Are you a student, teacher, engineer or scientist who wants to learn more about capacitors? Or are you just starting your career and not knowing what a capacitor is? Do you want to see a capacitor symbol on the wall at your workplace or in your lab? Then, you’ve come to the right place. We’re here to show you that capacitors are not scary and hopefully clear up some misconceptions about them.
Capacitors are highly present in many different circuits, including electronic devices, power supplies, and energy meters. Most electronic devices utilize capacitors to function properly. If you have used an electronic device off late, you have most probably interacted with a capacitor. But what exactly is a capacitor? What does it do that makes it super important in electronic equipment? And how can we calculate the Capacitance of a capacitor? Well, if these questions baffle you, worry not because we have got you. Here we cover a full tutorial on capacitors including:
- Types of capacitors
- Formulas utilized to calculate the Capacitance
- Capacitor symbol types
- How capacitors work
- Units utilized in capacitors
- Applications and functions of a capacitors
- And so much more
After reading this article, you will have all you need to know about capacitors and more.
So what is a capacitor?
Before moving on to capacitors, let us define Capacitance. Capacitance is an object’s ability to store electrical charge. Well, capacitors are electrical components with a capability to store electric charge. Capacitors are passive electrical components. This means that they can efficiently store energy in the electric fields present between pairs of conductors (plates). They regulate electrical power in an AC circuit.
In simpler terms, we define capacitors as electronic devices that store/hold, and release electric charge due to chemical reactions. The other names for capacitors include condensers, accumulators, secondary cells, and storage cells. A Layden jar is a good capacitor example though very useful in the olden days. Now we have more advanced capacitors that are more efficient.
We can also use a capacitor as an element that controls the flow of electric charge in a circuit. We derive the term capacitors from their capability to efficiently store charge, like tiny batteries.
Although they entirely function in different ways, capacitors are like batteries. You may be wondering how so? Well, here is how. We have already established that capacitors store electrical energy, which takes you back to batteries. However, unlike batteries, capacitors cannot produce any new electrons. They only store electrical energy.
Inside a capacitor
Inside a capacitor, you will find two terminals connected onto two metal plates with a non-conducting substances separating them. We also refer to them as dielectric substances. You can easily develop a simple capacitor using two aluminium foil pieces, an insulator (say a piece of paper), and electrical clips. Of course, it will not be the best capacitor, but at least it will work.
Theoretically, the dielectric substance used in capacitors can be any insulator. However, you should utilize specific materials for optimum output in practical applications. Teflon, Mylar, porcelain, cellulose, ceramic, and mica are some of the most appropriate dielectrics to use. The dielectric you utilize will dictate the type of capacitor you have made and the job it is best suited for. Some capacitors end up being great at high frequencies while some become great at high-voltage applications. The size of capacitor and type of dielectric in use bring such variances.
How exactly does a capacitor work?
Once you connect a capacitor to a battery, the following happens:
- The plate found on a capacitor that connects to the battery’s negative terminal accepts electrons produced by the battery.
- The capacitor’s plate that connects onto the battery’s positive terminal loses its electrons to the connected battery.
Once the capacitor is fully charged, it bears a voltage that equals that of the battery (if the battery has got 1.5 volts, then the capacitor will have 1.5 volts). Small capacitors have a small capacity, but huge capacitors can store a lot of charges. You can easily find capacitors as huge as a soda can; these capacitors have enough energy to light up a flashlight for one full minute or even more.
Capacitor test example:
To test out how a capacitor works, you can follow the following procedure:
Have these items at hand:
- A light bulb
- A battery
- A capacitor
Create a circuit with these three items whereby current passes through the bulb and onto the capacitor. To achieve this, connect the battery’s negative terminal onto the bulb. Then, connect the bulb with the capacitor’s plate that connects to the negative battery terminal. Finally, connect the remaining capacitor plate with the positive terminal to complete the circuit.
What you will note with this connection is that:
- Once you connect your battery, the bulb lights up as current flows through the lead wire to the capacitor to charge it.
