What is Dielectric constant: Definition and 96 Discussions

The relative permittivity, or dielectric constant, of a material is its (absolute) permittivity expressed as a ratio relative to the vacuum permittivity.
Permittivity is a material's property that affects the Coulomb force between two point charges in the material. Relative permittivity is the factor by which the electric field between the charges is decreased relative to vacuum.
Likewise, relative permittivity is the ratio of the capacitance of a capacitor using that material as a dielectric, compared with a similar capacitor that has vacuum as its dielectric. Relative permittivity is also commonly known as the dielectric constant, a term still used but deprecated by standards organizations in engineering as well as in chemistry.

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  1. N

    Dielectric constant and plasma membrane

    Hello! Electric force is inversely proportional to the dielectric constant. In a textbook, this is said to be forty-fold greater for water than the phospholipid membrane. As such, ions are unlikely to cross the plasmamembrane. I assume this has something to do with preferring to stay in...
  2. S

    Calculation of plasma frequency and static dielectric constant

    Calculation of plasma frequency and static dielectric constant (urgent) Hello: Can anyone tell me how to measure the plasa frequency of a metal and wherher energy band gap of a metal is equal to the plasma energy of that material which is equal to (plank constant * plasma angular...
  3. S

    Regarding calculation of Plasma frequency and static dielectric constant

    Hello: I want to calculate the plasma frequency of Au, Ag, Cu and Al. But wondering what is the most precise way to calculate the plasma frequency.If anyone can help me with that it will be really appreciated. I know that Plasma Energy = √(n*e^2/(m*ε°)) = plank constant * ωp Here...
  4. M

    Medical Dielectric constant of neurons

    Hello! First time poster. I hope this is not a wrong sub-forum for this kind of question. Can anyone tell me where can I find values for dielectric constants of neurons and nerve fibers for frequencies in the range of 1e12 - 1e14 Hz (optical and RF part of the spectrum)? I have found data...
  5. J

    Can dielectric constant of semiconductor be calculated or estimated?

    Greetings, Could anyone help to tell me how to estimate the dielectric constant of cobalt oxide? Cause I have looked for the database, and couldn't find the data. Very thanks, jovis
  6. C

    Calculating Dielectric Constant: Normalize Capacitance to Thickness & Area

    This may seem like a dumb question, but is a dielectric constant calculated from a measured capacitance normalized to thickness and electrode area, I’m having a brain fart.
  7. K

    Static dielectric constant of NaCl

    Hey, I have a question in how one can calculate the static dielectric constant, f, of NaCl. NaCl has density of 2170kg/m3, a lattice constant a= 5.6 A and a Young's modulus Y = 40GPa. the optical dielctric costant is 2.34. I couldn't find any formulas which connect these values together. We...
  8. R

    Find Dielectric Constant Given Charges

    Homework Statement When a certain air-filled parallel-plate capacitor is connected cross a battery, it acquires a charge (on each plate) of 130 μC. While the battery connection is maintained, a dielectric slab is inserted into and fills the region between the plates. This results in the...
  9. R

    Dielectric constant in the energy density function

    The energy density function for the electric field in vacuum is u=\dfrac{\epsilon_0}{2}E^2 And the cited textbook result for the energy density inside a dielectric is: u=\dfrac{\epsilon_0 \epsilon_r}{2}E^2 Now, one way to reach the upper formula is to look at the energy as...
  10. S

    Deriving the dielectric constant of water

    We derived a formula to calculate the dielectric constant for some materials. It works well for gases and some liquids. But, water has a extraordinary dielectric constant of ~80. I tried googling it up but couldn't find any place which explains (mathematically) why it's so big. The professor...
  11. G

    Relative dielectric constant - More than one dielectric in a capacitor

    Homework Statement A parallel plane capacitor with conducting plates area \Sigma= 400cm2, distant d=5mm, is half filled of mica (k1=5) and half filled of paraffin (k2=2). Calculate: a) C (Capacitance of the capacitor) ...othersHomework Equations None The Attempt at a Solution I haven't...
  12. L

    D-field -> E-field when the dielectric constant is a function of space

    Hello everyone, I am a little reluctant to post this question because it is a common problem type assigned for introductory electrodynamics courses, so I understand any level of vagueness that should be practiced with regards to answering the question so as to not make it too obvious how to do...
  13. P

    Anyone know the dielectric constant of OTS?

