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Electric Displacement

Last updated date: 21st May 2024
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What is Electric Displacement?

Electric Displacement primarily refers to the displacement of electric charge across a conductor positioned in an electric field. It fundamentally measures the charge per unit area, and you can also call it electric flux density. 

Therefore, it applies to free electric charges, thus eliminating the involvement of charges present in molecules or neutral atoms. It functions mainly because an electric field exists between two uncharged conductors when charge flows through them. 

As a result, one of the conductors assumes a positive charge, while the other possesses a negative charge. This, in turn, leads to the creation of an electric field between these conductors. This concept, therefore, aims to find the free-charge surface density. Moreover, it relates to the volume of free charge on one conductor, concerning the surface area of this conductor. 

How Does Electric Displacement Work? 

Electric Displacement thus calculates the density of electric flux within a charged field. However, it takes into account the instance when you introduce a dielectric into the apparatus. You must note, a dielectric refers to an insulating material that lacks any free or loosely-bound electrons. 

Consequently, they fail to necessitate the movement of free electric charges along their surface area. However, if you introduce an insulated object between an electric field, it witnesses a degree of polarization. It is because the strongly-bound negative charges move slightly towards the positive conductor. 

On the other hand, bound positive charges move by a certain extent towards the negative plate. This phenomenon results in an overall decrease in the electric field. 

Therefore, Electric Displacement ventures to find reactions of dielectric materials as they come in contact with electric fields. 

What is the Equation for Electric Displacement? 

First of all, you should note that ‘D’ stands for Electric Displacement. On the other hand, ‘E’ refers to the electric field that comes into the question. 

However, you should take a look at the following table to understand other components of this equation – 


Vacuum Permittivity 


Polarization Density

Therefore, the equation to find the Electric Displacement in a dielectric material is -  

D = ε0E + P

Its SI unit is C m-2 or Coulomb per meter square. In this unit, Coulomb stands for the unit of electric charge, whereas m-2 is the area of the material. 

Besides, you should also know what vaccum permittivity and polarization density imply. It will help you understand the factors working in the phenomenon even better. 

Vacuum permittivity: It is a physical constant that refers to the capability of an electric field to permeate a vacuum. It is, however, a relation between the units of electric charge and force. Length also becomes an essential component of this concept. Its value is ε0 = \[\frac {1} {\mu_0 c^2}\].

In this case, μ0 stands for magnetic constant, and c refers to a constant value of 299,792,458 m s-1

Polarization density: It indicates a vector field that deals with the density of dipole moments in a dielectric object. As discussed above, the introduction of such an object within an electric field results in a movement of charges. It refers to the electric dipole moment which polarizes a given object. 

Therefore, polarization density finds the electric dipole moment per unit volume of the dielectric material. 

How is Electric Displacement a Vector Quantity? 

When you introduce a dielectric material within an electric field, it undergoes a shift in the electron cloud of the free electrons. Consequently, it is known as a dipole. The negative and positive charges in the dielectric show an affinity towards positive and negative plates, respectively. 

As a result, they travel in specific directions along a particular line. The Electric Displacement vector thus measures the dielectric polarization vector. 

Therefore, Electric Displacement density duly measures the vector flux of electric density in a given dielectric material. On the other hand, its unit in the meter-kilogram-second system is Coulombs per meter square or C m-2. 

Now that you know what Electric Displacement is, browse through our website for an insight into similar topics. Also, you can download our Vedantu app for an advantageous experience in personalized learning. 

More About Electric Displacement

The feature of an electric field associated exclusively with the presence of separated free electric charges, omitting the contribution of any electric charges linked together in neutral atoms or molecules, is represented by an Electric Displacement, auxiliary electric field, or electric vector. When an electric charge is transferred between two parallel metal plates that were previously uncharged, one gets positively charged and the other becomes negatively charged by an equal amount, resulting in an electric field between the plates. When an insulated slab is put in between the charged plates, there happens the polarization of electric charges on the insulating material; Negative charges (atomic electrons) move a fraction of an atomic diameter toward the positive plate, whereas bound positive charges move just a fraction of an atomic diameter toward the positive plate.

