A capacitor is a two-terminal, electrical component. Along with resistors and inductors, they are one of the most fundamental passive components we use. You would have to look very hard to find a circuit which didn't have a capacitor in it.
What makes capacitors special is their ability tostore energy; they're like a fully charged electric battery. Caps, as we usually refer to them, have all sorts of critical applications in circuits. Common applications include local energy storage, voltage spike suppression, and complex signal filtering
Covered in this Tutorial
In this tutorial, we'll be examining all sorts of capacitor-related topics, including:
How a capacitor is made
How a capacitor works
Units of capacitance
Types of capacitors
How to recognize capacitors
How capacitance combines in series and parallel
Common capacitor applications
Symbols and units
There are two common ways to draw a capacitor in a schematic. They always have two terminals, which go on to connect to the rest of the circuit. The capacitors symbol consists of two parallel lines, which are either flat or curved; both lines should be parallel to each other, close, but not touching (this is actually representative of how the capacitor is made. Hard to describe, easier to just show
(1) and (2) are standard capacitor circuit symbols. (3) is an example of capacitors symbols in action in a voltage regulator circuit.
The symbol with the curved line (#2 in the photo above) indicates that the capacitor is polarized, meaning it's probably an electrolytic capacitor. More on that in the types of capacitors section of this tutorial.
Each capacitor should be accompanied by a name -- C1, C2, etc.. -- and a value. The value should indicate the capacitance of the capacitor; how many farads it has. Speaking of farads...
Not all capacitors are created equal. Each capacitor is built to have a specific amount of capacitance. The capacitance of a capacitor tells you how much charge it can store, more capacitance means more capacity to store charge. The standard unit of capacitance is called the farad, which is abbreviated F.
It turns out that a farad is a lot of capacitance, even 0.001F (1 milifarad -- 1mF) is a big capacitor. Usually you'll see capacitors rated in the pico- (10-12) to microfarad (10-6) range.
When you get into the farad to kilofarad range of capacitance, you start talking about special caps called super or ultra-capacitors.
Note: The stuff on this page isn't completely critical for electronics beginners to understand...and it gets a little complicated towards the end. We recommend reading the How a Capacitor is Made section, the others could probably be skipped if they give you a headache.
How a Capacitor Is Made
The schematic symbol for a capacitor actually closely resembles how it's made. A capacitor is created out of two metal plates and an insulating material called a dielectric. The metal plates are placed very close to each other, in parallel, but the dielectric sits between them to make sure they don't touch.