Education Journalist | Study Abroad Lead
Permittivity and Permeability are two different terms used in electromagnetism relating to electric and magnetic fields respectively. Permittivity determines the ability of a given material to store energy or produce an electric field. Permeability, on the other hand, measures its ability to form a magnetic field. Permittivity relates to the polarization of material however the permeability of a material is related to its magnetization.
Permittivity is the ratio of electric displacement to the electric field intensity. The SI unit for permittivity is farad per meter. The permittivity of a medium determines how many particles are needed to produce one unit of electric flux. The SI unit for permeability is Henry per meter.
| Table of Content |
Key Terms: Permeability, Permittivity, Diamagnetism, Paramagnetism, Resistance, Intensity, Vacuum, Electromagnetic Field, Polarization, Displacement, Electric flux, Electric field, Magnetic field
What is Permittivity?
[Click Here for Sample Questions]
Permittivity is defined as the ratio of electrical displacement to the frequency of the intensity of the electric field. It is the ability of a material to determine resistance.
- Permittivity measures the opposition offered by a material against the formation of an electric field.
- It is represented by the Greek letter ϵ.
- Permittivity measures the number of charges required in order to generate a unit of electric flux in a given medium.
- Farad per meter is the standard unit for permittivity.
- The vacuum has the least possible value of permittivity. This is known as the Permittivity of Free Space or the electric constant.
- Permittivity in a vacuum, denoted by ϵ0 is around 8.85 X 10-12 Faraday/meter.
Permittivity = \(Electric\ Displacement \over Electric\ field\ intensity \)
Discover about the Chapter video:
Current Electricity Detailed Video Explanation:
Read more:
Relative Permittivity
The permittivity of a dielectric, known as relative permittivity, is represented by the ratio of its absolute permittivity to the electric constant. The dielectric constant 
\(\epsilon\)r of relative permittivity is given by:
\(\epsilon_r = {\epsilon \over \epsilon_o}\)
Where,
- ϵ0 is the electric constant
- ϵr is the relative permittivity
- ϵ is the absolute permittivity of that material
Read More: Displacement Current
Measurement of Permittivity
The relative permittivity of a material can be determined using a variety of static electrical techniques. The complex permittivity is measured using different forms of dielectric spectroscopy over a large range of frequencies, spanning around 21 orders of magnitude from 10-6 to 1015 hertz.
Cryostats and ovens can be used to characterize a medium's dielectric properties over a wide temperature range. To examine systems for such varied excitation fields, a number of measuring setups are used, each suitable for a certain frequency range.
Using Coulomb’s law, the magnitude of the electrostatic force between two point charges q1 and q2, separated by a distance r in free space can be determined using relative permittivity(ϵr). It can be expressed as:
\(\epsilon_r = {F_a \over F_m}\)
Where, \(F_a = {1 \over 4\pi\epsilon_o}{q_1q_2 \over r^2}\)
\(F_r = {1 \over 4\pi\epsilon_o\epsilon_r}{q_1q_2 \over r^2}\)
Read More: Types of DC Motor
What is Permeability?
[Click Here for Previous Year Questions]
Permeability refers to a material's ability to create magnetic flux as it passes through a magnetic field. It is denoted or expressed by the symbol μ.
- The permeability of a substance is defined as the ratio of flux density to the field strength of the material.
- It is the extent to which the magnetic field lines can enter a given substance.
- Permeability also has a relationship with the speed at which magnetic lines of force are formed.
- μo represents the permeability constant, commonly known as the permeability of open space, which is roughly equivalent to 4 X 10-7 Henry/meter.
- Magnetic permeability helps to classify the magnetization property of a material.
- A material is diamagnetic if its magnetic permeability is less than μ0 and paramagnetic if its magnetic permeability is greater than μ0.
Permeability = \(Magnitude\ of\ magnetic\ induction\ (B) \over Intensity\ of\ magnetic\ field\ (H)\)
Read More: Magnetic Effects of Electric Current Formula
Units of Permeability
The intensity of the magnetic field is measured in Tesla (T) or Newton per Ampere meter (N/Am). A magnetizing field is measured in amperes per meter (A/m). As a result of the permeability calculation above, it is a unit Newton per Ampere square.
μ = Newton / Ampere Square
Or,
μ = N / A2
We may obtain the dimension of permeability as [M1L1T-2l-2] by computing their equations and units.
Also Read:
Types of Permeability
Permeability can be classified as magnetic, absolute, and relative permeability –
Magnetic Permeability
The magnetic permeability of a material is defined as the capability of the substance to enable a magnetic line of force to pass through it. The SI unit of magnetic permeability is Henry per metre.
