Engineering Circuit Analysis: Voltage, Current, and Resistance Basics

hello and welcome to the engineering circuit analysis tutor uh 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 uh 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 uh and so there's a lot of details there and a lot of techniques that have been developed

over the years to pull those things off you know 100 years ago circuits and and all of the things that we take for

granted today would 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 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 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 uh to really try to make it as

accessible as possible to anybody out here who wants to learn it right uh don't let the word engineering SK area

too much engineering is a big word makes it sound really hard but I'm going to try to break things down uh 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 many uh 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 the challenge with circuits comes is that I can uh draw a circuit on board

and you might know how to analyze it and figure out what's going on uh 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 on later later in the course not and not in the beginning we are going to use uh some calculus some integration later

later later on in the course uh 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 uh and you really have to understand what they are a lot of

students if they haven't already had an interest in circuits uh they get very confused at what the difference between

voltage current is and how 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 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 um a lot of people

think they know what a circuit is and most people probably do but what is a circuit

uh 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 Circ uh you think about a circuit of a

racetrack or a circuit an the nd500 it has to go all the way around if you don't have it going all the way back

around to the starting point then you don't have a circuit and no electricity can flow in such a situation unless it

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 to any kind of detail is um you know here's a source

I'm going to put a plus minus to different to to denote it as a source this could 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 are 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 can completes a circuit

the electricity can circle around and around and around here coming from one terminal back around 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 it'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 got to 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 heard of current electric current um 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 um 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 and 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 there'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 NE 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 talks them into moving moving

is the battery right is the battery 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 and go into the orbit of the next atom and at that moment the same time that happens it's a chain reaction this

guys goes to the next guy this electron moves to this guy and this electron moves to its Jason 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 lock step moving from one atom to the next and this movement is really

you know you can think of it as 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 uh draw this here I'm drawing these um

these negative electrons moving so this is what we call electron

current or electric current there's another way to say that so the electrons uh if you want to think of it this way

we'll 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 it can't Supply any more electrons or if

it's a wall it just keeps going and going forever and you get charged for it 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 uh in a basic basic circuits course like a hobby book like you know go to Barnes & Noble or

somewhere and just get a book on electricity they'll talk about the electrons moving but when you get into

engineering and you really start trying to analyze how a circuit's going to really behave it's a little bit

cumbersome to talk about the electrons moving even though that's really what's happening in real life the reason that

it's a little bit cumbersome is because 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 to have negative signs running around all of our equations so in 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 dire 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 and this one moves here but at the very moment that this um 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 I 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 um I hope that makes

sense to you qual aely um based on my drawing here but if it doesn't all you really have to remember is

that the real current that we talk about in engineering is called the whole 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 it's saving you thought process

so uh 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 whole current the reason it's called a whole 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 whole current actually comes out of the positive terminal like this right and we say we denote that current I in

electrical engineering or in engineering and it's the whole 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 that anytime you have a circuit the source is going to always have a positive and a negative

terminal always just like any battery if you pull a battery out of the box you'll see one side's labeled positive one

side's label negative in real life if you hook the battery up to something electrons are the really the objects

that come around from the negative terminal back to the positive but in in electrical or in any kind of an

engineering course when you're taking a 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 current's coming out of the positive terminal even though in reality the electrons are bleeding out the other

side now the units of uh electric current uh I talked I told you briefly current is denoted I right I it probably

is some history to it you could go look it up you would think current would be called C but it's not it's called I um

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 uh

units let's go and change colors a little bit the units for current is the

Ampere which is also called an amp right um or you can call it simply a right the higher the number of of amps

the um you know the higher the 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 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 in in a physics class you'd be talking about an individual charge moving there's so many coolum on a

charge moving right but in a circuit you got billions of charges in this in the guy so you don't talk about coolum and

and how many kums of charge are crossing through a boundary you just look at the aggregate which is how many ampers which

is a coolum per second how many kums per second really are going through that guy so an amp here represents how many kums

of charge are passing if you were to slice this wire and watch how many go through there that would be how many

coolum of charge go through there per second but really you don't have to deal with that too much in in a circuits

class we're always going to be talking about amps or ampers so bringing it back to the everyday language that everybody

already knows you you've heard of amps right everybody's heard of amps um that is the current flow the higher the

number of amps in that circuit is the the more it can potentially kill you right it doesn't take much current to

kill a person actually uh believe it or not so you might have a car stereo that has you know a 10 amp amplifier right it

means 10 amps of current are flowing around that amplifier because to push the sound into those speakers and get

them to move really loud um 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 the Ampere which is which is what we have right here all right so to sum it up uh

which is really so important I keep talking about it current uh 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 many people get

confused with current because it's kind of used interchangeably voltage is the push I'm going 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 n Vol battery that battery comes in a physical size it has 9 volts 9 volts

mean is a relative indicator to tell you how much oomph for lack of a better word um that battery can push in a circuit so

the um 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 to layman's terms think about a straw Pretend This Were a soda straw that you

get at a 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 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 the main thing to take away from this guy um so it usually comes from a where it always comes from

a battery or some kind of other source that you might get uh that's generated out of the wall now for the units of

voltage the units is the Volt or simply call it

V uh so that's just that's the uh 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 one volt um it's not because it's measuring how much current is going through your body it's just

that if I grab on to a 10,000 volt fence it has the potential to push a ton of current through my body right whereas a

