#### Introduction

Capacitor is also known as condenser. This is one of the passive components like resistor. Capacitor is generally used to store the charge. In capacitor the charge is stored in the form of “electrical charge”. This electrical charge in capacitor produces a potential difference across its two plates. Different types of capacitors are shown below.

Generally a capacitor has two parallel metal plates which are not connected or not touching each other. The two plates in the capacitor are separated by non conducting medium (insulating medium) this medium is commonly known as Dielectric. Some examples of dielectric materials are ceramic, waxed paper, mica, plastic or some form of a liquid gel.

There are different types and different shapes of capacitors are available from very small capacitors which are used in resonance circuits to large capacitors for power factor correction process. But all capacitors are doing the same work that is storing the electrical charge. The shape of a capacitor is rectangular, square, circular, cylindrical or spherical shape. Capacitors are mainly used as one of the parts in many common electrical and electronic devices. Unlike a resistor, an ideal capacitor does not dissipate energy.

If a capacitor is fully charged then it blocks the flow of DC current through it even though the supply voltage is connected to it. At this time the supply voltage is equal to the charging voltage of a capacitor. When AC supply voltage is applied to the capacitor, AC current passes through the capacitor with small amount of resistance or with no resistance.

Mainly the electrical charge is two types, they are positive charge (+ve) which has protons and negative charge (-ve) which has electrons. When a direct voltage (DC) is applied to the capacitor then the positive charge (+Q) is accumulate on one of the metal plates of a capacitor and the negative charge (-Q) is accumulates on another plate of capacitor. The capacitance value (C) of a capacitor is equal to the ratio of the total charge (Q) stored on a capacitor to the potential difference (V) produced across the plates. The capacitance value is measured in “Farads”. The expression is shown below,

Q = C * V

Charging current defines as the flow of electrons onto the plates of a capacitor which continues to flow until the voltage across both the metal plates is equal to the applied voltage V. The capacitor is ‘fully charged’ with electrons at this time. Now we say that the strength of this charging current is at its maximum value, and this charging current is said to be at minimum value when both plates are fully discharged.

### Why Capacitors are Important?

Capacitors are one of the passive components and also one of the basic components in electronics such as resistors, inductors and semiconductors. Capacitors are playing an important role in almost all circuits, because they provide energy storage and also have some important filtering applications. Capacitors are mainly used in power supply applications, in power factor correction circuits, and also used as decoupling capacitors in consumer electronics.

However one of their main uses is, in timing circuits as the discharge time for that energy can be calculated. The capacitor's greatest limitation is that it can only store a limited voltage. Mainly one of its benefits is it can release a whole lot of charge at a rapid rate. They are made with a preferably thin insulating material between two metal plates which will fail under high voltage.

In digital circuits we normally use capacitors to reduce unwanted signals i.e. noise. The electronics devices such as TV, phone, radio, microwave, calculator and etc are never work without capacitors.

### Capacitor Construction

A capacitor is one of the passive devices that stores energy in the form of electric field created between a pair of conductors on which electric charges of equal magnitude, but opposite sign have been placed.

A parallel plate capacitor is the simplest form of capacitor and this is better one to verify the dependence of capacitance on plate size and spacing between those metal plates. When a capacitor is connected across the two battery terminals, charge flows through the capacitor until its potential difference becomes equal to that of the battery.

This can be constructed using two metal or metalized plates at a distance parallel to each other with its capacitance value in Farads being fixed by the surface area of the metal plates and the distance of separation between them. By changing any one of these two values we can change the value of its capacitance.

In the above figure we observed that the capacitor has two metal plates and they are separated by dielectric. Now we connect the capacitor to the supply voltage V, then the +ve voltage charge is accumulated on one plate of capacitor represented by +Q and –ve voltage charge is accumulated on another metal plate which is represented by –Q. In this time the capacitor is in charging state and it is fully charged up to the voltage between the plates of capacitor is equal to the supply voltage. After that depending on the potential difference between the plates the capacitor is discharged slowly and finally it reaches to zero.