- The bulb gets dimmer progressively as the capacitor gets charged up. Once the capacitor is fully charged, the light bulb turns off.
- Now remove the battery complete the circuit using a cable. You will notice that the light bulb will light up again. However, the bulb will get dimmer as the capacitor discharges. It will eventually turn off once there is complete draining of the capacitor.
In most cases, we rate a capacitor via its Capacitance. However, there exist other factors that we can utilize to rate a particular capacitor:
- Working voltage – defines the voltage above which a specific capacitor may begin to short and eventually hold no charge
- Tolerance – the closeness of a capacitor to its charge rating
- Polarity – depends on the plate connected to the positive battery terminal and the negative battery terminal
- Leakage current – depending on how much current “leaks” through a dielectric, gradually discharges a capacitor over a certain period.
- Equivalent series resistance – the impedance of a capacitor at a high frequency
- Working temperature – the temperature range that a particular capacitor performs or works nominally at. When you use a capacitor in this temperature range, it should produce maximum results.
- Temperature coefficient – alterations that occur on the charge stored by a capacitor over a certain specified temperature range
- Volumetric efficiency – It is a crucial factor indicating how much Capacitance a particular component exhibits over a specific volume.
SI units for capacitors
We measure the storage potential, also known as Capacitance, using units known as farads.
- A one-farad capacitor usually stores one coulomb of charge at one volt.
A coulomb has 6.25e18 electrons. One ampere (amp) represents the rate of flow of one coulomb of electrons in one second. Hence, a one-farad capacitor can store one ampere per second of electrons at one volt.
Capacitor schematic symbols
As discussed above, there exist various capacitor types according to their:
This section will look at the different capacitor schematic symbols that exist and what makes them distinct.
Polarized capacitor symbol
Polarized capacitors cannot work with polarities that vary as per power supply. Therefore, they must have specific negative and positive terminals. There is current flow when you link the capacitor’s negative terminal onto the battery’s negative terminal, and the capacitor’s positive terminal to the positive battery terminal. The capacitor will function properly.
An electrolytic capacitor is an example of a polarized capacitor.
Non-polarized capacitors symbol
If you had trouble predicting how this capacitor work, then here is your answer. These capacitors can function even with polarities that differ as far as we consider the power supply. That means that these capacitors do not have specific negative and positive terminals.
Ceramic capacitors are great non-polarized capacitor examples.
Electrolytic capacitor symbol
The electrolytic capacitor comprises tantalum or aluminium and an oxide-based dielectric layer. The remaining electrode is more of liquid electrolytes.
Electrolytic capacitors fall under polarized capacitors. One should employ the correct polarity when supplying direct current (DC) voltage to the capacitor. In simpler terms, one should connect the capacitor’s positive lead to the battery’s positive terminal. To complete the circuit, attach the negative lead to the batter’s negative terminal. If you do not properly carry out the connection, you might damage the capacitor.
Electrolytic capacitors offer high Capacitance. However, they, in turn, have pretty low tolerance plus high explosion risk. Therefore, these capacitors are mostly useful where one requires the huge capacitors.
These incredible capacitors are further sub-divided into three types depending upon their dielectric:
- Tantalum electrolytic capacitors
- Aluminium electrolytic capacitors
- Niobium electrolytic capacitors
Ceramic capacitor symbol
Ceramic capacitors fall under non-polarized capacitors. One can develop them using two or more metal and ceramic alternating layers. The ceramic, in this case, plays the role of the dielectric, and metal plays the part of the electrodes.
Ceramic capacitors also go by the name disc capacitors.
These capacitors have a three-digit code imprinted onto them which helps users identify them according to their Capacitance. The initial two digits define the capacitor’s value, while the third number represents the number of zeros you should add.
Compared to other capacitors, ceramic capacitors are pretty cheap and also compact in design. Therefore, they are mainly good for high-frequency applications.
Ceramic capacitors only offer values of low Capacitance.