    Anyone know the dielectric constant of OTS?
  14. R

    Imaginary part of dielectric constant.

    in ac fields permittivity becomes complex quantity and has real and imaginary parts. in metals (may be few exceptions but i don't know) imaginary part is always positive and represents loss factor or energy absorbed. why the plot of imaginary part of dielectric constant as function of energy is...
  15. J

    Dielectric Constant: Solving Homework Problems

    Homework Statement A slab of dielectric is now inserted between the plates, the battery still being connected. 7.5μC of additional charge flows from one plate, through the battery and onto the other plate. What is the dielectric constant of the dielectric material?Homework Equations A 1.0μF...
  16. A

    Understanding the Complex Dielectric Constants of Metals

    What are the dielectric constants of metals and i have heard that some materials have dielectric constants that are complex numbers. Please tell me which materials have complex Dielectric constants?
  17. C

    Dielectric Constant Computation

    Homework Statement Say, i have a setup as shown on the photo below http://www.flickr.com/photos/47719498@N07/4375079183/ * setup also seen as attachment how can i be able to compute for the dielectric constant provided it is not parallel plate and considering two different area is...
  18. P

    Dielectric constant of a conductor

    i am reposting this question , earlier it had been deleted assuming it to be a "HOMEWORK QUESTION" , well my question is , can we define a dielectric constant for a conductor ?? is it conceptually meaningful?? if yes then why and what is it?
  19. A

    Complex dielectric constant implies absorption?

    Hi everyone, My very first post after simply using physicsforums as a (very) handy FAQ resource. Okay, so my question is probably pretty simple, but I've been unable to find anything on here already. How does a complex dielectric constant imply the absorption of EM radiation? I...
  20. M

    What is the dielectric constant of the slab on a parallel plate capacitor ?

    Homework Statement When a certain air-filled parallel-plate ca- pacitor is connected across a battery, it ac- quires a charge (on each plate) of magnitude 214 μC. While the battery connection is maintained, a dielectric slab is inserted into the space between the capacitor plates and...
  21. J

    Determine the dielectric constant

    Homework Statement Two flat metal circles of radius r=15 mm are brought a distance d=8.0 mm apart to form a parallel plate capacitor. The surface charge density of one plate is measured to be +1.0*10^-3 microCouloubs/mm^2. The potential difference across the capacitor is measured to be .12...
  22. D

    Dielectric Constant K & Plate Charge Density

    Let me know if the following reasoning is correct : If the surface charge density on the internal surface of one of the plates in a parallel plate capacitor is Sigma, which becomes Sigma/K, when a dielectric material is inserted between the plates with dielectric constant...
  23. D

    Higher dielectric constant : better insulator

    Higher dielectric constant means better insulator. Water has a dielectric constant of 8, which is enormous(according to Walter Lewin), but it still is a very good conductor of electricity, why?
  24. P

    Measyrement of Conductivity and Dielectric constant

    can you please tell me, how do we measures the conductivity and dielectric constant of silicone oil and castor oil, because resistivity of silicone oil is very high so that's why it is difficult to mesure with conductivity meter,
  25. W

    Calculating the Dielectric Constant of Cold Dilute Rubidium Gas

    assume that i have a cloud of cold dilute Rubidium atoms i know the atomic levels of the Rubidium atom How to calculate the dielectric constant of this gas? Which book can i consult?
  26. D

    Dielectric constant of the materials, k

    Homework Statement C1 = 12uF, C2=20uF, and the capacitors are charged so that the voltage across each capacitor is 6V. When a dielectric material is inserted between the plates of C1, the charge on C2 changes by 32 uC. Calculate the dielectric constant of the material, k. (PS. C1 is parallel...
  27. S

    Dielectric constant for aliminium nitride

    I know that a dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space. It is an expression of the extent to which a material concentrates electric flux, and is the electrical equivalent of relative magnetic permeability. or in english terms: A...
  28. Q

    Electric field with dielectric constant

    Homework Statement Two 5.0mm*5.0mm electrodes with a 0.10mm thick sheet of Mylar between them are attached to a 9.0 V battery. Without disconnecting the battery, the Mylar is withdrawn. (Very small spacers keep the electrode separation unchanged.) Dielectric constant for Mylar is k=3.1. What...
  29. C

    Dielectric constant and strength

    Hey all, I am currently working on a project with high voltage and wood. I have these values for dielectric constants of certain woods, but I can't seem to figure a way to convert this dielectric constant into dielectric strength. Anyone have a clue?
  30. A

    Capacitance - Dielectric Constant Relation?

