Series and Parallel Circuits

This page explains the difference between series and parallel circuits, why it matters, and the implications.

Summary

You have maybe heard of series and parallel circuits but not known what they are, or whether you even need to know. There are important differences in the way the voltage and current are distributed, which are helpful to understand.

Safety

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The water analogy

The flow of water is often a useful (though not perfect) analogy for the flow of electricity, as shown (humourously) in this xkcd cartoon.

Water pressure is rather like voltage, which is in fact the electrical "pressure" driving a current around a circuit against certain resistance.

Water flow (in litres/minute, or whatever you like) is analogous to the electrical current in Amps. A current of 1 Amp flowing around a circuit corresponds to 6.25 billion billion electrons per second passing any given point.

If a water pipe contains a constriction, there will be a greater pressure drop across the constriction than over the unconstricted length free flowing length. In the same way, there is a voltage (electrical pressure) drop across any resistance in a circuit, the greatest voltage drop across the greatest points of resistance.

If a river can flow through several alternate channels, the flow will distribute itself according to the width of the channels, with most flowing through the widest. In the same way, if electricity is given several paths it can follow, the most current will flow through the path offering the least resistance.

Unlike water, electricity can't just spill out, but can only flow if it can flow all the way around a circuit, perhaps through many different paths on the way.

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