What Is the Difference Between Series and Parallel Circuits?

What Is the Difference Between Series and Parallel Circuits?

Circuit topology is a fascinating and surprisingly accessible family of concepts. Today, we’re going to explore the difference between series and parallel circuits.

What is a series circuit? Moreover, what is a parallel circuit? Even if you have absolutely no clue, we can already tell you that you probably use both types of circuits every single day of your life.

Understanding the Difference Between a Series Circuit and a Parallel Circuit: Definition and Key Concepts

A series vs. parallel circuit diagram.

In the simplest possible terms: a series circuit offers the current of electricity one ideal path through the maze. Parallel circuits, on the other hand, are configured so that there are two or more paths through the circuit for the current to follow. These types of circuits are deemed “parallel” because the branching path of the current runs alongside itself as it passes through both loops concurrently.

The behavior of a current in a parallel circuit as it passes through a circuit is largely determined by the fact that an electric current will seek the lowest-voltage areas in a given system, occupying these areas in whatever way that it can.

It’s not exactly this simple, but you’ll be glad to know that there really are only a few other rules involved here. What exactly determines the current’s path of least resistance?

Related: How to Check Voltage With a Multimeter

Series vs. Parallel Circuits: What in Toledo Is Going On Here?

To visualize this phenomenon, we’re going to call out a few key vocabulary words to keep in mind:

  • Current: Electrical energy, drawn from a source and bound by a conduit.
  • Source: Where is the electricity coming from? A battery? A bolt of lightning?
  • Conduit: Anything conductive enough to draw electricity forward from its source. The copper wire inside your smartphone’s charging cable is one example of an electrical conduit, leading the current from your computer or from a block charger to the battery in need of a charge.
  • Closed Circuit: A closed electrical network, one in which the current has a direct path back to the source, forming a complete, continuous, and unbroken loop.
  • Voltage: A measure of the potential energy per unit when any two points in the circuit are compared with one another. This is the mechanism by which current finds its way through a circuit; excess voltage in one part of the system flows to points of lower voltage, constantly seeking equilibrium.
  • Resistance: Any factor that inhibits voltage compensation and flow. Silicone is one example of a highly resistant, insulative material used commonly in electronics. Resistant material is used to direct the flow of electricity throughout the circuit and to prevent it from escaping its conduit.


When visualizing an electric current, we’re dealing with the transfer of electrons from atom to atom along the conduit. An object becomes positively or negatively charged when it’s got more electrons hanging around than protons, which don’t leave the atom of their own accord.

Electrons are the currency of electricity. This transfer of electrons is integral to the way that a current is conveyed by every atom of the conduit.

How Do Electrons Pass Through Both Series and Parallel Circuits?

A bunch of wiring.

Think about all of these electrons riding the rails of the conduit as though they’re tiny cars driving on a miniature super-highway.

In a closed, complete circuit, the electricity follows its conduit to where it will eventually “sink”—that is, the point of lowest voltage available to the current, the place where it will physically feel most compelled to go. The electricity loops through the closed system neatly and continuously, its total conserved voltage distributing itself throughout the system naturally, assuming a specific quantum state.

In a parallel circuit, instead of traveling over and over again through this one, single, looped path, there are “on-ramps” and “off-ramps,” junctures of access offering the current an alternative scenic route through two or more parallel branches. The simple looped state is now distributing itself much differently throughout the circuit.

Related: DIY Electronics Project Ideas for Engineering Students

Voltage in Parallel: Kirchhoff’s Circuit Laws

We’ve seen parallel circuits described as resembling branching blood vessels to some extent. The entire network supports blood flow through every vein and capillary, reaching every corner of the body that the system is connected to.

German physicist Gustav Kirchhoff was one of the first to formalize circuit analysis mathematically. He was able to simplify the behavior of electricity in a circuit using two physical laws that go hand-in-hand.

A current coursing through any circuit obeys these laws physically, no matter what:

  1. The energy flowing into a node or the intersection of a branching circuit much be equal to the energy that flows out of it, conserving the system’s net total charge.
  2. The total sum of net potential electrical differences throughout the entire system must equal zero. Supply components, such as battery cells, contribute to this sum, feeding into energy-consuming components, such as resistors or appliances like lightbulbs.

Both of these clarify just what exactly is governing the current’s behavior through any given circuit. This second point, however, is particularly interesting.

Essentially, this second law asserts that every electron passing through the circuit must gain exactly as much energy as it loses along the way. If either requirement is not being met, the path being considered is not a viable path for the current to flow through naturally.

Related: Low-Budget DIY Electronics Projects for Beginners

Series and Parallel Circuits Examples

Some wiring and a multi-meter.

The most common example of voltage in parallel vs. in series: Christmas lights. Specifically, modern strings vs. vintage lights.

Originally, Christmas lights used to be strung in series, a one-way daisy chain of bulbs; if one bulb fails, the entire thing is extinguished, both before the burnt-out bulb and after. The circuit is now open and has effectively been broken.

It’s a sorry state of affairs, but don’t let this first example spoil circuits in series for you. There are still many circumstances where series circuits are, in fact, the appropriate type of circuit to choose:

  • Simple contraptions that only control one appliance—the little LED lights in some toys, for example
  • A flashlight, or any other simple device actuated by the flip of a switch
  • A fuse protecting a large appliance like a washing machine from overcurrent; they’re linked up in a series circuit so that the series is broken by consequence when the fuse is triggered

In contrast, parallel circuits are designed to remain in operation under any conditions. Modern Christmas lights use a parallel circuit to prevent the aforementioned unfortunate holiday disaster, for instance. Even if there’s only one bulb left standing, it’ll still be able to shine.

Other common examples of parallel circuits include the following:

  • Car headlights are wired in parallel so that one side remains functional even if the other side fails
  • Commercial speaker systems use parallel circuits for the same reason
  • Streetlamps rely on voltage in parallel in order to keep the majority of the street illuminated

Neither parallel circuits nor series circuits should be seen as “better” or “worse” than the other—both are incredibly useful in their own ways under different circumstances. If you know what you need to accomplish with the circuit that you’re designing, the side of the fence that you belong on should be completely obvious.

Related: What Is a Multimeter and Where Can You Use It?

The Basics on Circuits: Parallel and Series Circuits, and Why Both Matter

Electricity is dangerous. Understanding how circuits work is one way to keep yourself safe, no matter what you happen to be getting into.

The good news: if you’re able to attain a grasp on these concepts and others in this field, you’ll be armed and ready with everything that you’ll need to know in order to prevent your project from frying your body alive like a chicken nugget. Take it from somebody who’s been there.

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