What Is Electric Displacement?
Electric displacement, denoted by D, is the charge per unit area that would be displaced across a layer of conductor placed across an electric field. It is also known as electric flux density.
Electric displacement is used in the dielectric material to find the response of the materials on the application of an electric field E. In Maxwell’s equation, it appears as a vector field.
The SI unit of electric displacement is Coulomb per meter square (C m-2).
The mathematical representation is as follows:
\(\begin{array}{l}D\equiv \epsilon _{0}E+P\end{array} \) |
Where,
- ϵ0: Vacuum permittivity
- P: Polarization density
- E: Electric field
- D: Electric displacement field
It was found that if electric field E is applied on the dielectric material, the bound charges inside the material responds to the electric field such that the distribution of positive changes take place in the direction of the electric field while the distribution of negative charges takes place in the opposite direction of the electric field. Before the application of the electric field, the material is electrically neutral and there is a formation of electric dipoles.
You may also want to check out these topics given below!
- Angular displacement
- Electric Potential And Potential Difference
- Work, Energy and Power
- Electric Dipoles
What Is Dielectric Material?
A dielectric material is an electrical insulator such that when an electric field is applied it can be polarized. There is no flow of electric charges when placed in an electric field, but they do move from their average equilibrium position resulting in dielectric polarization.
These materials find applications in capacitors, radios, and transmission lines for radio frequency. The dielectric material in a capacitor is given as:
\(\begin{array}{l}C=\frac{\epsilon_{r} \epsilon_{0} A}{d}\end{array} \) |
Where,
- C: Capacitance
- ϵ0: Vacuum permittivity
- ϵr: Relative permittivity of the material
- A: Area of the plates used in the capacitor
- d: Distance between the plates
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What Is the Vacuum Permittivity?
Vacuum permittivity is the value of absolute dielectric permittivity, i.e., it is the capability of the vacuum to permit electric field lines. Following is the approximate value and formula of vacuum permittivity, which is represented by ϵ0:
\(\begin{array}{l}\epsilon _{0} = \frac{1}{\mu _{0}c^{2}}\end{array} \) |
What Is Polarization Density?
Polarization density is used in classical electromagnetism to express the density of induced electric dipole moments in a dielectric material. The electric polarization of the dielectric is the electric dipole moment induced per unit volume of the dielectric material. The mathematical representation is:
\(\begin{array}{l}P=\frac{\Delta p}{\Delta V}\end{array} \) |
Where,
- P: polarisation density
- Δp: dipole moment
- ΔV: volume element
Displacement Field in Capacitor
Consider a parallel-plate capacitor with no free charges except on the capacitor placed in space. Let A be the area of the capacitor with thickness t and separation d. To calculate the electric field between the conductors, the potential difference between the plates is given as:
\(\begin{array}{l}C=\frac{Q}{V}\end{array} \) |
Using a Gaussian cylinder that encloses some charge on one plate, we can find E and D:
The electric field outside and inside the plate are:
⇒ EV (d-t) + Edt = V
Therefore,
\(\begin{array}{l}C=\frac{Q}{V}\end{array} \) |
Sine ϵ ≥ 1, the capacitance is increased for fixed plate size and separation.
Frequently Asked Questions – FAQs
What is an electric charge?
An electric charge is a property of matter that forces it to encounter a force when it is in an electromagnetic field. An electric charge can be negative or positive. Unlike charges attract and like charges repel each other.
What is an electric field?
An electric field is a physical field that surrounds electrically activated particles or bodies. It exerts a force on every other charged particle or body in the field (repelling or attracting). In other words, it can be defined as the physical field for a body of charged particles.
What is meant by electric displacement?
Electric Displacement is the charge per unit area that is displaced across a layer of conductor positioned across an electric field.
What is the SI unit of electric displacement?
Coulomb per meter square is the SI unit of electric displacement.
What is the direction of an electric dipole moment?
The electric dipole moment is a vector quantity; it has a well-defined direction which is from the negative charge to the positive charge.
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