What is Dielectric: Definition and 730 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. 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...
  2. N

    Doubt regarding derivation of bound charges in dielectric

    In Griffiths, for deriving the bound charges for a given polarization P , the formula used is the general formula for dipoles .i.e ( equation 4.9) {Here the potential at r is calculated due to the dipole at r' ) V(r) = ∫\frac{x.P(r')}{X^2}d\tau' Here X = r - r' , and x = unit vector in...
  3. B

    EM waves: multiple planar interfaces (PEC-backed lossy dielectric)

    Homework Statement Our prof has told us we can get help from wherever/whoever we want as long as it isn't classmates. This is a take-home test. The relevant question: You have a three-layer dielectric. | Layer 1 | Layer 2 | Layer 3 | Layers 1 and 3 are semi-infinite. Layer 1 is air (εr =...
  4. S

    Which dielectric constant in media?

    Hi, In deriving a complex wave vector for waves in media, an equation D = ε E is typically used. Later though, it is common to relate D and E through a complex ε which is generally written as εcomplex = ε + 4 pi i σ / ω. It seems a contradiction to insert one relationship into the Maxwell...
  5. A

    Confuse about linear dielectric

    hello, I am learning electromagnetism and read the polarization in dielectric. The textbook tell me that in linear dielectric exists a simple relation: P=\chi*ε0*E where \chi is the susceptibility, ε0 is the permittivity of vacuum and E is total electric...
  6. A

    Dielectric constant is throwing me off

    A spherical capacitor is formed from two concentric, spherical, conducting shells separated by vacuum. The inner sphere has radius 0.39 m and the capacitance is 108 pF. What is the radius of the outer sphere? Give your answer in meters to the third decimal place. C-->Capacitance...
  7. A

    Dielectric Sphere in Time Varying Field

    Hi, I'm interested in how a dielectric sphere effects a (spatially) uniform time varying field. I'm sure I'm not the first to inquire about this very topic. Could anyone direct me to a resource? Thanks,
  8. A

    Can a material have both dielectric and resistance properties?

    Hi, Do material posses both dielectric as well as resistance properties? I imagine that when there is a difference in potential across a volume of some material, some current will flow (I=V/R <-- the material's resistance), but also the material may become polarized to a certain degree...
  9. D

    Exploring Energy of a Linear Dielectric

    I've examined and re-examined the proof that the energy density of a linear dielectric is u=\frac{1}{2}\mathbf{D}\cdot\mathbf{E}, but I still don't understand it. I'll rewrite it here and try to explain what I'm having trouble grasping. We first imagine that the free charge (as a function of...
  10. K

    Dielectric Slab Stack Configuration for Plane Wave Incidence

    Given the following statement: "A plane wave is incident (from the free space) upon a semi-infinite medium made of N=100 different lossless dielectric slabs." Visually/spatially, what does this look like? I can see two possibilities 1) the slabs are stacked on top of each other...
  11. I

    Thomas-Fermi approximation and the dielectric function

    1)What exactly is meant by the 'static limit' where the frequency is taken to zero, but the wavenumber is finite? I am getting confused because if the frequency is zero, then surely the probing electrons/photons/whatever have no wavelength, so how can the wavenumber be finite and non-zero? 2)...
  12. R

    Calc Height Dielectric Oil Coaxial Cylinder Tubes

    Homework Statement Fromm Griffiths Two long coaxial cylindrical metal tubes (inner radius a, outer radius b) stand vertically in a tank of dielectric oil (susceptibility \chi_{epsilon}, mass density \rho. The inner one is maintained at potential V, and the outer one is grounded. To what...
  13. T

    Force on a point charge due to a dielectric

    Homework Statement Given an infinitely long hollow dielectric cylinder of finite thickness and a single point charge find (a) the force on the point charge and (b) the potential energy of the configuration. Homework Equations P = Epsilon * Chi * E The Attempt at a Solution...
  14. R

    Field and Displacement Inside Carvities Within A Dielectric

    Homework Statement Suppose the field inside a large piece of dielectric is \vec{E}_{0}, so that the electric displacement is \vec{D}_{0}=\epsilon_{0}\vec{E}+\vec{P}. a. Now a small spherical cavity is hollowed out of the material. Find the field at the center of the cavity in terms of...
  15. R

    Dielectric and Parallel Plate Capacitor, the point?

