Dielectric Material
A dielectric material is a poor conductor of electricity i.e, an insulator, meaning that when a voltage is applied, no current can pass through the material. At the atomic scale, however, certain adjustments do happen. It is polarized when a voltage is applied across a dielectric surface. Because atoms consist of a positively charged nucleus and negatively charged electrons, polarization is an effect that slightly shifts electrons towards the positive voltage. They do not move far enough to generate a current flow through the material – the shift is microscopic but has a very important impact, especially when dealing with condensers.
Upon removal of the voltage source from the material, it either returns to its original non-polarized state or remains polarized if the material's molecular bonds are weak. The distinction between dielectric terms and isolator terms is not very well known. All-dielectric materials are insulators but one that is easily polarized is a good dielectric.
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Dielectric Constant
The dielectric constant is an object's ability to retain as much energy in the form of an electrical field as up to the degree that a substance concentrates electrical flux. It can also be regarded as the object's permittivity ratio to the permittivity of free space.
Types of Dielectric Materials
Dielectrics are grouped according to the type of molecule present in the material. There are two types of dielectrics – Non-polar dielectric and polar dielectric.
Polar Dielectric
The center of mass of positive particles in polar dielectrics doesn't coincide with the center of mass of negative particles. There's a dipole moment here. The shape of the molecules is asymmetrical. When applying the electric field, the molecules align with the electric field. The random dipole moment is observed when the electric field is removed, and the net dipole moment in the molecules becomes zero.
Example: H2O, HCl.
Non-Polar Dielectric
The center of mass of positive particles and negative particles coincides within the non-polar dielectrics. These molecules do not have a dipole moment. These molecules are in the form of symmetry.
Example: H2, O2, N2.
Example of Dielectric Material
A dielectric material may be vacuum, solids, liquids, and gases.
Ceramics, paper, mica, glass, etc. are some examples of solid dielectric materials.
Distilled water, transformer oil, etc. are liquid dielectric materials.
Dielectric gases are nitrogen, dry air, helium, various metal oxides, etc. A perfect vacuum is also a dielectric.
Applications of Dielectric Material
Dielectrics are used in capacitors for storing energy.
Ceramic dielectric is used in the Oscillator Dielectric Resonator.
The high permittivity dielectric materials are used to improve the performance of a semiconductor device.
Mineral oils are used as a dielectric liquid in electrical transformers, and they assist in the cooling process.
Electrets, a specially treated dielectric material, serves as an electrostatic equivalent to the magnets.
Plastic films were used as films in a variety of applications such as condenser insulation between foils and slot insulation in rotating electric machines.
Today, the main uses of liquid dielectrics, mainly hydrocarbon mineral oils, are as an insulating and cooling medium for transformers, earth reactors, shunt reactors, rheostats, etc.
What are Dielectric Properties?
Similar to an ideal capacitor, dielectric stores and dissipates electric energy. The main properties of dielectric material include Electric Susceptibility, Dielectric polarization, Dielectric dispersion, Dielectric relaxation, Tunability, etc
Electric Susceptibility: Electric susceptibility measures how easily a dielectric material will be polarized when subjected to an electric field. That quantity also determines the material's electrical permeability.
Dielectric Polarization: An electric dipole moment is a measure of the negative and positive charge separation within the system. The relationship between the moment of a dipole (M) and the electric field (E) gives rise to dielectric properties. When the electric field applied is removed, the atom returns to its original state. It happens in an exponential manner of decay. The time that the atom takes to reach its original state is called the relaxation time.
Dielectric Breakdown: When higher electrical fields are applied the insulator begins to conduct and act as a conductor. Dielectric materials lose their dielectric properties under these conditions. The phenomenon is called Dielectric Breakdown. That is a process that is irreversible. That leads to dielectric material failure.
Dielectric Dispersion: P(t) is the maximum polarization attained by the dielectric.
P(t) = P\[[\ 1- e (\frac {-t}{tr})\]]
tr is the relaxation time for a particular polarization process, The period to relax varies with various mechanisms of polarization. Electronic polarization followed by ionic polarisation is very rapid. The polarization of orientation is slower than ionic polarisation. The polarization of space charges is very slow.
