Permittivity and Permeability - Meaning, Formula, Comparison, FAQs

Magnetic permittivity and permeability are two fundamental characteristics of a physical medium, which define the interaction of the electric and magnetic fields. These parameters are basic to the study of electromagnetic waves, and how different materials interact with electric field and magnetic fields and light.

JEE Main 2025: Physics Formula | Study Materials | High Scoring Topics | Preparation Guide

JEE Main 2025: Syllabus | Sample Papers | Mock Tests | PYQs | Study Plan 100 Days

NEET 2025: Syllabus | High Scoring Topics | PYQs

This Story also Contains

1. What is Permittivity?
2. Unit of Permittivity
3. Types of Permittivity
4. What is Permeability?
5. Unit of Permeability
6. Types of Permeability
7. Difference Between Permittivity and Permeability

LiveJEE Main 2025 Live: Exam city slip soon at jeemain.nta.nic.in; admit card date, cut-off updatesDec 30, 2024 | 10:30 PM IST

Candidates can have a look at the JEE Main 2025 physics syllabus below.

JEE Main 2025 physics topics	Number of questions	Marks
Modern Physics	5	20
Heat and Thermodynamics	3	12
Optics	3	12
Current Electricity	3	12
Electrostatics	3	12
Magnetics	2	8
Unit, Dimension and Vector	1	4
Kinematics	1	4
Laws of Motion	1	4
Work, Power and Energy	1	4
Centre of Mass, Impulse, and Momentum	1	4
Rotation	1	4
Gravitation	1	4
Simple Harmonic Motion	1	4
Solids and Fluids	1	4
Waves	1	4
Electromagnetics Induction; AC	1	4

Read More

What is Permittivity?

Permittivity is the property of every substance that determines the amount of resistance it provides to the production of an electric field. Permittivity is denoted by $\varepsilon$, It indicates how many charges are necessary to produce one unit of electric flux in a given material.

S.I. unit of permittivity is Farad/metre.

Mathematical Expression of Permittivity

$$
\varepsilon=\varepsilon_0 \cdot \varepsilon_r
$$

• $\varepsilon_0$ : Permittivity of free space $\left(8.854 \times 10^{-12} \mathrm{~F} / \mathrm{m}\right)$
• $\varepsilon_r$ : Relative permittivity or dielectric constant of the material.

Also read -

• NCERT Notes For All Subjects
• NCERT Solutions for All Subjects
• NCERT Exemplar Solutions for All Subjects

Unit of Permittivity

Derived Unit from$$
\mu=\frac{B}{H}
$$
$$
\mu(H / m)=\frac{T}{A / m}=\frac{\mathrm{N}}{\mathrm{~A}^2}
$$

Thus, the unit of permeability is also expressed as: Newton per Ampere squared (N/A ${ }^2$ ).

Dimensional Formula of Permittivity

The dimensional formula of permittivity of free space is [M^-1L^-3T⁴A²].

Types of Permittivity

Dielectric Permittivity: Describes the ability of a material to polarize in response to an electric field.
Expressed as:

$$
\varepsilon=\varepsilon_0 \cdot \varepsilon_r
$$

where:
$\varepsilon_0$ : Permittivity of free space.
$\varepsilon_r$ : Relative permittivity or dielectric constant.

Relative Permittivity $\left(\epsilon_r\right)$: A ratio of the material's permittivity to the permittivity of free space:

$$
\varepsilon_r=\frac{\varepsilon}{\varepsilon_0}
$$
Absolute Permittivity ( $\varepsilon$ ): The actual value of permittivity for a specific material, including contributions from free space and the material's properties.

What is Permeability?

Permeability is the ability of a material to allow the formation of magnetic lines of force or magnetic fields within it in electrostatics. It refers to a material's ability to magnetise in response to an applied magnetic field. Permeability is denoted by $\mu$.

In simpler terms, magnetic permeability can be defined as "the extent to which magnetic field lines can enter a substance." or "the power of a substance to conduct magnetic field lines."

S.I. unit of Permeability is Henry per meter $(H / m)$

Mathematical Expression of Permeability

$$
B=\mu \cdot H
$$
Where:

• $B$ : Magnetic flux density (in Tesla, $T$ or $\mathrm{Wb} / \mathrm{m}^2$ ).
• $H$ : Magnetic field strength (in $A / m$ ).
• $\mu$ : Permeability (in $H / m$ ).

Unit of Permeability

Derived Unit: Permeability is defined as:

$$
\mu=\frac{B}{H}
$$

Substituting the units:

$$
\mu=\frac{T}{A / m}=\frac{\text { Weber per square meter }}{\text { Ampere per meter }}=\frac{\text { Weber }}{\text { Ampere } \cdot \text { Meter }}=H / m
$$
Dimension formula of Permeability is $\left[\mathrm{MLT}^{-2} \mathrm{~A}^{-2}\right]$

Types of Permeability

Magnetic permeability

The magnetic permeability of a material is defined as the ability of the substance to enable a magnetic line of force to pass through it. Magnetic permeability is measured in Henry per metre (SI units).

The ratio of flux density to magnetic force, or magnetic permeability, is defined as:

$\mu=\mathrm{BH}$

Absolute permeability

Absolute permeability is a constant value that is related to the permeability of free space and is written as:

$\mu_0=4 \pi \times 10^{-7} \mathrm{H} / \mathrm{m}$

Relative permeability

The ratio of the absolute permeability of magnetic material to the absolute permeability of air is defined as relative permeability of a magnetic material.

Relative Permeability, $\mu_{\mathrm{r}}=\mu / \mu_0$

It is a dimensionless quantity.

Relationship Between Permittivity, Permeability, and Speed of Light

Permittivity and permeability are interconnected through the speed of light ( $c$ ) in a vacuum:

$$
c=\frac{1}{\sqrt{\mu_0 \cdot \varepsilon_0}}
$$
This equation highlights that the speed of light depends on the fundamental constants of vacuum permeability ( $\mu_0$ ) and vacuum permittivity ( $\varepsilon_0$ ).

Difference Between Permittivity and Permeability