Name: dielectric polarization and capacitance
Uploaded: 2025-05-22T09:06:00.000Z
Duration: 1 min 26 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.10

SC.912.P.10.14

susceptibility-permittivity-and-dielectric-constant

Susceptibility, Permittivity and Dielectric Constant

In a polarized dielectric, the total charge density is the sum of the bound and free charge densities. Recalling the expression for bound charge density and rewriting the total charge density in terms of the total electric field gives the expression for electric displacement in terms of polarization.
In the case of linear dielectrics, the polarization is proportional to the total electric field. The constant of proportionality is called the electric susceptibility of the material, and the permittivity of free space makes the electric susceptibility dimensionless.
For an applied electric field, if electric susceptibility increases, the polarization increases.
Substituting the expression for polarization implies that the electric displacement is also proportional to the total electric field.
The new constant of proportionality is the permittivity of the material. The ratio of the material&#39;s permittivity to the permittivity of free space gives the relative permittivity, also known as the dielectric constant.
This estimates the ability to store charge for a given electric field. Materials with higher dielectric constants are used in capacitors to increase energy storage.

susceptibility, permittivity and dielectric constant

When placed in an external electric field, a dielectric material gets polarized. The charge density in the dielectric material is given by the sum of the bound and free charge densities, while the total charge density can also be written in terms of the total electric field. The bound charge density can be measured in terms of polarization, leading to the relationship between electric displacement and polarization.
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The polarization is proportional to the electric field for the linear dielectrics. This introduces a new proportionality constant called the electric susceptibility, a dimensionless quantity. The electric susceptibility is the tendency of any material to get polarized and is zero for free space.
<img alt="Organic chemistry mechanism, SN2 reaction diagram, nucleophilic substitution process, molecular arrows." src="/files/ftp_upload/14184/14184_Equation_2.png" style="text-align: center; height: 30px;" data-altupdatedat="1754904545000" data-alt="Static equilibrium diagram of forces: ΣFx=0, ΣFy=0, MA=0; illustrates balance concept.">
These expressions can be solved to give the second proportionality constant, or the permittivity of the material.
<img alt="Capacitance circuit diagram with parallel and series capacitors, illustrating charge distribution." src="/files/ftp_upload/14184/14184_Equation_3.png" style="text-align: center; height: 30px;" data-altupdatedat="1754904545000" data-alt="Lewis structures of acetic acid: COOH with Higgs oxoacid rules diagram, illustrating bonding.">
The ratio between the material's permittivity and the free space's permeability gives the third proportionality constant, called the relative permittivity or the dielectric constant.
<img alt="Spectroscopy setup for transient absorption and emission analysis; diagram with optical components." src="/files/ftp_upload/14184/14184_Equation_4.png" style="text-align: center; height: 42px;" data-altupdatedat="1754904545000" data-alt="Chromatography process diagram with labeled equipment; illustrates compound separation method.">
This is the same proportionality constant that gives the relationship between the capacitance of a capacitor with and without a dielectric medium. The value of the dielectric constant for free space is 1. The presence of a dielectric medium in a capacitor always increases the energy storage, thereby increasing the capacitance. Hence, the dielectric constant for any medium is always greater than 1.

When placed in an external electric field, a dielectric material gets polarized. The charge density in the dielectric material is given by the sum of the ...

Education

JoVE Core

Physics

Unit 1

Capacitance

KEY TERMS AND CONCEPTS

dielectric polarization and capacitance

Dielectric polarization explains how a material responds to an external electric field. When a dielectric is placed in the field, its charges shift so the material becomes polarized. The charge density in the dielectric is the sum of bound and free charge densities, and the total charge density can also be written in terms of the total electric field.

The bound charge density can be measured using polarization. This leads to a link between electric displacement and polarization. For linear dielectrics, polarization is proportional to the electric field. That proportionality introduces electric susceptibility, a dimensionless quantity that shows how easily a material can be polarized. For free space, electric susceptibility is zero.

These relationships can also be used to define permittivity, which is the second proportionality constant for the material. The ratio of a material’s permittivity to the permittivity of free space gives the relative permittivity, also called the dielectric constant. Free space has a dielectric constant of 1.

The dielectric constant is the same constant used to compare a capacitor with and without a dielectric medium. A dielectric in a capacitor increases energy storage and therefore increases capacitance. For that reason, the dielectric constant of a medium is always greater than 1.

