Lesson 1 - Voltage, Current, Resistance (Engineering Circuit Analysis)

hello and welcome to the engineering circuit analysis tutor I'm very excited to teach this course because I'm an electrical engineer myself so I was always very interested in electricity and electric circuits and things like that so what we're going to do in this class is exactly what the title is we're going to learn all about circuits we're going to learn about electricity we're going to learn about the components that go into circuits but mostly what you do in engineering courses is learn how to analyze them given a circuit what is going on where is the current going what is the purpose of the circuit and so there's a lot of details there in a lot of techniques that have been developed over the years to pull those things off you know hundred years ago circuits and and all of the things that we take for granted today will be super theoretical but they're all basically physics they're taking energy out of a battery or energy out of a wall and letting it run around in a loop and doing some useful work with it that work might be spinning a motor right to spin a fan or that work might be shooting a radio wave out across the world to talk to somebody else or that work might be to go into a microprocessor and you know flip a bunch of bits around and add a bunch of numbers together basically create what we call a computer but there's basically infinite number of ways that you can create circuits to do what we want them to do but before you can understand a microchip before you can understand an amplifier before you can understand a nuclear power plant you have to start at the basics you have to start at the really really simple questions the things that are so fundamental and that's what we're going to do in this course we're going to start with fundamentals and then we're going to go on and talk about circuits and the different kinds of circuits how to analyze circuits figure out what's happening in this inside these circuits and you'll find there's a broad array of tools that you learn in your classes to help you with that now I'll say right away the title of this guy is engineering circuit analysis but my goal is to really try to make it as accessible as possible to anybody out here who wants to learn it right don't let the word engineering scare you too much Engineering is a big word makes it sound really hard but I'm going to try to break things down so that everyone can get it now I will say the good news is and this is true with circuits in general there really aren't that any big-picture concepts to understand we in this section we're going to talk about voltage current and resistance because they're so important but really once you get past that there's a few other big picture concepts and then you understand really the basics they're challenged with circuits comes is that I can draw a circuit on the board and you might know how to analyze it and figure out what's going on and then I might change one little line one little branch of the circuit might completely change how the thing operates right so there's an infinite variety in how they can be constructed that's what really requires you to get a lot of practice and that's what this course is going to be it's centered around practice practice practice practice and to be honest with you you don't need to know much more than algebra to do very very well in this class yes we are going to use complex numbers a little bit later on later later in the course not and not in the beginning we are going to use some calculus and integration later later later on in the course but by and large you can do a ton of circuit analysis with just some basic algebra and that's the way I'm going to try to teach it to you so that you know everybody it can be accessible to everybody while also catering to the engineering student which is really the focus of the class all right so I had I had to figure out where to start I think the most important thing for everyone watching this to understand is the concepts of voltage current and resistance because those three things we're going to end up zooming in on and talking about for the next many many hours and you really have to understand what they are a lot of students if they haven't already had an interest in circuits they get very confused at what the difference between voltage and current is and why does resistance play into that so what we're going to do in this particular section is zoom in on that and I want you to really make sure you internalize and understand what they mean because as you go and solve a circuit and I'm asking you what the voltage is you need to kind of have a internal picture of what what that means even before you do any math so there's no math in this section you know this is all definitions I try to make it as interesting as I can but it's so incredibly important make sure you understand this first things first I think we all know this what is an electric circuit what is a circuit I mean a lot of people a lot of people think that the circuit is and those people probably do but what is a circuit the simplest one sentence definition is it's a closed it's a closed loop that carries what does it carry what do you think electricity you know like I say I have to start somewhere and start I start I never never never assume that you know anything about what I'm talking about so a circuit you think about a circuit of a racetrack or a circuit and the Indy 500 it has to go all the way around if you don't have it going all the way back round to the starting point then you don't have a circuit and no electricity can flow in such situation unless that goes all the way back around to where you start from so in order to have a circuit it has to come back to where it starts from so a simple example of that without really getting any kind of detail is you know here's a source I'm going to put a plus minus two different to denote it as a source this could be a battery you know this could be a battery that you pull out of you know you go buy it at the store and we're not going to put anything in the circuit with it we're just going to draw these lines here these lines or wires