 here's my circuitry tutorial from the big review package are there questions you would like me to go over go ahead yeah okay let me draw a circuit okay what's that okay and I'm gonna draw a fairly simple circuit I'm just gonna put in one big resistor here and I'm gonna make that resistor I don't know 15 ohms okay and I'm gonna temporarily do that I'm gonna add another resistor right here but we'll just scribble it on all right if I tell you that this has an emf of 30 volts what I'm really telling you because I haven't given you a built-in internal voltage I'm telling you the terminal voltage that's why I usually use the letter V there so if I wanted to find the current I would go what's my total voltage of this circuit what's my total resistance of this circuit amps okay now I'm gonna take this same circuit but I'm gonna break this battery apart I'm gonna show you the inside of the battery so I'm gonna have same battery same 15 ohm resistor but inside here there's a little tiny resistor as well an internal resistor I'll make it a 3 ohm resistor now I've already told you that when we hooked this circuit up I told you that the terminal voltage was 30 volts that included that there so when I went our total the total resistance of this circuit really isn't 15 really it was 18 so let's see if we can do a little bit of arithmetic here when we just looked at this overall battery we found that the current was 2 amps how many amps go through here what's the voltage drop here how many amps go through here what's the voltage drop here six now look at this then here's my chairlift how many volts do I lose here how many volts do I lose here so how high is my chairlift now this we call the emf this is what it would say on the side of the battery on the side of the battery it would say 36 volts that's what the battery gives you before you hook it up to anything hook it up to something and now you have your terminal voltage your terminal voltage is your maximum theoretical minus whatever you lose going through the battery that's where the 30 comes from that helps or not I hope that does a little bit and we'll do some more questions I know it was the last lesson and it is actually probably the single more confusing lesson emf maximum theoretical voltage what it says on the side of the battery that never changes the terminal changes depending on what resistor is right here what if that was a 20 ohm resistor good question so now I know this battery has an emf of 36 volts what do we say the internal resistance was equal to what did I say three ohms okay now you pull out that 15 ohm resistor and you replace it with a 20 ohm sure what's my terminal voltage going to be now well first thing I would say is I need to find total current it's gonna be a decimal sorry I was trying to make these work out evenly but there's only so much I can do with these numbers okay I should have made this 21 ohms and that would have been 24 would have been a little nicer what is 36 by 23 1.57 so now the total current is 1.57 amps that's 1.57 amps how many volts do you lose going through here 31.3 volts this is also 1.57 amps how many volts do you lose going through here 4.71 volts so the terminal voltage is going to be that original 36 minus what you lose going through the battery what do you lose going through the boundary now here's the equation that we this is the circuit version the equation you're correct that we came up with was maximum theoretical voltage minus total current and we use a little r to symbolize it's a small resistor inside the battery but where did that 4.71 come from i times r so the terminal voltage would be actually get the answer 36 minus 4.71 31.3 volts is your terminal voltage okay if I put a different resistor here terminal voltage would change because I get a different total resistance a different total current a different voltage drop through there a different maximum theoretical which never changes minus terminal voltage so does your emf change no that's on the side of that that's what you see on the side of the battery so if I look at these I think these are one the little tiny ones in here I think they're 1.5 volts over that's an emf I'm not getting 1.5 volts out okay now for what it's worth you'll notice here our total was this plus this how come I did oh because I hadn't given you an internal resistance I just given you the battery I'm giving you the terminal voltage here so this voltage already includes what you lose going through and what was our ski hill analogy we said what you lose going through is like the bump after the chairlift that you ski down that makes sense I hope that cleared it up a little bit for the second one if I wanted to find terminal voltage I could have been said 50 or are we 15 plus 3 is 18 so there's where my two amps came from from my emf 36 divided by 18 so that works if I started with this and work the way backwards I could have found the terminal voltage here I told you the terminal voltage we worked our way backwards to find what the emf had to be right I hope that helped I don't know I think so can you come to the office please no again here feel free to pick ones if you find one in there that has the little resistors and this dotted rectangle around the battery that's a terminal voltage question I'll happily do it anyways which one would you like to do 48 Jimmy you are great