you will also find magnetic fields or magnets measured in Gauss which is an American Imperial unit just like gallons and feet and inches but the SI standard science unit for magnetic field is Tesla's just to give you some idea Gary of numbers the Earth's magnetic field which is what pulls a compass is about 10 to the negative 7 Tesla's a very large magnetic field to the point where if you were exposed to it for a long time it would not be healthy only 50 Tesla's fact the magnetic field is about a thousand Tesla's probably the iron hemoglobin in your blood which carries oxygen to your organs would not be able to go in the same directions that it wanted to consistently you'd probably be having some fairly serious health issues yes we all heard that so there are two main types of magnets the kind that you have are permanent magnets they're made from what are called ferromagnetic materials in fact these ones are called rare earth magnets they're made from the cool millit I can't remember the particular element and they're pretty good they have their uses they're fun to play with and they're great for refrigerators your refrigerator magnets are permanent magnets far far far more useful are electromagnets electromagnets are magnets that are caused by a current and Amrit the reason that's so useful is it gives us a magnet that we can turn on and turn off big deal huge deal huge deal most of your electronic devices contain an electromagnet or several we use them all the time to move things around via electricity so we've talked about magnetic field what do the magnetic field lines look like similar to electric field lines they have arrows and Leslie the arrow points or shows the direction of the magnetic field the closer the lines the stronger the magnetic field the farther apart the lines are the weaker the magnetic field as you can see magnetic field lines run from what to what north to south because that's the direction of the magnetic field this is also the direction that a compass would point if you placed it in the diagram in other words Carly if you had a compass that was pointing this way don't write this down and you placed it right there it would suddenly swivel and point in the same direction as a magnetic field a compass right there with point this way a compass right here with point this way and so it's a very a compass very easy tool for you to figure out which way the magnetic field lines Hannah I should mention one more thing magnetic field lines have no beginning and no ending they actually continue going through this material and back out the other side I was used to say they're circular but they're not shaped like a circle they're non-ending oval-ish kind of shapey things whatever the earth is also a magnet which is how a compass works at the North Pole what does the magnet inside the earth look like so that's the North Pole and that's the South Pole because a compass points from north to south and I wrote here yep it's the opposite of what most people think example one draw in the magnetic field lines below so when you pull the part your little magnet chain and spun at a hundred degrees and we're repelling them I think that's what we have here the two North Poles will repel each other in fact if you had a magnetic field line it would start going this way but it would get repelled by this North Pole and it would very quickly start to bend and what's it gonna get attracted to South Pole and probably like this and probably like this and probably like this oh over on this other magnet probably like this and like this and like this and like this Cody how many lines does the left-hand magnet have how many lines does the right-hand magnet have that does that mean the magnetic field of the right-hand one is eight Teslas and the magnetic field left to one is for Tesla's know but it does mean the magnetic field of the right-hand one is twice as strong as two to one ratio. Excuse me. So, more terminology. We are going to have to draw three-dimensional diagrams for us to be successful in this unit. And so, so that our diagrams are a bit more legible. Well, how would I show something going up the page? Turn the page, by the way, if you haven't already. How would I show something going up the page? Victoria, Why would I show something going down the page? While I would point an arrow going. What if I wanted to show something going to the right? I would draw an arrow pointing to the. What if I wanted to show something going to the left? I would draw an arrow pointing to the What if I wanted to show that it was going straight into the page? Here is the notation we've come up with. If you want to show that something is going into the page, we draw a circle and then we put an X like like that and Madison that is supposed to represent the tail feathers of an arrow going away from you into the page and that can represent either a magnetic field or later on the current or something going into the page. To show that something is coming out of