so it would be just like you might think you get a battery you hook a wire up that goes all the way back around to the other side this completes a circuit the electricity can circle around and around and around here coming from one terminal background to the other one that means it's a circuit super super important but you know also very simple as well now let's get to something that's not quite so simple but you know a lot of people still may understand this what is current and when I say current I mean electric you know learn how to spell current first of all current electric current what is electric current okay the simplest definition to write down for what electric current is it is the flow of electrons in a circuit it's the flow of electrons in a circuit so everybody's heard of heard of current electric current an analogy to electric current would be current in a stream we all know what a current is in a stream right it's when the stream is moving there's a current it's pushing your boat right it's the movement of something don't confuse that because a lot of people get confused with voltage and current if you're not really familiar with these terms voltage has really nothing to do with anything moving we'll talk about what voltage is in a minute the current the electric current think of a stream think of something moving that is what's moving so in real life if you have a piece of wire which is metal the electrons are really and truly what's moving around in that wire so if you wanted to kind of zoom in and draw a little picture of that we could draw another little circuit here little simple one anyway like this goes up connect it all the way back around to the beginning so there's going to be current circulating around and around around but if I zoomed in let's say this is a piece of wire right if i zoom in this wire and get a microscope up on top of it and zoom in on it really really tight if I could see that what I would see inside is a bunch of atoms right so this atom is going to have a positive nucleus and this atom is going to have a negative electron orbiting around this atom now in real life this might be you know copper wire so it'll be lots of protons in the nucleus and lots of electrons but for the purpose of this drawing just pretend that there's a positive Center and there's a negative things orbiting now here's another atom here it's got a positive Center and it's got a negative thing orbiting this one's got a positive and a negative every atom has this positive Center and negative surroundings now in metals like copper and gold and silver that conduct electricity well these electrons they're not really tightly held to the atom they're there but they can be coerced so to speak to move they can be you know you can talk them into moving if you if you try hard enough the object that actually totten talks them into moving is the battery right is the better or the source coming from your wall for instance and when that happens when you hook a battery up to this wire like this since these electrons are not really really held on terribly tightly what happens is this electron you know down here this electron is going to jump literally it's going to jump over and grab it and go into the orbit of the next atom and at that moment the same time that happens it's a chain reaction this guy's goes to the next guy this electron moves to this guy and this electron moves to it's adjacent atom and this process happens at almost at the speed of light so you can't see this electron movement but that's what's in fact happening so it's a chain reaction and they're almost like in lockstep moving from one atom to the next and this movement is really you know you can think of it as energy of motion is the energy that the circuit uses to do whatever it's going to do you know turn a fan turn a light bulb on whatever that's where the energy from the battery is going it's going into pushing these electrons around which is electric current so when I draw this here I'm drawing these these negative electrons moving so this is what we call electron alright or electric current there's another way to say that so the electrons if you want to think of it this way will go draw it down here this is the negative terminal of the battery this is where the negative charges are sort of piled up so here this is called the electric current so the electrons literally bleed out of this negative terminal they go all the way around and they go back and they enter it back into the positive terminal because this is positive so it's going to attract the negative electrons and this process goes on on and on and on until the battery basically dies out if it's a battery and they can't supply any more electrons or if it's a wall it just keeps going and going forever and you get charged toward right it comes from the power plant but the electrons are really and truly what's moving now let me blow your mind a little bit here in a basic basic circuits course like a hobby book like you know go to Barnes & Noble or somewhere just get a book on electricity they'll talk about the electrons moving but when you get an engineering and you really start trying to analyze how a circuit is going to really behave it's a little bit cumbersome to talk about the electrons moving even though that's really what's happening and life the reason that it's a little bit cumbersome is because of really one reason electrons have a negative charge they have a negative charge and what we're going to do later on is we're going to have a circuit and we're going to write equations simple algebra equations so don't get too worried about them but they're going to be equations and they're going to describe how the current is moving if we do that for a bunch of negative electrons then we're going to have negative signs running around all of our equations for our electric circuits and that would totally work totally work however it's a little cumbersome to have negative signs running around all of our equations so when real life from from this moment on I'm just teaching you this to give you background but from this moment on we're not really going to talk about electron current flow or electric current flow