[Physics Class Notes] on Dielectric Properties Pdf for Exam

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.

 

()

 

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