you're conscientious about the homework everyone else appreciates that because you've probably done questions that they haven't got to yet oh and I'm seeing a terminal resistance a terminal sorry a terminal voltage and internal resistance choice they want me to find how much power is dissipated as heat inside the battery do batteries heat up when you use them yeah why right there power is vi now that's the one that's on your formula sheet also remember power is i squared r and v squared over r you can get those two Jimmy by plugging in that there whichever variable you get by itself okay how do I solve any circuit try and find the total current did they tell me the total current no my next step is I go find any resistor where they told me two things because if I know two I know four wait a minute I thought it was three one oh no we said also now if I know power there's four things resistance voltage current and power I'm gonna start here so let's see what I can figure out I think I can figure out the current because the power is I squared r I is going to be power divided by resistance square root the total current is going to be 3.2 divided by 10 square root well let's try that again square root the total current is 5.657 sorry 0.5657 so what's the current right here 0.5657 hey Pat what's the current inside this little resistor then 0.5657 amps if I know two I could find power I don't know another one yet well what else can we figure out here now that we know I and R I think we can figure out the voltage drop what's the voltage drop I times R I think I can multiply by 10 in my head I hope I think I hope I think 5.66 volts so Savannah you're ready they didn't give me terminal voltage they gave me chairlift height how high is the chairlift six volts how high is the only ski hill so how high must the bump off the chairlift be 0.34 0.34 volts by the way that means the terminal voltage of this is 6 minus 0.34 the terminal voltage of this is 5.66 volts that's the terminal voltage they're not asking that they're asking for the power inside this resistor power is the I it's gonna be 0.34 volts that's what we lose going through that resistor times the current 0.5657 0.19 watts terminal voltage to terminal voltage is the voltage after you've gone down the bump off the chairlift and if they don't mention a bump off the chairlift then we just assume I guess it's a smooth chairlift and there was no yeah they wouldn't you if they didn't have if they didn't show me the little resistor they just had a battery they wouldn't use the e-symbol there they would have used V because it would have been the terminal voltage good question Jimmy does that make sense the way we handle it okay any more and don't feel bad if you're the only one asked but whoever wants to ask Pat you got one I'm not sure Chica you alive Kevin and Lingling anybody number nine I don't remember number nine let me see number nine 12 getting closer eight oh nine oh great question this also ties in terminal because they want me to find the EMF chairlift height and then there's a part B make sure Kevin I do part B as well but I'll do part A first what's my strategy gonna be here now they want me to find the EMF they want me to find how high this chairlift is it's gonna be that voltage plus either of these guys plus that voltage that's gonna be my chairlift height find total current did they tell me total current anywhere no step to find any resistor where they told me two things haha right here okay I'm working right here because if I know two I know four but I'm really interested in voltage what's the voltage in that resistor seven what's the voltage in this resistor then has to be seven has to be seven because the kit skiers can break apart and join together they have to be able to break apart and join together at the same height same voltage oh I know two in both of these now I know three I can find the current current is voltage divided by resistance so here it's gonna be seven divided by thirty three point two one two one point two one two here it's gonna be seven divided by sixty eight point one zero three and tada I now know the total current in this circuit don't I kept the total current is gonna be point two one two plus point one four plus point one zero three point four five five amps point four five five amps that means point four five five amps up there and that also means oh I times are I can multiply by ten in my head four point five five volts lost oh and that means point four five five amps there point three six four volts lost I times are so now I can walk an entire ski run and end up at the chair lift starting here if I go through there through there and there will I end up back at ground zero that means that this chair lift has to have a total height of four point five five volts plus seven volts plus point three six point three six four eleven point nine fact I'd be willing to bet that's probably a 12-volt battery but I'll put eleven point nine that's what I got mathematically but I'm willing to bet the sticker on the side says 12 that's what they call it even if it wasn't an 11 volt battery battery no no no EMF is the height of the chair lift EMF is the maximum theoretical voltage of your battery and the way to find it is add up all the hills in one path and don't forget to include the little bump at the bottom of the chair lift