the page towards me we draw a circle with a little dot that's the tip of an arrow coming out of the page towards you you'll need to know those conventions we're gonna use them all the time right let's look at magnetic fields caused by electricity or electromagnets the first one if you have a wire you put a current through it and pier and Faraday and a bunch of other scientists noticed that if you take a wire and you put a compass by it the compass gets deflected but would deflect the compass a magnetic field so here's my imaginary great big wire right here if you ran a current through this wire to your right to my left that way it would generate a magnetic field it would deflect a compass and what we want to ask ourselves is what direction and to figure out the direction we use what are called the right hand rules there's three of them and they involve your right hand so get your right hands out and put your pencils out of your right hand because often the pencils get in the way here is the first one I want to figure out what direction the magnetic field is around this wire which way did I say the current was flowing I point my thumb in the direction of the current right thumb my fingers curl in the direction of the magnetic field so in this instance here on the side of the wire closest to you guys which way is the magnetic field down which way is the magnetic field underneath the wire towards me away from you which way is the magnetic field on the side of the wire closest to me straight up and which way is the magnetic field above the wire towards you away from me that's the right hand rule the right hand rule says if you want to figure out the direction of the magnetic field created by a current point the thumb of your right hand in the direction of the current your fingers curl in the direction of the magnetic field let's try one together Leslie once you're done yawning I know I'm fighting it to it's muggy it's warm it's last block let's deal with it oh now this time I gave you the wire what does that X mean which is which way is the current flowing inside this wire what does this symbol here mean I'm gonna say more specific yeah that's the phrase we're gonna use so all of you right now so that all of our papers look the same lift your paper up so it's 90 degrees please I want it to be parallel to the big screen behind me so I knew I would face this diagram take your right thumb pointed into the page which way to your fingers curl that's the direction of the magnetic field around that wire it seems to me right here above the wire which way is the magnetic field up down left or right right here above the wire which way is the magnetic field up down left or right point your thumbs into the page right now and tell me which way is the magnetic field at the top of the page up down left or right is it not that way which way is the magnetic field right here up down left or right down Which way is the magnetic field right here? Which way is the magnetic field right here? In fact, probably if I wanted to show this, I would just draw a circle, a better circle than that, Mr. Doeck. I would just draw a circle, and I would put the arrows on it. It's a clockwise magnetic field. And then there would be another one here, a little weaker, a little weaker, a little weaker, and eventually close enough to zero that you can't detect it. Example three. In example three, I've given you a wire, but I don't know whether the current is flowing to the left or to the right. Which way is this magnetic field above the wire? Ah! Got you now. Sorry, they're used to it. You guys with me? You're back? You're here? Oh, that's on video. I thought for- am I gonna- you know, you need it. I gotta get you back. Leslie's got her adrenaline rush now. Let's try this again. No zoning out. You're my top kids. I expect more. Which way is this magnetic field? What does that symbol there mean? Cody. Cody's on a roll. Cody's on a roll. Come on. Take the challenge here. Cody, which way is the magnetic field underneath this wire? So let's- all of us lift our paper up 90 degrees. You guys hopefully recovered from a little yelling. Sorry. Whatever works, right? I'm going to then curl my fingers, Cody, so that they're coming out of the page above my thumb. And into the page below myself. Which way is my thumb pointing to the left or to the right? Right to the right is correct. We need to practice a few more of these. I can't draw these to save my life. Those diagrams there, and I cheated and used my tablet to just hand write, took me ages, so I have got several for us to try. All right. Take a look at this, please. We're going to try a few of these. And the first one I'd like you to turn to, if you would be so kind, is question number six, please. These are the type of multiple choice questions that are on the provincial. So I'll throw a few of these at you on your test. Number six, Amrit, that's the one that comes after number five. Find it? I don't think I've seen you- there we go. I knew we'd get you there. Number six. So in number six, it says, which of the following diagrams best illustrates the magnetic field lines around a wire carrying conventional current in the direction above? Okay. So it looks like the wire in all four diagrams is carrying current in which direction? Which way is the current flowing in all four of those diagrams? What does that their symbol mean? Out of the page towards us? So all of you right now, with your paper flat, put your thumbs down pointing straight up, your right thumbs. There's the current coming out of the page towards you. Well, which way is the magnetic field? Which way are your fingers curling? What's the correct answer here? A, B, C, or D? Justin, A. By the way, a couple of comments. Every year I see students that try and do the right hand rule while holding onto their pen and the number of times I've seen them think this is the, because it's got the pointy part and go the wrong direction, strongly advise you that secondly, and I learned this from my physics prof, who was a great physics prof. And I will assume he knew what he was talking about. Here's how you can get the right hand rule questions wrong. Do them embarrassed, all tucked in here and all like that. You'll get them wrong. He used to yell at us and get us to stick our hands up and the reason is it needs to be in front of you so you have perspective so that you can see what's going on. When you guys are writing the test or if you are writing the provincial, I will know you're not giving each other secret code hand signals and I'll make sure whoever's supervising the provincial exam knows you're not trying to cheat or anything like that. You're back here, you with me? Okay. That was number six. Can you all also try question number, I know there's one more here, 14. Try number 14 on your own right now using the right hand rule for a current carrying wire. You're probably going to have to sort of pencil down because, wait, trust me, easier with an open hand. By the way, those of you that are left hand, this is the only time in your whole life you have an advantage because you can write and right hand rule at the same time. As a lefty, as far as I know, that's the only advantage in life. And for that, I get a six year shorter lifespan. Lefties on average live six years less. Oh yeah, it's a harsh world for a southpaw. A, B, C, or D. What do you think? Sorry, I heard an answer. Oh, maybe I didn't. A, and it says A, convince me. Yeah, now you've already found the tricky, but the problem is going to be, they're going to give you a three dimensional diagram, which is kind of slanty. And so you're really going to have to use your imagination a little bit. Sorry, we're stuck with two dimensional paper, three dimensional diagrams. So I think A, current coming this way, my fingers pearl that way. Or if I face my diagram here, it looks like this A. Is there one more? I think, oh yes. Last one, 17. 17, number 17, try 17 on your own. So if you find number 17, it says, which diagram shows the magnetic field created near a conductor carrying current towards the right? So each wire is going to the right. Which of those magnetic field diagrams best matches? Kelvin, which one? See, let's see. So if I point my thumb this way over the top of the wire, I'm coming out towards me. Is that correct? And underneath, I'm going in. What's the symbol for going out towards me? What's the answer, Kelvin? D, yeah, yeah. D, these are tricky. But unfortunately, about half your test is going to be direction questions. And this is only the first of three right hand rules. OK, back to our notes. Little note, sometimes instead of telling you which way the current, the positive charges are moving, sometimes Justin will tell you which way the negative electrons are moving. Some teachers will say, OK, but the electrons use your left hand. Hannah, I find that confusing. I don't want to have to use more than one rule. Instead, the second option is whichever way the electron is moving, the positive is moving in the opposite direction. In other words, electrons going up is the same as current going which way down. Electrons traveling to the left is the same as current going which way to the right. Electrons going into the page is the same as current going which way out of the page. And then you can use your right hand rule. So I prefer the second method, solenoids. So a new term. If you take a piece of wire and you wrap it over and over and over and over and over several hundred times, going in the same direction, not changing direction suddenly, going in the same direction, you wrap a coil of wire around an object called a solenoid. We call it a solenoid. Here's one. So here's a manufactured solenoid. It's a coil of wires. It's also wrapped in plastic to help it keep from rusting. Pass it around if you wish. That particular solenoid that you're passing around, it's a hollow solenoid. We'll talk later on about why you might want one not to be hollow. And