Dielectrics and Electric Polarization

A dielectric material is the non-metallic material having a high specific resistivity, a negative resistance temperature coefficient and with large resistance of insulation.

Dielectric

A dielectric is a substance that becomes polarized when exposed to an electric field. The charges present in the molecules move away from each other due to the action of the external electric field, which reduces the strength of the electric field in this medium. Metals have free electrons.

When a conductor is held in an external electric field, a force is experienced by the free electrons which is due to the electric field, producing a potential gradient in the conductor and due to this gradient, an induced electric field opposite to the external electric field is created. electric field. Because of this induced electric field, in the case of electrostatics, the total electric field is zero in most of the conductors.

Types of Dielectrics

There are two types of dielectrics which are as follows

1. Polar Dielectric
2. Non – polar dielectric

• Polar Dielectrics

For polar dielectric we have the inherent polarity of the molecule. In other words, the center of mass of the positive element and the center of mass of the negative element do not coincide. Hence it has an inherent dipole moment and when held in an electric field it orients itself accordingly.

H2O, CO2 are polar dielectrics.

• Non – Polar Dielectrics

For non-polar dielectrics we don’t have the inherent polarity of the molecule. In other words, the center of mass of the positive element and the center of mass of the negative element coincide. Hence it does not have an inherent dipole moment.

H2, CH4 are non – polar dielectrics

Electric Polarization

When a dielectric plate is placed in an electric field, the molecule attains a dipole moment. In this circumstance, the dielectric is said to be polarized. The electrical polarization of a dielectric material is defined as the dipole moment per unit volume. P is the polarization symbol.

Dielectric Constant

Dielectric Constant is defined as the ratio of strength of applied electric field to the strength of the reduced value of electric field capacitor when a dielectric is kept between the parallel plates.

Dielectric constant is given as

ɛr = E0/E

Here,

ɛr = Dielectric constant

E0 = electric field applied

E = net electric field

The higher the dielectric constant, the more charge can be held. The capacitance of a capacitor increases by a factor of dielectric constant when the space between the plates is filled completely with a dielectric.

C = C0ɛr

C0 = capacitance of plates without dielectric 

Dielectric Polarization

Dielectric polarization arises when an external electric field is applied across a dielectric material. When an electric field is applied, it moves charges (both positive and negative). The main goal of dielectric polarization is to combine macroscopic and microscopic properties.

The polarization is given as

P = ɛo(ɛr – 1)E

Induced Electric Dipole Moment

When an external electric field is applied to a non-polar molecule, all of the protons move in the same direction as the electric field, and the electrons move in opposite directions. This process continues unless internal pressures are equalized due to the presence of an electric field. This creates two charge centers. We call them induced electric dipoles as they are polarized.

Dielectric Material

A dielectric material is defined as a non – metallic material having high resistivity, negative temperature coefficient of resistance, and high insulation resistance. The other way to define dielectric material is that it is a non-conductive material that stores electrical charges.

• Dielectric material can be solid, liquid and gas.
• Ceramic, plastic, glass are solid dielectrics.
• Distilled water is a liquid dielectric.
• Nitrogen and helium, dry air are gas dielectrics.

Properties of Dielectric Material

There are following properties of dielectric material which exhibit them.

1. Dielectric materials have a very large energy gap.
2. Dielectric materials have negative temperature coefficient of resistance and high insulation resistance.
3. Resistivity of a dielectric material is high.
4. The attraction is very strong between electrons and the parent nucleus.
5. The electrical conductivity of dielectric material is very low because there are no free electrons which can carry current.

Capacitance of a Parallel Plate Capacitor with dielectric filled between the plates

The charges are shielded on the two plates by the small dipole moment of the material. As a result of this, the impact of the dielectric substance are changes which are put between the two plates. The permeability of a material is represented by the relative permeability k.

The capacitance of the parallel plate when dielectric is filled is given as

C = ɛA/d =kɛoA/d

Capacitance of a parallel plate capacitor is increased by putting a dielectric between the two plates and the value of permeability k is more than 1 (one).

Conclusion 

A dielectric is a substance that becomes polarized when exposed to an electric field.

There are two types of dielectrics which are as follows

1. Polar Dielectric
2. Non – polar dielectric

H2O, CO2  are polar dielectrics.

H2, CH4  are non – polar dielectrics

The electrical polarization of a dielectric material is defined as the dipole moment per unit volume.

Dielectric constant is given as

ɛr = E0/E

Dielectric material is a non-conductive material that stores electrical charges.

Dielectric material can be solid, liquid and gas.

Ceramic, plastic, glass are solid dielectrics.

Distilled water is a liquid dielectric.

Nitrogen and helium, dry air are gas dielectrics.

Resistivity of a dielectric material is high.

The main goal of dielectric polarization is to combine macroscopic and microscopic properties.

The polarization is given as

P = ɛo(ɛr – 1)E