# Capacitors and Capacitance – Working, Unit, Types and Specification

- Link: https://studyelectrical.com/2019/10/capacitance-working-unit-types-specification.html
- Published: 2019-10-27T08:01:08+00:00
- Author: Tesla

In this article, you’ll learn about electrical components that oppose the flow of
AC by temporarily storing energy as electric fields. These devices are called **
capacitors**, and their action is known as **capacitance**.

This article discusses capacitors and capacitance. By the end of this article, you
will learn the following.

 * What is capacitor and capacitance and how a practical capacitor work?
 * What are the different units of capacitance?
 * What are the different types of capacitors?
 * Series and parallel capacitors and their connection
 * Advantages and disadvantages of fixed and variable capacitors

We all know that, electrical components can oppose the flow of alternating current
in three ways.

 1. Resistance
 2. Inductance
 3. Capacitance

**Resistance** slows the flow of ac or dc charge carriers (usually electrons) by**
brute force**. **[Inductance](https://studyelectrical.com/2019/11/inductors-inductance-working-unit-function-types-uses.html)**
restricts the flow of ac charge carriers by temporarily storing the energy as a **
magnetic field**.

**Capacitance**, about which you’ll learn in this article, impedes the flow of ac
charge carriers by temporarily storing the energy as an **electric field**.

## What is Capacitance?

Imagine two huge, flat sheets of metal that are excellent electrical conductors.
Suppose each of the metal plates is of the shape of a huge rectangular football 
stadium and are placed one over the other, separated by only 1 foot of space.

![A hypothetical capacitor](https://studyelectrical.com/wp-content/uploads/2019/
10/A-hypothetical-capacitor.jpg)

A hypothetical gigantic capacitor

If these two sheets of metal are connected to the terminals of a battery, they will
become charged electrically, one positively and the other negatively.

If the plates were small, they would both become charged almost instantly, attaining
a relative voltage equal to the voltage of the battery. But because the plates are
gigantic, it will take a little time for the negative plate to reach full negative
potential, and an equal time for the other plate to reach full positive potential.

Eventually, the voltage between the two plates will equal the battery voltage, and
an electric field will exist in the space between the plates. This electric field
will be small at first because the plates don’t charge up right away.

But the charge will increase over a period of time, depending on how large the plates
are, and also depending on how far apart they are.

![Electric field vs Time](https://studyelectrical.com/wp-content/uploads/2019/10/
Intensity-of-the-electric-field-between-the-plates-as-a-function-of-time.png)

The intensity of the electric field between the capacitor plates as a function of
time.

The figure above is a relative graph showing the intensity of the electric field
between the plates as a function of time, elapsed from the instant the plates are
connected to the battery terminals.

Energy will be stored in this electric field. The ability of the plates, and of 
the space between them, to store this energy is the property of capacitance.

As a quantity or variable, capacitance is denoted by the uppercase italic letter**
C**.

## Practical Capacitor

It’s out of the question to make a practical capacitor of the preceding dimensions.

But two sheets, or strips, of foil, can be placed one on top of the other, separated
by a thin, nonconducting sheet such as paper, and then the whole assembly can be
rolled up to get a large effective surface area. When this is done, the electric
flux becomes great enough so that the device exhibits significant capacitance.

![Practical Capacitor ](https://studyelectrical.com/wp-content/uploads/2019/10/Practical-
Capacitor-Construction-Parts.png)

Practical Capacitor

Alternatively, two sets of several plates each can be meshed together with air in
between them, and the resulting capacitance is significant at high ac frequencies.

In a capacitor, the electric flux concentration is multiplied when a dielectric 
of a certain type is placed between the plates. This increases the effective surface
area of the plates so that a physically small component can be made to have a large
capacitance.

The voltage that a capacitor can handle depends on

 1. **the thickness of the metal sheets or strips,**
 2. **the spacing between them,**
 3. **and the type of dielectric used.**

In general, capacitance is directly proportional to the surface area of the conducting
plates or sheets.

Capacitance is inversely proportional to the separation between conducting sheets.
In other words, the closer the sheets are to each other, the greater the capacitance.

The capacitance also depends on the dielectric constant of the material between 
the plates.

A vacuum has a dielectric constant of 1; some substances have dielectric constants
that multiply the effective capacitance many times.

### The Unit of Capacitance

When a battery is connected between the plates of a capacitor, the potential difference
between the plates builds up at a rate that depends on the capacitance. The greater
the capacitance, the slower the rate of change of voltage in the plates.