The formula for magnetic permeability is \(\mu = {B(Tesla) \over H({A-t \over m})}\)
Absolute Permeability
Absolute permeability is a constant value that is related to the permeability of open space.
Absolute permeability is a constant value given as μ0 = 4π × 10-7 H/m
Relative Permeability
Relative permeability is defined as the ratio of a medium's permeability to the permeability of free space. As a result, a medium's relative permeability is a dimensionless quantity that may be represented as μr = µ/μ0. The relative permeability of open space, according to this concept, is 1. Typically, a material's permeability is stated as relative permeability.
- A paramagnetic material's relative permeability is somewhat higher than 1.
- A diamagnetic material's relative permeability, on the other hand, is slightly less than 1.
- Ferrous metals are a different sort of magnetic substance. A ferrous material's relative permeability is significantly higher than 1.
Permeability and Relative Permeability of Materials
| Material | Permeability (μ) (H.m-1) | Relative Permeability (μr) |
|---|---|---|
| Air | 1.257 × 10-6 | 1.000 |
| Copper | 1.257 × 10-6 | 0.999 |
| Vacuum | 4π × 10-7 | 1 |
| Water | 1.256 × 10-6 | 0.999 |
| Wood | 1.257 × 10-6 | 1.00 |
Read More: Magnetic Susceptibility
Differences Between Permittivity and Permeability
[Click Here for Sample Questions]
The fundamental differences between permittivity and permeability are explained below:
| Basis | Permittivity | Permeability |
|---|---|---|
| Definition | Permittivity is a property of a substance that is concerned with its polarization. | The permeability of a substance is a measurement that is concerned with the magnetization of that material. |
| Symbol | Permittivity is denoted by the symbol ϵ. | The symbol for permeability is μ. |
| SI unit | The SI unit for permittivity is Fm-1 | The SI unit for permeability is Hm-1 (kgms-2A-2) |
| Open Space Value | In open space, permittivity is equal to 8.85 Fm-1 | In open space, permeability has a value of 1.26 Hm-1 |
| Fields | The electric fields are the subject of permittivity. | Magnetic fields are involved with permeability. |
| Determination | Permittivity is determined by polarization. | Permeability is determined by magnetization. |
| Formula | The value of permittivity is calculated by dividing the displacement field strength by the electric field strength. Permittivity = \(Electric\ Displacement \over Electric\ field\ intensity \) | The value of permeability is calculated by dividing the magnetic field density by the magnetic field strength. Permeability = \(Magnitude\ of\ magnetic\ induction\ (B) \over Intensity\ of\ magnetic\ field\ (H)\) |
| Responsible | Permittivity is responsible for the property of a material that determines how much energy can be stored within it. | Permeability is responsible for the property of a material that determines how well it supports the creation of a magnetic field within it. |
| Uses | Dielectrics in capacitors can be made from the use of products with high permittivity. | Inductors and transformer cores can be made from the use of products with high permeability. |
| Principal involved | Polarization of electric charge. | Magnetization. |
Things to Remember
- Permittivity is the ratio of electrical displacement to the frequency of the electromagnetic field.
- Permeability is a material's ability to create magnetic flux as it passes through a magnetic field.
- A substance's permittivity is proportional to its polarization, whereas a material's permeability is proportional to its magnetization.
- Permeability assesses a material's ability to generate an electrical field in the same way. Permeability does not mention the difficulty or easy level, whereas permittivity does.
- The SI unit for permittivity is Fm-1.
- The SI unit for permeability is Hm-1.
Read More: Dielectric Properties
Previous Year Questions
- Just after key K is pressed to complete the circuit, the reading will be …. [KEAM 1999]
- The resistance between any two terminals is when connected in a triangle is…. [NEET 1993]
- The potential difference per unit length of the wire will be… [NEET 1999]
- The electrical permittivity and magnetic permeability of free space are… [DUET 2003]
- Value of R for which the power delivered in it is maximum is given by... [NEET 1992]
- When two resistances R1 and R2 are connected in series, they consume 12W power….[KEAM]
- Nichrome is used as electrical heating element because of its…[KEAM]
- In a potentiometer of wire length ll, a cell of emf V is balanced at a...[KEAM]
- A potentiometer wire AB having length L and resistance 12r is joined to… [JEE Main 2019]
- The resistance between any two vertices of the triangle is...[JEE Main 2019]
Sample Questions
Ques. What influences permittivity? (3 Marks)
Ans. The permittivity is a state-dependent thermodynamic function. It can be affected by the applied field's frequency, amplitude, and direction. Permittivity varies depending on the position in the medium, the frequency of the applied field, humidity, temperature, and other factors. The permittivity of a nonlinear medium can be affected by the strength of the electric field.