The property of a capacitor to store charge on its plates in the form of an electric field is called as Capacitance of the capacitor, but capacitance is also the property of a capacitor which resists the change of voltage across it. The capacitance of a capacitor is denoted by ‘C’ and this value is calculated using the equation which is given below.

We know that,

Q = C * V ==> C = Q/V

When electric charge accumulates on the plates, an electric field is formed in the region between the plates. And that is proportional to the amount of accumulated charge. This electric field can produce a potential difference V = E•d between the plates of this simple parallel-plate capacitor without dielectric material. The amount of charge require to produce a potential difference between the plates of a capacitor is depends on the below factors.

# Surface area (A) of the capacitor.

# Separation Distance (d) between the plates.

# Dielectric or insulating material used between the plates.

The capacitance of a parallel plate capacitor, with dielectric material between its plates is given by

**C = k ε _{0} A/d**

Where ‘k’ is the Dielectric constant for the non conducting material and ‘ε_{0}’ is the permittivity of free space which is equal to 8.8542 * 10^{-12} C^{2} / (Nm^{2}).

### The Capacitance of a Capacitor

Capacitance is the ability of a capacitor to store maximum amount of electrical charge in it. Capacitance exists in any object if that can be electrically charged. A parallel-plate capacitor is a general form of energy storage device. The capacitance is measured in the units of “Farad” and this is obtained from the name of ‘Michel Farad’.

One farad is defined as the capacitance of a capacitor when capacitor is charged with One Coulomb of electricity and there is a potential difference of One volt across the plates.

Capacitance has always positive (+ve) value and it has no negative (-ve) values. Usually the Farad is a large unit; it has some sub units for measurements of the capacitance. They are micro-Farads (uF), nano-Farads (nF) and pico-Farads (pF).

The capacitance of a parallel plate capacitor is directly proportional to the surface area (A) of the metal plates and it is inversely proportional to the separation distance between the plates (d). If the charges on the plates are +Q and -Q respectively, and V is the potential difference between the two plates, then the capacitance C of a capacitor is given by

C = Q/V

This gives the voltage and current relationship as,

I (t) = C*dV(t)/dt

### Standard Units of Capacitance

The basic unit of capacitance is ‘Farad’, but this farad is generally a large unit for the practical tasks. So the capacitance is usually measured in some sub-units, such as micro-farads (uF) or pico-farads (pF).

Most of the electrical and electronic applications are covered by the following standard unit (SI) prefixes for easy calculations,

- 1 mF (millifarad) = 10
^{−3}F = 1000 μF = 1000000 nF - 1 μF (microfarad) =10
^{−6}F = 1000 nF = 1000000 pF - 1 nF (nanofarad) = 10
^{−9}F = 1000 pF - 1 pF (picofarad) = 10
^{−12}F

To convert µF to nF or pF or to a wide range of other units and vice versa, we need to use the Electric Capacitance Unit Converter.

### Capacitance of a Parallel Plate Capacitor

The above figure shows a parallel plate capacitor. We know that the capacitance of a parallel plate capacitor is proportional to the area (A) of the metal plates and inversely proportional to their distance or separation or thickness of dielectric constant (d) giving us a value for capacitance,

C = ε A/d

**C = k ε _{0} A/d**

Where ‘k’ is the Dielectric constant for the non conducting material and ‘ε_{0}’ is the permittivity of free space which is equal to 8.8542*10 ^{-12} F/m.

But in the free space, k=1

So, the capacitance C = 8.8542*10 ^{-12} (F/m)*(A/d)

### The Dielectric of a Capacitor

Capacitor has two metal plates which are separated by non conducting medium. This medium is generally known as “Dielectric” which acts as an insulator between the capacitor plates. This dielectric material can be made from a number of insulating materials or combinations of these materials. The most commonly used dielectric materials are air, paper, polyester, Mylar, polypropylene, ceramic, or oil, glass, or a variety of other materials. The various insulating materials used as the dielectric in a capacitor differ in their ability to block or pass an electrical charge through it.

