What is Permittivity: Definition and 142 Discussions

In electromagnetism, the absolute permittivity, often simply called permittivity and denoted by the Greek letter ε (epsilon), is a measure of the electric polarizability of a dielectric. A material with high permittivity polarizes more in response to an applied electric field than a material with low permittivity, thereby storing more energy in the material. In electrostatics, the permittivity plays an important role in determining the capacitance of a capacitor.
In the simplest case, the electric displacement field D resulting from an applied electric field E is





{\displaystyle \mathbf {D} =\varepsilon \mathbf {E} .}
More generally, the permittivity is a thermodynamic function of state. It can depend on the frequency, magnitude, and direction of the applied field. The SI unit for permittivity is farad per meter (F/m).
The permittivity is often represented by the relative permittivity εr which is the ratio of the absolute permittivity ε and the vacuum permittivity ε0








{\displaystyle \kappa =\varepsilon _{\mathrm {r} }={\frac {\varepsilon }{\varepsilon _{0}}}}
.This dimensionless quantity is also often and ambiguously referred to as the permittivity. Another common term encountered for both absolute and relative permittivity is the dielectric constant which has been deprecated in physics and engineering as well as in chemistry.By definition, a perfect vacuum has a relative permittivity of exactly 1 whereas at STP, air has a relative permittivity of κair ≈ 1.0006.
Relative permittivity is directly related to electric susceptibility (χ) by



{\displaystyle \chi =\kappa -1}
otherwise written as









{\displaystyle \varepsilon =\varepsilon _{\mathrm {r} }\varepsilon _{0}=(1+\chi )\varepsilon _{0}}

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  1. Istiak

    Find electric field inside a material

    From the second equation I get that, ##\vec D =\frac{q}{4\pi \vec r^2}\hat r## From first equation I get that ##\vec E = \frac{q}{4\pi \vec r^2 \epsilon}=\frac{q}{4\pi \vec r^2 K \epsilon_0}## But I saw that the answer is ##\vec E=\frac{\vec E_0}{K}## While writing the comment my mind said...
  2. DuckAmuck

    I Are permittivity and permeability quantities that can be predicted?

    For example, can you predict the permittivity and permeability of a substance if you know what the atomic composition is? Is it a stat mech problem?
  3. L

    I Permittivity as a tensor

    If I have an anisotropic material with permittivity: $$\epsilon= \begin{pmatrix} \epsilon_{ii} & \epsilon_{ij} & \epsilon_{ik} \\ \epsilon_{ji} & \epsilon_{jj} & \epsilon_{jk} \\ \epsilon_{ki} & \epsilon_{kj} & \epsilon_{kk} \\ \end{pmatrix} $$ What exactly does each element represent in this...
  4. LarryS

    Electrical Permittivity of Classical Vacuum - Physical?

    The Vacuum Permittivity of the classical vacuum seems to be for just conversion of units in Coulomb's Law, like Coulomb's Constant in disguise. Does the Electrical Permittivity of the Vacuum in classical electromagnetism have any real physical significance other than in the above context...
  5. Efeguleroglu

    How does permittivity in Coulomb's law work?

    Coulomb's Law $$ \vec{F} = \frac{1}{4 \pi \epsilon} \frac{q_1 q_2}{r^2} \hat{r} $$ $$ \vec{E} = \frac{1}{4 \pi \epsilon} \frac{Q}{r^2} \hat{r} $$ Let's say we want to find electric field with a distance r from charge Q. How does permittivity effects the magnitude? Will I choose the permittivity...
  6. A

    Can you calculate optical density from permittivity and permeability?

    Does electric perm and magnetic perm give you enough info to work out OD? Thanks in advance
  7. Mircro

    Material between capacitor plates - viewed as two capacitors in series

    This is a second grade high school problem, translated from my native language. I don't have a problem with calculating, but with understanding the concept. There is an instruction with the assignment that says: The capacitor can be viewed as a combination of two capacitors in series with...
  8. R

    B Planck-like values out of permeability and permittivity

    What happens if we make a dimensional analysis of permeability and permittivity ? Will we get a minimum possible amount of electric and magnetic values?
  9. currently

    Schrodinger's Equation in terms of vacuum permittivity?