1vt source since it's so much less of a push so to speak um it's not really going to do very much to me uh right so

that's really the main difference so current and voltage tied at the hip but two different things U the biggest faux

paw you can kind of get into is saying boy that was a really impressive circuit that had 39,000 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 uh 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 all right 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 blow 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 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 air flow 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 directly translates to uh to electric circuits as well if I

literally have a wire a uh you know a copper wire as big around as my as I'm demonstrating here this 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 etched 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 for 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 all

so intertwined because of 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 a

lower voltage right and and 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 tight at the hip really as as far as being interrelated now the units of

resistance the units is called the ohm ohm but you never actually write ohm

in a circuit you always use this Omega this Capital Omega and so when you have a a five 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 flow to a 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 the

little examples 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 size wire different resistors uh different circuit

components are going to manifest themselves as different uh values of 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 1,000th of an amp right or you might talk about micro amps right 10 Theus 6 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 ohms you're talking about in the circuit but it might make more sense to talk about milliohms if

it's a very small resistance or even if it's tiny tiny micro ohms right that's 10us 6 ohms right or if it's a large

value maybe you have kiloohms or maybe you even have mega ohms which is millions of ohms right or here kilohms

is thousands of ohms so the the metric system applies here there's nothing special and for voltage maybe you have

Mill volts you know maybe you have kilovolts you know maybe you have mega volts maybe a nuclear power plant is

operating at so many megga volts or something like that very very important Concepts I can't stress them enough so

uh we've talked about current we've talked about voltage we've talked about resistance in detail uh 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 uh General things that you probably

heard growing up uh General uh definitions so to speak that you probably heard first one is DC and AC uh

DC versus AC let's talk about that for just a second uh because it's you know it's something that we need to make sure

you understand DC this stands for direct current right and uh basically what it means is

constant current flow basically all of the batteries you've ever used in your life the aaa's

the doublea's the 9 volts watch batteries I mean anything that anything built into a little device that we

called 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 it's

providing the current that comes out is 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 uh and this

means um well exactly what it 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 uh actually much easier to understand what the what the purpose of uh with the a 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 uh out to you what this means and this

is a a great 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 and

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 electricity 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 UH 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 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 um 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 alternating current and uh 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 um you know really all of our power plants whether they're gas or nuclear or 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 a wire inside of a magnetic field which is what's inside of a generator because of that motion of

rotation is is a direct result of how we get alternating current and that's the really the reason why the power plants

do that when we build a battery it's a chemical reaction you it's either on or it's off there's no motion inside of a

battery right so it's just going to give you that constant deal the constant current the 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 circuits um because really when you get to AC it's what once I show you the method it's really not

that different so we're we're going to do DC first get really good at it and then we're going to introduce the

Alterna and current uh mechanism just a couple of other definitions I want to get to real quick before we call a day

everybody's heard of this what is an open circuit what do you think an open

circuit is uh well if you have a circuit right if you have a circuit um 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 uh 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 what we call an open circuit now let's also take a moment to talk about a 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 um 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 uh 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 is 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 the 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 uh develop a short circuit because the two wires that that are supposed 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 spin 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 uh and it's very bad uh for lots of reason 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 wies 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 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 uh 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 Circ 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 in a circuit analysis we don't talk about that we talk about the positive current going in the other

direction has a symbol of I all right uh in in terms of our equations right the unit is amp or or a of course we can

talk about milliamps microamps uh kiloamps things like that as well uh 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 talk about or of course you have Mill

volts microvolts Etc uh 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 could

have million microohms kiloohms 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 you're 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 I 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 operat ating

circuit that you that you um 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 do

some more background stuff we'll talk about taking an overview of of the circuit components out there and then

we'll do another lesson on on what we call ohms law which in mathematical terms relates uh resistance current and

voltage together and I promise you Ohm's law is so simple that you know you'll you it'll just Boggle your mind it's

very very simple to understand and then once we get those Foundation things going going on then we can really start

diving into some real real circuits and looking at the current is 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 dodes

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 circuit 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 alpha numeric 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 and dive into all of these circuit analysis techniques I'll try to

make them as simple as possible but you do need to practice your problems practice the problems that we present

here and also the extra problems that are in your textbook