**The unit of capacitance is an expression of the ratio between the current that
flows and the rate of voltage change between the plates as the plates become charged.**

A capacitance of **1 farad (1 F)** represents a current flow of 1 A while there 
is a voltage increase of 1 V/s. A capacitance of 1 F also results in 1 V of potential
difference for an electric charge of 1 C.

**A farad is a huge unit of capacitance. You’ll almost never see a capacitor with
a value of 1 F.**

Commonly employed units of capacitance are the **microfarad (µF) and the picofarad(
pF)**.

 * 1 µF represents 0.000001 (10^(−6) ) F
 * 1 pF is a millionth of a microfarad or 0.000000000001 (10^(−12) ) F

Physically small components can be made to have fairly large capacitance values.
Conversely, some capacitors with small values take up large physical volumes.

The physical **size of a capacitor**, if all other factors are held constant, is**
proportional to the voltage** that it can handle. The higher the rated voltage, 
the bigger the component.

## Connection of Capacitor in a Circuit

A capacitor can be connected in a circuit in two forms.

 1. Series
 2. Parallel

The value of capacitance changes when we connect the capacitors in these two forms.
Let’s learn how to calculate equivalent capacitance in both circuits.

### Capacitors in Series

With capacitors, there is rarely any mutual interaction. This makes capacitors easier
to work with than inductors. We don’t have to worry about mutual capacitance very
often, the way we have to be concerned about mutual inductance when working with
wire coils.

**Capacitors in series add together like resistors or inductors in parallel.**

Suppose you have several capacitors with values C1, C2, C3,. . . , Cn connected 
in series.

You can find the reciprocal of the total capacitance, 1/C, using the following formula:

**1/C = 1/C1 + 1/C2 + 1/C3 + . . . + 1/Cn**

The net capacitance of the series combination, C, is found by taking the reciprocal
of the number you get for 1/C.

If two or more capacitors are connected in series, and one of them has a value that
is tiny compared with the values of all the others, the net capacitance is roughly
equal to the smallest capacitance.

### Capacitors in Parallel

Capacitors in parallel add like resistances in series. The total capacitance is 
the sum of the individual component values.

![capacitors connected in parallel](https://studyelectrical.com/wp-content/uploads/
2019/10/capacitors-connected-in-parallel.jpg)

Two capacitors connected in parallel

The net capacitance of the parallel combination is,

**C = C1 + C2 + C3 + . . . + Cn**

If two or more capacitors are connected in parallel, and one of the capacitances
is far larger than any of the others, the total capacitance can be taken as approximately
the value of the biggest one.

## Different Types of Capacitors

The capacitors are broadly divided into two types.

 1. **Fixed Capacitors**
 2. **Variable Capacitors**

Read more: [Different Types of Capacitors](https://studyelectrical.com/2016/12/different-types-classification-of-capacitors.html)

## **Fixed Capacitors**

A **fixed capacitor** has a value that cannot be adjusted, and that (ideally) does
not vary when environmental or circuit conditions change.

The following are some of the common types of fixed capacitors.

 1. **Paper Capacitor**
 2. **Mica Capacitor**
 3. **Ceramic Capacitor**
 4. **Plastic-Film Capacitors**
 5. **Electrolytic Capacitors**
 6. **Tantalum Capacitors**
 7. **Semiconductor Capacitors**

Related: [Application of different types of fixed capacitors](https://studyelectrical.com/2016/12/different-types-classification-of-capacitors.html)

**Dielectric Materials in Fixed Capacitors**

Just as certain solids can be placed within a coil to increase the [inductance](https://studyelectrical.com/2019/11/inductors-inductance-working-unit-function-types-uses.html),
materials exist that can be sandwiched in between the plates of a capacitor to increase
the capacitance.

The substance between the plates is called the **dielectric of the capacitor**.

Air is an efficient dielectric; it has almost no loss. But it is difficult to get
very much capacitance using air as the dielectric.

Some kind of solid material is usually employed as the dielectric for most fixed
capacitors. Dielectric materials accommodate electric fields well, but they are 
poor conductors of electric currents. In fact, dielectric materials are known as
good insulators.

![Dielectric inside capacitor](https://studyelectrical.com/wp-content/uploads/2019/
10/how-dielectric-are-placed-inside-capacitor.png)

Dielectric inside capacitor

Solid dielectrics increase the capacitance for a given surface area and spacing 
of the plates. Solid dielectrics also allow the plates to be rolled up, squashed,
and placed very close together. This geometry acts to maximize the capacitance per
unit volume.