    Hi, Does anyone know if there is a relation between a materials capacitance (C) and its dielectric constant (K)? Thanks,
  31. L

    Understanding Dielectric Constants and Their Impact on Capacitance

    The higher the dielectric constant, the higher the capacitance right? I am reading that water has a dielectric constant of 80. This means the capacitance is 80 times greater (if there was water between the parallel plate capacitor) than if the capacitor was in vacuum. What is the...
  32. S

    What Is the Dielectric Constant of Oil in a Capacitor?

    Homework Statement an air gap capacitor is charges with a 50 volt battery. the battery is then disconnected and oil is introduced between the plates. the potential difference between the plate drops 10 volts. a) what is the dielectric constant? b) what fraction of the original stored...
  33. morrobay

    Index of refraction = sqrt dielectric constant

    Can someone explain in terms of electric fields how the index of refraction squared = the dielectric constant of the material ?
  34. T

    What is the physical explanation and results for a negative dielectric constant?

    Hi Guys, I was reading about plasmons on wikipedia and I found that there are some materials with negative dielectric constant, what I know is that there are complex dielectric and reflection coefficient constants due to reflection in metals, can we relate the the complex dielectric constants...
  35. M

    Complex Dielectric Constant Question

    Hello, I'm trying to follow along in my Solid State Physics book, but I'm getting hung up on an equation for the complex dielectric constant. \widetilde{\epsilon_r}=\epsilon_L+j\widetilde{\sigma}/\omega Multiply through by the definition of the complex conductivity, so that we get...
  36. E

    Supressing dielectric constant of water?

    Hey Everyone. I am doing a project proposal where I am calculating the coupling efficiency between a quantum dot and a wire and I need to enter in values for the dielectric constant of the wire and the surrounding medium. I am working off a paper (doi:10.1103/PhysRevB.76.035420) where he uses...
  37. E

    Dielectric constant depression of water?

    Hey Everyone. I am doing a project proposal where I am calculating the coupling efficiency between a quantum dot and a wire and I need to enter in values for the dielectric constant of the wire and the surrounding medium. I am working off a paper (doi:10.1103/PhysRevB.76.035420) where he uses...
  38. C

    Dielectric Constant: Understanding Quantum Optics in Ultra Thin Semiconductors

    One of my professors sent me an article on quantum optics in ultra thin semiconductors. In various graphs and text, the dielectric constant is discussed, and I have no idea what this is.
  39. M

    Dielectric constant, metals, frequency a bit confused

    A metal is not a good dielectric. A vacuum is a decent dielectric. There are much better dielectrics than a vacuum. A high dielectric constant, k, means the material exhibits good dielectric behaviour. A vacuum has k = 1, better dielectrics have k > 1. What is the dielectric constant of...
  40. K

    Refractive index & dielectric constant

    We know,n=(rel.permittivityxrel.permeability)^(1/2) For natural transperant mediums (to visible light of EM spectrum)are non-magnetic.So, rel.permeability=1 hence n=(dielectric constant)^(1/2)...
  41. I

    Optics: refractive index and dielectric constant

    Dear all, i am a bit confused with a very simple equation connecting refractive index of water and its dielectric constant for visible range of wavelengths and room temperature. i hope, You can help me as we know, the refractive index 'n' can be defined as n=sqrt(epsilon*mu)...
  42. S

    Finding The Dielectric Constant?

    Hi, I'm currently an A2 student and was wondering is it possible to find dielectric values for different materials placed within parallel plate systems. I have an idea but i think doing this is more complicated than i expect. I found the equation: k=Cd/epsilonzero*A d = distance between...
  43. S

    Dielectric constant and index of refraction

    I'm a little confused. My source says the dielectric constant for water is 80. Then I have the equation that gives the index of refraction as n=\sqrt{\epsilon_r} (since it isn't very magnetic). But the index of refraction for water is 1.33. What am I missing?
  44. Gokul43201

    How Does Helium's Dielectric Constant Vary with Temperature?

    I'm having trouble finding reliable data on the dielectric constant of helium(4) gas as a function of temperature, from 4K up. Grateful for any help
  45. C

    Power transmission and dielectric constant

    How do I find the reflectivity of a combination of ice on top of water(infinite half-space) as a function of the thickness of ice? I know how to find it for each material, it's just rho = ((root(dielectric constant)-1)/(root(dielectric constant)+1) )^2. I'm given dielectric constants for both...
  46. A

    Dielectric constant for a plastic kitchen bag?

    Hello! I'm making some home-made capacitors for an up-coming lab, and I was thinking of using Market Basket/DeMoulas' plastic kitchen bags as a dielectric. I'm really hoping to use it because the packaging info includes the thickness of the bag (19 micrometers), which should increase the...
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