What is Dielectric: Definition and 729 Discussions

In electromagnetism, a dielectric (or dielectric material) is an electrical insulator that can be polarized by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor, but instead only slightly shift from their average equilibrium positions, causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field (for example, if the field is moving parallel to the positive x axis, the negative charges will shift in the negative x direction). This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field.The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important for explaining various phenomena in electronics, optics, solid-state physics, and cell biophysics.

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  1. X

    Finding the bound charge in a dielectric

    MODERATOR'S NOTE: problem statement is mistaken, please see https://www.physicsforums.com/showthread.php?t=723342 Homework Statement The space between the plates of a parallel plate capacitor is filled with a dielectric material whose dielectric constant $\epsilon_r$ varies linearly from 1 at...
  2. C

    Capacitance Calculation for Dielectric-Filled Coaxial Cable

    Homework Statement A long cable consists of two coaxial conducting cylindrical shells of radius b and 3b. The region with radius ##\delta## between b and 2b is filled with a material of relative permittivity ##\epsilon_r \neq 1## and relative permeability ##\mu_r = 1##; the remaining space...
  3. F

    What Is The Difference Between These Dielectric Terms?

    What Is The Difference Between These "Dielectric" Terms? Can someone please explain to me what the difference between these terms are? 1. Dielectric constant 2. Relative dielectric constant 3. Dielectric loss I came across them on this website: http://www.lsbu.ac.uk/water/microwave.html#pen...
  4. A

    Solve Dielectric Problem: Parallel Plate Capacitor w/ Wedge Insert

    Homework Statement A parallel plate capacitor has a capacitance C when there is no dielectric inside of it. Suppose a wedge of material with dielectric constant K is inserted in between the plates of the capacitor (see figure). The bottom face of the wedge has the same area as the plate of...
  5. N

    Dielectric Constant of Food in microwave

    I made the experiment up myself so my errors may be a result of this, but I heated up marshmallows, eggs and cheese in the microwave and measured the distance between the hotspots in order to get the wavelengths. For the marshmallows I got 0.13cm, for the eggs I got 0.16cm and for the cheese I...
  6. C

    Interface (Maxwell-Wagner) Polarization and Dielectric Loss

    Maxwell-Wagner polarization is generally described in literature as the polarization of interfaces, such as grain boundaries, with an applied electric field. In the Wikipedia article (http://en.wikipedia.org/wiki/Maxwell–Wagner–Sillars_polarization), it's mentioned that "the charges are often...
  7. S

    Magnetic field energy inside a linear dielectric

    Homework Statement A Sphere made of a linear magnetic of radius a and permeability μ is placed in an external uniform magnetic field Bo. 1) Assuming Laplace equation solutions find magnetic field at an internal and external poinnt. 2) Find the demagnetization factor of the sphere. 3)...
  8. K

    How Does Inserting a Dielectric Material Affect Capacitor Charge?

    A parallel-plate air capacitor of area A= 21.0 cm2 and plate separation d= 3.20 mm is charged by a battery to a voltage 50.0 V. If a dielectric material with κ = 4.80 is inserted so that it fills the volume between the plates (with the capacitor still connected to the battery), how much...
  9. D

    Find the dielectric flux and polarization values

    Homework Statement In a slab of Teflon (εr=2.1), the electric field is E= 6Ux+12Uy-20Uz V/m. Find D and P (BTW εr stands for the relative dielectric constant) Homework Equations D=(ε0)(εr)E P=D-(ε0)E The Attempt at a Solution (a)...
  10. D

    Calculate the dielectric constant of the material

    Homework Statement two point charges in free space are separated by distance d and exert a force 2.6 nN on each other. The force becomes 1.5 nN when the free space is replaced by a homogeneous dielectric material. Calculate the dielectric constant of the material. Homework Equations I...
  11. Y

    Dielectric Charges: Polarization or Dielectricity?

