Dielectrics

Introduction

Dielectrics materials plays a major role while studying Solid State Physics. As we know matter can be found in three states. They are gaseous state, solid state and liquid state. Atoms or ions or molecules combine to form a substance. Solid State Physics is a branch of physics that describes the physical properties of matter in a solid or solid state.

Initially, the field was considered a branch of metals and later, it expanded into a field of study of all types of solids. This field of science is at the forefront of today's modern science and technology. The sector is particularly important in electronics, integrated circuit design and the development of various sensitive instruments.

What is Dielectric?

• Materials with constant electrical dipoles are called dielectric materials.

• A material is said to be dielectric if it has the property of forming a large number of induced electric dipoles when an electric field is applied to it.

• Also, this material is devoid of free electrons. The behaviour of this material changes due to the action of the electric field.

• Mostly these materials are used to store electrical energy. All electrically conductive materials can be insulators. But not all insulators are necessarily dielectric materials.

What is Dielectric Constant?

• The dielectric constant is the ratio between the permittivity of a medium and the permittivity of a vacuum. The dielectric property of a material can be known by this value.

• The Dielectric constant is the property that determines the distribution of electrical current absorbed by an insulating material. As the dielectric constant increases, the capacitance of the insulating material also increases.

Permittivity of a Vacuum

$$\mathrm{\varepsilon_r=\frac{\varepsilon}{\varepsilon_0}=\frac{C}{C_0}}$$

$\mathrm{\varepsilon}$ =the permittivity of a medium

$\mathrm{\varepsilon_0}$ =the permittivity of vacuum

C= the capacitance of parallel plate capacitor filled with dielectric

$\mathrm{C_0}$ =the capacitance of parallel plate capacitor filled with dielectric in vacuum

• The dielectric constant is a property that measures the electric polarization of a dielectric material.

$$\mathrm{\varepsilon_r=\frac{E_0}{E_0-E_p}}$$

$\mathrm{E_0}$ = applied electric field

$\mathrm{E_p}$ = polarised electric field

If there is more polarization in material then $\mathrm{E_p}$ will be more. So $\mathrm{\varepsilon_r}$ will be higher in that case.

Dielectric Constant Units

There is no unit for this value. Because the formula for the dielectric constant is $\mathrm{\varepsilon_r=\frac{\varepsilon}{\varepsilon_0}}$

It is the ratio between the same quantities.

$\mathrm{\varepsilon}$ = the permittivity of a medium

$\mathrm{\varepsilon_0}$ = the permittivity of vacuum

Dielectric Constant Symbol

The symbol of the dielectric constant is $\mathrm{\varepsilon_r}$. In some cases, the dielectric constant is also denoted as k.

$$\mathrm{k=\frac{\varepsilon}{\varepsilon_0}}$$

Hers k is the Greek letter kappa.

The Theory Behind Dielectric Constant

• A dielectric material is a non-metallic material with high electrical resistivity and anti-thermal resistivity. Dielectric materials play a very important role in electronic devices.

• The main characteristic of a dielectric material is that when an electric field is applied, the material becomes polarized.

• The dielectric property of a medium is defined as its permittivity. It indicates the polarization nature of an object. Its unit is $\mathrm{farad\:meter^{−1}}$

For example, the value of permittivity of the vacuum is $\mathrm{\varepsilon_0=8.854\times 10^{−12}\: F/m}$

Dielectric Constant Value

The Dielectric constant value is calculated by using the formula $\mathrm{\varepsilon_r=\frac{\varepsilon}{\varepsilon_0}}$ For example, the dielectric constant of water is 78.39 at room temperature (25°C or 77°F). The high boiling point of water is due to hydrogen bonding in water. For air, the dielectric constant value is 1.00059 at the same temperature.

Factors Affecting Dielectric Constant

Temperature

• Dielectric materials can also be used in high-temperature applications. These materials should be capable of withstanding high temperatures without affecting other properties.

Frequency

• Discharges occur in dielectric materials at radio frequency ranges when the static dipole moment in the material is rotated by an electric field or if ions are present, they jump from one equilibrium position to another.

Conclusion

Dielectric materials are the materials with constant electrical dipoles. We study about dielectric materials in Solid-state physics. A material is said to be dielectric if it has the property of forming a large number of induced electric dipoles when an electric field is applied to it.

Dielectric constant is the property that determines the distribution of electrical current absorbed by an insulating material. The main characteristic of a dielectric material is that when an electric field is applied, the material becomes polarized. The dielectric constant of water is 78.39 and air is 1.00059. Mica, Rubber, Glass and Ceramic are some examples of dielectric materials.

FAQs

Q1. What is dielectric strength?

Ans. Dielectric strength is the minimum voltage required per unit thickness of a material to cause a dielectric breakdown. As the temperature, humidity and lifetime of a material increase, the dielectric strength of the material decreases. Its unit is $\mathrm{volt\: m^{−1}}$

Q2. What is dielectric loss?

Ans.

• When an alternating electric field is applied to a dielectric medium, most of the energy of the electric field is absorbed by the medium. gy loss is called dielectric loss.

• Thus, the molecules in the medium heat up as energy are absorbed. Hence absorbed energy is lost as heat energy. This energy loss is called dielectric loss.

Q3. What are capacitors?

Ans. A capacitor is a device that helps store charges and electricity. It is made up of two conductors separated at a certain interval. Capacitors are widely used in many electronic circuits and in many fields of science and technology. Inserting dielectric materials like mica, glass or paper between the plates changes the capacitance of the capacitor.

Q4. What is electric polarization?

Ans. The displacement of the positive charge in the direction of electric field and displacement of negative charges in the opposite direction creates a dipole in an object. Therefore, when an electric field is applied across a dielectric it shows polarization. The phenomenon of the formation of dipoles is known as polarization. It depends on the frequency of the applied electric field and the temperature.

Q5. Define dielectric breakdown

Ans.

• Dielectric materials are those with high resistance and negative thermal resistance coefficient.

• In a dielectric material, as the field strength increases, the charge displacement also increases.

• Above a certain variable field value, electrical breakdown occurs in the dielectric material and current flows. There are many causes of dielectric breakdown.

Q6. Explain the chemical properties of insulating materials

Ans.

• When insulating materials are placed along with conductors, the properties of the insulating materials change.

• For example, chemical reactions take place when rubber is added to copper. To prevent chemical reactions, the surface of the copper should be coated with tin.

• A chemically resistant material can be considered the best insulating material.

Q7. Define electric susceptibility

Ans. Placing a dielectric material in an electric field will produce an electric polarization. Hence the polarization vector P is directly proportional to the electric field E. That is,

$$\mathrm{polarization\:vector\:P\varpropto\:Electric \:field\:E}$$

$$\mathrm{P\:\varpropto\:E}$$

$$\mathrm{P=\chi^{E}}$$

$$\mathrm{\therefore\:\chi=\frac{P}{E}}$$

Therefore, electric susceptibility is the ratio between the polarization vector and the applied electric field.