# What is a capacitor in electronics? [Learning Capacitor Basics]

Hi. Hope you are having a good life. In this post, I am going to share my knowledge about the capacitor basics, and try to answer the question, what is a capacitor in electronics?

Hopefully, this post will help.

## What is a capacitor in electronics?

You can generally refer to the term capacitor in electronics as something that has capacity just like a water tank. A water tank has the capacity to store water. So, we can call it a capacitor of some sort. But technically, capacitors are known to store energy.

A capacitor is a passive two-terminal electrical component that stores potential energy in an electric field.

The most basic and important thing about a capacitor is that it stores energy. Now one important thing to clarify here is, that they are storing energy, not charge. And this is what it actually is and does. The next question arises how? The answer is coming next.

## Working of a capacitor

You might have or not, read theories about capacitors, its composition and working in details everywhere. I will not be boring you with lengthy stuff here. I will be providing you with to the point information and try to make it in an interesting manner.

A capacitor works as a storage tank. You can compare it with a battery which stores charge. But its size is small. To understand how it works in detail, we need to look at its structure.

The sandwich-like structure that you see in the figure is a construction of a capacitor. Now let your imaginations go wild for a moment.

Relate this sandwich like structure to actual chicken sandwich, with the two plates as the pieces of bread and the middle portion being the filling. Imagine that the leads of a capacitor are two straws, one is pumping ketchup and other is pumping mint sauce into the sandwich.

What happens after a while?

The side where ketchup is pumped is coated with ketchup and the other side with mint sauce. This is what is happening in a capacitor too. The two plates of the capacitor are separated by some dielectric medium and then a voltage is applied across its ends. One side is connected to the positive terminal and the other to the negative terminal.

Opposite charges are accumulated on each plate and there is always a potential difference between them.

This potential difference causes an electric field to set up between the plates. This field stores potential energy and holds the charges in place, as long as there is some applied voltage. At this point, you might be having questions about the dielectric medium popping in your mind.

Let’s not keep you wondering.

### What is a dielectric?

Dielectric is an insulator that gets polarized under an electric field. It is only present to separate the plates so that the charges don’t get mixed and the electric field is kept between them.

To understand this, we go back to our chicken sandwich. As long as there is chicken piece between the sauces, they won’t get mixed.

Same is the case with the capacitor in electronics. Removing the dielectric medium will cause the charges to attract each other and there will no longer be an electric field between them. Hence no energy can be stored.

## What is the capacitance of a capacitor?

Capacitance, in general, is the capacity of storage, i.e. the capacity of a tank to store water is its capacitance. In terms of a capacitor, the capacitance will then be defined as the capacity to store energy. The formal definition of capacitance is;

The ratio of the electric charge possessed by each conductor to the potential difference between them.

The mathematical representation of this definition is:

$C=\frac{Q}{V}$

Where Q is the charge stored on the plates, and V is the potential difference between them. The standard unit of measurement of capacitance is FARAD. One thing to remember here is, the plates of the capacitor are equally charged with opposite polarities.

## What is the electrical symbol of a capacitor in electronics?

As an electronics design engineer, or an electronics engineering student, you must be aware of the importance of electrical symbols of devices and components. To remember and recognize a capacitor in a circuit, you need to remember its physical construction as well as its electrical symbol. The electrical symbol of a capacitor is as follows:

You can compare it to anything you like to remember it.

Believe me or not, comparing things to others is a fun and interesting way to remember them forever. This also helps in building concepts about that thing. In this case, the easiest way, in my opinion, is to compare it with its own structure. Its composed of two parallel plates, and so does it symbol… Two parallel lines.

Now, there can be variations to these symbols as well. You might observe the following symbols as well:

While they may appear different, they are all the same with only little variations that represent different types of capacitors.

You can bring your own imagination to life and share with me what you would compare it to? It would be fun to see the capacitor according to your perspective.

## How can you identify capacitor in circuits?

As opposed to a resistor, which we observed in another post, a capacitor does not have any specific shape or size that makes it distinctive in circuits. However, for you guys, I will be sharing some of the images that might help you as a beginner. But it is only a matter of experience that helps you identify the capacitors in actual circuits.

Did that picture scare you?

Don’t worry.

If you look closely, almost all of these capacitors are variants of two basic shapes only. These shapes are separately shown above (Figure with capacitors symbol) for your ease. As a beginner, you will only be dealing with these two types of capacitors only and you will find them in various sizes in different circuits.

Now let’s look at the following actual circuit having capacitors and try to identify them. When you do identify, share it in the comments section. Trust me I would love to see them.

## How can you measure the capacitance of a capacitor?

The most important thing while designing a circuit or using your components somewhere is to know their values. i.e. when you are using a capacitor in your circuit you might want to know its capacitance values so that you can decide whether to connect it or not.