    Homework Statement When the bound charges in a dielectric arrange themselves in an electric field, this is called: A) Bound Charge Alignment B) Dielectricity C) Polarization D) Reactance Homework Equations - The Attempt at a Solution I know that this is a straightforward...
  12. D

    Find the dielectric flux density and the abilty to polarize

    Homework Statement In a slab of Teflon (epsilon=2.1), the electric field is E= 6Ux+12Uy-20Uz V/m. Find D and P (BTW epsilon stands for the relative dielectric constant) Homework Equations Upload The Attempt at a Solution Upload
  13. I

    Capacitors: why is the dielectric constant defined the way it is?

    usually when we have some initial variable U(0), and we have some factor K that changes this initial variable, we usually express the new variable U(f) like so.. U(f)=KU(0) and NOT the other way around... so why is the dielectric constant expressed in the following way? Eκ=E0 this...
  14. S

    Dielectric & Magnetic Nanoparticles with EM field

    Hi all, Homework Statement 1. What are the impacts of EM field on Aluminium Ferrite nanoparticles (carry both dielectric & magnetic features), compare to EM field applied on Aluminium oxide (pure dielectric)? 2. If solenoid is used to generate magnetic field; what is it use to generate...
  15. Z

    Calculating the Dielectric Function of metals - Units trouble

    Hello everyone here! See i got my hands on this paper: Optical properties of metallic films for vertical-cavity optoelectronic devices by Rakic et al. A simple google search of the title will give you access to the paper. Now, i am writing the function in MATLAB to calculate the...
  16. S

    Point charges and dielectric

    Hello. I am not sure if I must post here. The problem is not for homework, it derived from a classmate's question. Homework Statement We have a large quantity of liquid dielectric with relative permittivity \varepsilon and a charge Q immersed in the liquid in depth h. We bring another...
  17. L

    Two quick questions conerncing potential and dielectric

    Hi everyone, I have a question about electric potentials and dielelectrics: 1. when I have a dielectri in the half space x<0 and air in x>0 is the potential steady at x=0? 2. does a potential depend on the relative permittivity ? I know that the electric field gets weaker in a...
  18. L

    Method of images with dielectric

    Hi everyone I have an understanding problem concerning the method of images method Homework Statement Jackson uses this kind of problem in his textbook but I don't understand it. We have a charge q on the z axis at distance d. the dielectric constant is e1 when z>=0 and e2 when z<0. Now...
  19. P

    What is the dielectric momentum density 4-vector?

    Assume that there is a dielectric material with a mass density of ρ0 observed in the dielectric-rest frame. And further, it is assumed that observed in the lab frame, v(x,y,z,t) is the velocity distribution, β=v/c is the normalized velocity, and γ=(1-β2)-1/2 is the relativistic factor, with c...
  20. F

    Change in energy stored on a capacitor when dielectric is changed.

    Homework Statement the separation of a parallel plate capacitor is 2mm with a potential difference between them of 45V. (i) Find the electric field between the plates. (ii)Find the charge per unit area of the plates if the permittivity of the dielectric medium is 20 \epsilon_0 (iii) Find...
  21. O

    Deriving the local field and Clausius Mossotti formula in a dielectric

    (My last https://www.physicsforums.com/showthread.php?p=4424810#post4424810 post did not get much attention so I try again without all these formulae. Think this will be more clear...) To derive the local field in a non-polar dielectric you assume a very small spherical cavity in which (since...
  22. O

    Paradox in evaluating the Lorentz field in a dielectric

    Can someone help me in understanding where I am wrong when thinking about the derivation of the Lorentz field in a dielectric. I give the derivation in italics (although the familiar reader should not need to read it) and after that I present the paradox. The basic idea is to consider a...
  23. A

    Dielectric Boundary Condition Question

    Hi, I have a question regarding the boundary condition present for a dielectric immersed in a static field. I hope one of you physics guru's can shed some light on this. Suppose we have a dielectric in space subjected to some external static electric field. I have read (without explanation)...
  24. A

    Dielectric Sphere in Uniform Field

    Hi, One of the boundary conditions when solving for the potential, \Phi, outside a dielectric sphere placed within a uniform electric field is \lim_{r→0}\Phi(r,θ)<\infty Can anyone explain/prove why this so. Thanks,
  25. A