    Summary:: How can Schrodinger's Equation be written relative to vacuum permittivity I am wondering why a particular problem uses this equation: It is stated to be Schrodinger's equation. Where does the potential come in, as well as the e^2/r ? An explanation would be greatly appreciated. Thanks.
  10. L

    Capacitance with dielectric permittivity that depends on r

    The first part (which I believe I've done correctly) asks us to find the electric displacement everywhere. For this: $$\int D \cdot da = Q_{f,enc}$$ For a < r < b: $$D = \frac{Q}{4\pi r^2} \hat{r}$$ Otherwise, D = 0 When finding the capacitance, I'm unsure how to handle the r dependence. I...
  11. uzi kiko

    A The relation between imaginary part of permittivity to conductivity

    Hi When I read the following article: http://nopr.niscair.res.in/bitstream/123456789/14183/1/IJPAP%2050%286%29%20405-410.pdf I tried to convert the value of the conductivity for saline in 500 MHz. At the article, they present the conductivity as ε'' = 70. Which ε'' is the imaginary part of...
  12. Sadek

    Permitivitty of graphene

    i'm working on a project about the surface plasmon in graphene. i found on some articles that we don't use Drude model to calculate permitivity on graphene but they didn't mention what's the right model ! can you help me please and give me the relation that link links between permitivity and...
  13. N

    A Symmetry of the permittivity tensor of lossless media

    I read in various sources (such as page 8 of these notes) that the dielectric permittivity tensor of a lossless medium is always symmetric. I am wondering how this can be the case, when: Phase accumulation in the medium could in theory depend on direction Coordinate system may be rotated to...
  14. tworitdash

    Relation between conductance and dielectric relaxation time

    I am studying about dielectric materials and their relaxation properties. There are several ranges of electromagnetic frequencies where different material show different kinds of resonance starting from molecular to atomic motions. Based on the frequency dependence of the imaginary part of the...
  15. Y

    I Resultant of Different Permittivity substances

    Say the space is divided into two parts: one has permittivity e1 and other e2. A charge q1 is placed at a distance d1 from the interface of two media in region in permittivity e1 and another charge q2 is placed at a distance d2 in region of permittivity e2. What is the force experienced by a...
  16. qnach

    Connection between relative permittivity and bandwidth

    What is the connection of relative permittivity and bandwidth of an antenna? Higher relative permittivity resulted in high wider bandwidth?
  17. S

    I How was the value of the permittivity of free space determined?

    The permittivity of free space, ε0, is usually given without any derivation or historical context as to how it was experimentally determined. Could you explain to me how the value of ε0 was first determined experimentally or provide a resource that gives such a derivation? Thanks!
  18. I

    I Drude Model Permittivity Formula - e^iwt or e^(-iwt)?

    I've been having a sign problem while deriving the permittivity formula using Drude model, and I found out that the problem came from the fact that complex field vectors are expressed with e-iwt, not eiwt, thus producing (-iwt) term when differentiated...
  19. T

    Refractive index of light from permittivity

    Homework Statement Given that the relative magnetic permeability and relative electric permeability of water are respectively, ##\mu_{rel}=1## and ##\epsilon=1.769## calculate the following 6 parameters. 1. Index of refraction of water ## n ## 2. speed of electromagnetic waves in water ## c...
  20. A

    Calculating permittivity in a constant field

    Homework Statement Having a conducting sphere with radius ##R## and charge ##Q##, dielectric is put on it so that a spherical shell with inner radius ##R## and outer radius ##3R## is formed. Calculate: 1. Electric permitivitty ##\epsilon## such that ##E(r), R<r<3R## is constant and there's...
  21. A

    How charge density of plate is changed by permittivity

    Homework Statement Distance between plates of a parallel-plate vacuum capacitor is d. The capacitor is attached to a battery that keeps it at a voltage V. The space between plates is now filled dielectric relative permittivity epsilon. How will charge density of the plates change? Homework...
  22. Conductivity

    Permittivity in Gauss' law and Ampere's law

    In the derivation of the electric field inside a non conducting sphere, We still use the permittivity of free space even though we are in a medium. The same applies for ampere's law in a solid wire. http://physics.bu.edu/~duffy/semester2/c15_inside.html...
  23. T

    What is the difference between PP(polypropylene) and CPP?