we're not really going to be talking about the direction that the electrons are moving let me show you what we are going to talk about in this very same wire you may have to stare at this a little while to realize this but I think you should be able to convince yourself that since this charge is jumping this direction for a temporary moment like it's we're talking about a chain reaction right this one moves here then this one moves here in this one moves here but at the very moment that this negative charge jumps away for a split second this atom has lost an electron right so it's an electrically neutral atom it's zero charge altogether because the electrons and the protons cancel out they're the same number but as soon as I lose one of these electrons they have sort of a positive charge left over right same thing happens here when I lose this guy for a split moment I have a positive charge here so as these negative charges jump this direction mathematically it's the same thing as pretending that I have positive charges jumping this direction the opposite direction because this guy's lost an electron and then the guy before it loses one and before it so as these guys move this way it's the same as saying mathematically a positive charge goes the other direction I hope that makes sense to you qualitatively based on my drawing here but if it doesn't all you really have to remember is that the real current that we talked about in engineering is called the hole current and it goes in an opposite direction from the electric current which is the real-life thing that's happening and it's a mathematical convenience because since now instead of talking about negative electrons moving this way we talk about positive charges moving this way now we have positive charges in all of our equations and all of our equations are have rid themselves of all these negative signs or at least a lot of the negative signs right and it makes it a lot easier to deal with so it's really saving you time if you think about it that way saving you a thought process so the real electrons are going this way but we pretend that we have an equal and opposite number of positive charges going the same direction we call it a hole current the reason it's called a hole current is because for a split second when this electron leaves it's left like a hole behind on this atom which is making it that guy positive so the hole current actually comes out of the positive terminal like this right and we say we denote that current I and electrical engineering or in engineering and it's the hole current this is such an important concept that you really should not go on until you truly internalize and make sure basically all you need to remember in the big picture is it anytime you have a circuit the source is going to always have a positive and a negative terminal oh it's just like any battery if you pull a battery out of the box you'll see one sides labeled positive one sides labeled negative in real life if you hook the battery up to something electrons are there really the objects that come around from the negative terminal back to the positive but in in electrical error in any kind of an engineering course when you're taking circuits class you never ever ever talk about the electron flow in this this direction this way you always instead talk about the positive current flow it's the same value going in opposite directions and it makes the equations much much simpler and in fact all the power calculations the the function of the circuit the energy all everything is completely and totally described by talking about this sort of like this pretend current that's going in the opposite way so just get used to seeing that you're always going to pretend that your currents come the positive terminal even though in reality the electrons are bleeding out the other side now the units of electric current I talked I told you briefly current is denoted I right I it probably is some history to it you can go look it up you would think current would be called C but it's not it's called I so anytime you see I labeled in a circuit that is the electric or that's the current flowing through that branch of the circuit or something of that nature now what are the units of current a lot of you have already heard this units let's go and change colors a little bit the units for current is the ampere which is also called an amp right or you can call it simply a right the higher the number of amps the you know the higher the current going through the circuit basically an ampere is telling you how many charges are moving through your circuit per second and there's a definition in physics that you could go look up for that and that's fine it's not terribly important because you know really we're always talking in circuits you know fit in a physics class you'd be talking about an individual charge moving there's so many coulombs on a charge moving right but in a circuit you've got billions of charges in this in this guy so you don't talk about coulombs and and how many coulombs of charge are crossing through a boundary you just look at the aggregate which is how many amperes which is a Coulomb per second how many coulombs per second really are going through that guy so an ampere represents how many coulombs of charge are passing if you were to slice this wire and watch how many go through there that would be how many coulombs of charge go through there per second but really you don't have to deal with that too much in a circuits class we're always going to be talking about amps or amperes so bringing it back to the everyday language that everybody already knows you've heard of amps right everybody's heard of amps that is the current flow the higher the number of amps in that circuit is that the more it can potentially kill you right doesn't take much current to kill a person actually believe it or not so you might have a car stereo that has you know a 10 amp amplifier right means ten amps of current are flowing around that amplifier because to push the sound into those speakers and give them to move really loud you need a lot of physical electricity to do that right to actually get it to move like that but in a