    Relationship Between Conductance and the Dielectric Constant

    Hello all, I'm new to the forum so I hope I'm posting this in the correct section. I'm currently conducting an experiment in which I'm examining how the dielectric constant of a binary mixture changes with concentration and temperature using a parallel plate capacitor for measurements. The...
  26. Saitama

    Electrostatic potential energy - dielectric between concentric spheres

    Homework Statement A conducting sphere of radius ##a## carries an initial charge ##q_o##. It is surrounded by another concentric sphere of radius ##b##. The space between the two spheres is filled with a dielectric of permittivity ##\epsilon## and conductivity ##\sigma##. Find the electrostatic...
  27. I

    Why is dielectric breakdown damaging?

    Dielectric break down... i understand that there is current passing through the insulator but why is this damaging to the insulator? please go as deep as you can. thankyou
  28. C

    Induced surface charge on a dielectric

    Homework Statement A point charge Q is placed at a perpendicular distance a from an infinite planar LIH (linear, isotropic, homogeneous) dielectric of relative permittivity ε. By considering the normal component of the electric field at an arbitrary point just inside the dielectric to be the...
  29. S

    Variable Dielectric Spherical Capacitor: Calculating Capacitance

    Homework Statement Calculate the capacitance of a spherical capacitor of inner radius A and outer radius B which is filled with a di-electric varying as e=c+dcos^2θ . c and d are constants and θ is the angle made with the z axis.(also known as the polar angle) Homework Equations $C=εA/d$The...
  30. K

    Why is the index of refraction dependent on the dielectric constant

    and frequency? Could someone point me in a direction where this is explained in depth? I understand polarization and the dielectric constant as I've taken E&M 1
  31. skate_nerd

    LC circuit, space between dielectric plates

    Homework Statement If the max E-field in the capacitor is E=1.2(103) N/C and the space between the plates is filled with a dielectric of constant 100,000, what is the separation between the plates? Homework Equations I know C=kεoA/d where k is the dielectric constant, A is the area of...
  32. J

    Can negative dielectric possible

    can negative dielectric constant be possible?if yes then for which one.
  33. Saitama

    Force on Dielectric Medium in the Presence of Point Charges

    Homework Statement Two point charges of magnitude q and 3q are located at a distance of 'a' from each other within an infinite dielectric medium of dielectric constant k. The force by the larger charge 3q, on the dielectric equals A)zero B)##\frac{1}{4\pi \epsilon_o}...
  34. D

    Effect on electrostatic force due to dielectric medium.

    Hi! I have a high school physics question. I know the concept of induction, and I also know what happens when a dielectric slab is placed between 2 plates of a capacitor. 2 charged particles are kept at a distance r. The mutual force of attraction/repulsion is F. What happens to the force...
  35. M

    Electromagnetism - Dielectric and Various Cavities

    Homework Statement A large block of dielectric contains small cavities of various shapes whose sizes are much smaller than the block. The dielectric has uniform polarization P except those cavities which are assumed not to disturb the polarization of dielectric. (a) Show that, inside a...
  36. C

    Engineering Equivalent circuit for lumped capacitance with dielectric losses

    Homework Statement Draw the equivalent circuit for a lumped capacitance with dielectric losses that would be appropriate at RF frequencies. Homework Equations Possibly Xc=-j/ωC The Attempt at a Solution I do not really know what the question is asking. I know that a lumped capacitance...
  37. Sunil Simha

    Electrostatics problem: Find charges on the surface of the dielectric

    Homework Statement An arbitrarily-shaped object is given a charge q and is then surrounded by a dielectric of permittivity ε as shown in the figure below Find the charges induced in the inner and outer surface of the dielectric. Homework Equations I'm not sure but Gauss's law may...
  38. C

    Do magnetic fields have any effect on dielectric breakdown

    Would a magnetic field have any effect on the dielectric breakdown of insulators? For example, the dielectric breakdown of air is 3 Mega volts per meter at a gap of one meter; if you applied a magnetic field to that breakdown, would it help guide the electrons along the path and therefore reduce...
  39. P

    Find the dielectric constant of the medium?

