18 Questions
How is the vacuum permittivity represented?
Ɛ0
What is the relative dielectric constant denoted as?
Ɛr
How many piezoelectric crystal classes lack a center of symmetry?
Twenty piezoelectric crystal classes lack a center of symmetry.
What unique characteristic do pyroelectrics exhibit in the absence of stress and electric field?
Pyroelectrics exhibit spontaneous polarization in the absence of stress and electric field.
What does the polarization density P represent in dielectric materials?
P represents the polarization density in dielectric materials.
What happens to cations and anions in a material when an external electric field is applied?
Cations are displaced in the direction of the electric field, and anions are displaced in the opposite direction.
What causes a change in dimension in dielectric materials?
The displacement of positive and negative charges within a material causes a change in dimension.
What happens to the dipole moments in nonpolar dielectric materials upon the removal of an external electric field?
The induced dipole moments disappear.
What type of dielectric materials do not possess an electric dipole moment in their atoms?
Nonpolar dielectric materials.
In which type of dielectric materials does each molecule or atom possess a dipole moment?
Polar dielectric materials.
What effect arises in materials when a small change in dimension results in a change in electric polarization?
Ferroelectric, piezoelectric, or pyroelectric effect.
What are dielectric materials?
Insulating materials that can get polarized in the presence of an electric field.
What property makes the dielectric materials polar or nonpolar?
The presence or absence of an electric dipole moment in their atoms.
Define dielectric polarization.
The shifting of charges from their mean position in a dielectric material when subjected to an electric field.
What is the electric breakdown field or dielectric strength?
The maximum electric field that a material can withstand before becoming conductive.
How does the electric field affect the surface of a dielectric material?
Causes electric charge to accumulate at the surface of the material.
What is electric displacement D?
The amount of charge Q per unit surface area A in a dielectric material.
What happens to positive and negative charges in a dielectric material when an electric field is applied?
Positive charge displaces in the direction of the electric field and negative charges move in the opposite direction.
Study Notes
Dielectric Materials
- Dielectrics are insulating materials that can get polarized in the presence of an electric field.
- When an electric field is applied, positive charges displace in the direction of the electric field and negative charges move in the opposite direction.
Polarization
- Polarization can be expressed as the sum of induced polarization due to the displacement of space charges, ions, and electrons in the material, and spontaneous alignment of dipole moments.
- Polarization density (P) is related to the relative dielectric constant (Ɛr) and vacuum permittivity (Ɛ0).
Classification of Dielectric Materials
- There are 32 point groups of crystals based on orientation, of which 20 lack a center of symmetry and are called piezoelectrics.
- Ten of these piezoelectric crystal classes, called pyroelectrics, demonstrate a unique polar axis and exhibit spontaneous polarization in the absence of stress and electric field.
Properties of Dielectrics
- Dielectric materials undergo a change in dimension when subjected to an external force, such as a mechanical stress, an electric field, or a change in temperature.
- This is caused by the displacement of positive and negative charges within a material.
Pyroelectric Materials
- Pyroelectric materials exhibit spontaneous polarization in the absence of stress and electric field.
- They can be used for infrared detection and have various applications.
Electric Breakdown Field
- The maximum electric field that a material can withstand before becoming conductive is called the electric breakdown field or dielectric strength (Eb).
Electric Displacement
- The amount of charge (Q) per unit surface area (A) is called electric displacement (D).
Dielectric Parameters
- Polar dielectric materials have molecules or atoms with dipole moments, whereas nonpolar dielectric materials do not.
- Nonpolar dielectrics have symmetric shapes and induce dipole moments upon application of an external electric field.
Learn about the definition and classification of dielectric materials, as well as the polarization mechanisms involved in materials under an electric field. Explore the relationship between induced polarization and spontaneous alignment of dipole moments.
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