computer inside of a microchip you might have a teeny tiny amount of current going around because those are very delicate circuits you might have a milliamp or a micro amp inside of those guys but the base unit of current is always going to be the ampere which is which is what we have right here all right so to sum it up which is really so important I keep talking about it current in general in real life is the flow of electrons however in all circuits from henceforth that we're going to talk about we're not even going to talk about this we're just going to say the current comes out of the positive terminal and the unit is ampere that's really the bottom line all right now the next thing we have is the concept of voltage which many many people many people get confused with current because it's kind of used interchangeably voltage is the push when I put in quotes the push that causes the current to flow so in other words it's the source right it's the source so when you look at a 9-volt battery that battery comes in a physical size and has nine volts nine volts mean is a relative indicator to tell you how much who for lack of a better word that battery can push in a circuit so the current and the voltage are very very closely related you cannot have any current flowing without something pushing it and so you have to have some source there to push it which is usually a battery or a wall socket or something like that and that's always measured in volts so when you when you see on TV you know oh boy you could be killed by 10,000 volts well 10,000 volts is not really how much current is flowing through you that's just how much push there is so to kind of bring it down to two layman's terms think about a straw pretend this were a soda straw that you get restaurant right and let's say it's a pretty narrow straw like a almost like a straw that you use to stir your coffee okay now if I blow on it like this then I'm going to be pushing air through that straw the current is the air that's actually moving through the straw right that's what the current is that's what's actually doing the movement and doing the work all right now I'm actually blowing on it so I'm pushing I'm actually increasing the pressure at the end of that thing that's causing the current to move that's the voltage the push that I give it the pressure that I give it is what's actually causing the current to move or the in this case the air to move through the straw if I don't blow and I don't give any pressure then there's no current there's no flow of air through the straw same thing in a circuit if the voltage is zero you know coming out of the source here then there's no current so the two are very closely related it's just that the voltage is the push and the current is actually what's moving that's really the main thing to take away from this guy so it usually comes from up where it always comes from a battery or some kind of other source that you might get that's generated out of the wall now for the units of voltage the units is the Volt or simply call it V so that's just this that's the the same thing as the current the more the more volts you have the higher the voltage you have the more potential to move current through a circuit you have so that's why 10,000 volts is so much more dangerous than 1 volt it's not because it's measuring how much current is going through your body it's just that if I grab onto a 10,000 volt fence it has the potential to push a ton of current through my body right whereas a 1 volt source since it's so much less of a push so to speak it's not really going to do very much to me all right so that's really the main difference so current voltage tied at the hip but two different things the biggest faux pas you can kind of get into is saying boy that was a really impressive circuit that had 39 thousand volts of electricity flowing through your body that sentence makes no sense voltage does not flow through your body only current does voltage is what actually pushes the current through your body that's really the main distinction now tied to all of this is it the very very important concept of resistance all right resistance resistance is very very simple to understand it opposes the current flow in a circuit this might be a little bit confusing at first but think about our soda straw alright for a second pretend for a second we didn't have actually a soda straw let's say we had something really big like a paper towel tube like you have you get the paper towels at the grocery store and there's a giant cardboard tube in the middle I stick that to my mouth and I blow it's pretty easy to blow through a paper towel tube because it's so big right so I can blow all day as long as my lungs can do it I can do lots and lots and lots of air through there right with really not much effort I don't really have to push that hard to actually make that air move because it's just so big so we say that the resistance for lack of a better word of this guy to air flow is not very big it's got a low resistance right now let's compare and contrast that let's go back to our coffee stirring straw very very tiny diameter so for that one to get any kind of air movement through it I've got to blow pretty hard and I can feel it in my lips I'm I'm really blowing because we say that the resistance of that smaller straw is much higher the resistance to airflow is higher because it's physically constrained you cannot force that much air through that straw very easily I mean you can do it but you have to blow really hard so we say the resistance is much higher for that guy and actually that analogy could directly translates to two electric circuits as well if I literally have a wire a you know a copper wire as big around as my as I'm demonstrating here let's big around it has a very very very low resistance the cross-section mean is so big that tons of electrons can move through there tons of electricity can move through there without really much resistance because it's so big but if I go get a wire thinner than my hair or maybe I go get a tiny wire edge onto a computer circuit chip which are so small that you have to have a microscope to see them then the cross-section of a