Ques. Does the speed of light affected by space's permittivity and permeability? (3 Marks)
Ans. Yes, because the speed of light is reliant on the inverse square of the product of these two values. Because different materials have different permittivity and permeability characteristics, the speed of light varies. Relativity merely requires that the speed of light in a vacuum is constant in all reference frames, assuming there is no violation.
Ques. Is the permeability affected by pressure? (3 Marks)
Ans. Yes, permeability is affected by pressure. As the permeability of the gas increases the pressure rises. The inner and outer radius of the hollow fibre grow as the pressure increases, and as a result, the selected layer area increases while the thickness reduces, resulting in an increase in permeability.
Ques. In terms of physics, what does permittivity imply? (3 Marks)
Ans. The permittivity is the variation between the force a charge (test charge) feels in the medium (where it stays) and the force it would feel in a vacuum space. Assume a positive charge is applied to a force F in a vacuum space. If the situation remains unchanged, the charge is inserted in a medium, such as water, the relative permittivity of which may be estimated using the formula. The same test charge will experience a force F/80 due to the same parameters in the field of electricity as the permittivity of water/Vacuum Permittivity = 80.
Ques. How should metal permittivity and negative permittivity be described? (4 Marks)
Ans. Negative permittivity, complex permittivity, permittivity less than one, and other seemingly magical and baffling quantities are the result of our minds being stuck in the time domain while looking at variables specified in the frequency domain.
Charges are pushed around by electric (and magnetic) forces, causing materials to respond electrically. The charged particles create tiny secondary waves that mix out of phase with the applied wave as they move around. Furthermore, because the charges are linked to the atoms, they function as a mass on a spring, with a resonance frequency and other properties. In reality, the Lorentz oscillator model can be expressed as a charge motion equation. It properly predicts how materials would behave. It explains the observed dispersion, as well as anomalous dispersion, negative permittivity near resonance, and other phenomena.
Ques. Write the difference between permittivity and permeability. (4 Marks)
Ans. Permittivity and permeability differ in the following ways:
- Permittivity is the ability of a substance to allow magnetic lines to pass through it, whereas permittivity is the obstacle produced by the material in the production of an electric field.
- The permittivity is denoted by, while the permeability is represented by.
- Permittivity is measured in Henry/meter, while permeability is measured in Faraday/meter.
- Permittivity comes from polarization, whereas permeability comes from magnetization.
- The permittivity's free space is 8.85 F/m, but the permeability is 1.26 H/m.
- The electric field is developed by permittivity, while the magnetic field is developed by permeability.
- The capacitor develops a high permittivity, whilst the inductor and the transformer cores develop a high permeability.
Ques. Write the difference between diamagnetism and Paramagnetism. (5 Marks)
Ans. The difference between diamagnetism and Paramagnetism is as follows:
| Basis | Diamagnetism | Paramagnetism |
|---|---|---|
| Definition | Diamagnetism is the process through which diamagnetic materials are repulsed by a magnetic field. | Paramagnetism is the process by which paramagnetic materials are faintly pulled by a magnetic field. |
| Align | Magnetic fields in diamagnetic materials align in the opposite direction of external magnetic fields. | Magnetic fields in paramagnetic materials are aligned in the same direction as external magnetic fields. |
| Properties | External magnetic fields have no effect on diamagnetic materials. | External magnetic fields pull paramagnetic materials quite weakly. |
| Separation | The diamagnetic materials can be separated by the repulsions to magnetic fields, because they may be clearly distinguished from many other materials. | The use of high-intensity magnetic separators to separate paramagnetic materials |
| Electrons without a Pair | There are no unpaired electrons in atoms or ions in diamagnetic materials. | The atoms or ions in paramagnetic materials have unpaired electrons. |
Ques. Write in detail about the permeability. (4 Marks)
Ans. The ability of a material to create magnetic flux when it travels through a magnetic field is referred to as permeability. Magnetic frequency, temperature, field strength, and humidity are all factors that influence it. It is represented by the symbol μ. The ratio of flux density to material field strength determines a substance's permeability. It also has something to do with how fast magnetic lines of force conduct. The number 0 denotes the permeability constant, often known as the permeability of free space, which is approximately 4 X 10-7 Henry/meter.
There are three types of permeability:
- Magnetic Permeability: The ability of a substance to allow a magnetic line of force to pass through it is characterized by its magnetic permeability.
- Absolute Permeability: The permeability of open space is measured in absolute permeability, which is a constant number.
- Relative Permeability: For a magnetic substance, relative permeability is defined as the ratio of absolute permeability to absolute permeability of air.
For Latest Updates on Upcoming Board Exams, Click Here:https://t.me/class_10_12_board_updates
Also Read:
Comments