What is a capacitor?
Hi there! My name is Patty. I am a type of electronic component called a Capacitor. Sometimes I am referred to as a “cap,” for short. I am a two-terminal component. That means that I have positive and negative sides, like my friend Ed the LED.
Also like Ed, my positive terminal, lead or leg is longer than my negative side.
You can find Capacitors in all-kinds of circuits, like greeting cards that play sounds or music, your TV, your car and more. What makes us capacitors special is our ability to store energy: I am like a fully-charged electric battery. Unlike a battery, I am not a source of energy, but I can store up energy provided by a battery or another source.
In circuits, people use capacitors for energy storage, preventing voltage spikes and for complex signal filtering. These things may sound complicated, but I’ll explain a bit more about what they mean shortly. First, we need to talk about Capacitance.
Capacitance
Every capacitor has a certain amount of something called capacitance. That means the amount of charge that a capacitor can store up inside of itself. The term people use to describe capacitance is farad. We abbreviate this with the letter F. The word “farad” comes from Michael Faraday. He was a famous scientist from a long time ago who studied the basic principles of electricity. He’s kind-of my hero.
A single Farad represents a LOT of capacitance, far more than many circuits need. There are lots of capacitors like me that have a smaller amount of capacitance, so we use other letters in front of the F to signify just how much. One of those letters is the µ, which means micro. So when you see “µF,” that means micro-farad.
Take me, for example. I am a 2.2 µF, or microfarad capacitor. That means I have 0.0000022 Farads of capacitance. See what I mean about 1 Farad being a lot? I am used in smaller circuits and things like toys and games that light-up, make sounds or move. Bigger circuits, like TVs, use capacitors that have a lot more capacitance. Those capacitors can be quite large. They can also be dangerous, even when unplugged. So if you ever see a large capacitor as a part of a circuit, don’t mess with it without an adult or a professional around!
How a Capacitor Works
Capacitors contain two metal plates and a piece of material that sits between them. The two metal places are close together, but the material between keeps them from touching. The plates contain material that conducts electricity, like aluminum or silver. The material in the middle is always something that does not conduct electricity.
When you send current into a Capacitor, the charge gets stuck on the metal plates. Because the material between them keeps them separate, the charge cannot pass from one plate to another. Because they are separate, the capacitor creates an electric field that stores up energy like a battery.
And like a battery, a capacitor can hold that charge until it has somewhere else to go. Once a capacitor fills up, or reaches its capacitance, it will repel any new current that comes through. If there is somewhere else for it to go, it will go there instead.
For example, if we connect a capacitor in a circuit next to an LED, once it fills up, it will pass current along to the LED, which will light it up.
If the capacitor is large enough, it can function for a short time like a battery after removing a power source from the circuit. A 470 µF capacitor, for instance is large enough that when removing power from a circuit that contains an LED, the light in the LED will fade, as opposed to going out immediately. This happens because, once we remove the power source, the capacitor discharges its remaining power, keeping the LED lit for a short time.
Types of Capacitors
There are lots of different types of capacitors out there. Many are much larger than me, and some look quite different. On the small side, there are capacitors called “Ceramic capacitors.” They have this name because the insulation between the two plates is ceramic. These usually look like small yellow, red or orange bulbs. They have a very small capacitance, so they can’t store much charge, but they can still be useful. Can you spot a few examples of these in the picture above?
There are also Electrolytic, Aluminum and Tantalum capacitors. These can pack a lot of capacitance into a small size. The aluminum variety looks like a little tin can. That’s what I am. We happen to be the most popular type of capacitor, so if you check out a circuit, chances are you’ll see a capacitor that looks like me. Often, capacitors like me are the largest components on a circuit, so you shouldn’t have a problem finding us.
Like an LED, we also have two legs, or leads. And like an LED, one leg, the positive, is longer than the other. I also have a strip on my body which indicates which side is negative.
Applications of Capacitors
Did you know that many power sources don’t provide a steady supply of power over time? It’s actually quite common for the voltage in a circuit to change as power flows through it. Sometimes its higher than you need, and sometimes lower. For many types of circuits, it can damage components on the circuit if the voltage changes too much.
Capacitors like me can actually help with this! If you put me in front of another component that might be sensitive to changes in voltage, I ensure that the supply of power remains steady. When the power drops from the source, I step in and provide the power needed to keep the flow steady. When a capacitor does this job, we call it a “Bypass Capacitor.”
In this way, capacitors can also be very helpful in converting the power that comes out of your wall into something that your electronics can depend on. Our houses use a type of power called Alternating Current, or AC. Among other things, this means that the power changes and isn’t a steady voltage over time. Most of our electronics need Direct Current, or DC. That means the power needs to be more-or-less steady for our electronics to work.
I bet you’ve seen a plug that looks like this, in your house.
This type of plug is a AC wall adapter and it’s very common to see these with certain types of electronics. Have you ever wondered what’s inside one of these plugs? Well, there’s actually a circuit in there, including several capacitors!
Together with some of the other items in here, capacitors keep the flow of power to connected electronics steady, which helps them operate and keeps them safe.
You can also find capacitors in audio equipment like speakers and in the flash bulbs of fancy cameras.
For audio equipment, we work in a similar way to a Bypass capacitor or a AC converter in that we keep the signal to the circut steady and predictable. For audio, this means that we are important in delivering music that sounds great.
Capacitors can seem like complicated things, but we are actually quite simple. We keep other electronics safe and ensure that the power stays steady and predictable. And you’ll find us almost everywhere!
Thanks for learning about me today! Want to learn more about electronics? Pre-order our first children’s book now!