teeny tiny wire like that is going to be so small it's going to actually resist the current the electricity is going to get to move through there but it's going to cause friction there's just not as many atoms there for it to move so the resistance is going to be higher so if the smaller the object the resistance is always going to be higher the bigger the object the resistance is going to be smaller so think of it that way it's resisting and it's opposing current flow not because something intelligent is in charge of it it's just because of the size of it usually or the way it's constructed so current voltage resistance they're also intertwined because of the analogy with the soda straw really the resistance when the resistance is smaller like the big paper towel tube right then I can move a lot of air a lot of current without much effort with a lower voltage right and then when I go to a smaller straw I can still move current but it's going to take more effort more voltage to get the same amount of current flow or to get the same amount of current flow through that resistance so current voltage resistance are really all tied at the hip really is as far as being interrelated now the units of resistance the unit's is called the ohm but you never actually write home in a circuit you always use this Omega this capital Omega and so when you have a 5 ohm resistor has more resistance than a 1 ohm resistor a resistor we'll talk about in the next section but they actually have a circuit component called a resistor whose job is to resist current flow seems weird why you would ever need that we'll get to the reasons why you would need that later but that little guy is going to try to stop the current to flow to assert up to a certain point and so the higher the value the more it's trying to resist the current flow right just like the example that we were given before so very very important topics current is the flow of electricity voltage is how much push you are pushing to make this current flow and you're always flowing through something that something is always going to have a resistance different sized wire different resistors different circuit components are going to manifest themselves as different values of however many ohms now for all of these guys I've kind of hinted here but I'll just spell it out we can use the metric prefixes for all of these guys right because these are standard units we can use the metric prefixes so for instance if you're talking about amps which is current flow it may not make sense to talk about amps you might need to talk about milliamps right milliamps just like a millimeter that's one one thousandth of an amp right or you might talk about micro amps right ten to the minus six amps etc something like this right so the base unit is always amps it's just you have a metric modifier on the front you might have resistance how many owns you're talking about in the circuit but it might make more sense to talk about milli ohms if it's a very small resistance or even if it's tiny tiny micro ohms right that's 10 to the minus 6 ohms right or if it's a large value maybe you have kilo ohms or maybe you even have mega ohms which is millions of ohms right or here kilo ohms is thousands of them so the the metric system applies here there's nothing special and for voltage maybe you have millivolts you know maybe you have kilovolts you know maybe you have mega volts maybe a nuclear power plant is operating at so many mega volts or something like that very very important concepts I can't stress them enough so we've talked about current we've talked about voltage we've talked about resistance in detail because it's so important for you to understand what that stuff is it'll make my job easier whenever we start talking about circuits that you're not scratching your head what's the voltage again I can't remember I mean I really need you to understand that before we get to anything else now let's talk about some general things that you've probably heard growing up in general definition so to speak that you probably heard first one is DC and AC DC versus AC let's talk about that for just a second because it's you know it's something that we need to make sure you understand DC this stands for direct current right and basically what it means is constant current flow basically all of the batteries you've ever used in your life the triple A's double A's and nine volts watch batteries I mean anything the anything built into a little device that we call battery always generates a direct current it means that when you hook it up to the circuit it's giving you a constant voltage at the source location right that's pushing current around and because it's a constant voltage is providing the current that comes out as constant never changes now in reality the battery is going to die down and it's going to get weaker and weaker so the current does eventually bleed off but I mean if you take a snapshot and look at it the current is a constant it's called direct current all right now let me contrast that to AC which I know you've heard of and that's called alternating current alternating current and this means well exactly what sounds like it's it's a wall socket and it means the current for lack of a better word moves back and forth and this is really actually much easier to understand what the with the purpose of a with the drawing here so let's draw a quick little circuit like this now normally we've been putting plus/minus but here I'm just going to kind of put a little wave in here to kind of indicate to you that this is a alternating current and we'll get into all these symbols later you know in detail I'm just trying to get the idea out to you what this means and this is a great model for what's happening in your wall socket when you plug something in you know into the wall what happens is at first the current comes out this direction and flows this way and then it starts to slow down then it goes back the other way like this and then it goes back the other way and it goes back the other way it literally alternates the direction of the current if you could actually see the tricity coming out of your wall like if you could if you I'm looking