    To my knowledge, CPP means cast-polypropylene, which I've seen used in a coaxial cable. Some cables use CPP as dielectric material. My question is: 1. what is the difference between PP(polypropylene) and CPP? 2. How is CPP made? 3. Is the permittivity and loss tangent of CPP different from that...
  24. P

    I Free space Permittivity

    I have a doubt about coulomb's force equation in free space..ie 1/4πε0... Actually coulomb found that force exerted b/w charges are directly proportional to the product of charges and inversely proportional to the sqr of the distance bw them.we can measure force exerted and distance of...
  25. M

    A Permittivity of aluminium

    Consider a metal such as Al. How do we look up or determine the relative permittivity of the metal? Suppose we have some known incident frequency, say about c/500nm for visible light. We can look up the bulk plasma frequency (3.7 PHz for Al), can it be calculated from that? For context, what I...
  26. M

    Effect of electrical permittivity on the speed of light

    Why does an increased electrical permittivity reduce the phase velocity of light in a medium? Furthermore, what interactions do we see on an atomic level? I am aware of the equation that defines the speed of light in terms of the electrical permittivity and magnetic permeability, but I do not...
  27. M

    Effect of electrical permittivity on the speed of light?

    Why does an increased electrical permittivity reduce the phase velocity of light in a medium? Furthermore, what interactions do we see on an atomic level? I am aware of the equation that defines the speed of light in terms of the electrical permittivity and magnetic permeability, but I do not...
  28. Pushoam

    Electric Permittivity, Magnetic Permeability & Suceptibility

    Can anyone please explain me the physical significance of these concepts?? Electric permittivity, Magnetic Permeability & suceptibility
  29. mpolo

    B Permittivity and Permeability changes

    I have a question about permeability and permittivity of free space. Theoretically speaking. If either one or both were to increase in value would that make the speed of light be faster or slower. I know they are constants. I am just curious if they did change what would happen.
  30. shishi

    Negative permittivity of metals – light-trapping and plasmon

    Negative permittivity of metals – The effect of light-trapping via plasmonics I’m trying to understand the effect of light-trapping by plasmonics (for example - Localized Surface Plasmon Resonance, Surface Plasmon Polariton, Scattered Plasmons), and how negative permittivity related to that...
  31. Radiosan

    Uncertainty analysis of 2 port measurement

    I analyzed uncertainty analysis of 2 port measurement. I referenced 2 book "Transmission Reflection and Short Circuit Line Methods for Measuring Permittivity and Permeability" at pages 31 equation(2.83) "Transmission and Reflection and SCL Permittivity Measurements" at pages 44 equation(2.67)...
  32. W

    I Data needed: Relative permittivity of air

    Where can I found values of the relative permittivity of air at different temperatures, frequencies, pressure, humidity, etc. or its dependence? I'm particularly interested in data around 1.4 GHz, 25ºC, 1 atm. 50% hum. Thanks in advance.
  33. C

    B Does gravity change the permittivity/ permeability of vacuum?

    For example if you send a light beam towards a massive object the propagation speed will reduce if μ and ε are increasing, but the spacetime curvature will compensate for that reduction.
  34. M

    The Permittivity of Insulators

    I just have a few conceptual questions: Is it as difficult to remove electrons from an insulator as it is to add to it? I understand insulators have a lower permittivity than conductors, and that they still allow charges to build upon the surface. However, I read that when you rub an insulator...
  35. P

    Permittivity of a Lossy Medium using Antennas

    First of all I will being with I'm not an electric engineer so I might be out of my wits, but I will give it a try. So I have an instrument which reads relative permittivity using a transmitter and two receiver placed at different distances. The instrument is calibrated to read either in a...
  36. D

    Do the Relative Permittivity and Refractive Index of Water Match Up?

