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

Simple Series Circuit
Simple series circuit - The current needs to pass through each bulb in turn to complete the circuit
Photo showing simple series circuit


 [Photo of First circuit series]

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:

Simple Parallel Circuit 2
Simple Parallel Circuit - The current is available to the three bulbs separately.
Photo showing simple parallel circuit

The same circuit could also be represented like this:

Alternative representation of a simple parallel circuit
Figure 3 A budget Analogue Multimeter with the needle indicating the value being measured


The bulbs in our parallel circuit all have a direct electrical path to the battery supply, allowing them to all each share access to the current. 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.

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

Circuit containing series and parallel elements
This circuit contains three bulbs in parallel, which are in turn in series with the remaining bulb.
photo showing series and parallel combination circuit


To work out what the circuit will do, we need to break the circuit down into smaller parts. The three parallel bulbs would act as a second bulb in series, although when calculating factors such as resistance of the circuit, they will need to be calculated first.

We will cover series and parallel circuits later on, providing formulas and laws for calculations as we introduce new components.

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