at a plug right now over there in the wall if you can visualize a plug you know everybody kind of thinks and realizes there's electricity coming out but if you could see the electricity you would see the electricity racing out and then slowing down and then going right back into the wall and coming out the other way and then racing back into the wall and coming back the other way and it alternates back and forth back and forth back and forth back and forth how many times does it do that well in the United States it's 60 times a second 60 60 Hertz that's a unit of frequency that's how fast it's coming back and forth 60 times every second that electricity is switching directions right now you might say I should say the number one question you get when you explain alternating current direct current is why do we have a difference why do we have a difference well the reason mainly is is a lot of history actually but truthfully whenever you generate electricity at a power plant to feed houses it's much easier to generate it as an alternating current and it's much easier to transmit it out to the homes as alternating current and that goes into a lot of theory that I can't get into right now but just trust me on that it's a little bit easier you know really all of our power plants whether they're gas or nuclear or coal or anything all they do is generate a lot of heat and that heat heats up steam usually and that steam turns a generator so all of our power plants no matter how fancy even the wind farms out there they're just turning a generator so since they're moving like this the current that's generated actually alternates back and forth and it comes directly because every time we generate electricity the only way we really know how except for solar panels we're doing it by rotating wire inside of a magnetic field which is what's inside of a generator because of that motion of rotation is because direct result of how we get alternating current and that's the really reason why the power plants do that when we build a battery it's a chemical reaction it's either on or it's off there's no motion inside of the battery right so it's just going to give you that constant deal the constant current constant voltage so that's the difference between DC and AC in this class we're going to focus on DC first we're going to learn all the techniques of analyzing DC Circuit's because really when you get to AC it's once I show you the method it's really not that different so we're going to do DC first get really good at it and then we're going to introduce the alternating current mechanism just a couple of other definitions I want to get to real quick for call of the day everybody's heard of this what is an open circuit what do you think an open circuit is well if you have a circuit right if you have a circuit it's supposed to come all the way back to where it started if you have an open circuit it means somewhere along that path it's broken basically so an open circuit would be if I had some kind of source here like here and then I had a break in it make this break a little bigger then there's no more current flow you cannot have current flow in an open circuit by definition so this open here this is what your wall switch does when you flip the wall switch it just breaks open the circuit so no electricity can flow anymore that's we call an open circuit now let's also take a moment to talk about a short circuit short lots of people have heard of short circuit most people know that short circuit is not really good thing but a lot of people don't know what a short circuit really means when you think about it if you have a circuit you've got a source and you're supplying energy or electricity to some load over here we call it could be a light bulb could be a fan could be a anything right so in general for every circuit that's operating we're going to have something over here that we're supplying power to right this could be anything at all I'm going to put a giant box here this could be you know a fan for instance right and this electricity is coming out this current coming out into the fan causing the fan to turn and I'm leaving a lot of details out but that's basically it now inside of your circuit let's say I somehow a piece of wire kind of accidentally connects from here to here maybe you're working in a building let's say you're building the building you're pulling a wire through the building and somehow a stray piece of wire gets connected to two terminals like this or maybe inside of your lamp you develop a short-circuit because the two wires that debtor's to go to the light bulb maybe they start to touch on accident what happens is the electricity is coming out here and when it gets to this Junction right here it has a choice to go this way through the fan or this way now let me ask you a question what do you think is going to be the lower resistance do you think it's going to be lower resistance for the electricity to go through this giant fan and spend something around or do you think it's going to be a lower resistance for this electricity to try to go through this little piece of wire that you put there it's going to be much much easier for the electricity to go through the wire and so electricity is always going to do that it always tries to go through the path of least resistance just like you do when you're in traffic right you try to go the path of least resistance so because of that the electricity never even gets to the fan so that's called a short circuit it's called short because it kind of truncates the circuit or it shortens off the circuit and it's very bad for lots of reasons but because whenever you start to get current going through a wire like this with no resistance or very low resistance you can actually generate a lot of heat and you can actually cause a fire actually and that's why you have those circuit breakers outside of your home those are there to detect if any short circuits happen to detect the extra current the increased current that comes from it and to shut them off if you get any kind of a short-circuit in your washer or your dryer maybe some wires start to touch the current is going to start to go up really really fast