Umair Gaines
Dielectric materials are poor conductors of electricity and are also referred to as insulators. They are non-metallic substances with a high specific resistance and a high insulating resistance. When a dielectric is placed in an electric field, no current flows through it because it has no loosely bound or free electrons. Instead, positive and negative charges are displaced in the direction and opposite direction of the electric field, respectively, causing dielectric polarisation. This phenomenon is used to increase the capacitance of a capacitor.
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What You'll Learn
Dielectric materials are poor conductors of electricity
Dielectric materials support dielectric polarisation, which enables them to act as dielectrics rather than conductors. This phenomenon occurs when a dielectric is placed in an electric field and positive charges are displaced in the direction of the electric field, while the negative charges are displaced in the opposite direction. This creates an internal electric field that reduces the overall electric field within the dielectric itself.
The force between two electric charges in a dielectric medium is less than it would be in a vacuum, while the quantity of energy stored in an electric field per unit volume of a dielectric medium is greater. The capacitance of a capacitor filled with a dielectric is greater than it would be in a vacuum. The presence of dielectric material affects other electrical phenomena.
Dielectric materials have high resistivity. The attraction between the electrons and the parent nucleus is very strong. The electrical conductivity of these materials is very low as there are no free electrons to carry current. Dielectric properties of materials are defined as a molecular property that is fundamental in all the materials that are capable of impeding electron movement, resulting in polarisation within the material on exposure to an external electric field.
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Dielectric materials are insulators
Dielectric polarisation causes positive charges to be displaced in the direction of the electric field and negative charges to shift in the opposite direction. This creates a strong internal electric field that reduces the overall electric field within the dielectric itself. The presence of dielectric material affects other electrical phenomena. The force between two electric charges in a dielectric medium is less than it would be in a vacuum, while the quantity of energy stored in an electric field per unit volume of a dielectric medium is greater.
The term "insulator" typically implies low electrical conductivity, while "dielectric" is used to indicate the energy-storing capacity of the material. A common example of a dielectric is the electrically insulating material between the metallic plates of a capacitor. The polarisation of the dielectric by the applied electric field increases the capacitor's surface charge for the given electric field strength. Dielectric materials are also used in transformers as insulators and as cooling agents.
Dielectric materials can be solids, liquids, or gases. Solid dielectrics are the most commonly used dielectrics in electrical engineering, and many solids are very good insulators. Examples include porcelain, glass, and most plastics. Air, nitrogen, and sulfur hexafluoride are the three most commonly used gaseous dielectrics. Dry air is an excellent dielectric and is used in variable capacitors and some types of transmission lines.
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Dielectric polarisation
Dielectric materials are poor conductors of electricity because they do not have any loosely bound or free electrons that may drift through the material. When a dielectric material is placed in an electric field, the charges do not flow through the material as they do in an electrical conductor. Instead, they shift slightly from their average equilibrium positions, causing dielectric polarisation. This is because the positive charges within the dielectric are displaced in the direction of the electric field, and the negative charges are displaced in the opposite direction. This creates an internal electric field that reduces the overall field within the dielectric itself.
The total polarisation of a dielectric comes from the sum of four sources of charge displacement: electronic displacement, ionic displacement, orientation of permanent dipoles, and space charge displacement. Electronic polarisation occurs in all atoms under the application of an electric field. Ionic polarisation occurs in ionic solids such as ceramic materials, where the cations and anions are attracted to opposite directions when an electric field is applied. Dipole polarisation occurs in certain solids with permanent molecular dipoles that rotate in the direction of the applied field when an electric field is applied, creating a net average dipole moment per molecule. Space charge polarisation arises from extraneous charges that come from contaminants or irregular geometry in the interfaces of polycrystalline solids.
Each type of polarisation has a different time response capability to an applied field frequency, and the net effect of polarisation on the dielectric constant is frequency-dependent. Electronic displacement is very rapid, occurring at frequencies of up to 10^17. Ionic polarisation is slightly slower and occurs at frequencies up to 10^13. Dipole polarisation occurs at frequencies less than 10^10, and space charge polarisation is the slowest, occurring at less than 10^4. Therefore, the dielectric constant always decreases with increased frequency, as the polarisation mechanisms become less effective.
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Dielectric constant
The dielectric constant, also known as the relative permittivity, is a property of dielectric materials. It is a measure of a substance's ability to store electrical energy. It is a relative measure of how easily a dielectric material can be polarised when subjected to an electric field. The dielectric constant is the ratio of a material's permittivity to the permittivity of free space, or a vacuum. This is why it is also known as relative permittivity.
The dielectric constant is the extent to which a substance concentrates the electrostatic lines of flux. It is a crucial factor in designing capacitors. When a dielectric is inserted between the plates of a parallel-plate capacitor, it increases the capacitor's capacitance, i.e., its ability to store opposite charges on each plate. The relative permittivity is the factor by which the electric field between the charges is decreased relative to a vacuum.
The dielectric constant of a material is affected by temperature and current frequency. For example, when water is heated from 0°C to 100°C, its dielectric constant falls from 80 to 55. The dielectric constant is also dependent on the material's composition. For instance, dry air, distilled water, and most pure, dry gases such as helium and nitrogen have low dielectric constants. In contrast, metal oxides generally have high dielectric constants.
The dielectric constant is an essential parameter in various applications, such as in the use of buffers as eluants in HPLC. It also affects interactions in solutions involving ions and polar molecules, influencing the intermolecular energy.
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Dielectric breakdown
Dielectrics are electrical insulators that can be polarised by an applied electric field. They are poor conductors of electricity because they do not have any loosely bound or free electrons that may drift through the material. When a dielectric material is placed in an electric field, the positive and negative charges within the dielectric are displaced minutely in opposite directions, creating an internal electric field that reduces the overall field within the dielectric itself. This phenomenon is called dielectric polarisation.
During dielectric breakdown, the number of charge carriers in the material suddenly increases by many orders of magnitude, causing its resistance to drop and allowing it to conduct current. This can happen within solids, liquids, or gases, and even theoretically in a vacuum. Electrical breakdown is often associated with the failure of solid or liquid insulating materials used inside high-voltage transformers or capacitors, resulting in a short circuit or a blown fuse.
The phenomenon of dielectric breakdown is utilised in cigarette lighters and similar devices where a spark is required to ignite the fuel. This is achieved by building up a charge on electrodes on either side of a small air gap until the strength of the field across the gap exceeds the dielectric strength of the air, resulting in a spark.
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Frequently asked questions
Dielectric is another word for an electrical insulator. It is a non-metallic substance that is a poor conductor of electricity.
Dielectric materials are poor conductors of electricity because they do not have any loosely bound or free electrons that may drift through the material. Examples of dielectric materials include ceramics, plastics, distilled water, dry air, and nitrogen.
When a dielectric is placed in an electric field, electric charges do not flow through the material. Instead, positive charges are displaced in the direction of the field and negative charges shift in the opposite direction. This creates an internal electric field that reduces the overall field within the dielectric.
Dielectric polarisation occurs when electric charges in a dielectric material shift slightly from their average equilibrium positions. This creates a separation of charge, or polarisation, which reduces the electric field within the dielectric.
