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Electrical Engineering Materials
What is an Atom?
Atomic Energy Levels
Classification of Engineering Materials
Classification of Electrical Engineering Materials
Electron Configuration of Atom
Physical Properties of Materials
Mechanical Properties of Engineering Materials
Rutherford Atomic Model
Bohrs Atomic Model
Chemical Properties of Materials
Energy Bands in Crystals
Electrical Properties of Engineering Materials
Fermi Dirac Distribution Function
Magnetic Properties of Engineering Materials
Selection of Material for Engineering Application
Bases of existence of properties in materials
Low Resistivity or High Conductivity of Conducting Material
High Resistivity or Low Conductivity Conducting Material
Factors Effecting the Resistivity of Electrical Materials
Materials used for Heating Elements
Materials used for Precious Works
Materials Used for Transmission Line Conductor
Electrical Stranded Conductors
Materials used for Rheostats
Materials for Lamp Filaments
Classification of Electrical Conducting Material
Applications of Carbon Materials in Electrical Engineering
Selection of Materials Used for Electrical Contacts
Mechanism of Polarization
Dielectric Material as an Electric Field Medium
Electric Arc Furnace
Thermal Conductivity of Metals
Free Electron Theory of Metals
Thomson Plum Pudding Model (1911)
Dielectric materials have no free charges because, all the electrons are bound and associated with the nearest atom. The polar molecules in the material will be in random alignment when there is no peripheral electric field as shown in figure 1. Now, when an electric field is implemented to this material, it will get polarised by aligning the dipole moments of polar molecules. The positive charges within the material are shifted slightly in the direction of electric field and the negative charges in the direction opposing the direction of electric field.
When we place a dielectric material in an electric field, practically no current is flowing through them, rather polarisation of molecules happens. It transfers electrical energy through the shifting of current and not through the process of conduction. This is shown in Figure 2. The dielectric material which is used in capacitors fulfils the following functions.
- Decreases the useful electric field between the capacitor plates.
- Boosts the capacitance of the capacitor plate structure.
- Keep the conducting plates from coming in contact.
- Reduce the possibility of shorting out by sparking during high voltages.
As said above, the presence of dielectric material will decrease the electric field produced by the charge density. The effective electric field which is produced by the charge density can be given by σ - Charge density in A/m2 κ - Dielectric constant. ε0 - Permittivity of free space in F/m = 8.854 × 10-12 F/m. The effective field is decreased by polarisation of the dielectric by a factor κ. It is called the dielectric constant of the material. For a vacuum, it is equal to 1. The capacitance of the normal capacitor; The capacitance of the capacitor which is filled with the dielectric will be increased by the factor called the dielectric constant, κ which is given by κ’ is defined as the relative permittivity of a dielectric material and it is an important parameter in deciding the capacitor characteristics. Every insulator can be forced to conduct electric current or electricity. This phenomenon is known as dielectric breakdown. During high voltages, a capacitor with a dielectric will reduce the chance of short circuit by sparking (that particular voltage which cause breakdown is called dielectric breakdown voltage and its field strength is known as dielectric strength). Another important property of a dielectric is its ability to support an electric field with dissipating minimum energy as heat. A good dielectric should have minimum dielectric loss.
Types of Dielectric MaterialsVacuum, Solids, Liquids and Gases can be a dielectric material. Some of the examples of solid dielectric materials are ceramics, paper, mica, glass etc. Liquid dielectric materials are distilled water, transformer oil etc. Gas dielectrics are nitrogen, dry air, helium, oxides of various metals etc. Perfect vacuum is also a dielectric.
Application of Dielectric MaterialsDielectric materials can be used in capacitors for energy storage. It is used in photosensitive materials for charge storage in laser printers and copying machines. It is used for mechanical actuation, sound generation, piezoelectricity, cap sense etc.
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