Series & Parallel Capacitors

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  • 0:04 Definition of a Capacitor
  • 1:15 Capacitors in Parallel
  • 3:01 Capacitors in Series
  • 4:49 Capacitors in Series…
  • 5:38 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

A capacitor is used to store electrical energy in a circuit. In this lesson, learn how to calculate the equivalent capacitance of circuits containing series and parallel capacitors.

Definition of a Capacitor

Did you know that there's one special type of electrical device that's an essential component of almost all modern technologies? These critical components can be tiny, like the ones that store information in your computer's memory, or large, like the ones that are used to power hybrid and fuel cell vehicles. This important electrical device is called a capacitor, and it works by storing and releasing electrical energy.

Capacitors store energy by having two oppositely charged plates held very near each other (but not touching). The ability of a capacitor to store charge is known as its capacitance, which is measured in units of Farads. Capacitance equals the ratio of the charge stored on the capacitor to the voltage applied. In other words:

A parallel plate capacitor stores energy by storing opposite charges on plates held near each other, but not touching
capacitor

In electric circuits, there are often multiple capacitors that work together to store energy and charge. In many cases, you need to connect several capacitors together to get the capacitance you need. There are two basic ways that capacitors can be joined together in an electric circuit: series and parallel.

Capacitors in Parallel

If two or more capacitors are joined together in parallel, then each capacitor is connected independently to the same voltage source, which is often a battery. This means that each capacitor has the same voltage across its plates.

Capacitors in Parallel: Each capacitor is independently connected to the battery, so each capacitor has the same voltage across its plates
Capacitors in Parallel

Based on the configuration of the capacitors, you can calculate an equivalent capacitance for the entire circuit. Since we know that each capacitor has the same voltage across its plates, we can calculate the equivalent capacitance with the formula you're looking at on your screen right now:


Equivalent capacitance - parallel


The equivalent capacitance of capacitors in parallel (Ceq) equals C1 + C2 + C3, and so on until you've summed up all the variables. This means that the equivalent capacitance of any number of capacitors connected in parallel is simply the sum of all the individual capacitances. The equivalent capacitance is more than the capacitance of any one of the individual capacitors.

If you had a circuit with two capacitors in parallel, one with a capacitance of 12 F and the other with a capacitance of 8 F, what is the capacitance of a single capacitor that could be used to replace both of these?

To answer this question, you need to calculate the equivalent resistance of the circuit, which you can see worked out on your screen right now:


Parallel capacitors example


As you can see, after running the variables through the formula, the equivalent capacitance is 20 F.

Capacitors in Series

In addition to being joined together in parallel, capacitors can also be connected in series in an electric circuit. If two capacitors are in series with each other, they're in the same branch of the circuit. Because they aren't independently connected to the voltage source, each capacitor may have a different voltage across its plates. However, because they're all connected directly to each other, each capacitor in series will store the same amount of charge.

Capacitors in Series: Each capacitor is connected to the next in the same circuit branch, so each capacitor stores the same amount of charge
Capacitors in Series

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