Fixed capacitor symbol
Fixed capacitors have one unique characteristic; they always offer constant capacitance values. Therefore, you cannot vary or alter the capacitance of fixed capacitors.
Examples of fixed capacitors include:
- Ceramic capacitors
- Normal compact electrolytic capacitors
Variable Capacitor symbol
Variable capacitors fall under non-polarized capacitors. They comprise a fixed and a moving plate that determines Capacitance. These types of capacitors are useful in receivers and transmitters, transistor radios, et cetera.
We can group variable capacitors into:
- Trimmer capacitors
- Tuning capacitors
Trimmer capacitors symbol
Trimmer capacitors fall under variable capacitors, which is also a non-polarized capacitor. These types of capacitors utilize dielectric medium trimming of the capacitor to alter the capacitance value.
Capacitor circuit symbols
We group capacitor circuit symbols into three, namely:
As we all know, circuits mean the connection between different electronic devices using cables. Well, you can only connect capacitors in three ways depending on whether fall in the polarized, non-polarized, or variable category.
Polarized circuit symbols are useful in circuits that use polarized capacitors. In the case of polarized capacitors, you have to construct a correct circuit as per polarity; doing it in any other way might damage the capacitor.
Non-polarized circuit symbols represent circuits that utilize non-polarized capacitors. In the case of non-polarized circuits, the polarity does not matter. Therefore, you can make your connections in any way you like, which means with the polarities being the same or with the polarities not being the same. These capacitors are sometimes referred to as bi-polar capacitors; you can guess why.
The last circuit symbol that we shall look at is the variable capacitor circuit symbol. Well, this represents a circuit that utilizes a variable capacitor to function. In the case of a variable capacitor, you can vary the capacitance repeatedly.
The main formula we use to govern capacitance calculations is:
Charge = capacitance x voltage
Which we can also represent as:
Q = C x V
The answer you get from this calculation should be in farads.
Throughout this section, we shall utilize this formula to see how we can measure Capacitance. We will also make formula variations of the same to achieve more details on Capacitance.
From the formula, we can gather that charge is directly affected by Capacitance and voltage. However, we can also rearrange the formula to get:
V = Q/C
Now with this formula in that format, we can gather more interesting information. This formula, in the rearranged format, implies that voltage is directly proportional to the total amount of charge the capacitor stores. This makes capacitors disadvantageous as per prolonged power delivery. As per prolonged use, capacitors do not hold a lot of charges. That fact, combined with our discussions, means that you should not depend on capacitors for prolonged power delivery. Doing so will only leave you with no power at all. If you intend to utilize a lot of energy, use batteries. They offer somewhat steady energy until they become depleted.
Time constant and power smoothing
When you put prolonged power utilization aside, capacitors become pretty good at their job. They are also pretty efficient in evening out momentary power drops. Here is the formula that proves this point:
We can also denote it as:
T = R x C
We refer to the formula above as the time constant tau; it indicates the capacitors capability to even out momentary power drops.
The tau formula indicates the total amount of time (in second) that a voltage takes to decay exponentially to thirty-seven per cent of its initial/original value. While at five times of this number, capacitors become fully discharged.
Make a circuit and connect your capacitor across a varying capacitor source (or just a voltage that momentarily cuts supply off) over some time. in this experiment you will see why evening out is crucial. With this connection in place, if you pass a voltage across the capacitor, it will even out the load using a charge that drops up to thirty-seven per cent in just one time constant. The inverse of this is also true when we consider the charging. After a single time constant, a capacitor will be sixty-three percent charged, while after a period of five minutes, a capacitor becomes fully charged.
Here is an example of an RC circuit time constant to help you understand this concept better:
1000 ohms x 47 x 10-6
Here you will note that the time constant stands at 0.47 seconds. What this means is that whenever we disconnect our power source, in this case let us use a five volts power source. It takes the capacitor 0.47 seconds to drop drastically to 1.85 volts. When you multiply this time constant by five, you get 0.235 seconds. Well, this is the amount of time required to discharge the capacitor utilized in the circuit that generated the equation above. Even if the capacitor used in the circuit above got fully charged, it would still take the same amount of time to discharge fully.