### 1. Paper Capacitors

In the early days of electronics, capacitors were commonly made by placing paper,
soaked with mineral oil, between two strips of foil. Then rolling the assembly up,
attaching wire leads to the two pieces of foil, and enclosing the rolled-up foil
and paper in an airtight cylindrical case.

![Paper Capacitor ](https://studyelectrical.com/wp-content/uploads/2019/10/Paper-
Capacitor-Construction.jpg)

Paper Capacitor

Paper capacitors can still sometimes be **found in older electronic equipment**.

They have values ranging from about **0.001 µF to 0.1 µF**.

These capacitors can handle low to moderate voltages, usually up to **about 1000
V**.

### 2. Mica Capacitors

Mica is a naturally occurring, solid, transparent mineral substance that flakes 
off in thin sheets. It makes an excellent dielectric for capacitors.

![Silver_mica_capacitors](https://studyelectrical.com/wp-content/uploads/2016/12/
Silver_mica_capacitors.jpg)

Silver mica capacitors

Mica capacitors can be manufactured by alternately stacking metal sheets and layers
of mica, or by applying silver ink to sheets of mica. The metal sheets are wired
together into two meshed sets, forming the two terminals of the capacitor. This 
scheme is shown in the figure.

![Meshing of plates to increase capacitance](https://studyelectrical.com/wp-content/
uploads/2019/10/Meshing-of-plates-to-increase-capacitance.png)

Meshing of plates to increase capacitance

Mica capacitors have **low loss**, and are therefore highly efficient, provided 
their **voltage rating is not exceeded**.

Voltage ratings can be up to several thousand volts if thick sheets of mica are 
used. But mica capacitors are large physically in proportion to their capacitance.

The main application for mica capacitors is in **radio receivers and transmitters**.

Their capacitances are a little lower than those of paper capacitors, ranging from
a **few tens of picofarads up to about 0.05 µF**.

### 3. Ceramic Capacitors

Ceramic materials work well as dielectrics. Sheets of metal are stacked alternately
with wafers of ceramic to make these capacitors. The meshing/layering geometry is
used. Ceramic, like mica, has low loss and allows for high efficiency.

For small values of capacitance, only one layer of ceramic is needed, and two metal
plates can be glued to the disk-shaped material, one on each side. This type of 
component is known as a disk ceramic capacitor.

![Ceramic Capacitors](https://studyelectrical.com/wp-content/uploads/2019/10/Ceramic-
Capacitors.jpg)

Ceramic Capacitors

Alternatively, a tube or cylinder of ceramic can be employed, and metal ink applied
to the inside and outside of the tube. Such units are called tubular capacitors.

Ceramic capacitors have values ranging from a **few picofarads to about 0.5 µF**.

Their voltage ratings are comparable to those of paper capacitors.

### 4. Plastic-Film Capacitors

Plastics make good dielectrics for the manufacture of capacitors. Polyethylene and
polystyrene are commonly used.

The method of manufacture is similar to that for paper capacitors. Stacking methods
can be used if the plastic is rigid. The geometries can vary, and these capacitors
are therefore found in various shapes.

Capacitance values for plastic-film units range from about **50 pF to several tens
of microfarads**.

Most often they are in the range of **0.001 µF to 10 µF**.

Plastic capacitors are employed at **audio frequency (AF) and radio frequency (RF),
and at low to moderate voltages**.

The efficiency is good, although not as high as that for mica dielectric or air-
dielectric units.

### 5. Electrolytic Capacitors

All of the aforementioned types of capacitors provide relatively small values of
capacitance. They are also nonpolarized, meaning that they can be hooked up in a
circuit in either direction.

An electrolytic capacitor provides greater capacitance than any of the preceding
types, but it must be connected in the proper direction in a circuit to work right.**
An electrolytic capacitor is a polarized component**.

Electrolytic capacitors are made by rolling up aluminum foil strips, separated by
paper saturated with an electrolyte liquid. The electrolyte is a conducting solution.

When dc flows through the component, the aluminum oxidizes because of the electrolyte.
The oxide layer is nonconducting and forms the dielectric for the capacitor. The
layer is extremely thin, and this results in a high capacitance per unit volume.

Electrolytic capacitors can have values **up to thousands of microfarads**, and 
some can handle thousands of volts.

