# Series and Parallel Circuits

## Series Circuits

### Nodes and Current Flow

Before we get too deep into this, we need to mention what a **node** is. It’s nothing fancy, just the electrical junction between two or more components. When a circuit is modeled on a schematic, the nodes are the wires between components.

*Example schematic with four uniquely colored nodes.*

That’s half the battle towards understanding the difference between series and parallel. We also need to understand **how current flows** through a circuit. Current flows from a high voltage to a lower voltage in a circuit. Some amount of current will flow through every path it can take to get to the point of lowest voltage (usually called ground). Using the above circuit as an example, here’s how current would flow as it runs from the battery’s positive terminal to the negative:

*Current (indicated by the blue, orange, and pink lines) flowing through the same example circuit as above. Different currents are indicated by different colors.*

Notice that in some nodes (like between R_{1} and R_{2}) the current is the same going in as at is coming out. At other nodes (specifically the three-way junction between R_{2}, R_{3}, and R_{4}) the main (blue) current splits into two different ones. *That’s* the key difference between series and parallel!

### Series Circuits Defined

Two components are in series if they share a common node and if the **same current** flows through them. Here’s an example circuit with three series resistors:

There’s only one way for the current to flow in the above circuit. Starting from the positive terminal of the battery, current flow will first encounter R_{1}. From there the current will flow straight to R_{2}, then to R_{3}, and finally back to the negative terminal of the battery. Note that there is only one path for current to follow. These components are in series.