Series and Parallel Circuit Basics

There are different ways of connecting components in a circuit, each giving different results. We will use a circuit with 3 bulbs to demonstrate:

Series Circuit:


Here, the bulbs are placed in line, one after the other, forming a simple series circuit. Current flowing through the circuit can only take one path, which is through each bulb. As this happens, the current is reduced as each bulb uses up energy. The result is that the current used in the circuit is split between the number of bulbs it has to pass through. Subsequently, the bulbs glow about half as bright, with about the same current used in total as of there was a single bulb. The more bulbs you add this way, the dimmer they’ll glow as there are more to share the restricted current.

Parallel Circuit:

Our circuit with 3 bulbs looks something like this when arranged in parallel:


The same circuit could also be represented like this, but if you follow the wires, you'll see it's identical:


The bulbs in our parallel circuit all have a direct electrical path to the battery supply, allowing them to all share the current directly. More current is drawn from the battery, so for each bulb added would run the battery down that many times faster than if the bulbs were in series, but they’ll glow at full brightness while the battery has enough power.

A more complex circuit can have parts that are both series and parallel:


To work out what the circuit will do, we need to break the circuit down into smaller parts. The group of parallel bulbs would act as like second bulb in series, although they would draw more current from the battery.

We will cover series and parallel circuits in more detail later on, providing calculations for current, voltage, etc. as we introduce new components.