 So questions from the homework from lesson 5 lesson 7 first thing I would have checked is hey Is there anywhere where they told me two things or total current? No, no I'm gonna have to rewrite this as one single solitary resistor Okay, I Said this here by the way, this is probably tougher than would be considered fair game just letting you know Or if this did make it on to a provincial It would be like a multiple choice the nasty one that year I Look Freddy that are in series first these two are in series This is a 12 ohm resistor Is that okay? I'm gonna combine these two because they're in parallel. I'm gonna say 1 over r parallel Equals 1 over 6 plus 1 over 12 1 over 6 plus 1 over 12 Take the result of 4, okay So if I temporarily we redraw this number 7 I have a battery I Have a 10 ohm I have a 5 ohm I have a 2 ohm I have a 2 ohm There and there but this whole monstrosity here is the same as a single 4 ohm resistor Is that okay so far Sally and what I like is can you see these three are in series now? 2 plus 4 plus 2 you know what I can replace this with a single solitary 8 ohm resistor Here's the advantage of doing this on the tablet. I can go new and it's way easier to do my scratch diagram 8 ohm resistor oh And you know what I might not even need to do all this because I didn't read the question Sally I didn't even notice it says three amps goes through the six ohm. How many amps goes through here three? How many volts goes through here? 18 You know what I don't think I need to redraw all this that was silly of me because this is one single 12 ohm resistor Okay, can I start here and end up here going through this or both of these? These together have to lose 12 volts These together have to lose 12 volts and these together are a single 12 ohm resistor What's the current flowing through this resistor then? Loud are you right one amp which means if I got three amps and I got one amp How many amps are going through this to ohm resistor? 18 what's 18? Oh the eight. I'm sorry not 12 volts. Good gosh. Mr. Dewick. Thank you 18 volts I'm tempted to restart the video lesson and change it but I'll leave that in because I make mistakes just like you guys do and I learned from them just like you guys do Usually my mistakes are of the dumb variety, which is why I've told you it's the toughest stage to get out of is Not tripping on our brain. Sorry 18 volts 12 ohms. How many amps are flowing through this little branch here? One point five. Okay One point five amps and what that means is I got three amps going here I got one point five amps going here when they join together. How many amps are flowing through this resistor? 4.5 with me so far kiddo. Oh And you know what? How many amps are flowing through this resistor if they break up into three and one point five? It's got to be four point five amps flowing through there, too. Oh Which means I know the voltage in both of these as well if I go I times are you know what the voltage drop is How's that help? Well, look look look look look if we start here and End here if we go through these three hills. How many volts do we lose? 36 That must mean if I go through this one hill I also better lose 36 because we're leaving and meeting together the skiers can go this way or This way this has to be 36 volts Which tells me what the current is in this particular resistor 36 divided by five 7.2 oh Which look look look 7.2 amps going this way and 4.5 amps going this way What's the current when they all join together? 11.6, so I think there's 11.6 amps flowing through this overall circuit. Oh oh, oh now I know the Voltage drop here, too. If you go I times are 11.7 amps not 11.6 that makes more sense to me. I was going I'm getting a two and a seven I'm getting a two and a five seven eleven point seven or you could just talk louder anyways That's okay sally in a nice loud voice. What's the voltage drop through here? 117 So you know what this was all a big waste of time because I didn't read the stupid question my fault Start at the battery. How high is this battery? I don't know let's walk through a ski run There's one ski run that gets me to the bottom of the battery How many volts do I lose going through here? 117 how many volts do I lose going through here? 36 how high must the chairlift be if I'm losing a hundred and seventeen and a hundred and thirty six It's got to be a hundred fifty-three volts That makes sense after I thoroughly botched that explanation, but hopefully I recovered at the end there This is why that whole if you know two You know three things that also helps the diagrams fall apart because then you can start hopscotching your way along and along and along and along Is that all right any others we're good so today is more of the same Except we're going to at one point also ask. Hey, what if you got more than one battery like most of your electronic devices? So less than six voltage difference Let's talk about how your electronic devices work If you look at most electronic devices for example those you that have a graphing calculator Take the battery case off right now and take a quick peek Are your batteries in series or in parallel are your batteries in series or in parallel in your graphing calculators? They're in parallel. They're in parallel in series is when you have the batteries touching end-to-end We're going to talk about what the difference is they both have their advantages and they both have their disadvantages So if we were to connect to one point five Volt cells in series what would be the net voltage as recorded by the voltmeter? Well, let's go back to our ski hill analogy if you go up a one point five