through this tiny little leg and your circuit breaker is in the circuit with that it detects that and then it shuts the circuit down so that's basically how that how that works that is about how all I want to talk about in this lesson we've covered a lot of things we haven't done any math that's okay because you know sometimes in the beginning you really need to take some time to understand the fundamentals so we learned about the circuit you always have to have a complete circuit to have any electricity flowing we learned about current it's the flow of electrons in real life but in a circuit analysis we don't talk about that we talk about the positive current and going in the other direction has a symbol of I all right in there in terms of our equations right the unit is amperes or a of course we can talk about milliamps micro amps kiloamps things like that as well and then we talked about the voltage which is related the voltage is the push that pushes the electric current around in the circuit the higher the voltage then the more push you have the more current you're going to end up getting because you're pushing you're pushing through with more force for lack of a better word right the units is a voltage that we talked about or of course you have millivolts micro volts etc and then we talked about resistance which is integral to all that that is sort of a property of the circuit or the property of the wire the property of the components and it literally tries to oppose the electric current the unit is the ohm which is the capital Omega here of course you can have milli ohms micro ohms kilo ohms with that guy just like you have for the others and then we talked about some other random definitions that people have heard over the years of growing up direct current DC alternating current AC this guy is usually coming from a battery some constant current source usually a chemical reaction is giving you a constant voltage constant current coming out all the time alternating current comes out of your wall the reason it's alternating is because it's easier to generate because you have rotating generators and you have easier transmission to the homes there's a lot of theory in that but that's basically the the deal and both are you know both are electricity the fact that it alternates doesn't really mean much I mean your your light bulb you don't see it flickering but the electricity is actually going through your light bulb back and forth 60 times every second you don't see it because it's so fast so don't get too wrapped up or hung up on the difference here they're both electricity they both deliver energy and then we talked about open circuit you have a circuit where you literally take a piece of scissors and cut it open no electricity can flow anymore and a short circuit is when you have an operating circuit that you that you accidentally bridge or connect two pieces across together and it basically causes the electricity to not even go into the load at all so the load stops working you get tons of current built up here and it can actually lead to smoke and fire if you let it go and that's why we have those circuit breakers in our homes so that's what we want to cover in this section the title was voltage current and resistance it's so important to understand so make sure and watch this until you feel pretty comfortable with it the next few sections I want to do some more background stuff we'll talk about taking an overview of the circuit components out there and then we'll do another lesson on on what we call ohm which in mathematical terms relates resistance current and voltage together and I promise you Ohm's law is so simple that you know you'll you know it was boggle your mind very very simple to understand and then once we get those foundation things gone and going on then we can really start diving into some real real circuits and looking at how the currents going to move through the branches how they're going to sum together what's going to be the value of the voltage here the voltage there and then we can get into some more complicated circuit components like capacitors and inductors and much later even what we call transistors and diodes and things like that and you'll be introduced slowly but surely over time to this beautiful thing I think that we have in the 21st century called you know electric circuits so the nice thing about it is you can learn this stuff you can you know academically understand it it's good for your career and things if that's what you plan to go into but also you can take a trip to the store buy a few components once you know what you're doing and you can build a radio if you want to you can build a blinking light if you want to you can build an alphanumeric display if you want to so it's one of the few things that you can really learn that once you understand it you can really go out there and build it if you learn about nuclear power plants they're amazing but you're not going to be able to go build a nuclear power plant if you learn about Einstein's theory of relativity it's amazing I love that stuff but I'm not going to be able to really test it myself but with circuits once you understand it and learn it you can actually play around with it and that's what I find so fascinating about it so I hope I've kindled your interest a little bit stay with me we're going to go through the sections and dive into all of these circuit analysis techniques I'll try to make them as simple as possible but you do you need to practice your problems practice problems that we present here and also the extra problems that are in your textbook

Channel: Math and Science

Views: 2,725,268

Rating: 4.9277334 out of 5

Keywords: circuit analysis, voltage, current, resistance, circuit, circuit theory, electrical engineering, electronics, ohm's law, voltage source, current source, resistors, circuits, tutorial, voltage current and resistance, engineering circuit analysis, current voltage and resistance, circuit analysis tutorial, circuit analysis lectures, circuit theory basics, circuit theory laws, electrical engineering lectures, ee lectures

Id: OGa_b26eK2c

Length: 41min 24sec (2484 seconds)

Published: Thu Feb 04 2016