Circuitry 101: Examples of Series Circuits & How They Work

By Helen LinLast Updated May 12, 2021 7:36:03 PM ET
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When it comes to electrical circuits, there are two basic varieties: series circuits and parallel circuits. The major difference between the two is the number of paths that the electrical current can flow through. Here, we'll zero in on series circuits, delving into how they work and which common electronic devices utilize them.

What Is a Series Circuit?

In a series circuit, there’s only one pathway the electricity can flow through. While a single series circuit may power multiple devices, every part of the circuit, including all of the devices, wires, and the power source, are connected along the same path.

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Need a visual of how it works? Think of a group of people standing in a circle, each holding a candle. One person in the circle lights their candle — and then they light the candle of the person to their left. That second person will then use their newly lit candle to light that of the person to their left — and so on. That pattern would continue until everyone’s candle was lit.

In essence, that’s how a series circuit works. The power source sends electricity to the first device; the electricity flows through that first device and into the second, and so on, until, eventually, all of the devices are connected, one right after the other.

Series Circuit Problems

As efficient as a series circuit can be, it isn't without its downside. Since electricity travels through each device along a path, all it takes is one device to burn out to put the rest in jeopardy. Going back to our candle example, if the second person in the circle has a candle that just won't light, they can't pass the flame on to the third person.

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With electricity, things are even worse. All it takes is for one device to malfunction and the entire operation is a mess. Back in the old days, this was a common problem with Christmas lights. All it took was one bulb burning out to render an entire strand of lights incapable of producing their signature seasonal glow.

Another downside? Because all of the devices share the same power source, they all get an equal amount of energy. This isn’t inherently a bad thing in and of itself — well, unless you want to add a large number of devices. With each new device you add, there's less energy to go around, so, in the case of lights, each of the lights in the circuit would grow dimmer with each new addition.


Series Circuit Advantages

Series circuits tend to be popular because they are definitely not without their advantages. One of the more obvious perks of the series circuit is that it tends to be much easier and efficient to set up.

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Consider the case of string lights, for instance. Because they utilize a series circuit, it's not necessary to connect every single light to a power source with its own wire. Instead, a single strand of wires simply connects one light to the next so that they all form a handy line.


Another advantage? Each light in a strand gets its equal share of electricity. Otherwise, you might have two or three lights that shine like rockstars while the others produce a weak glow.

It's also easier to read a series circuit with an ammeter or a voltmeter, should you desire to do so. Since the current flows evenly throughout the entire circuit, you'll get the same readings no matter what part of the circuit you measure.


Series Circuit Examples

In order to better understand the additional advantages of series circuits, let's take a look at some common household items that tend to use them. Water heaters, for example, illustrate how useful series circuits can be when one needs to cut off the flow of electricity.

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That is, power flows to a water heater through a thermostat, which is rigged to be able to tell the temperature of the water. The power is able to flow through the thermostat and into the heating element, which in turn heats the water. But when the thermostat can tell that the water has reached its target temperature, it's able to switch off. This breaks the series circuit and keeps the water from getting any hotter than intended.


Lamps are another example of why a series circuit can come in handy. In basic terms, the series circuit is made up of a power source that travels through a path connected to the switch, then up to the bulb, and back again. When you turn off a lamp, you're really just breaking the series circuit.

Series Circuit Diagram

A circuit diagram uses symbols that represent different parts of said circuit. Engineers use these series diagrams to map out a potential circuit much like an architect uses blueprints. Some diagrams are pretty straightforward, while others can be incredibly complex.

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The two you'll see above are examples of very basic series circuit diagrams and show some of the basic symbols used to represent different parts of each circuit. In the first diagram, you'll see two parallel lines over on the left-hand side which represent an energy cell.

The straight lines on each diagram represent wires that the electric current flows through. The squiggly lines in the diagram on the left represent resisters. At the bottom of the second diagram, you'll see a different set of parallel lines that together make up the symbol for a battery. As you follow the wires around the series circuit, you'll see three circles, each of which has an x in the middle. This is the symbol used to indicate a light bulb.


If you're interested in learning more about circuit diagrams, and how to read them, check out this great breakdown from Teach Engineering.