because your chair lift was a little higher you lost a little bit of voltage going to the little bump so the EMF is going to be dope EMF is going to be point three six four plus four point five five plus seven eleven point nine volts I I would say when you're dealing with a circuit that's one of the ways to find it yes I can think of other I can think of other questions where this method wouldn't work so I can't say I'll do it all the time but but probably you'll get that'll get you there but I can think of other weird circuits where this method wouldn't work specifically I guess I would say this okay and if you can do a closed path ending starting at the top of the battery ending at the bottom of the battery going through the resistor internally and always going downhill then yes but I had to add those conditions because otherwise some kid might say well why can't I go like this well no that's not going to get you there okay be the heck was be oh find the power in the internal resistance I times VI right so point three six four times point four five five there's the power or you go I squared R or you could go B squared over R but I got V and I good that okay cap for part B I'm guessing you're wondering about part A yeah yeah yeah you're assuming I know what we're talking about give me a second okay five this one is so easy that it's tough is part D okay let me let's go look at number five then mr. Duke number five what the heck was D what do you get for C so about 60 watts light bulb they will somewhere on the provincial and I have during your unit tests asked you to quantify certain values you'll notice every swap and I said you should have a good idea of what a really big number and what a really small number is so I have seen them on the provincial for example say a resistor is exerting a power of 2,000 watts which appliance is this resistor most likely to be in a a light bulb be hairdryer see washing machine probably in fact that microwaves are like you know a thousand watts so it's something that pulls out a lot of heat or they've done stuff with I've seen them do it with momentum or energy for that matter magnetic field magnetic field I'll be talking about well here's the earth's magnetic field so this is what a big magnetic field business will kill you this is a small magnetic field this is what would cause something to stick to something else and then here's the earth magnetic field that we exist in all the time it doesn't affect us at all okay so yeah how many marches is worth by the way one and it's a fairly I mean it's almost close to 60 watts yes so I don't think that's a stretch certainly calculated would be a bad idea I don't think the least your counters don't glow and get hot so well you know what bulb is though right see I think the kettle just put on there as a distractor a kettle would probably take more though because does it throw does it use way more heat so it burns more energy per second and that's the definition of what right power was worth per second it must be more than a lifeboat yeah 21 this one you'll notice no internal resistance Savannah on number 21 did they use a letter E next to the battery so technically they're asking me to find the terminal voltage they just called it the potential difference it's voltage in this case it is because they didn't give me an internal resistor potential differences voltage they want me to find V they didn't include an internal resistor or a letter E I'll do it anyways for some reason I'm missing that line there so what would I do and start here right I know the voltage here as well V equals I times are 60 volts what's the voltage have to be through this resistor then 60 volts fact I think this is the same diagram I gave you on your quiz but I changed the question I think can't remember now oh what's the current have to be six amps what's the total current then 1.5 amps six amps yeah 7.5 amps so you're ready up here is 7.5 amps and what's the voltage drop through this resistor six times 7.5 what's that 45 someone's already got the numbers for me I went down here is four times 7.5 amps 30 is that right let me down here four times 7.5 it is it is 30 right and now yeah we can walk a path that's got to be the total voltage the potential difference okay now what you have found is the terminal voltage here's how I know first of all did they give you the internal resistance here anything like that did they give you the EMF no and also because they told me what kind of current I'm getting from this circuit I'm willing to bet that current includes whatever we lost going through this internal resistance so fine what do we get 45 60 and 30 hundred and 135 oh number eight by the way 135 volts that's probably a plug that's a 140 volts I think is what you get out of your plug so probably plug with an adapter to give you direct current so probably what I'm getting from this thing number eight and then 12 sure eight total power okay total power is going to be the power here plus the power here plus the power here because power is a scaler so I'll just add it up oh they told me to means I know for let's see what we got here power equals I squared R I know it's VI but it's also I squared R right Lingling and they gave me the power they gave me the resistance so I can find the current it's going to be the power divided by the resistance square rooted