Dielectric Polarization and Capacitance

capacitors and capacitance

Parallel Plate Capacitors and Stored Charge

Parallel plate capacitors store electric charge between two conducting plates. The plates are separated by a distance, and the space between them is either a vacuum or an insulating material called a dielectric. Capacitors are used in many ways, from reducing static in radio reception to storing energy in heart defibrillators. When the two conductors are identical parallel plates, the device is called a parallel plate capacitor. If a battery is connected to an initially uncharged capacitor,...

spherical and cylindrical capacitor

Capacitance in Spheres and Cylinders

A spherical capacitor uses two concentric conducting spherical shells. The inner shell has radius R1, and the outer shell has radius R2. The shells carry equal and opposite charges, +Q and −Q. For an isolated conducting spherical capacitor, the outer shell can be treated as if it were at infinity. By symmetry, the electric field between the shells points radially outward. Using Gauss’s law on a spherical Gaussian surface of radius r gives the field magnitude between the shells. That electric...

capacitors in series and parallel

How Capacitor Networks Combine Charge

Capacitor networks combine charge and voltage in different ways, depending on how the capacitors are connected. When several capacitors act together, they can be treated as one equivalent capacitor. The total capacitance depends on the capacitance of each capacitor and on the connection type. In a series connection, the capacitors are connected one after another. The negative terminal of the first capacitor connects to the positive terminal of the second. When this series group is connected to...

equivalent capacitance

Finding Net Capacitance in Capacitor Networks

Capacitor networks can be arranged in series or parallel, and the connection type changes how charge and voltage are shared. When the network is connected to a battery, the potential drop across each capacitor and the charge stored in each one depend on that arrangement. The full network can then be replaced by one equivalent capacitor that stores the same charge for the same potential difference. To find the net capacitance, a capacitor network is grouped into series and parallel parts. A...

energy stored in a capacitor

Capacitor Charging and Stored Electric Energy

A charged capacitor stores electric potential energy by doing work during charging. This idea is similar to an archer pulling back a bowstring and storing elastic potential energy. When the arrow is released, that stored energy becomes motion. In the same way, the work put into a capacitor is stored as electric potential energy. For a parallel plate capacitor, the process starts when it is connected to a battery. The plate attached to the negative side of the battery gains extra electrons.

energy stored in a capacitor: problem solving

energy-stored-in-a-capacitor-problem-solving

Capacitor Energy and CDI Ignition

Capacitors store electric potential energy, and that energy can be released over a short time. This makes them useful in a range of applications. Benjamin Franklin coined the word battery in 1749 for a series of capacitors connected to store energy. One common use is capacitor-discharge ignition, or CDI, in small engines. In a CDI system, the energy from a capacitor ignites an induction coil, which then fires the spark plug. To find the energy stored in a typical CDI capacitor, at least two of...

capacitor with a dielectric

How Dielectrics Boost Capacitor Storage

A dielectric can help a parallel plate capacitor store more charge. In a basic capacitor, two conducting plates are separated by a set distance. Keeping the plates parallel can be mechanically difficult, especially when the plates are large and cannot touch each other. A dielectric is a non-conducting material with no free or loosely bound electrons. Placing this material between the plates creates a small gap and helps hold the plates together. It also increases the capacitor’s capacitance,...

dielectric polarization in a capacitor

How Dielectrics Change Capacitor Fields

Dielectrics change the electric field, voltage, and capacitance in a capacitor. A dielectric is an insulating material placed between the plates. Its presence affects how the field behaves inside the capacitor. Dielectrics are usually described as polar or nonpolar. In a polar dielectric, positive and negative charges are already separated, so each molecule has a permanent dipole moment. In a nonpolar dielectric, that charge separation is not present until an external electric field acts on...

gauss's law in dielectrics

Dielectric Effects on Electric Fields

Dielectric effects on electric fields explain how an insulating material changes the field between capacitor plates. When a polar dielectric is placed in an external field, its dipoles line up with the field. The opposite charges on nearby dipoles cancel each other, so the dielectric as a whole remains neutral. When the dielectric is inserted between the plates of a capacitor, bound charges appear near the edges of the dielectric and at the metal surface. These induced surface charges create...

potential due to a polarized object

Bound Charges in Polarized Dielectrics

Polarized dielectrics form when charges inside atoms or molecules shift slightly in an electric field. A neutral atom has a positive nucleus and a negative electron cloud. An external electric field pulls them in opposite directions. The pull is balanced by the attraction between the nucleus and electrons, so the atom becomes polarized. Some molecules, such as water, already have separated positive and negative sides. In a uniform electric field, the forces on those sides cancel. Even so, a...

Dielectric polarization explains how a material responds to an external electric field. When a dielectric is placed in the field, its charges shift so the material becomes polarized. The charge density in the dielectric is the sum of bound and free charge densities, and the total charge density can also be written in terms of the total electric field. The bound charge density can be measured using polarization. This leads to a link between electric displacement and polarization. For linear...

electrostatic boundary conditions in dielectrics

electrostatic-boundary-conditions-in-dielectrics

Field Behavior at Dielectric Interfaces

Field behavior at dielectric interfaces changes when an electric field crosses from one homogeneous medium into another. That change creates a discontinuity, or sudden jump, in the field. The boundary conditions depend on which materials meet at the interface. When the two sides are different dielectric materials, the electric field and the electric displacement are linked through the material’s permittivity. Replacing the electric field with the electric displacement in the boundary...

key terms and concepts

Learn how dielectric polarization, electric susceptibility, permittivity, and dielectric constant connect to capacitance and energy storage in capacitors.

Dielectric Polarization and Capacitance | JoVE K12

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Dielectric Polarization and Capacitance

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