    Homework Statement Two point charges a distance d apart in free space exert a force of 1.4∗10^−4 [N]. When the free space is replaced by a homogeneous dielectric medium, the force become .9∗10^−4 [N]. What is the dielectric constant ϵr of the medium? Homework Equations E=F/Q The...
  40. jaumzaum

    Difference between Corona Discharge and Dielectric Breakdown?

    What's the difference between Corona Discharge and Dielectric Breakdown? For me both stand for the same process, but wikipedia (as many other sites) says they are different. Actually they say corona discharge occurs when the electric gradient is high but not enough to create an electrical...
  41. D

    Effects of Dielectric on capacitors

    Homework Statement 2 parallel plate capacitors of distance separation d between the plates are connected in parallel of capacitance C_1 and C_2 respectively and charged with a voltage V after that the Voltage is disconnected and a dielectric of κ is inserted into C_2 I) Express the charge on...
  42. B

    Finding The Dielectric Constant

    Homework Statement The voltage across an air-filled parallel-plate capacitor is measured to be 181.0 V. When a dielectric is inserted and completely fills the space between the plates as in the figure below, the voltage drops to 27.0 V. What is the dielectric constant of the inserted...
  43. S

    Good dielectric yet hole conductor?

    Is there some material that could withstand relatively high voltages before it starts to conduct electrons,but in the same time a good hole conductor? Could such material be obtained by doping some dielectric similar to SiO2?
  44. N

    Polarization density in a dielectric?

    This is polarization density. Can somebody explain to me why exactly this is so? My book just says that's how polarization is defined.. Can you guys give me an intuitive understanding of why? Only thing I know is that χ is related to κ, the dielectric constant, and κ is related to how well a...
  45. E

    Use of tensors for dielectric permittivity and magnetic permeability

    Hello! In the study of electric and magnetic fields, two equations are called the constitutive relations of the medium (the vacuum, for example): \mathbf{D} = \mathbf{\epsilon} \cdot \mathbf{E}\\ \mathbf{B} = \mathbf{\mu} \cdot \mathbf{H} But in a generic medium (non linear, non...
  46. S

    The dielectric function of a metal using LD model.

    I'm studying the dispersive properties of metals using Lorentz-Drude model, but I'm confused about the equation set-up. What is LD model different from the classical dielectric function using for other dielectrics? Namely: ε(w) = ε’ + iε’' where the imaginary part is the attenuation. In...
  47. fluidistic

    Jackson's problem 4.10, dielectric between 2 spheres

    Homework Statement Two concentric conducting spheres of inner and outer radii a and b, respectively, carry charges +/-Q. The empty space between the spheres is half-filled by a hemispherical shell of dielectric (of dielectric constant ##\varepsilon / \varepsilon _0## ). a)Find the electric...
  48. K

    Energy stored in capacitor w/ dielectric

    Suppose a (parallel plate) capacitor of capacitance C is charged to a potential difference V and then disconnected and isolated. Energy stored E1= Q2/2C. Now if a material of appropriate dimensions and dielectric constant K is fully inserted between the plates, energy stored E2= Q2/2KC. E2...
  49. W

    Speed of light in lossy dielectric medium

    It is usually written that the speed of light in a dielectric medium is ##v=\frac{c}{\sqrt{\epsilon_r}}##, where ##c## is the speed of light in vacuum and ##\epsilon_r## is the relative permittivity. But, how can it be calculated for lossy and not necessarily low-loss dielectrics, i.e. those...
  50. O

    How to determine the dielectric constant of egg tray?

    Hi, can i know how to get the dielectric constant of the egg tray (the one with the paper) beside using dielectric probe technique? is it have same dielectric constant of paper? or it is different? i hope someone can help me. if the egg tray mix with the carbon or graphite, as i know the...
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