These capacitors are most often seen in **AF circuits and in dc power supplies**.

### 6. Tantalum Capacitors

Another type of electrolytic capacitor uses tantalum rather than aluminum.

The tantalum can be a foil, as is the aluminum in a conventional electrolytic capacitor.
It can also take the form of a porous pellet, the irregular surface of which provides
a large area in a small volume. An extremely thin oxide layer forms on the tantalum.

Tantalum capacitors have **high reliability and excellent efficiency**.

They are often used in **military applications** because they almost never fail.

They can be used in **AF and digital circuits** in place of aluminum electrolytic.

### 7. Semiconductor Capacitors

Semiconductor materials can be employed to make capacitors. A semiconductor diode
conducts current in one direction and refuses to conduct in the other direction.

When a voltage source is connected across a diode so that it does not conduct, the
diode acts as a capacitor. The capacitance varies depending on how much of this 
_reverse voltage_ is applied to the diode.

The greater the reverse voltage, the smaller the capacitance. This makes the diode
act as a **variable capacitor**. Some diodes are specially manufactured to serve
this function. Their capacitances fluctuate rapidly along with pulsating dc. They
are called **varactor diodes or simply varactors**.

Capacitors can be formed in the semiconductor materials of an integrated circuit(
also called an IC or chip) in much the same way. Sometimes, IC diodes are fabricated
to serve as varactors.

Another way to make a capacitor in an IC is to sandwich an oxide layer into the 
semiconductor material, between two layers that conduct well.

Most ICs look like little boxes with protruding metal prongs. The prongs provide
the electrical connections to external circuits and systems.

Semiconductor capacitors usually have **small values of capacitance**.

They are **physically tiny** and can **handle only low voltages**.

The advantages are miniaturization and ability, in the case of the varactor, to 
change in value at a rapid rate.

## **Variable Capacitors**

The capacitance of a component can be varied at will by adjusting the mutual surface
area between the plates, or by changing the spacing between the plates.

The two most common types of variable capacitors (besides varactors) are the air
variable and the trimmer. You will also sometimes encounter coaxial capacitors.

Here you will learn the following three variable capacitors

 1. Air Variable Capacitor
 2. Trimmer Capacitor
 3. Coaxial Capacitor

### 1. Air Variable Capacitor

By connecting two sets of metal plates so that they mesh, and by affixing one set
to a rotatable shaft, a variable capacitor is made.

The rotatable set of plates is called the rotor, and the fixed set is called the
stator.

This is the type of component you might have seen in older radio receivers, used
to tune the frequency. Such capacitors are still used in transmitter output tuning
networks.

The figure below is a functional drawing of an air-variable capacitor.

![Air Variable Capacitor](https://studyelectrical.com/wp-content/uploads/2019/10/
Air-Variable-Capacitor.jpg)

Air Variable Capacitor

Air variables have a maximum capacitance that depends on the number of plates in
each set, and also on the spacing between the plates.

Common **maximum values are 50 to 500 pF; minimum values are a few picofarads**.

The voltage-handling capability depends on the spacing between the plates. Some 
air variables can handle many kilovolts.

Air variables are used primarily in **RF applications**.

They are **highly efficient**, and are **nonpolarized**, although the rotor is usually
connected to common ground (the chassis or circuit board).

### 2. Trimmer Capacitors

When it is not necessary to change the value of a capacitor very often, a trimmer
can be used.

It consists of two plates, mounted on a ceramic base and separated by a sheet of
plastic, mica, or some other solid dielectric. The plates are flexible and can be
squashed together more or less by means of a screw.

![Trimmer Capacitor Parts](https://studyelectrical.com/wp-content/uploads/2019/10/
Trimmer-Capacitor-Parts.png)

Trimmer Capacitor

Sometimes two sets of several plates are interleaved to increase the capacitance.

Trimmers can be connected in parallel with an air variable so that the range of 
the air variable can be adjusted. Some air-variable capacitors have trimmers built-
in.

Typical maximum values for trimmers range from a** few picofarads up to about 200
pF**. They handle low to moderate voltages, are highly efficient, and are nonpolarized.

### 3. Coaxial Capacitors

You know that sections of transmission lines can work as inductors. They can act
as capacitors, too.

If a section of the transmission line is less than 1 ⁄ 4 wavelength long and is 
left open at the far end (rather than shorted out), it behaves as a capacitor. The
capacitance increases with length.

The most common transmission-line capacitor uses two telescoping sections of metal
tubing. This is called a coaxial capacitor.