The factors which effect the total capacitance of a capacitor are the overall size of the metal plates and the distance between them and one more factor which influences the overall capacitance of a capacitor is the type of dielectric material used between the plates, because the capacitance of the capacitor depends on the permittivity (ε) of the dielectric material.

The ‘Dielectric Constant (k)’ is a factor of the dielectric material or non conducting material which increases the overall capacitance of a capacitor compared to air. With a high dielectric constant (k), a dielectric material is said to be better insulator than a dielectric material with less dielectric constant (k). The Dielectric constant (k) is a quantity with dimensionless because it is relative to the free space.

### Complex Permittivity

The product of the relative permittivity (εr) of the dielectric material which is used between the metal plates of a capacitor and the permittivity of the free space (εo) is known as “Complex permittivity” or “Actual permittivity” of the dielectric material. The expression for the complex permittivity is given as follows,

ε = ε_{0} _{*} ε_{r}

The value of complex permittivity will always be equal to the relative permittivity, because the permittivity of free space is equal to ‘one’. The value of dielectric constant or complex permittivity varies from one dielectric material to another. Some standard values of complex permittivity (ε) for common dielectric materials are Air = 1.0005, Pure Vacuum = 1.0000, Mica = 5 to 7, Paper = 2.5 to 3.5, Wood = 3 to 8, Glass = 3 to 10 and Metal Oxide Powders = 6 to 20 and etc. The final equation for the capacitance of capacitor using dielectric constant or complex permittivity is given by,

C = ε_{o *} ε_{r} (A/d)

The method of interleaving more plates together within a single capacitor’s body is very useful to increase the capacitance of a capacitor. In this method a capacitor can have many individual metal plates connected together instead of only one set of parallel plates, this cause increasing the surface area (A) of the plates. Here the capacitance will increase because the capacitance of a capacitor is directly proportional to the surface area of the plates.

Presently existing capacitors can be classified according to the properties and characteristics of their insulating or dielectric material, they are given below as

- High Stability & Low Loss Capacitors --- Mica, Low-K Ceramic, and Polystyrene capacitors are examples for this type.
- Medium Stability & Medium Loss Capacitors - Paper, Plastic Film, and High-K Ceramic capacitors are examples for this type.
- Polarized Capacitors – Example for this type of capacitors are Electrolytic, Tantalum’s.

### Voltage Rating of a Capacitor

The voltage rating of a capacitor is the maximum amount of voltage that a capacitor can safely perform their operations. The maximum amount of voltage that can be applied to the capacitor without any damage to its insulating material is generally given in the data sheets by manufacturers. Generally this voltage is called as working voltage (WV) or DC working voltage (DC-WV).

If high voltage is applied to the capacitor then the dielectric of a capacitor may break down, due to this reason the capacitor will damage by obtaining the arcing between the plates of a capacitor. So the designers must take care about the voltage rating when they are designing the capacitors. The working voltage of a capacitor depends on the factors that the dielectric material which is used between the capacitor plates, dielectric thickness and also depends on the type of circuit which is used.

Different types of capacitors are available different voltage ratings. So the designer of a circuit must take care while choosing a capacitor for the circuit, Capacitor working voltage should be greater than the circuit operating voltage. For example if the circuit operating voltage is 5V then it is necessary to choose a capacitor with voltage rating of 5V or above.

The DC working voltage of a capacitor is the maximum DC voltage which we can apply to the capacitor. But this DC voltage is not equal to the AC working voltage of a capacitor, because the AC voltage is the rms voltage of the capacitor. For example assume AC voltage of the capacitor is 100V rms but its actual peak voltage is 141V. (V_{rms} = V_{m}/√2).

So we need to choose the capacitor in the circuit which is having the working voltage 50% greater than the maximum voltage applied to the circuit. For example if you want to use a capacitor in the circuit which is operating at 100V AC then the capacitor working voltage should be at least 200V.

