 In this video, we're going to be talking about a balanced bridge circuit. Commonly you'll see a balanced bridge circuit in a wheat stone bridge, which we use to determine very small resistances. So the way that this works is, we have four resistors, one, two, three, four resistors, and we're going to assign some values to each resistor except for one of them. We're going to show you how to determine for that fourth one. So let's say that this is 10 ohms. This is 20 ohms. Let's say this is 3,000 ohms, and let's say this one is unknown. What we need to do now is figure out what this one is going to be. Now if we know that this is a balanced bridge circuit, basically what we're saying is, is from this point here and this point here, if I was to measure my voltmeter across these points, let's measure my voltage across this, I should read zero volts because whatever the voltage is going to be here should be the same here and the voltage here should be here as well. So we can build a very easy proportion to determine what this is. Let's go about doing that right now. So if I say that 10 is to 20 ohms as 3,000 is to X, that is how we determine our ratio. So then we're just going to take that, we're going to cross multiply and divide. So I'm going to go, basically here is going to be 10 times X is equal to 20 times 3,000. So if I do that, I end up with this in the formula. Let me just write this up for you, 10X equals 60K ohms or 60,000, then X is going to equal 60K divided by 10, therefore X is going to equal 6K ohms. So then we can take this one here and replace it with 6,000 and we'll change that to 6K ohms. So you can see that the proportion actually works out because 10 is half of 20 as 3,000 is half of 6,000. So the proportion works out. This one was a pretty easy one to work through but it will work for you every single time just so that we know that we want in a balanced bridge circuit, this voltage and this voltage will have to equal each other, this voltage and this voltage will have to equal each other, therefore the proportions have to be the same, which is why this is half of this and this is half of this.