Series vs. Parallel Circuits

Series and Parallel Circuits

Simple circuits (ones with only a few components) are usually fairly straightforward for beginners to understand. But, things can get sticky when other components come to the party. Where’s the current going? What’s the voltage doing? Can this be simplified for easier understanding? Fear not, intrepid reader. Valuable information follows.

In this tutorial, we’ll first discuss the difference between series circuits and parallel circuits, using circuits containing the most basic of components – resistors and batteries – to show the difference between the two configurations. We’ll then explore what happens in series and parallel circuits when you combine different types of components, such as capacitors and inductors.

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.


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:


Notice that in some nodes (like between R1 and R2) the current is the same going in as at is coming out. At other nodes (specifically the three-way junction between R2, R3, and R4) 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: