 So now let's talk about Kirchhoff's rules. There's actually two rules that he came up with to help us analyze electrical circuits. The first rule, sometimes called the current rule, is also sometimes referred to as the junction rule. The second rule, the voltage rule, is sometimes referred to as the loop rule. And once we start seeing what these rules are, you'll see why there's a connection between current and junction, and voltage and loop. So for the current rule, it states that at any junction, the total current in equals the total current out. Now graphically, we can depict it using this section of a circuit. And if I pick my junction here, then the total current coming into that junction has to be equal to the sum of the currents coming out of that junction. If I were to label these currents as I1, I2, and I3, I could write this up as an equation giving us I1 equals I2 plus I3. Alternately, I could express all the currents coming into the junction as positive values, and the currents coming out of the junctions as negative values, in which case the total current has to be zero. Now I could look at the voltage rule. For the voltage rule, around any closed loop, the sum of the voltages equals zero. Now another way to look at this is to remember that each voltage is a potential difference. So we could phrase this rule as around any closed loop, the potential returns to its original value. This is a little more complicated, so let's take a look at an example that actually has some numbers in it. So let's say we've got a circuit here. I start at some point in the circuit, and it doesn't actually matter where I start. But as I work my way around the circuit, I have to determine what happens to the potential. After at this battery, my potential is going to increase ten volts. As I move across this resistor, I might drop seven volts. I then move across another battery where I might have an increase of five volts. Finally, moving across the last resistor, I could have a minus eight volts. Now these particular numbers, well, I just kind of picked them, but I had to pick them in such a way that when I added up all of the increases and decreases across the entire loop, I came up with a value of zero. If you were analyzing a real circuit, you'd probably have your voltages for your batteries, and you'd figure out the voltage for the resistors using Ohm's law. So you need to take a little bit more time, and these voltage rules can become very complicated depending on our loops. But overall, this is an introduction to Kirchoff's rules.