The value of the electric field before the insulation was applied is reduced by this charge shift or polarization. As a result, the actual average value of the electric field E includes two components: P, which is determined by the bound polarization charges, and D, which is determined by the free separated charges on the plates. In the meter-kilogram-second (mks) or SI system, the relationship between the three vectors D, E, and P is D = 0E + P (where 0 is a constant, the permittivity of a vacuum). The relationship is D = E + 4P in the centimeter-gram-second (cgs) system.

The Electric Displacement's value 'D' can be calculated by dividing the quantity of free charge on one plate by the plate's area. Because of the strong link between electric flux and electric charge, D is sometimes referred to as the electric flux density or free charge surface density. In the MKS system, the dimensions of Electric Displacement come out as charge per unit area, and the units are coulombs per square meter. D in the centimeter-gram-second system has the same dimensions as the principal electric field E, which is measured in dynes per electrostatic unit or statvolts per second.

What is Dielectric Material?

A dielectric substance is an electrical insulator that can be polarized when an electric field is applied. When electric charges are placed in an electric field, they do not flow, but they do migrate away from their normal equilibrium location, causing dielectric polarization.

These materials are used in capacitors, radios, and radiofrequency transmission lines. C=(εrε0A)/d is the formula for the dielectric material in a capacitor.

Where 'ε0' is known as the Vacuum permittivity, 'r' is known as the Relative permittivity of the material, 'C' is known as the Capacitance, 'A' is known as the Area of the capacitor's plates and 'd' is known as the Distance between the plates. 

What Does Vacuum Permittivity mean?

The value of absolute dielectric permittivity, or the ability of the vacuum to permit electric field lines, is known as vacuum permittivity. The estimated value and formula for vacuum permittivity, which is symbolized by ε0 are as follows: ε0 = 8.854187... *10-12 degrees F.m-1

ϵ0= \[\frac {1} {\mu_0 c^2}\]

What is Polarization Density? 

Polarization density (also known as electric polarization or just polarization) is a vector field in classical electromagnetism that reflects the density of permanent or induced electric dipole moments in a dielectric substance. When a dielectric is exposed to an external electric field, its molecules acquire an electric dipole moment, causing the dielectric to become polarized. The electric polarization of the dielectric is the electric dipole moment induced per unit volume of the dielectric material.

Polarization density is known to determine how a material reacts when it is subject to an external electric field and how that electric field is affected due to it, and it may also be used to define the forces that come from such interactions. It is comparable to magnetization, which is the measurement of a material's response to a magnetic field in magnetism. Coulombs per square meter is the SI unit of measurement, and polarization density is represented by a vector P.

FAQs on Electric Displacement

1. What is Electric Displacement? 

Electric Displacement refers to the charge per unit area of a dielectric material when in contact with an electric field. 

2. What is the Equation for Electric Displacement? 

Electric Displacement D = ε0E + P. In this case, ε0 is vacuum permittivity, E is the electric field, and P is polarization density. 

3. What is the SI Unit of Electric Displacement? 

The SI unit of Electric Displacement is Coulomb per meter square or Cm-2.

4. Is Electric Displacement a vector quantity, if yes, how? 

To determine whether the Electric Displacement is a vector quantity or not, you can do a little experiment. You can put a dielectric material in an electric field, the cloud of the free electrons shows a shift and becomes a dipole. This means that both positive and negative charges appear on this dielectric. The electrons in this dielectric move in a particular direction. Hence, the Electric Displacement shows the properties of a vector quantity. 

5. How can I find Electric Displacement?

To find the Electric Displacement, we first need to define the quantities that are used to find it. The Electric Displacement is denoted by 'D' and to denote the electric field, we use 'E'. To find the Electric Displacement, we use the equation that involves the physical quantities like the electric field, polarization, etc. The equation to find the Electric Displacement in a dielectric material can be written as D = ε0E + P.