To increase the amount of time that the capacitor takes to discharge, you can utilize a bigger capacitor. Using a bigger capacitor also alters all the values described in the equation above.
Capacitors in parallel and series
Capacitors, just like resistors, can also be in a series or parallel connection to each other in a circuit. However, the resulting effect is pretty different once you compare the two electronic devices. When you connect capacitors in parallel, they mimic adding the dielectric surface area and conductor of each capacitor in the connection. In the case of parallel connection, Capacitance is equal to the sum of every capacitor’s value.
Capacitors placed in series reduce the amount of Capacitance drastically. The amount of capacitance in total become less than the value of the tiniest capacitor value in the circuit. The capacitor series equation is as follows:
1/CT = 1/C1 + 1/C2 + 1/Cn
We use series connections more often compared to parallel configurations. However, dividing through the voltage applied to each component poses some limitations when we consider the usage.
More ways that we can utilize capacitors
Although capacitors are just famous for storing charges, they have other uses that are pretty awesome.
Capacitors as power conditioners
Capacitors are responsible for power supply conditioning in electronic devices. How are capacitors able to condition the power supply? You might ask. Well, here is how. Capacitors only allow AC (alternating current) signals to pass, and they block any DC (direct current) signals from passing when fully charged.
Capacitors can efficiently split DC and AC signals; hence they clean the supply of power. However, electricians have managed to decouple or separate different electrical circuit parts using this effect. Thus, they reduce noise, which could ultimately reduce the device’s efficiency.
Capacitors are also important in a utility substation. They efficiently counteract the inductive loading induced by lines.
Using capacitors as sensors
We can also use capacitors as sensors to measure a couple of things. Such include mechanical strain, fuel level, and air humidity. But how? Well, the Capacitance of different devices depends upon their structure. Any alteration in the device’s structure can be a gain or loss in capacitance that we can measure. You can apply two different aspects in sensing applications:
- Distance between parallel plates
- The material between the plates
The former is useful in detecting any mechanical changes like pressure and acceleration. Even a minute worth of change in a given material between said plates can be enough to alter the Capacitance of the given device totally. This effect is extensively useful in sensing air humidity.
Capacitors for processing signals
Capacitors play a big role in the information technology sector. One application of capacitors in the IT sector is the Dynamic Random Access Memory, also known as the DRAM. In DRAMs, capacitors represent the binary information in the form of bits. When one fully charges a capacitor, the device dictates this as a certain value, say “ON”. When the capacitor undergoes discharging, the device dictates this as another value, maybe “OFF”.
Charge couple devices or CCDs utilize capacitors in analogue form. Capacitors in conjunction with inductors are in extensive use to efficiently tune a circuit to a specific frequency. Radio receivers, analogue equalizers and speakers extensively exploit this effect.
Capacitors as timers
We can utilize capacitors as a timer whereby one can use the time that a capacitor takes to fully charge to affect another section of the same circuit. Microcontrollers, integrated circuits and RF tuning utilize capacitors as timing functions.
Capacitors as touch screens
Even though they might be exotic compared with all other circuits utilized in this section, a capacitor touchscreen is a pretty standard way of using capacitors. Capacitors sense change in Capacitance at a certain point on a screen display. They then translate this into X-Y plane coordinates.
Over time, capacitors have proven to be pretty helpful in different sectors. The sectors range from the mechanical industry, IT sector, research sector, etc. Their uses seem to grow rather than diminish. Their application areas are popping up every single day. However, even though millions of people use this device every day, it never ceases to amaze many. We have tried to bring out everything that there is to know about capacitor symbols types, formulas used to calculate Capacitance and even the capacitor applications. We hope that this article has answered all the questions you might have had regarding the topic and added on some more knowledge.