 In this video, I'm going to take a complete walkthrough of a series circuit with a battery. Let me just get my point out here, my battery, and three resistors in series. We're going to walk through some common characteristics of a series circuit and a couple of laws that apply to them. Now, before we get anywhere, let's apply some values to these things. We have a 120 volt battery. I have a negative terminal and a positive terminal. Each resistor of assigned a value, I've got 30 ohms, 20 ohms, and 10 ohms. And in this circuit, it's going to flow from negative to positive. We are going to use electron current flow, not conventional. Conventional tells us positive to negative, but we're going to use negative to positive. Now to determine the total circuit resistance, because in a series circuit, the key that unlocks everything is current, we need to determine what the total circuit resistance is, because the current is going to have to go across this guy, this guy, and this guy. In order to figure out where current, we're going to have to figure out what 30 plus 20 plus 10 is. I think we can do this, everybody. It's going to be 60. I did that in my head. So we've got 60 ohms of total circuit resistance. Our next step is to figure out what the current is. In order to do that, we're going to use Ohm's Law. So we're going to use this variation of Ohm's Law. It can be transposed into many different things, but we're going to determine current is equal to voltage divided by resistance. So we're going to figure out we've got 120 volts here. We've got a resistance of 60 ohms. So therefore my current is going to be, I'm going to do this in my head as well, 2 amps. And lo and behold, I'm correct. Now we have got our total circuit resistance, our total circuit voltage, and our total circuit current. The thing with current in a series circuit is it remains the same throughout. Once it gets flowing, you've got 2 amps here, here, and here, and it doesn't change. So we can use that to determine what our bolt drops are going to be across each one of these resistors. One going to the Ohm's Law. This time we're going to transpose it a bit. We're going to go V is equal to I times R. So we're going to use the current of 2 amps and the resistance of each resistor to determine the bolt drop across each resistor. 2 amps times 10 ohms gives me 20 volts. So there's that. 2 amps times 20 ohms gives me 40 volts. Next up, 2 amps times 30 ohms gives me 60 volts. There you go. We have now determined what the bolt drop is across each one of the resistors. It wasn't that hard, was it? Next up, a good way to double check your work on this is there's Kirchoff's Law talks about how you have to take the algebraic sum of a circuit and it has to equal zero. What that is saying is that you're going to take this 120 and subtract 60, subtract 40 and subtract 20 and you end up with the zero as your answer. An easier way to look at the Kirchoff's Law is that the sum of the bolt drops in the circuit has to equal the source. So I've got 60 plus 40 plus 20 that equals 120 volts. Therefore I've done everything correctly. The next step in this circuit to determine everything because we've now determined current, we've determined bolt drops, now we have to determine the power being dissipated by each resistor. There's two ways we can go about that. We can go I squared R or E squared over R. In a series circuit, get in the habit of going I squared R because I squared doesn't change. Your I, your current, is the one constant in this circuit. If you went with E squared over R, you'd have to remember to use 20 squared over 10. You'd have to remember to use 40 squared over 20. You'd have to remember to use 60 squared over 30. It's a really easy way to make a mistake. So just stick with the I squared R in a series circuit. You're going to be fine. So there we go. The power is equal to I squared R. So let's get busy here. I squared being 2 squared, 2 squared times 10 gives me power being dissipated, 40 watts. 2 squared times 20 gives me power being dissipated, 80 watts. And 2 squared times 30 gives me power being dissipated, 120 watts. So look at this. We're filling this little page up. Isn't it a thing of beauty? We have 40 watts, 80 watts, 120 watts, 60 volts, 40 volts, 20 volts. The only thing left to determine really now is my overall power being dissipated. Again, two ways I can do this. I can go and I can add these up. 120 watts plus 80 watts plus 40 watts gives me 240 watts total. That's one way to determine it. Now let's double check our work. We can punch into a calculator, I squared R, 2 squared times 40, which is 4 times 60, gives me 240 watts. And that's it. You've now successfully navigated your whole way around a series circuit. We've determined everything that you could possibly want to determine. Series circuits are quite simple once you understand the tricks of them.