Permittivity vs Permeability
Permeability and Permittivity are two concepts found in electromagnetic theory developed by James Clark Maxwell. They are equivalent concepts where permittivity is used in the electric fields and permeability is used in the magnetic fields.
Permittivity (ε)
Permittivity is a measure of the resistance in forming an electric field through a medium. It is defined as the ratio between the electric displacement (D) in a medium and the intensity of the electric field producing it (E). It is an important electric parameter of the materials, especially in the case of insulators.
ε = D/E
Permittivity is measured in Farads per meter (Fm-1), in the international system of units.
The permittivity of the medium describes the amount of flux generated per unit charge in the medium. The high permittivity indicates a high rate of polarization within the medium and more electric flux to create the opposing electric field. Therefore, the net field strength inside a dielectric medium is low if the permittivity is high.
Permittivity in a vacuum is a constant and is the lowest possible permittivity. Vacuum permittivity is denoted by ε0 , and has value 8.854×10-54 Fm-1. Sometimes it is convenient to give the permittivity of a dielectric medium as a multiple of the vacuum permittivity which allows easy mathematical usage and comparison between the permittivity of different media. Relative permittivity is the ratio between the absolute permittivity and the vacuum permittivity. Absolute permittivity (ε) is the real permittivity of the medium.
εr = ε/ε0 and hence ε = εr ε0
Relative permittivity has no units and always greater than 1.
Permittivity is closely related to the susceptibility of the medium, which is a measure of the ease of polarization of dipoles in the medium. If the susceptibility of the medium is χ,
ε = εr ε0 = (1+χ) ε0 and hence (1+χ) = εr
Permeability (µ)
Permeability is a measure of a material’s ability to form magnetic fields within it. It is defined as the ratio between the magnetic field density (B) within the medium and the external magnetic field strength (H). It is an important property when considering the magnetic properties of a material.
µ = B/H
SI unit of Permeability is Henry per meter (Hm-1). Permeability is a scalar quantity.
Permeability can also be described as the inductance per unit length. It describes the amount of magnetic flux created within the medium when external magnetic fields are applied. If the created flux supports the external field, it is known as the paramagnetism. If the flux opposes the external field, then it is called the diamagnetism.
The permeability in free space (vacuum) is the lowest possible permeability, and its values is 1.2566 ×10-6 Hm-1 or NA-2. Likewise in permittivity, it is convenient to define relative permeability. The expression for relative permeability is as follows:
µr = µ/µ0
Magnetic susceptibility is a measure of the magnetization of a material, in addition to the magnetization of the space occupied by the material, and it is denoted by χm and it is a dimensionless quantity.
µ = µr µ0 = (1+χm) µ0 and hence (1+χm) = µr
What is the difference between Permittivity and Permeability?
• Permittivity and permeability are two concepts found in electromagnetic theory. Permittivity concerns the electric fields while the Permeability concerns the magnetic fields. They are analogous properties in the electromagnetic fields.
• Permittivity is defined as the ratio between the displacement field strength to the electric field strength, whereas the permeability is defined as the ratio between the magnetic field density and the magnetic field strength.
• The permittivity accounts for the polarization effect within the material while permeability accounts for the magnetization of the material.
• Permeability is measured in Henry per meter Hm-1, while permittivity is measured in Farads per meter Fm-1.