it's going to be 30 whoop 9.2 divided by 33 square root of that looks like the current is 0.528 so right here I have 0.528 amps oh what's the voltage right here well I times R times 33 17.4 you know what the voltage through here has to be then 17.4 volts right oh you know what the voltage has to be here then if I'm starting by the way this is a terminal voltage not an EMF because they didn't give me the internal resistance that's fine that's why they use a letter B 24 I lose 17.4 24 I lose 17.4 how many are left for the final hill this has got to be 6.6 volts I know 2 now I know 3 current is voltage divided by resistance the current is going to be 6.6 divided by 10 which I think I can do in my head point 6 6 amps that's total current haha now this question fell apart because if that's the total current and I got 0.528 coming from that junction I bet you it's going to be 0.66 minus 0.528 the amount of current over here is going to be 0.132 amps and now I'm almost done what's the power in the first one voltage times current 6.6 times 0.66 that's how many watts are in the first one what's the power in the second one 9.2 what's the power in the third one 17.4 times 0.132 I times V or me times I so 2.3 watts plus 4.4 watts plus 9.2 watts the total power in this circuit 15.9 I bet you the answer is 16 yep and then sorry which one 12 ooh nice twist finding a resistor well I'm gonna start where they gave me two things obviously here they gave me power and resistance it's really handy I have this one memorized that power equals I squared R which means that I equals P over R square root P 0.4 divided by 10 square root I think it's gonna work up evenly ah a lovely current of 0.2 amps oh and what's the voltage if I go 0.2 times 10 in your head 2 volts by the way how many volts are we starting out with and that would include the bump off the chair lift apparently since they didn't bother separating it 12 I lose to this and this better add to 10 because I got to get rid of my 10 volts somehow oh um what's the total current here yeah no no no no no no no no no no no no no no no no no no oh what is the total current here then what's the voltage drop here i times r at 3 I lose 2 volts and I lose 3 volts I start with 12 volts how many volts must I lose through here right not only that because these guys are identical 0.1 amps 0.1 amps the same current will go through each of them do I know 2 I know 3 R equals V over I think I never do I'm making fun of you guys for doing it R equals V over I so that's how you got through science tan I just my beef against them is that I would rather teach a student how to do the algebra so that whatever equation like haven't you got way better at your equation solving this year to the point where you're doing stuff you never thought you could do in your head in your head so not push them that way instead of giving them the crutch but I understand that 7 divided by 0.1 and 70 I think each resistor is 70 ohm that's how I would handle that one I think pretty sure next 45 lucky so here's an example of a recharging one I said it shows up once in a while as a multiple choice are you having a head stick around for two minutes and I'm going to do hints above the test can you I'll do this question and they remind me and I'll do the hints thing I always do that for the people that show up for the tutorial right or watch it online but people that actually take the time to put an effort to want to improve their grade and what was your question will there be one like this on the test um I don't think I did okay it's clearly fair game although this is from 1997 and the course has gotten easier in some ways which is the bigger battery that's the winner the current is going to flow that way which kind of makes sense bigger chairlift higher mountain or whatever okay as a matter of fact your net voltage is 3 volts because this is in the opposite direction it's sort of like gaining eight but then climbing down five volts of stairs what's your total resistance they're all in series right 11 and 1 and 2 11 and 1 to 14 ohms what's your total current which happens to be the current going through the 11 ohm resistor it's going to be v over whatever the heck that is that to me is a fair game one as a multiple choice because I don't think that one was too unreasonable what they're not going to do is that one of the last ones I did with you they had like the two batteries and they all over they're not going to go up like that okay the review that I gave you is a pretty good indication there are a couple on that review that have multiple batteries that's about the level difficulty they'll throw at you if one shows up and they hardly ever show up okay is that the right answer I hope I think what is the correct answer what you get a b c or d a that's how I handle that hints about the tests and I'll still take more questions hint number one if you're not sure what to do draw the circuit I type this test up sometimes rather than do the graphic circuit I just described it hey you have a battery that's this big you have one resistor that's this big an eternal resistor that's this big find blah so draw it if you're not sure make sure you know how volt meters and ameters are supposed to go that was from like lesson one there's several of those in your review anyways no kilowatts and and no make sure you know the difference