as it turns out, if one wire generates a magnetic field, a coil of wires will also generate a pretty big magnetic field. What direction? Put the magnets and the pencils down and look up. Here is right hand rule number two. This is called the right hand solenoid rule. So we had the right hand rule for a current carrying wire. Here is the right hand solenoid rule. And to do this, you have to analyze the diagram just a little bit. Hannah, which way is the current going out of this battery? Is the current going up this way or down this way? Up. I draw a little arrow right there. And I follow that arrow through my diagram. I notice that my current goes underneath the solenoid. And when it comes over the top, it's heading to the left. It's heading to the left. It's heading to the left. It's heading to the left. It's heading to the left. Write those arrows on there. So you have to analyze your diagram just a tiny bit. And once you've analyzed it, here is the right hand solenoid rule. You imagine you're holding the solenoid in your right hand. Here's my imaginary solenoid. And you curl your fingers in the direction of the current in my diagram. When it comes over the top, which way is the current moving left or right? In my diagram, when it comes over the top, which way is the current moving left or right? So I can't hold it this way. I have to curl my fingers this way. If you do that, Hannah, your thumb points north. You know where the north pole of your diagram right there is? Top or bottom? Bottom. Bottom. That's north. That's south. OK. That's a typical solenoid. Now, the one that's being passed around is a hollow solenoid. As it turns out, you can dramatically increase the strength of the magnetic field by instead of making the solenoid hollow, putting an iron core in the middle and it'll increase it by a lot by an awful lot. We call this an electromagnet and it has thousands and thousands and thousands of uses. What are some of the uses? Well, first of all, let's practice the direction. So here is a write up of the right hand solenoid rule. If you imagine holding the solenoid in your hand, you curl your right fingers in the direction of the current. Your thumb points north. Example four. Now, it says what direction is the magnetic field below? And I left this diagram blank on purpose because I always think it's important to teach you how to draw your own solenoid because that helps you to analyze them. So here's what we're going to do. We're going to put a battery right here and then we're going to have the wire, the current to the solenoid going like this and ducking underneath behind the solenoid. And then I'd like you to put your pencil down. What I want to do, Greg, is I want to create a roughly three dimensional looking diagram and you know me. I have absolutely no artistic talent, but this is what my physics prof taught me. He said, if you want to create a reasonably three dimensional looking diagram so that you can figure out what's the top and what's the bottom. He drew this. He said, the wire is going to pop out here to make it look 3D. He used elongated S's like this. Does that look sort of 3D-ish? Kind of. Sort of from Mr. Do it gets about as good as it's going to get. There's my solenoid. If you just do straight lines, you can't tell which way the current is going to be going. Using long S's, either forward S's or backwards S's, it doesn't matter. I use forward S's. Hannah, that's about as good a diagram as you're ever going to get from me. You guys have had me long enough to know. Yeah. So here's my question now. Let's see if we can figure out which way the current is going from the battery. Which way is the current going, Eric, to the left or to the right? Did you say to the right? No, actually, you said this. So loudly with confidence because you are correct, sir. Give it to me. To the right. Yes. And then, Eric, as I follow it, it ducks underneath. I think it comes out here. I think right now it's heading downwards when it comes over the top. Is that right? It's heading downwards. It's heading downwards. It's heading downwards. I'll quickly add those arrows without hopefully making too many mistakes. That's going to tell me how I want to hold this solenoid. I want to hold this solenoid in my hand so that my fingers curl in the same direction as the current, which side is north, left or right? Put your pens down and try this one. I don't know. Let's see. Regulously. Which way is the current coming over the top downwards? So hold your hand like this. That make sense? Which way is your thumb pointing? Here's the north pole. Here's the south pole. In fact, we could even draw in magnetic field lines. Magnetic field lines always point from what to what? Remember? What do we say? North to south. So here's a good magnetic field line. And here's another one. Which way would a compass point right here? Which way would a compass point right there? Give you a hint. Same direction as the magnetic field. Which way would the compass