Dielectric material will become damaged due to high supply voltages and high temperatures. So we never use a capacitor in the circuit which having the working voltages too much high than the capacitor voltage ratings. One more factor which influences the circuit operation is the dielectric leakage. This dielectric leakage will occurs in a capacitor due to the leakage current flowing through the dielectric of capacitor.

### Summary

The capacitor is one of the passive components like resistor. The capacitor is used to store the electrical charge on to its plates, such that it charges and discharges depending on the supply voltage applied to it. The amount of the charge stored in it is called “capacitance” of the capacitor. This capacitance of the capacitor will depends upon the three main factors. They are given below,

- Surface Area (A) – The surface area (A) of the two conductive plates of the capacitor is directly proportional to the capacitance. So if the surface area of the capacitor increases then it causes to increase the capacitance.
- Separation Distance (d) – The separation distance (d) between two metal plates of a capacitor is inversely proportional to the capacitance. So if the separation distances between the plates increases then it causes to decrease the capacitance value.
- Dielectric Material – The dielectric is an insulating material which separates the two metal plates of a capacitor. It is also directly proportional to the capacitance value. If the permittivity of the insulating material or dielectric is high then it causes to high capacitance value.

Glass, waxed paper, mica different plastics and etc are the dielectric materials of a capacitor. These dielectric materials provide the following benefits,

- One of the properties of dielectric material is its “Dielectric constant (k)”. This dielectric constant k varies from one dielectric to another dielectric. This dielectric constant is directly proportional to the capacitance, so it will increase the capacitance value of a capacitor by a factor of k.
- The two metal plates are separated by the dielectric material. It gives the mechanical support to the two metal plates of a capacitor allowing the plates to be closer together without touching.
- A capacitor will have a high capacitance value if its dielectric material has high permittivity.
- The dielectric material which is used between the plates will cause to increase the maximum operating voltage of a capacitor when compared to air.

Capacitors block the DC current when it is fully charged even though the supply voltage is applied to it. This property of capacitor is used to separate the DC pulses from mixed signals, such as audio signals, alternating current or pulses or other time varying wave forms. This technique is also used to smooth the output voltages of power supplies and spikes (unwanted) from signals otherwise they may cause to damage the circuit. So these capacitors can also used in audio circuits to adjust the frequency response.

There are a large variety of capacitor styles, shapes and types; each capacitor has its own particular advantages, disadvantages and characteristics. The shape of a capacitor is square, circular or rectangular, cylindrical or spherical shape.

### What is Capacitor?

Capacitor is also known as **condenser**. This is one of the passive components like resistor. Capacitor is generally used to store the charge. In capacitor the charge is stored in the form of “electrical field”. Capacitors play a major role in many electrical and electronic circuits.

Generally, a capacitor has two parallel metal plates which are not connected to each other. The two plates in the capacitor are separated by non conducting medium (insulating medium) this medium is commonly known as **Dielectric**.

There are different types and different shapes of capacitors available , from very small capacitors which are used in resonance circuits to large capacitors for stabilising HVDC lines. But all capacitors are doing the same work that is storing the electrical charge.

The shape of a capacitor is rectangular, square, circular, cylindrical or spherical shape. Unlike a resistor, an ideal capacitor does not dissipate energy.As the different types of capacitors are available different symbols were available to represent them which are shown below.

### Why capacitors are important?

Capacitors have many properties like

- They can store the energy and it can dissipate this energy to the circuit when ever required.
- They can block DC and allow AC to flow through it, and this can couple one part of the circuit with the other.
- Circuits with capacitors depend on the frequency, so can be used to amplify certain frequencies.
- As the capacitors when applied with AC input , the current leads the voltage and thus in power applications it increases the pay load power and makes it more economical.
- It allows high frequencies and so it can be used as a filters either to filter low frequencies or to collect high frequencies.
- As the reactance and frequency of the capacitor are inversely related, this can be used to increase or decrease the circuit impedance at certain frequency and can be used as filter.