between current and electron flow current is which way the positives would flow if they could that's which way of battery we point the battery but the electrons fell in the opposite direction so yeah here's a fairly standard circuit to analyze it has an emf as well as a terminal voltage so we've done a few of those so big you knew that was going to be in there it's a pretty straightforward test I'm trying to give hints that I can give you weird stuff but I kept it pretty straightforward there's a question you know be prepared for switches opening and closing that those are good ways to do using principles of physics right to explain questions and if you're doing a use of principles of physics and you're not sure of the theory make up numbers or crunch the numbers and see oh is there more power or less power is there more current or less current is there more voltage or less voltage or I guess the resistance will change but don't be scared to crunch numbers I think you'll find the written very straightforward I have a lot of kids get perfect on the multiple choice so I'm gonna be more specific how many multiple choice questions are there eleven multiple choice and one two three written questions on the multiple choice out of those eleven I think six of them are pretty conceptual of the remaining five two are tricky not nasty nasty tricky but tricky draw the circuits as my advice to you and I'll be giving you the same advice tomorrow on the test okay you asked me will I do a question with more than one battery there is a question on here where I have more than one battery but they're not facing each other they're in series which is just like two chairlifts in a row yeah okay and we did we did do that for me I think in this case I think in the one that I'm thinking of each of them also has a little internal resistor so you'd have to say oh what's the emf and then minus what I lose plus what's the emf and then minus what I lose and that's how high I am right make sense so there's your hands back not really many hints because I think it's a straightforward one jimmy which one 1616 power okay no problem I say this one is as tough as it'll come because did they tell me total current no did they give me any resistor with two things no then I have to rewrite this as one resistor it's the only way I can do it they did give me the voltage the terminal voltage of 80 so let's see I have this parallel resistor right here I'm going to say that's going to be 1 over r parallel equals 1 over 12 plus 1 over 8 1 divided by 12 plus 1 divided by 8 okay the parallel resistor is 4.8 ohms that's a terrible ohm signal let's try that again so what's the total resistance jimmy well the total resistance is this is the same as a 4.8 ohm resistor plus I hit a 10 plus I hit a 12 and these are all in series so I can just add them up total resistance is 22 26.8 ohms and now I can find total current total current is going to be total voltage divided by total resistance what's my total voltage 80 divided by 26.8 what's my current 80 divided by 26.8 and I get two point you know what I'm going to use 2.985 I'll carry an extra sig fig amps all right so jimmy how many amps are going through this resistor here yep 2.985 and how many amps are going through this resistor on the top here 2.985 amps and amps now they split up here I'll I'll figure that out in a second ooh but since I know two I know three I can get the voltage of each of these two resistors I times r I can do this one on my head 29.85 volts and then 2.985 times 12 35.82 volts how high is our chairlift to begin with 80 going through here we lose 29.85 volts going through here we lose 35.82 volts you know how many volts we have left to go through either of these ski hills how high either of these ones has to be this is 14.33 volts jimmy do I know two that I know four I can find the power now I know resistance and voltage uh let's see power equals vi but I also know that i equals v over r so power equals v times v over r or v squared over r it's going to be 14.33 squared divided by 8 25.7 watts that's how much power that particular resistor just makes I'd take it but I would also say try not to round off part way through don't go stick figs until the very very very very very end 26 this one hopefully won't be too bad because they told me total current although to be honest usually when they do that there's going to be a curve ball later on because otherwise it's just three let's see how high back to zero how high how high oh here I know two so I know three what's the current here so do I need to draw the triangle please don't make me draw the triangle 1.5 amps and Savannah what's the total current in this circuit so if I got 1.5 amps that went this way how many amps went that way I don't know what you're trying to do but ski hill yep 27 I I think this is a question that I hate and I think the reason I hate it is because when you round off the rounding off numbers that you get are confusing let's see if this is the one that I remember yeah did I write a note about that okay you know what Jimmy I'm going to show you my answer to that question and I'll talk about it did they give me a picture of the circuit so I drew it okay yeah I wrote bad question here's why all right actually no I didn't draw it I used the the formula it says the cell has an internal resistance they gave me