– [Voiceover] Now we’re

ready to start hooking up our components into circuits,

and one of the two things that are going to be very useful

to us are Kirchhoff’s laws. In this video we’re gonna talk about Kirchhoff’s voltage law. If we look at this circuit here, this is a voltage source, let’s

just say this is 10 volts. We’ll put a resistor connected to it and let’s say the resistor is 200 ohms. Just for something to talk about. One of the things I can do

here is I can label this with voltages on the different nodes. Here’s one node down here. I’m going to arbitrarily

call this zero volts. Then if I go through this voltage source, this node up here is

going to be at 10 volts. 10 volts. So here’s a little bit of jargon. We call this voltage here. The voltage goes up as we go

through the voltage source, and that’s called a voltage rise. Over on this side, if we are standing at this point in the circuit right here and we went from this

node down to this node, like that, the voltage

would go from 10 volts down to zero volts in this circuit, and that’s called a voltage drop. That’s just a little

bit of slang, or jargon that we use to talk

about changes in voltage. Now I can make an observation about this. If I look at this voltage

rise here, it’s 10 volts, and if I look at that voltage

drop, the drop is 10 volts. I can say the drop is 10 volts, or I could say the rise on

this side is minus 10 volts. A rise of minus 10. These two expressions mean

exactly the same thing. It meant that the voltage

went from 10 volts to zero volts, sort of going

through this 200 ohm resistor. So I ran a little expression for this, which is, v-rise minus v-drop equals what? Equals zero. I went up 10 volts, back down 10 volts, I end up back at zero volts,

and that’s this right here. This is a form of Kirchhoff’s voltage law. It says the voltage rises minus the voltage drops is equal to zero. So if we just plug our

actual numbers in here what we get is 10 minus 10 equals zero. I’m gonna draw this circuit again. Let’s draw another

version of this circuit. This time we’ll have two

resistors instead of one. We’ll make it… We’ll make it two 100 ohm resistors. Let’s go through and label these. This is again 10 volts. So this node is at zero volts. This node is at 10 volts. What’s this node? This node here is… These are equal resistors, so this is gonna be at five volts. That’s this node voltage

here with respect to here. So that is five volts. This is five volts. And this is 10 volts. So let’s just do our visit again. Let’s start here and

count the rises and drops. We go up 10 volts, then we

have a voltage drop of five, then we have another voltage drop of five, and then we get back to zero. We can write the sum of the rises and the falls just like we did before. We can say 10 volts minus

five minus five equals zero. Alright. So I can generalize this. We can say this is general

we can do the summation, that’s the summation symbol, of the v-rise minus the sum

of the v-fall equals zero. This is a form of Kirchhoff’s voltage law. The sum of the voltage rises minus the sum of the voltage falls is

always equal to zero. There’s a more compact way to write this that I like better, and that

is, we start at this corner… We start at any corner of the circuit. Let’s say we start here. We’re gonna go up 10

volts, down five volts, and down five volts. So what we’re adding is the voltage rises. We’re adding all the voltage rises. Rise plus 10. That’s a rise of minus five

and a rise of minus five. So I can write this with

just one summation symbol. The voltages around the

loop, where i takes us all the way around the loop, equals zero. So this means I start

any place on the circuit, go around in some direction,

this way or this way, up, down, down, and I end up back at the same voltage I started at. So let’s put a box around that too. This is Kvl, Kirchhoff’s voltage law. Now I started over here in this corner, but I could start anywhere. If I started at the top and went around clockwise, if I started here say, I would go minus five,

minus five, plus 10, and I’d get the same answer. I’d still get back to zero. If I start here and I

go around the other way, the same thing happens. Plus five rise, plus five rise, and this is a 10 volt drop, so it works whichever way

you go around the loop, and it works for whatever

node you start at. That’s the essence of

Kirchhoff’s voltage law. We’re gonna pair this

with the current law, Kirchhoff’s current

law, and with those two, that’s our tools for

doing circuit analysis.

what happens when charges move flat I mean why does potential drop occurs only at resistors? I mean when an electron travels from negative end towards the positive end it continuously loses potential so why we don't consider potential at flat areas where no resistors are present ?

Why the voltage drops?

useless video bring back our sal

no offense dude. but you suck at explaining and giving good examples.

bharat mata ki jai

why we taken conventional current +ev to _ev??

the voltage directions are wrong so the numbers become wrong too. this is very misleading

Thank you

Y u no discuss complex circuits??I get stuck in the maths given in my book

resistance only reduce current.. which mean input voltage does not change.if input is 10v and output is also 10v.

where the hell has sal gone??

couldn't understand…

This is the most disappointing video of khan academy…… ?????

(For 2:19) If I connect one voltmetre across the battery and another voltmeter across the resistor will the voltmeter across the battery show +10V and the voltmeter across resistor show -10V ?

khan academy is the legendary site my boy

ever had of LOGIC gate ntwana yam?

Thank you so much for this video! I have been really struggling with understanding when voltage and amp sources are equated as being negative verses positive, especially when there is a mix of both in the circuit!

Plzz give at least answer of a single "why this is true" in ur explanation.

Great review, had all this 40 years ago in college, but basics are always applicable.

Good

So complicated explanation of a sumple thing

Very useless.

Hey, in 3:03 there is a error is guess, look, u have taken voltage rise as -10 and voltage drop as +10. The formula u told is saying voltage rise minus voltage drop=0 . If i substitute that " minus 10 minus 10 which leads to -20. Can u xplain on this.

Thanks mate for the video.. It's good!

If drop is 10 volts and rise is -10 volts. Formula V rise – V drop = 0; in this case -10 (rise) – (+10) drop= -20?

This video was totally not correct. With different resistances, it is totally different

Pretty badly explained because 'rise' has nothing to do with the perception of view, it has to do with the travel of conventional flow. Just to further prove this, imagine the resistor is sideways, left to right instead of up and down. There is still a drop on that resistor even though it's going sideways. The problem with this instructors explanation is that he is inferring that voltage is a sort of travel, but it is not gradual travel, it is explicitly a measure of the difference between two points. Here's where this video fails and it is the problem with the conveyance of the teaching.

ATTENTION: EVERYONE WHO IS ASKING ABOUT -20 VOLTS….

His equation Vrise – V drop = 0 is the equation for the whole circuit. On the left side, where the battery is, there is a 10V rise….on the right, where the resistor is, there is a 10V Drop…this is where he is getting 10(rise)-10(drop)=0 | That rise= -10 is, like he said, just another way of writing a drop. I understand the confusion, there is not much point of writing that unless he wrote 0=sum of voltage rise … in which case that specific "rise" on the right would technically be negative due to the resistor, however that is often confusing and he just was using this as a way to get you to understand that this is a decrease in voltage. His math however is all correct.

This video is really informative unlike half of those Indian videos which one can't even understand the language

Sorry but this series of videos isn’t up to the usual standards. What are we doing and why ?

Thanks a lot

Thank you… It was very helpful ?