Likewise, capacitors exhibit many properties , when used in AC or DC circuits and hence they play important role in electrical and electronic circuits.

### Construction of a Capacitor

As said before , there are different types of capacitors. These different types will have different type of construction. A Parallel plate capacitor is the simplest capacitor. Let us understand the construction of this capacitor.

It consists of two metal plate separated by a distance. The space between these two plates is filled with a dielectric material. The two leads of the capacitor are taken from these two plates.

The capacitance of the capacitor depends on the distance between the plates and area of the plates. Capacitance value can be changed by varying any of these parameters.

A variable capacitor can be constructed by making one of these plates fixed and other moving.

#### Dielectric Of a Capacitor

Dielectric acts as an insulating material between the plates . Dielectric can be any non conducting material such as ceramic, waxed paper, mica, plastic or some form of a liquid gel.

Dielectric also plays an important in deciding the value of capacitance. As the dielectric is introduced between the plates of the capacitor ,its value increases.

Different dielectric materials will have different dielectric constants ,however this value is >1.

Below table gives value of dielectric constant for each dielectric material

Dielectric can be of two types

- Polar dielectrics: These dielectrics will have permanent dielectric movement
- Non Polar dielectrics: These will have temporary dielectric moment. By placing them in a electric field they can be induced with dipole moments.

##### Complex Permittivity

The product of the relative permittivity (εr) of the dielectric material and permittivity of free space (εo) is known as “Complex permittivity” or “Actual permittivity” of the dielectric material. The expression for the complex permittivity is given as follows,

ε = ε0 * εr

The value of complex permittivity will always be equal to the relative permittivity, because the permittivity of free space is equal to ‘one’. The value of dielectric constant or complex permittivity varies from one dielectric material to another.

Some standard values of complex permittivity (ε) for common dielectric materials are Air = 1.0005, Pure Vacuum = 1.0000, Mica = 5 to 7, Paper = 2.5 to 3.5, Wood = 3 to 8, Glass = 3 to 10 and Metal Oxide Powders = 6 to 20 and etc.

capacitors can be classified according to the properties and characteristics of their insulating or dielectric material, they are given below as

- High Stability & Low Loss Capacitors — Mica, Low-K Ceramic, and Polystyrene capacitors are examples for this type.
- Medium Stability & Medium Loss Capacitors – Paper, Plastic Film, and High-K Ceramic capacitors are examples for this type.
- Polarized Capacitors – Example for this type of capacitors are Electrolytic, Tantalum’s.

### Working

As said before capacitor consists of two conductor separated by a dielectric , when there is any potential difference between the two conductors electric potential is developed.This causes the capacitor to charge and discharge.

Let us understand this in a practical way. When the capacitor is connected to a battery(a DC source) , current starts flowing through the circuit .

Thus negative charge is accumulated on one plate and positive charge is accumulated on the other plate. This process continuous until the capacitor voltage reaches supply voltage.

When the charging voltage is equal to the supply voltage capacitor stops charging further even though the battery is connected. When the battery is removed two plates will be accumulated with positive and negative charges. Thus the charge is stored in the capacitor.

But when the supply voltage is from an AC source it charges and discharges continuously .The rate of charging and discharging depends on the frequency of the source.

#### Example

Working can be understood using simple example here. Below circuit shows two switches A and B. When switch 1 is closed , current starts flowing from from the battery to the capacitor. When the capacitor voltage reaches the supply voltage ,it stops charging further.

Now connect the switch to position B. Now you can observe the LED starts glowing and this slowly fades out as the capacitor is discharging.

Capacitance of the capacitor is given by

C=KεA/d

or

C= εA/4πd

or

C = εo * εr (A/d)

Where,

C – Capacitance of the capacitor

A – Area between the plates

D – Distance between the two Plates

εo – Permittivity of free space

εr – Relative permittivity.

K- Dielectric Constant

### Capacitance of a Capacitor

Capacitance is the property of the capacitor that defines the maximum amount of electrical charge stored in it.it exists in nature everywhere.