![Coaxial Variable Capacitor](https://studyelectrical.com/wp-content/uploads/2019/
10/Coaxial-Variable-Capacitor.png)

Coaxial Variable Capacitor

It works because there is a certain effective surface area between the inner and
the outer tubing sections. A sleeve of the plastic dielectric is placed between 
the sections of tubing.

This allows the capacitance to be adjusted by sliding the inner section in or out
of the outer section.

Coaxial capacitors are used in **RF applications, particularly in antenna systems**.

Their values are generally from a **few picofarads up to about 100 pF**.

## Capacitor Specifications

When you are looking for a capacitor for a particular application, it’s important
to find a component that has the right specifications for the job.

Here are two of the most important specifications to watch for before selecting 
a capacitor:

### Tolerance

Capacitors are rated according to how nearly their values can be expected to match
the rated capacitance. The most common tolerance is ±10%; some capacitors are rated
at ±5% or even at ±1%.

The lower (or tighter) the tolerance number, the more closely you can expect the
actual component value to match the rated value.

For example, a ±10% capacitor rated at 100 pF can range from 90 to 110 pF. But if
the tolerance is ±1%, the manufacturer guarantees that the capacitance will be between
99 and 101 pF.

**Example**

A capacitor is rated at 0.10 µF ± 10%. What is its guaranteed range of capacitance?

First, multiply 0.10 by 10 percent to get the plus-or-minus variation. This is 0.10
× 0.10 = 0.010 µF. Then add and subtract this from the rated value to get the maximum
and minimum possible capacitances. The result is a range of 0.09 to 0.11 µF.

### Temperature Coefficient

Some capacitors increase in value as the temperature increases. These components
have a positive temperature coefficient.

Some capacitors decrease in value as the temperature rises; these have a negative
temperature coefficient.

Some capacitors are manufactured so that their values remain constant over a certain
temperature range. Within this span of temperatures, such capacitors have zero temperature
coefficient.

The temperature coefficient is specified in **percent per degree Celsius (%/°C)**.

Sometimes, a capacitor with a negative temperature coefficient can be connected 
in series or parallel with a capacitor having a positive temperature coefficient,
and the two opposite effects cancel out over a range of temperatures.

In other instances, a capacitor with a positive or negative temperature coefficient
can be used to cancel out the effect of temperature on other components in a circuit,
such as inductors and resistors.

### Related posts:

 [ ⌊Collection of different types of capacitors⌉Different Types of Capacitors and their Uses](https://studyelectrical.com/2016/12/different-types-classification-of-capacitors.html)
[ ⌊Types-of-Electric-current⌉Types of Electric Current – Steady (DC), Varying & Alternating (AC) Current](https://studyelectrical.com/2019/11/types-of-electric-current-steady-dc-varying-alternating-ac-current.html)
[ ⌊Silver oxide minature cell battery⌉Miniature cells and Batteries – Silver Oxide, Mercury and Lithium Cells](https://studyelectrical.com/2019/11/miniature-cells-batteries-silver-oxide-mercury-lithium-type.html)
[ ⌊Air Variable Capacitor⌉How Charge is Stored in a Dielectric?](https://studyelectrical.com/2020/02/how-charge-is-stored-in-a-dielectric.html)
[ ⌊capacitor charging and discharging⌉Charging and Discharging a Capacitor](https://studyelectrical.com/2020/02/charging-and-discharging-a-capacitor.html)
[ ⌊electrical fuse⌉What is an Electrical Fuse? Types, Properties, and Application](https://studyelectrical.com/2020/06/electrical-fuse-types-properties-application.html)
[ ⌊dc voltage source⌉What is a Voltage Source? | DC and AC Voltage Sources Explained](https://studyelectrical.com/2021/12/voltage-source-dc-ac.html)
[ ⌊Thin film application iin electronics⌉The Various Applications Of Thin Films In Electronics And Other Equipment](https://studyelectrical.com/2023/01/thin-films-applications-in-electronics.html)
[ ⌊Capacitor in Parallel⌉Combination of Capacitors | Series & Parallel with Problems](https://studyelectrical.com/2024/04/combination-of-capacitors.html)
[ ⌊Complete Guide on Ground Fault Circuit Interrupters⌉GFCI (Ground Fault Circuit Interrupter) – Working, Types, Installing and Troubleshooting](https://studyelectrical.com/2019/03/gfci-ground-fault-circuit-interrupter-breaker.html)