Fun Facts
Liquid Crystal Displays use dielectrics.
The dielectric material is used as an insulator and as a cooling agent in a transformer
FAQs on Dielectric Properties
1. What is a dielectric material and what is its primary function in physics?
A dielectric material is an electrical insulator that can be polarised when subjected to an external electric field. Unlike a conductor, it does not allow electric current to flow through it. Its primary function is to store electrical energy. When placed in an electric field, it reduces the net field strength, which is a crucial property used in manufacturing capacitors.
2. What is the key difference between a dielectric and a regular insulator?
While all dielectrics are insulators, not all insulators are effective dielectrics. The key difference is polarisability. An insulator simply resists the flow of electric current. A good dielectric, however, is an insulator that can be easily polarised by an external electric field, allowing it to store energy effectively. This high polarisability is what makes materials like mica or ceramic ideal for use in capacitors, whereas materials like wood are just insulators.
3. Can you provide some common examples of dielectric materials?
Dielectric materials can be found in solid, liquid, and gaseous forms. Here are some common examples:
- Solid Dielectrics: Mica, glass, plastics, and various ceramics.
- Liquid Dielectrics: Distilled water, mineral oil (used in transformers), and transformer oil.
- Gaseous Dielectrics: Dry air, nitrogen (N₂), and sulphur hexafluoride (SF₆).
4. What are the most important properties of a dielectric material?
The most important properties defining a dielectric material include:
- Dielectric Constant (K): The ratio of the permittivity of the material to the permittivity of free space, indicating its ability to store energy.
- Dielectric Strength: The maximum electric field a material can withstand without breaking down and becoming a conductor.
- Electric Susceptibility (χe): A measure of how easily a dielectric material can be polarised when subjected to an electric field.
- Polarisation: The alignment of molecular dipoles in response to an external electric field.
5. How do polar and non-polar dielectrics differ in their fundamental behaviour?
The difference lies in their molecular structure and response to an external electric field:
- Polar Dielectrics: The molecules (e.g., H₂O, HCl) have a permanent electric dipole moment because their centres of positive and negative charge do not coincide. In an external field, these randomly oriented dipoles align with the field.
- Non-Polar Dielectrics: The molecules (e.g., H₂, O₂, N₂) have zero permanent dipole moment as their charge centres coincide. An external field induces a dipole moment by slightly distorting the molecule and separating the charge centres.
6. How does inserting a dielectric slab increase the capacitance of a capacitor?
When a dielectric is placed between the plates of a capacitor, the external electric field (E₀) polarises the material. This creates an internal, opposing electric field (Eᵢ) within the dielectric. The net electric field inside the capacitor is reduced (E = E₀ - Eᵢ). Since potential difference is V = E × d, a lower electric field results in a lower potential difference for the same amount of charge (Q). As capacitance is defined as C = Q/V, a decrease in V leads to a significant increase in the capacitance.
7. What is dielectric breakdown and why is it considered an irreversible process?
Dielectric breakdown is a phenomenon where a dielectric material, under the influence of an extremely strong electric field, loses its insulating properties and begins to conduct electricity. The field becomes so strong that it strips electrons from the atoms, creating a conductive path. It is considered irreversible because the intense current flow causes physical damage, charring, or structural changes to the material, permanently altering its molecular composition and destroying its ability to function as an insulator.
8. What are some important real-world applications of dielectric properties?
The unique properties of dielectrics make them essential in many technologies. Key applications include:
- Capacitors: Used for storing energy in electronic circuits, from smartphones to power supplies.
- High-Frequency Circuits: Ceramic dielectrics are used in oscillators and filters for mobile communication.
- Electrical Transformers: Mineral oils act as both a dielectric insulator and a cooling agent.
- Semiconductors: High-permittivity dielectrics are used to improve the performance of transistors and memory devices.
- Liquid Crystal Displays (LCDs): The technology relies on the ability to change the orientation of liquid crystal dielectrics with an electric field.
