Do you need information on capacitance? How about you read through this article to get the information you need.
All information you need on capacitance is contained in this article.
To make your reading easier, I will start with an overview. Then, I will explain two conductors can store energy and charges.
Immediately after this, I will explain the electronic device that offers capacitance to an electronic circuit. A capacitor is the name of this device.
In the next section, we will discuss the factors that affect the capacitance of a capacitor. Then, I will explain how capacitor stores energy mathematically.
The next sections will contain the connection of capacitor in a circuit sequentially, uses of the capacitor, its pros and cons, and capacitance in an AC circuit.
In conclusion, I will provide answers to some frequently asked questions on capacitance.
What Is Capacitance: Overview
Capacitance is the feature of an electrical conductor or a set of conductors. It measures the amount of charge the conductor stores per unit change in electrical potential.
In other words, it is the ratio of the number of charges the conductor stores to its potential difference. However, these charges are both positive and negative.
Also, capacitance could imply the ability of a device to store charges. However, they will become charged if you have two conductors in parallel and transfer electrical charge through them.
Hence, they will have equal numbers but opposite charges – positive and negative. Thus, it establishes a potential difference.
C = Q/V.
C = capacitance of the conductors.
Q = quantity of charges (coulombs).
V = potential difference between the conductors (volts).
The SI unit of capacitance is Farad. The unit is represented by the letter “F”.
More so, the unit of capacitance is named after Michael Faraday.
Other capacitance units frequently used are microfarad (uF) and picofarad (pF).
1 microfarad = 1uF = 1 × 10−6 F = 1/1000000 F.
Also, 1 nanofarad = 1nF = 1 × 10−9 F = 1/1000000000 F.
Even so, 1 picofarad = 1pF = 1 x10−12 F = 1/1000000000000 F.
Therefore, 1 farad is the ratio of 1 coulomb to 1 volt. In electronic circuits, capacitance is introduced with a device called a capacitor.
Also, the two closely related notations of capacitance are self-capacitance and mutual capacitance.
Self-capacitance is a property of any device that you can charge electrically. At the same time, mutual capacitance is used in studying the operations of capacitors.
What Is Capacitance: How It Works
For charges to be stored, two conductors are placed such that there is an insulating medium between. This insulating medium is called dielectric.
The dielectric could be air or any other insulating medium.
Furthermore, the charges accumulate in the conductors. Thus, the energy is stored in the dielectric.
A capacitor has two parallel conductors. These conductors are separated from each other by a dielectric substance.
Depending on the manufacturer and purpose, this could be mica, paper, etc.
The conductors store charges while the dielectric stores the energy.
A capacitor is an electronic device that stores energy in the form of electric charges in a DC circuit. It produces a potential difference across the plates of the capacitor.
The capacitor consists of two parallel plates with overlapping area A and is d distance apart. Its dielectric has a permittivity of ε.
Then, the capacitance of the capacitor varies directly as the overlapping area, if other properties are constant. Also, the capacitance varies inversely with the distance between the parallel plates.
C = ε * A/d
Where ε = absolute permittivity.
However, ε = εr * εo.
εr = relative permittivity of a material.
εo = vacuum permittivity or permittivity of free space.
If εr = 1, then, C = εo * A/d.
Where ε0 ≈ 8.854×10−12 F/m.
Factors Affecting The Capacitance Of A Capacitor
The capacitance of a capacitor is simply the ability of a capacitor to store charges. Also, the amount of energy the capacitor stores is dependent on three factors.
These factors are the plate area, the distance between the plates, and the dielectric material.
When a capacitor has a bigger plate area, its capacitance will be great. However, less plate area offers less capacitance.
Furthermore, the larger plate possesses more field flux, for a given force. The field flux is the charge the plates collect. Thus, the force refers to the potential difference across the capacitor.
Distance Between The Plates
The larger the distance between the plates, the less capacitance, and vice versa.
For any given voltage across the parallel plates, closer plates result in a greater field force. As a result, the field flux increases.
With all other factors being equal, a material with a high permittivity gives greater capacitance. Also, a material with less permittivity gives less capacitance.
A dielectric material with greater permittivity offers less resistance to field flux. Hence, it will collect greater field flux. As a result, its capacitance will be high.
Permittivity refers to the ability of a substance to store electrical energy in an electric field.
The table below shows some materials and their relative permittivity.
|Polypropylene||Between 2.20 and 2.28|
|ABS Resin||Between 2.40 and 3.20|
|Polystyrene||Between 2.45 and 4.00|
|Transformer Oil||Between 2.50 and 4.00|
|Hard Rubber||Between 2.50 and 4.80|
|Silicones||Between 3.40 and 4.30|
|Bakelite||Between 3.50 and 6.00|
|Glass||Between 4.90 and 7.50|
|Muscovite Mica||Between 5.00 and 8.70|
|Mica (Glass-bonded)||Between 6.30 and 9.30|
Energy Stored/Work Done On A Capacitor
The energy stored in a capacitor equates to the work done in charging a capacitor. However, equal but opposite charges are present on adjacent plates of a parallel plate capacitor.