Capacitance may vary depending on the shape of the capacitor. Capacitance can be calculated by using the geometry of the conductors and dielectric material properties. Let us see the capacitance of a parallel plate capacitor.

Capacitance is defined as the ratio of charge (Q) on the either plates to the potential difference(V) between them ,

C =Q/V,

Thus current can be obtained as

I(t)=C[d(v)/d(t)]

This can can be expressed Farads (F) which is named after English physicist Michael Faraday.

From the above definition we can observe that capacitance is directly proportional to the charge (Q) and is inversely proportional to the voltage (V).

Capacitance of the capacitor can be increased by increasing the number of plates, which helps to maintain the same size of the capacitor. Here, area of the plates is increased.

#### Standard units of capacitance

Generally Farads is a high value so, capacitance is expressed as sub units of capacitor real time such as as micro farads(uF) , nano farads(nF) and pico farads(PF).

Most of the electrical and electronic applications are covered by the following standard unit (SI) prefixes for easy calculations,

- 1 mF (milli farad) = 10−3 F = 1000 μF = 1000000 nF
- 1 μF (microfarad) =10−6 F = 1000 nF = 1000000 pF
- 1 nF (nano farad) = 10−9 F = 1000 pF
- 1 pF (picofarad) = 10−12 F

To convert µF to nF or pF or to a wide range of other units and vice versa, we need to use the Electric Capacitance Unit Converter.

### Voltage Rating of a Capacitor

This is not voltage until which the capacitor charges but the maximum voltage until which the capacitor can operate safely. This voltage is called as working voltage (WV) or DC working voltage (DC-WV).Below figure shows the voltage rating of the capacitor.

If the capacitor is applied with voltage greater than this voltage, it may be damaged by producing an arc between the plates due to dielectric break down.

While designing the circuits with capacitors, care should be taken such that the voltage rating of the capacitor is greater than the voltage used in the circuit. For example if the circuit operating voltage is 12V then it is necessary to choose a capacitor with voltage rating of 12V or above.

This working voltage of a capacitor depends on the factors like dielectric material used between the capacitor plates, dielectric thickness and also on the type of circuit which is used.

Kavi says

Awesome article… can you please provide download option in pdf format.

Burak Erdem says

@Kavi If you are using Safari, you can easily save the article in PDF. Safari has a feature called “Reader”. You can view the article in Reader mode (SHIFT+CMD+R on Mac or View->Show Reader menu) and save it in PDF. While you are in Reader mode, print the article and you will see “Save as PDF…” option if you are using Mac. I’m not sure if this option exists on Windows.

Ralph says

What a great article.It is very.informative and well written.

Thank you

Ralph

Girish Deshmukh says

Best article, first I would like to say thanks to you for posting such wonderful article. Can you please explain me how to select value of Capacitance while designing any circuit? As you explain nicely how to select rated voltage capacitor for particular application, just like that can you please tell me how to choose specific value of capacitance value in the circuit.

SAIRANJAN ROUT says

Awesome article and many many thanks to the uploader , keep it up (y)

arjuna gaddipally says

realy its evry use full to understanding eveven a poor stdt in a direct to know pareticular pt.

thanks a lot for giving the appartunity.

Marisol Jane says

Thank you so much for this…

naga says

i am applying 12V to the capacitor ,which capacitor should i select i mean 1uF/25V or 10uF/25V

how can i calculate the capacitor

pravin desai says

thanks for the article

Ndukwe Daniel says

Very interesting to read and will also like to get the ebook of all those electronics components listed.

raj says

good enough for beginners in a simplest form.

Vishwajeet says

Really this was awesome…. utilising deep concept in less time.

Thanks for such kind of gainful

article.

Keep it up……

sravani devarakopnda says

awesome, i got clarity about capacitor.

Srinivas R Kalwad says

wonderful explanation loved it. understood about capacitor.

chinthada sudheer says

sir/madam, congratulations to such a wonderful information passed out.

how did you identifying the value of capacitor

star lord says

its really amazing,,but i can’t download it