One way to do so is to read the label on capacitors. The other way is to use a multimeter. To measure capacitance using this method, you will need:

1. A multimeter
2. A capacitor (of course!!!), and
3. To make sure that your capacitor is completely discharged

To make sure that your capacitor is discharged, you short its legs. You can do so by connecting both the legs to some wire, metallic object of placing a resistor between its legs.

Now that you have made sure that your capacitor is discharged, we move on to measure its capacitance. The steps are as follows:

1. Search for the capacitor symbol on your multimeter and turn the multimeter knob to it. Some multimeters have F written next to the capacitance measuring mode which means Farads.
2. If there are two symbols on the same spot, refer to the user manual of the multimeter to see which button to press to switch between the measurements.
3. If the multimeter has several capacitances measuring ranges, select the appropriate range for you. Else, the multimeter will automatically detect the range for you.
4. Identify the positive and negative terminals of your capacitor. Usually, the positive terminal of the capacitor is longer than the negative one.
5. Connect the leads of a multimeter to capacitor terminals and wait. The multimeter sends a signal to capacitor and measures voltage across it. Then uses this voltage to measure the capacitance. So, you may need to wait for some time before the values are shown on screen.

## What is the reactance of a capacitor in electronics?

Capacitors in electronics, just like resistors, offer resistance to flow of charges. This property is known as their reactance.

It is the opposition offered to the change of voltage. When AC signal is applied across it, the capacitor keeps charging and discharging and during those intervals, a certain current flow through it. The reactance then prevents that current to flow.

Mathematically, it is given as:

$X_{c}=\frac{1}{2\Pi fC}$

## Testing a capacitor using a multimeter

When you are building circuits, there are certain instances that regardless of correct connections, your circuit does not behave as expected.

Believe me or not, this happens almost every time. You keep checking the connections, breaking and remaking them, but your circuit would not behave normally.

In such cases, you need to test your devices.

For your convenience, I’ll be sharing with you some techniques with which you can test your capacitor in electronics before plugging it in your circuit. By doing so, you will be sure that you connected the right thing in your circuit and this will save you time and effort later on.

There are several ways by which you can be sure that your capacitor is working, but I will be sharing the techniques that use a digital multimeter.

You can use a digital multimeter either is the resistive mode or capacitive mode to check the working of your tiny device.

### Testing using resistive mode

To test your device in resistive mode, you need to follow the following steps

1. Set your multimeter to resistive mode.
2. Make sure the capacitor is disconnected from any voltage source.
3. Connect multimeter leads to capacitor terminals (check polarity).
4. Measure the resistance shown by the multimeter. This value will immediately change to the value which was on the screen before you connected the leads. In most cases, it the OL reading.
5. Repeat steps 3 and 4 several times. If the result is the same, the capacitor is good. If for any of the measurements, the value of the resistor did not change, the capacitor is dead.

### Testing using capacitive mode

To test your device using capacitive mode of a multimeter, you need to follow the following steps.

1. Set your multimeter to capacitive mode.
2. Make sure the capacitor is disconnected from any voltage source.
3. Connect multimeter leads to capacitor terminals (check polarity).
4. Note down the value shown on the multimeter screen and compare it to the value shown on the capacitor label.
5. If the value is close to the labeled value (account for the tolerance), the capacitor is good. For very low values or 0 value, be sure that your capacitor is dead.

## Combinational circuits (series/parallel) of a capacitor in electronics

When building practical circuits, multiple capacitors may be used together. They can appear in either series or parallel to one another or to the circuit elements. Each configuration offers its own benefits and has its own effect on the circuit.

### Series Combination of a capacitor

When capacitors are connected in series, they are connected end to end. In this configuration, the same amount of current will flow through each capacitor as there is a single path to follow.

When the same current passes through each capacitor each capacitor will be charged to the same value irrespective of its capacitance. The series combination is given as follows:

Mathematically, a series combination of capacitors is given by the following equation:

$\frac{1}{C_{eq}}= \frac{1}{C_{1}}+\frac{1}{C_{2}}$

The effect is similar to resistors connected in parallel to one another. So,

The total capacitance in series is lesser than the smallest capacitance.

To understand it further, let us consider there are 2 water tanks being fed from the same source or a tank. Now when they are filled, the water from the source is divided into both. So, each receives half the amount of water compared to the source.

This is just like a voltage divider configuration.

We have already seen in the post that capacitance is the ratio of charge that can be stored by a capacitor and voltage applied across its ends. Also, since the same current flows through each one of them, they are store equal charge on them.

So, the voltage must be divided in order to conserve the law

$C=\frac{Q}{V}$

Another way it can be seen is, when capacitors are in series, they are acting as a capacitor whose plates are far from one another with layers of dielectric between them. So, when the plates are placed farther from one another, the capacitance is reduced.