Furthermore, these charges create an electric field between the plates. Thus, the charges are made up of a certain amount of energy in the circuit.
Hence, the energy stored in a capacitor is electrical potential energy. Even so, the SI unit for this energy is joules.
More so, if we have a capacitor with C capacitance, with Q quantity of charges on the capacitor plates, and V voltage is applied to it. Then, energy E stored on the capacitor is given by the expression below.
E = 1/2 * C * V²…………..(1)
However, C = Q/V.
Thus, if we substitute Q/V for C in equation 1;
Then, E = 1/2 * Q * V………………(2)
Furthermore, V = Q/C.
Even so, substitute Q/C for V in equation 1.
Therefore, E = 1/2 * Q²/C………………(3)
Nevertheless, equations 1, 2, and 3 can be used to estimate the energy stored or work done on a capacitor depending on the available parameters.
Connection Of Capacitors In A Circuit
You can connect capacitors either in series or parallel in a circuit. However, can perform some mathematical operations to estimate certain quantities in the circuit.
Even so, the quantities you can calculate are energy stored or work done, equivalent capacitance, the number of charges, and voltage.
Ideally, the equivalent capacitance of two or more capacitors is the value of one capacitor that can be used in a circuit and it will function the same way those capacitors will function.
Nevertheless, calculating the equivalent capacitance depends on the circuit connection.
Capacitors In Series
Supposing you have capacitors C1 and C2 connected in series to a common potential difference V, then the number of charges flowing through them are equal. More so, they drop different amounts of voltage depending on their capacitance.
Let the voltage drop on C1 be V1 and the voltage drop on C2 be V2. Also, let the energy stored in each capacitor be E1 and E2 respectively.
Thus, the total quantity of charges in the circuit Q = Q1 = Q2.
However, to determine the equivalent capacitance, we sum the reciprocals of each capacitor.
1/C = 1/C1 + 1/C2.
Therefore, C = (C1 * C2)/(C1 + C2).
The voltage drop for each capacitor is given as:
V1 = Q/C1.
V2 = Q/C2.
According to Kirchhoff’s Voltage Law, V = V1 + V2.
Furthermore, the energy stored in C1 and C2 is given as:
E1 = 1/2 * Q²/C1.
E2 = 1/2 * Q²/C2.
However, you can use equations 1 and 2 to determine the energy on each capacitor depending on the circuit parameters you have.
Nevertheless, it must be parameters attributed to that particular capacitor, not the entire circuit. More so, you should use the general formula for the entire circuit operation.
Note, that you must determine the equivalent capacitance first.
Capacitors In Parallel
Also, if you connect the same capacitors in parallel with a common potential difference, then the voltage drop across each capacitor will be the same as the supply voltage.
However, the number of charges will differ according to the capacitance of the capacitor.
Thus, the voltage in the circuit V = V1 + V2.
Furthermore, the equivalent capacitance in a parallel circuit is a summation of the capacitance of all capacitors in the circuit.
C = C1 + C2.
More so, the quantity of charges in each capacitor is given as shown below.
Q1 = C1 * V.
Q2 = C2 * V.
Even so, Q = Q1 + Q2.
In addition, you obtain the energy stored in each capacitor by using the formulas below.
E1 = 1/2 * C1 * V².
E2 = 1/2 * C2 * V².
Nevertheless, depending on the circuit parameters you have, you can still use equations 2 and 3 to determine the energy stored in each capacitor. Thus, the parameters must be attributed to the individual capacitor.
What Is Capacitance: Types Of Capacitors
Generally, capacitors are two types of capacitors. These are Fixed and Variable capacitors.
More so, the fixed capacitors have fixed capacitance values. While the variable capacitors are capacitors with adjustable values of capacitance.
However, below are the different types of fixed capacitors. These capacitors are named according to their dielectric material or application.
The electrolytic capacitor has a thin metal film layer as one of its electrodes (anode). More so, the second electrode (cathode) is a semi-liquid electrolyte solution in paste or jelly form.
Furthermore, it has a thin layer of oxide as its dielectric plate. However, it has large capacitance values (above 1uF).
Hence, these capacitors are polarized and can only be useful in a DC circuit. Thus, you must use it with correct polarity to avoid damage.
Ceramic capacitors use a ceramic material as their dielectric. Also, there are two common types of ceramic capacitors which are multilayer ceramic and ceramic disc capacitors.
Furthermore, the multilayer ceramic capacitor is made using surface-mounted technology. They are small in size and are widely used.