Volt high chairlift and then you get off it and you go on another one point five volt high chairlift What's your net voltage three three? Explain your answer using principles of physics Excuse me explain your answer using principles of physics. Well, um Just makes sense at my chairlift analogy. I'm not going to give you a big fancy explanation Now here's what I do want you to notice. What's my overall resistance in this circuit? What does it say? 10 ohms With three volts What's my current? You don't need to go to a calculator to go three divided by ten. Please God. You don't need to what's my current? Exactly to one decimal place, please Okay point three amps What if it had been one point five volts? What if it had been one point five volts there? How many amps would it be? Okay, the advantage with series is you step up the voltage The disadvantage is you drain the batteries twice as fast Twice the current and current is electronic gears. You drain the batteries twice as fast But it's a way for you in a small electronic device Dylan to get a much much higher voltage So what's an electronic device that's almost always in series a flashlight? Right put the batteries in a flashlight. They're always touching end-to-end. Are they not? So what you're doing there is you're stepping up the voltage. You're getting a bigger current getting a brighter bulb Drain the battery way faster way faster The advantage with parallel is you split the current say in your graphing calculators four ways You don't get as high a voltage, but your graphing calculators don't need a high voltage But those batteries last a long time. I've got one at home that I haven't put the batteries in for four years I don't use it all that often. I use it when I'm marking But it's been going pretty good so and Many a portable appliances CD players is another one Portable CD players who had the LK fine. These were typed about seven years ago fair enough But flashlights which are still around I hope for the most part two or four batteries are used in series as in the diagram above in Series the effect increases the total voltage The problem is that each cell now has twice or four times as much current flowing through it as it would otherwise It dramatically decreases the length of the of the battery lasting the life of the battery What would the effect be of connecting the cells in parallel? Well, what we're really saying is Some skiers can go this way Some skiers can go this way, but how high are they when they get to the top of the chair lifts it? 1.5 here you don't increase the voltage what you do is Because really and now my ski hill analogy breaks down the source of the skiers is the chairlift You're splitting the source of the skiers up That means the chair lifts will last twice as long now. Here's a question How could I figure out? The net overall voltage well, I would actually put my voltmeter Right there because that voltage has to match that one and it has to match that one because skiers can go through this this path and end up back where they started from and they can go through This path and end up back where they started from So this would be odd to measure the voltage across the battery. You could actually measure it across the resistance Now we're near the battery Then we have the idea of a rechargeable battery a rechargeable battery is charged by connecting them to a cell That forces current back through the cell if we connect a 1.5 volt battery To a six volt charger then What would be the direction of the current and what would be the net voltage? What do you think would make sense if you have six volts going this way? And 1.5 volts going that way. What do you think the net voltage would read? 4.5 I guess in my ski hill analogy what we're really saying is they go up this chairlift but this chairlift is taking people down the mountain a little ways and The stronger cell would force the current in the stronger direction. So the current would be This way we have to have a protective resistor because we don't want to have a short circuit Current would be counterclockwise and the net voltage would be 4.5 volts So if the net voltage would be 4.5 volts and the net resistance is 10 ohms What's the current flowing through this and you could calculate it, right? For I think point point four five or four point point four five point four five amps What if you didn't have that resistor there? You'd have an current approaching it but it would get very hot to be a short circuit not good things would melt So you put a small Protective resistor there you don't want to put a big resistor because then this would heat up and you're not using the energy to charge The battery up they're gonna take longer to charge the battery up But this is how a battery recharge your works now You have to have a chemical inside your rechargeable battery that is capable of having the chemical reaction Reversed to set it back to normal So you can't just stick any battery into a rechargeable. I don't think anything or it might get warm Okay, there you go You're sending a current through but because the current that's going through you're isn't doing any work All that's happening is the energy gonna go somewhere heat in terms of our ski hill analogy Cells in series are like two chairlifts Cells in parallel like example to turn the page are like two chairlift chairlifts Both of which lead to the top of the mountain Megan you go up that chairlift. I'll go up this chairlift They're both gonna end this off at the same spot opposite cells Are like one up chairlift followed by one down chairlift And so by properly labeling the circuit