    Many textbooks and online sources give the relative permittivity of water as about 80 and the refractive index as 1.33. If you use the definition of refractive index to find the speed of light in water, you will find v = c/n ~ 2.56e8 m/s. However, if you use the equation to find the speed of...
  37. Twigg

    I Interpreting the Permittivity of Metals

    In a dielectric material, permittivity makes sense, because it's easy enough to interpret the polarization density as the number density of molecules times their induced dipole moment. I'm basing this description off chapter 4 of Griffith's E&M textbook. In this model, the charges are all...
  38. TheSodesa

    Electromagnetic wave in glass

    Homework Statement A harmonic EM-wave is propagating in glass in the +x-direction. The refractive index of the glass ##n = 1.4##. The wave number of the wave ##k = 30 \ rad/m##. The magnetic portion of the wave is parallel to the y-axis and its amplitude ##H_0 = 0.10A/m##. At ##t=0## and ##x =...
  39. S

    B Free space permittivity

    Why does the free space permittivity has the value it has?
  40. N

    Voltage of a point in varying permittivity medium problem

    Homework Statement - A point charge is placed at the origin of the medium. - The relative permittivity of the medium, \varepsilon_r = a / r, a is a constant, r is the radius from origin to any point around the charge. - Objective of this question is to find the expression for voltage.at any...
  41. gracy

    B Permittivity of free space

    What actually is permittivity of free space I know it is εo and I know it's value but I want to know it's physical meaning,what does it actually do ?I have referred this https://www.physicsforums.com/threads/what-is-permittivity.763156/#post-4804922 but did not get the answer. I have also...
  42. Antonino Tobia

    Space-time varying permittivity in comsol

    Hi everybody, I need to know if someone of you have ever simulated time-space varying permittivity media in RF mode with COMSOL. Thanks to all !
  43. naiasetvolo

    Why do we multiply permittivity of vacuum with relative permittivity?

    Why do we multiply permittivity of vacuum with relative permittivity? What does this calculation mean?
  44. G

    Electrostatics: Find relative permitivitty

    Homework Statement Spherical capacitor with two linear and uniform dielectrics with relative permitivitty Ɛr1 and Ɛr2 is connected to constant voltage U. When second dielectric is removed, intensity of electric field by inner electrode is reduced by 1/3, and electric field by outer electrode...
  45. B

    Physical cause of a negative real part of the permittivity

    I originally posted the following question on physics.stackexchange, but no one was able to answer it. I did find this answer on PhysicsForums, but I was already aware of the oscillation of electrons in response to an external electric field. What is the physical cause behind a material having...
  46. LarryS

    Does classical vacuum permittivity have a QM analog?

    According to Maxwell's Equations, the classical vacuum permittivity and permeability have a very important role: They determine the speed of light. But it seems like these two important concepts are not as precisely defined in the quantum world. Are there rigorous analogs of these two...
  47. J

    Relative permittivity

    Homework Statement I've been given a question where I have to find the electric field strength at a point between two charges. Now I understand the mathematics but the question I'm trying to solve says two point charges of value 2C and 3C are position within a medium of relative permittivity...
  48. W

    Permittivity of free spaces

    Hi please tell me physical significance of permittivity of free space, how can we explain its value having unit of F/m
  49. K

    Tungsten permittivity

    Good evening, So... I am looking for the Tungsten permettivity and i don't find this feature... I have searched on Wikipedia, some material data but i don't find... Do you know what is the Tungsten permettivity? Thanks.
  50. T

    Classical Looking for a book on the causes of permittivity

    I'm currently working with some materials that have a high permittivity in order to improve image quality of MRI scanners but finding it hard to find a good book that explains the various effects that contribute to a material's permittivity/dielectric constant. Can anybody point me in a good...