Ideally, their capacitance values range from 1nF to 1uF. However, you can find these capacitors with values up to 100uF.
On the other hand, ceramic disc capacitors have multiple layers. Also, they are made by coating a ceramic disc with silver contacts. They have high-frequency responses.
These types of capacitors use silver mica or clamped mica as their dielectric materials. Also, they are chemically, electrically, and mechanically stable.
Furthermore, they are useful with high frequencies and have a low loss. This is because of its specific crystalline and layered structure.
These capacitors have two thin foil sheets. Also, it has oiled paper or thin waxed paper as the dielectric.
More so, its capacitance ranges from 0.001uF to 2uF. Even so, it can operate with a voltage as high as 2000 volts (2kV).
The film capacitors use thin plastic as their dielectric material. It uses a film drawing process in its production.
However, there are different types of films in the film capacitor. These include polyester film, metalized film, polystyrene, etc.
This capacitor offers very high capacitance values (up to thousands of Farads). Automotive devices also use capacitors.
Alternatively, they are also called “super caps” or “ultra-capacitors”.
Uses Of Capacitors
All electronic devices in our homes use DC and at the same time, we plug them into an AC outlet. However, these devices have a rectifier in them.
Also, the rectifier circuit has a capacitor that smooths the rectified signal. This process makes the input AC come out of the rectifier as DC.
The capacitors charges and discharges regularly at intervals. Thus, they could be useful in any time-dependent circuit.
However, flashlights with regular beeping use a timing capacitor.
Capacitors are used in coupling two systems that operate with different electrical properties. For instance, a loudspeaker operates with AC.
If a DC by any chance gets to the loudspeaker, it will damage the system. Thus, you can use a capacitor to stop any DC from going into the loudspeaker.
Also, AC generators use capacitors to block the DC that tends to flow as a result of the commutator and brush action. Hence, allowing the supply of only AC.
If you connect a variable capacitor to an LC oscillator, you can use it in a tuning circuit. The capacitor discharges into a coil and generates a magnetic field as a result.
However, the magnetic field collapses when the capacitor fully discharges. Thus, it recharges the capacitor.
Furthermore, this charges and discharges in intervals. Hence, this regular interval portrays a particular frequency.
If you change the capacitance of the capacitor by varying it, the regular interval changes. As a result, the frequency also changes. This applies to FM radio.
Energy storage is the basic application of a capacitor in a circuit. It can store energy in its dielectric and charges flow through the conductors.
Pros And Cons Of A Capacitor
- It can store energy.
- Also, it has low energy losses.
- Even so, it requires no maintenance.
- However, it is simple to use.
- In addition, it has a long service life.
- It is cheap.
- Furthermore, it can work with both AC and DC.
- Lastly, it has a wide range of applications.
- They have limited energy storage.
- Also, they have less storage capacity compared to batteries.
- Even so, storage energy depletes.
- Lastly, its stored voltage level may vary.
Capacitance In An AC Circuit
Capacitance is one of the basic parameters of an AC circuit, especially in a transmission line. Even though it does not absorb real power, it plays a role in reactive power.
Hence, capacitance plays a vital role in power factor correction.
Xc = 1/wC, but w = 2πf.
Hence, Xc = 1/(2πfC).
Xc = Capacitive Reactance ( in Ohms).
C = Capacitance (in Farad).
f = Frequency (in Hertz).
Frequently Asked Questions
Capacitance is the ability of a device or circuit to receive and store energy in the form of charges.
Farad is the SI unit for capacitance.
A resistor is an electronic component that resists the flow of electric current in a circuit. While a capacitor stores electrical charges.
C = εA/d.
Where C is capacitance, A is parallel plate area, d is the distance between the plate, and ε is permittivity.
The basic need of a capacitor in a circuit is to store electrical energy in the form of charges.
Inductive reactance releases energy in form of a magnetic field. While capacitive reactance releases energy in form of an electric field.
Reactance is the opposition to the flow of current due to inductance or capacitance.
Capacitors are used to store electrostatic energy in electric fields. Whereas, whereas transistors are used to amplify or switch signals.
AC reverses direction periodically. Hence, the capacitor only charges and discharges without storing any charges.
However, capacitors store only DC.
A battery converts chemical energy to electrical energy. While a capacitor stores electrical energy in the form of charges.
What Is Capacitance: My Final Thoughts
Capacitance is necessary for every circuit both AC and DC. It has a vital role to play in the flow of charges. Also, its ability to store energy shows that the battery is not the only device that stores electrical energy.
Although its storage capacity is low when you compare it to a battery, it can store energy that is needed for a short period in an electronic circuit. Its various type depends on the dielectric material or its application.
However, this article gives you every information on capacitance. Also, it contains every detail on its role in AC and DC circuits.
Therefore, you have all the information you need here.
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