I hope that you have now gotten the idea about how the series capacitance works.

The next comes the parallel capacitance.

### Parallel Combination of a Capacitor

In parallel combination, the capacitors are connected such that same voltage is being applied across each. It is the current that is being divided this time. This means the amount of current received by each capacitor is dependent upon how much resistance it offers to the current. Also, more current a capacitor receives, more charge it can accumulate.

The parallel combination of capacitors is shown in the figure below:

In parallel combination, the effective area of plates that is storing charge is being increased. So, the total capacitance is increased. We have seen earlier in the post that reactance (resistance) of the capacitor is inversely proportional to its capacitance.

So, when the capacitance is high, its reactance is reduced. Hence the current can flow smoothly, charging the capacitor.

The parallel combination of capacitors is given as:

$C_{eq}=C_{1}+C_{2}$

In parallel combination, the total capacitance is always greater than either of the capacitance values.

## Applications and Uses of Capacitor in Electronics

A capacitor in electronics finds many applications. Following are some which I have learned so far, will update it as I learn more. You can also add more applications on your own in comment sections as well.

### Storing Energy

The most basic use of a capacitor in electronics is what it does i.e. to store energy. This finds its applications in devices such as cameras, where energy is temporarily stored and then released. They can be used for this purpose in car audio systems, uninterruptible power supply (UPS) and other electronic device having volatile memory. In all these cases, it acts as a temporary battery and provides power where required.

### Smoothing

Another use of a capacitor in electronics is smoothing, which is kind of filtering a signal. This use is derived from the basic use of storing energy. As I have already mentioned above that capacitors hold a charge for a while and provide it when needed. So, in case of smoothing, the load draws energy from capacitors when required.

As the capacitor has only stored a certain amount of energy, so the amount of energy provided to the load is smoothed. Smoothing finds its applications mostly in power supplies, where AC is smoothed and DC is delivered.

### Coupling

A capacitor is known to allow AC and block DC signal. So, as a coupler, it allows AC and blocks DC components of any signal coming to it. This effect is called an AC coupling or capacitive coupling. This usage of the capacitor in electronics has found its applications in amplifiers e.g. speakers which is an audio amplifier.

### Decoupling

The word decouple means to separate, disengage, or dissociate. As a decoupler, capacitor breaks signals at nodes so that it is not forwarded to the next circuit. This is required in cases when some AC signal has some DC bias added to it, or the signal is varying and can be damaging to the components next to it. So, it prevents the signal to be conveyed to those parts of the circuit to avoid any damage. It has found its applications in power supplies as a bypass capacitor.

### Tuning

For the purpose of tuning, they are used in combination with the inductors to select certain specific frequency components. It has found its applications in radios to tune to a specific channel.

### Timing

As I have already mentioned above that a capacitor charges and discharges when a signal is applied to it, and it does so at regular intervals. So, it can be used in time-dependent circuits. The most common example that you can around you is the beeping objects, they are time-dependent because they produce a beep after a certain amount of time.

Another example can be of blinking LED’s or fairy lights that are used for decorative purposes. They also use capacitors to create those blinking modes. The blinking LED on your phones is also an example. You can find more such examples around you. All you have to do is observe.

## Buy capacitor kit on Amazon

Most capacitors are available at every electronics shop at very economical prices. They are available in all sizes and shapes. Application specific and very huge ones are not available locally because they are not for commercial use.

As a beginner, a student or an experimenter,  you will involve in many basic electronics projects. Each project would have its own specification and requirements. You will use many values capacitors in your electronics projects, and you need to be very organized. It is a very big problem, you don’t know what value of capacitor you need any time soon in your projects. Well, the solution to the problem is Joe Knows Electronics 33 values 645 pieces capacitor kit (Amazon link). You get so may values capacitors in one pack, and very important thing, they are well organized.

## Summary of capacitor basics

• A capacitor is a passive two-terminal electrical component that stores potential energy in an electric field.
• Capacitance is the ratio of the amount of charge stored by a capacitor to the voltage applied across it.

$C=\frac{Q}{V}$

• Capacitance can be measured easily using a multimeter.
• Capacitors can be easily tested using a multimeter.
• The reactance of a capacitor is the opposition offered to the current flow and is given by:

$X_{c}=\frac{1}{2\Pi fC}$

• They can be used in series or parallel depending upon their application and use as both have different effects
• They offer advantages as filters, tuners, timers, couplers, and de-couplers in electronic circuits

This is all I want to share about capacitor basics and try my knowledge best to answer the basic question, what is a capacitor in electronics. Hopefully, it has helped you in some way.

You can also check my other following posts too.

Thank you and have a good life.

## Special thanks to

Engr. Tuba Tanveer, MS Electrical Engineering from National University of Science and Technology (NUST), Islamabad

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