we can easily find the difference in voltage at various points Principles to keep in mind positive means higher negative means lower and Current flows downhill from positive to negative Positive to negative when you're going through a resistance means you're losing voltage Negative to positive when you're going through a resistance means you're gaining voltage And I have a lovely foxtrot comic there. You can read it yourself. Let's look at example four Example four says find the voltage difference between points a and d and Then it's gonna say graph the voltage on the grid provided. I think we're gonna pass on the graph We're just gonna find the voltage difference. So the first thing I want to check is did they tell me total current? Look at you. They did. Oh, then this is probably gonna fall apart Did they tell me total voltage? Do I know all of the chairlift or lifts? Yeah, okay So first of all Ryan how many amps are going through this resistor? Careful point seven How about here Point seven how about here Point seven. Oh, I know two. I know four. I'm really interested in voltage though How many volts are going through this resistor? I times are oh? We're losing seven volts going through that resistor So what would the voltage measure right here? 38 how many yeah, sorry oh Point seven volts I times are let's try that again. Thank you point seven volts. Thank you captain. Obvious. Good gosh, mr. Do it thank you gourd. So Actually would measure 44.3 right there. How many volts do I lose going through this one four times seven is 28? Is it 28? 28 so if I'm starting out 45 volts high How many volts must I lose going through here if that's my last chance to lose the voltage and get back to the bottom? sorry 16.3 How big is our? 23 point 23.3 says graph the voltage on the grid provided It's nerdy cool, but I'm not that interested in the graph right now, so I'm gonna skip it an Example five says in the previous example. What is the resistor are we figured that out already? We said it was 23.3. Let's go to example six. Okay? Here's a nastier one two batteries Which battery is bigger? Six I'm pretty sure it's the winning current so where it says current direction Current is going that way Right here current is moving to the right Right here current is moving to the right Now this four volt is also pushing current up But this point five amps is it going to be moving to the left? No, no because this is the winning battery the current is moving to the right The current is moving downhill The current is moving to the left Now some current must be going up because we have point five amps up But I'm also positive that some of the current heads that way Jordan you see how we kind of reasoned our way towards it by the way this way tougher than you on the provincial So if you follow all that now Did they tell me total current anywhere? Nope Did they tell me anywhere with two things? Oh? Yeah, okay. Let's see what we got here. What's the current in this three ohm resistor? Gotta be point five What's the voltage drop in this three ohm resistor? 1.5 is that right? So we lose 1.5 volts We gain four volts Excuse me as I cough here So if we're four volts and I go through this resistor And I go through here losing 1.5 and that gets me to the bottom of the chairlift Let me draw that path just so you can see if I follow that path for high Lose 1.5. How many must I lose over here? 2.5. How does that help me? Well, if I walk this ski hill I Can also get to ground level. Can I not? How many volts did I lose in this resistor? 2.5 how many had I better lose because this is the only other ski how we ski down how many must I lose over here? Gotta be 3.5 volts. I Have to lose 3.5 volts. Oh, do I know two? I know three how many amps must be going through this section of the circuit? One amp. Hey, let's follow it. Let's follow it. I got one amp here. I got point five amps here Okay, the current direction is going this way. You know how many amps are going through this resistor? 1.5. Do I know two? I know three. What's this resistor? 1.6 repeating yeah 1.67 ohms Let's see I know all three here. I know all three here. I know all three here Oh, I think I I found everything they wanted me to find it. Did I not? It says find the unknown currents and voltages using Kirchhoff's laws. I think we did. Oh, and then it says note The complete analysis of this two-cell and parallel circuit is beyond the level of physics 12 But the voltage and currents we can certainly handle extra batteries. Excuse me Homework number one number Two sure three is good. Sure four is good pretty quick actually Five is nice so ask yourself What happens to the voltage in this five ohm resistor when we close the switch? These are the kind of using principles of physics right to explain questions and especially they love stuff like number six Where they say if every bulb is identical what happens to the brightness of the bulbs now Here's what I would do to solve number six. You can do it algebraically You can do it Kirchhoff's laws nerdy or probably what I would do since they're all identical bulbs I would make them all a nice resistance Maybe 10 Actually probably to Make that to make that to make that to you know the voltage you should be able to find the total current You should actually be able to solve this whole circuit and then go vi vi vi Remember when they say brightness what they really mean Sally is power Seven sure eight is good nine. Have I given so far one two three four five six seven eight nine? Okay Sure a ten and eleven. I think I signed all of them. Sorry hadn't looked at them for a while. Those are all pretty good