Key Takeaways
- Permittivity (ε) measures how a material responds to an electric field, while permeability (μ) measures how a material responds to a magnetic field.
- Permittivity determines how a material stores electrical energy in an electric field, while permeability describes how a material supports the formation of a magnetic field within it.
- Permittivity and permeability affect the speed of electromagnetic waves in a material. The product of permittivity and permeability in a vacuum is equal to the speed of light squared (c²), and their values in a specific material determine the wave’s velocity, wavelength, and other characteristics in that material.
What is Permittivity?
The concept of electromagnetism, also explained by the ratio of electric displacement to the applied electric field intensity, is known as permittivity. When an electric current is developed in a material, it will most likely create a resistive force against it. This factor of opposition is known as permittivity.
The symbol of Epsilon is used to denote permittivity. The value of permittivity found in a vacuum medium is approximately 8.85*10-12. A certain amount of charges is required to generate a single unit of electric flux in a channel, and we use permittivity to measure them.
The standard international (SI) unit used for permittivity is Farad per metre. Instead of absolute terms, permittivity is expressed in relative terms. In materials science and electromagnetics, permittivity is essential to electric field propagation.
The value of the permittivity of a material is directly proportional to the measure of electric polarization—the smaller the electric polarization, the smaller the measure of the material’s permittivity.
Depending on the environment and the usage, there are three types of permittivity: absolute permittivity, relative permittivity and static permittivity.
Temperature, frequency, applied voltage, humidity, and the strength of the applied electric field are some factors that affect permittivity.
What is Permeability?
In electromagnetism, the ability of a specific material to allow magnetic lines or magnetic force or magnetic field to form within itself is known as the permeability of that material. A material allows magnetic lines or the magnetic field to be included. It conducts the magnetic fields and discontinues after it reaches its peak permeability.
The Greek alphabet mu is used to represent the permeability of a material. To identify the magnetization property of a material, it is essential to know the magnetic permeability of a material. Depending on that, the substance is considered a paramagnetic one if its magnetic permeability is high.
The standard international (SI) unit of permeability is Henry per metre. There are four subtypes of permeability, namely, effective permeability, magnetic permeability, absolute permeability, and relative permeability.
The concept of absolute permeability includes permeability in free space. It is a constant value. The ratio where absolute permeability is divided by the absolute permeability of air is known as relative permeability.
In different fields, the definition of permeability differs along with the substance. For instance, in geology, the ability of rocks to allow a fluid to enter and pass through it is known as rock permeability.
Difference Between Permittivity and Permeability
- In permittivity, the resistivity of a substance is measured; on the other hand, in permeability, the maximum extent to which a material can allow a magnetic force to form is measured.
- The ratio of electric displacement to the electric field density differs in permittivity and permeability.
- Permittivity is caused due to polarization; on the other hand, permeability is caused due to magnetism.
- Permittivity develops an electric field; however, permeability extends a magnetic field.
- The devices that develop high permittivity include capacitors; conversely, the machines that generate high permeability include inductors and transformers.
Comparison Between Permittivity and Permeability
| Parameters Of Comparison | Permittivity | Permeability |
|---|---|---|
| Inventor | Oliver Heaviside | William Thomson |
| Represented by | Epsilon | Mu |
| Core principle | Polarisation | Magnetisation |
| SI unit | Henry per metre | Farad per metre |
| Applications | Capacitor design | Oil exploration, designing the core of the transformer, petroleum geology etc. |