terminal voltage and they gave me uh so I wrote this down which is the emf equals terminal plus ir I just rearranged it said okay I need the total current the total current is going to be the total voltage that they gave me the terminal voltage divided by the resistor that they gave me now this terminal voltage I'm not going to use the 5.5 ohms total resistance because that terminal voltage already includes the bump off of the chairlift so total resistance five is that okay and what I didn't like about this is I get an emf of 1.54 which to two sig figs says my maximum theoretical voltage is 1.5 volts then we replace this with a 10 ohm resistor and they want me to find uh they want me to find the new current now I know the emf is 1.54 so I'm going to use 1.54 because I'm using an emf I'm going to include that 0.5 in this when I did that I got a new current of 0.146 repeating when I use that to find the terminal voltage I got 1.5 volts here's what I don't like what's my voltage before I start 1.5 volts if I go to two sig figs what's my voltage after I start after I hook it up 1.5 volts if I go to two sig figs I don't like that question because you already said oh so the voltage is always small yeah it should be smaller once you hook it up but here because of just the weird rounding it's not okay I don't like that question I understand what they were trying to do I just want to pick different numbers and in hindsight if I was doing this again I would draw a circuit so it'll be clear when I first did this answer key I still wasn't very good at the ski lift method 24 a or b or both oh it just isn't a so I didn't include b b used to be there but it got thrown out b they closed the switch and then they asked you some questions the problem was when you close the switch what you've actually done is you've created a short circuit because skiers can get from this height to that height without going through a ski hill it was just that's a bad circuit that's the definition of a short circuit it's going to get really hot and it's going to burn so they threw that question out apparently I found that out all right let's see eight volt battery oh each bulb has five watts I guess I have 1.5 amps going through this internal resistor oh how many amps are going through this lamp won't gotta be do I know two now I know all four for this one uh what what I like to find I'd love to find the voltage here so 3.33 gonna be five divided by 1.5 I agree so this is 3.33 volts how many volts must this be then oh I don't know because I'm losing a little bit going through here oh but wait a minute how many amps go through here also 1.5 because none can go through there as long as the switch is open so that means this is going to have the same voltage as well 3.33 volts right so Kevin I have this starting out with eight volts and I'm going to lose 3.33 volts twice is that okay so when I get right to here I still have 1.34 volts that I need to lose in order to get to the bottom of the chairlift do I know two I know three uh r equals v over i 1.34 divided by 1.5 internal resistors 0.893 I hope that's the answer I think that is 0.89 ohms does that make sense okay okay deep breath which one 30 oh too far 30 120 volt power supply is connected to a heater of resistance 15 ohms okay we want the same power output if we connect it to a 240 volts let's look at this first one here power for this first one is vi I don't know you know what it's going to be v squared over r it's going to be 120 square divided by 15 the power that we're talking about here is 120 square divided by 15 960 watts which sounds high no wait a minute it's a heater that moves a lot of heat probably would take a lot of power now here we're also going to use power equals v squared over r except they want us to find the resistance so the resistance is going to be the voltage squared divided by the power what's the voltage 240 square divided by what's the power same power as they told me we're drawing originally uh 960 because they said same power output uh 240 squared divided by 960 oh this would have to be a 60 ohm resistor and that would give you the same power output 39 and 41 so here's another good EMF kind of a question but this time Savannah they're wanting us to find the internal resistance okay Kevin what's the current flowing through this bulb do I know two I know four let's find the voltage uh power equals vi so the voltage is going to be power divided by current 3.5 divided by 0.4 uh I lose 8.75 volts through the bulb what's my EMF how high is my chairlift nine so Savannah what must I lose going through here if that's my terminal voltage and that is my terminal voltage because that's the only other skill that shows up 0.25 oh and Kevin what's the current going through here are equals v over i 0.25 divided by 0.4 0.25 try that again Mr. Duke 0.25 divided by 0.4 0.625 0.625 ohm that's part a what did b ask here is a good using principles of physics question we replace the bulb with a lower resistance so this resistor here gets smaller if this gets smaller if this gets smaller what happens to your total resistance gets smaller right if that's smaller total resistance is the point uh sorry the 0.625 plus whatever resistor this is total resistance gets smaller now total resistance gets smaller what's going to happen to your total voltage what's actually first of all what's