point right there? More specific, how about to the left? Which way to compass point right here? Outside the solenoid, a compass with point to the left to the left. But Malcolm, we said magnetic field lines have no beginning and no ending. If I continue, which way would a compass point inside the solenoid, not to the left? Which way to the right? So if they ask you a compass question, make very sure you know where the compass is. Outside or inside? We use solenoids all over the place. A solenoid is a magnet that you can turn on or off using electricity. How many of you have powered door locks in your car or your parents car? OK, when you flip that switch, all that's happening is the solenoid is getting turned on and the magnet is pulling the lock down. Then when you push the switch in the other direction, all they're doing is reversing the current in the solenoid. And now instead of attracting, you know what it does? Repel, the fire alarm bells are an old school solenoid. All that happens now in the fire alarm, it's alternating current. What that means, Kelvin, is the magnetic field goes north and south, the north and south, the north and south. Then they're very, very fast. There's a piece of metal right next to the bell. The magnet attracts it, repels it, ding attracts it, repels it, ding attracts it, repels it, ding. There's your fire alarm. In fact, how many of you have a cell phone with a vibrator in it? That's a solenoid, I guarantee it, just going like that back and forth. Simple, simple. When the Xbox control or the PlayStation controller shakes, it's a solenoid in there. Actually, I think the PlayStation, it's spinning an electric motor, which involves a solenoid that's other electric device we'll be looking at at this unit. Loudspeakers, televisions, cell phones, powered door locks, the old, the old telephones that actually used to ring any kind of a bell that would ring. It's a solenoid, very easy to set up, very easy to set up. In fact, I think my friend lives in downtown Vancouver in a very old building. The building is about 70 years old and nerd that I am. I was in his building and here is the fire alarm in his building. Can you see the coil of wires right there? There it is. And it pulls this back and forth, reversing and alternating the current, causing the clapper to ring the bell. Beautiful. No big moving parts, nothing complicated, works just fine. And then, yes, I was a nerd enough to absolutely have to take a picture of that when I saw that. Oh, cool. And, yes, they need someone to clean up the cobwebs or something. Yeah, well, can you once again get out this right hand rule sheet? Let's practice a couple of solenoid questions. Number nine, number nine. So here's a picture of a solenoid, a little sketch says a DC power supply is connected. It wants the direction of the magnetic field inside the solenoid, and it wants which is going to be the North Pole. Before we do any of that, Leslie, we're going to need to label the current from this battery, Leslie, which way is the current going left or right? Now it ducks underneath Leslie. When it comes out over the top is the current heading upwards or downwards. You think the current's going this way? Which one convinced me? Let's see. Here's the current. It ducks behind and underneath. Follow this wire. I think you'd be doing this, yes. I'm going to change colors instead of black so it stands out of it. I think the current is doing that. So. Pretend to hold the solenoid in your hand, in your right hand. Curl your fingers in the same direction as the current. Can't be curling over the top towards you. It's like this, yes. Leslie, my angel, which way is your thumb pointing? Which is the North Pole X or Y? Which way is your thumb pointing? So which is the North Pole with authority? Yes, yes, no, yes, no, North, South. Now, that means that this magnetic field line, Carly, is going to go from North to South. But inside, so out here, it's going to point to the right. But inside the solenoid, which way is that magnetic field line going to point to the left? From what letter to what letter? From Y to X. No, no, yes, yes. And now I step back. What is the correct answer to this? A, B, C or D? Kelvin, C, right hand rule for solenoids. I think there's one more solenoid question on this I seem to recall. Or is there? Did I miss it? Maybe I did. That'd be terrible. There isn't one. Back to our notes. We're going to skip temporarily, well, permanently. Example five. Example six, try this one on your own. Which end is North A or B? Try it on your own, please. A or B, B is North, right? Curling over the top towards me. B is North. I can sense that you're kind of zoning on me. I'm going to pause here. I'll carry on with some of this on Thursday of next week. Because what's tomorrow? Tomorrow is your test. What's your homework? Your homework right now is to study for the test. It's about 10 minutes left in class. It's a chance for you to work on the review. I'm going to right click and hit.