going to happen to your total current your total current is going to be your maximum theoretical voltage divided by the little internal resistance plus this new resistance here which is now smaller you know what's going to happen to your total current if this number here gets smaller emf doesn't change nine if this number here to get smaller what's going to happen to your total current gets bigger so ready terminal voltage is your maximum theoretical unchanging voltage minus i times little r this hasn't changed this can't change that's a physical part of the battery what has changed current went up so if this number gets bigger and you're subtracting what's going to happen to your terminal voltage now that's the algebraic approach look i didn't like that no problem here's how what you also could have done do you know uh current do you know voltage what is the resistor of this bulb well it would be v divided by i it would be 8.75 divided by 0.4 this bulb right now has the resistance of 21.7 0.875 in the using principles of physics it says replace it with a lower resistance fine what's its resistance right now make it a 10 ohm bulb and now re crunch the numbers okay so let's make it a 10 ohm bulb temporarily what's my total resistance in this circuit then 10 plus 0.625 total resistance would be 10.625 and of course i'll carry a few extra sig figs just for the heck of it total current is maximum theoretical total voltage nine divided by total resistance total current is going to be nine divided by 10.625 0.847 amps what was the current before what was the current before what is it now would the current get bigger or smaller bigger okay now nine minus 0.847 times little r little r little r 0.625 nine minus that answer times 0.625 and i get a terminal voltage of 8.47 volts versus uh what do we say the terminal voltage was here 8.75 wasn't it because it was nine minus 0.25 volts so originally 8.75 new one 8.47 definitely less than so you could also crunch the numbers but it's kind of a weird one because strangely by lowering the resistance because that made the current bigger the bump after the chairlift somehow also got bigger your net terminal voltage got smaller and you said 39 and 41 is that what somebody said hey savannah terminal voltage savannah on the circuit diagram terminal voltage is this minus sorry let's try that again mr. d is this minus whatever voltage through there that's terminal voltage okay and that's probably how i'm going to end up finding it let's see um have they told me the total current have they told me anywhere with two gonna have to say total current is going to be total voltage divided by total resistance now my total resistance is 2.7 2.7 isn't it total voltage is total current is i'll carry a few extra digits just in case so you know what the terminal voltage is it's that six minus i times r little r oh did i do it times sorry chairlift minus bump at the end 5.56 5.6 36 b probably at 36 there's a well i'm probably gonna have to copy the circuit to do it anyways so let's do that mr. d heck it's good practice for you what's the current 1.5 amps what's the voltage down here it's going to be 2.7 i'll bet you yeah you know how i knew that because they told me the terminal voltage since that's my battery and this is my only other voltage drop this has to be exactly equal to the terminal voltage uh 2.7 volts uh let's see 1.5 amps how many volts do i lose going through here can you go i times r here for me 0.3 so the emf let's see how high is the chairlift well i lose 2.7 going through the ski hill but i also lose 0.3 just getting off the chair lift that chairlift must have been there's my emf that's a three volt battery that's out of the side okay now let's do part hello b and c the 1.5 ohm external resistance is replaced by other resistors and the current and the terminal voltage are measured in each case which graph best represents terminal voltage versus current as these resistors are changed say what well terminal voltage equals emf minus ir i can't remember how i explained this one let me go check my answer key i'm having a long day what number was that okay so i said terminal voltage equals that i said as your current increases that also automatically gets bigger because your emf doesn't change so as your current gets bigger this answer should decrease so i picked a graph whereas current got bigger terminal voltage decreased that makes sense to me as this gets bigger this gets bigger this can't change in fact eventually you can have such a big resistance sorry such a big current that your terminal voltage is zero your battery is going to overheat pretty quickly because you're using all of the energy just across the battery did that make sense sorry i blanked on that long day this one at number 13 question 13 i don't know what question 13 is go find out ohm's law ohm's law is just v equals i times r okay so ohm's law is v equals i times r uh so what are we comparing here as that gets bigger what's going to happen to that yep and are there any squares or anything like that so it's linear ah very nice yes as it turns out i think there's one later on where they give you one of those graphs to analyze and i think you have to clue in oh the slope of this graph is the i think it's the internal resistance or something to the battery one down okay i'm going to hit stop first of all