    Hi, so I'm having a little trouble understanding why... you would put a dielectric in between a parallel plate capacitor? I know it increases the capacitance but it does so by lowering the potential difference sooo... The charge is still the same, I believe the potential energy also decreases as...
  16. K

    Point Charge in a Dielectric Sphere

    Homework Statement A point charge q is located at the center of a dielectric sphere of radius a. Find D, E, and P everywhere and plot your results. What is the total bound charge on the surface of the sphere? (I assume by "everywhere" my professor meant inside and outside the sphere.) (D is...
  17. R

    Definition of the dielectric function in the linear response regime

    Sometimes the dielectric function is defined as the connection between the total electric field in a material and the external field, \mathbf{E}(\mathbf{r},\omega) = \int \epsilon^{-1}(\mathbf{r},\mathbf{r'},\omega) \mathbf{E}_{\text{ext}}(\mathbf{r'},\omega) d \mathbf{r'}, and sometimes...
  18. S

    Capacitor with two angled dielectric materials

    Homework Statement Find the capacitance of the capacitor shown in the figure. Asume H << L. http://imageshack.us/a/img39/1935/capacitor.png Homework Equations Capacitance of a plate parallel capacitor with a dielectric material e: eA/H where A denotes the area of the plate, and H...
  19. C

    Planar wave normally incident on dielectric boundary

    PROBLEM: I am asked to consider a parallel polarized planar wave with frequency ω is normally incident on a dielectric boundary. The incident time average power flux P_i = 100 w/m^2. The first medium is free space and the second has vacuum permeability but ε=4ε_0. We are also given that the...
  20. ShayanJ

    Electric polarization of a dielectric due to a magentic field

    Imagine a dielectric cylinder placed in a uniform magnetic field parallel to its axis. Then we make it rotate around its axis. The nuclei and electrons should feel a radial lorentz force because of their rotation around the axis of cylinder.The forces applied to electrons and nuclei are in...
  21. P

    Calculate capacitance with a dielectric

    Homework Statement An isolated charged parallel-plate capacitor with the plate separation d=2 mm and area of A=10 cm2 is initially empty. One slides a polystyrene dielectric slab with thickness equal to half the plate separation and with only half the area of the plates into the region between...
  22. B

    Linear isotropic dielectric mixture two materials

    Homework Statement Consider an x1:x2 mix of two linear isotropic dielectrics (by volume). x1+x2=1. On large length scales the mixture is homogenous and can be characterized with a dielectric constant ε_mix but on short length scales the material is granular so the dielectric constant is...
  23. A

    Bound charge in linear dielectric

    How can we show that the bound charge in a homogeneous linear dielectric is proportional to the density of the free charge. I have a handful of equations but still I can't work this out.
  24. S

    Inserting dielectric into isolated capacitor

    U = (1/2)CV^2 = (1/2)Q^2 /C Increasing C while keeping Q constant (isolated capacitor) will decrease the energy contained in the capacitor by and amount X Where does this X energy come from? Case 1 (slab polarizes immediately when it crosses the electric field of the plates) The capacitor...
  25. tomwilliam2

    How Does Group Speed Differ from Phase Speed in a Dielectric Medium?

    Homework Statement I'm given the refractive index of a piece of glass: $$n(\omega)=A+B\omega$$ And I have to find the speed at which a pulse of radiation will travel through the glass at an angular frequency $$\omega = 1.2 \times 10^{15} s^{-1}$$ I also have A = 1.4, B=3.00 x 10^-17. Homework...
  26. S

    A dielectric hemisphere

    Homework Statement we put a dielectric hemishphere with radius (a) and dielectric coeeficient(k) on an infinite conducting plane.the system(hemsiphere and the plane) are in a constant electric field E0. find the surface charge distrubution on the plane as a function of (r). and explain what...
  27. M

    What is the differecenbetween insulator and dielectric ?

    What is the differecenbetween insulator and dielectric ? hello friends , please clear me the difference between them.
  28. D

    High Temperature Dielectric Coating

    I'm looking for some sort of dielectric coating that can be used at high temperatures. I'm working on trying to create a voltage point charge in a high temperature steam environment using a coated accupuncture needle. The goal is to be able to coat the needle thinly and uniformly, leaving only...
  29. Z

    Finding E, D and P in a Dielectric Slab

    Homework Statement For a dielectric slab of relative permeability er fills the space between z = ±a in the xy-plane, and contains uniform density of free charge ρf per unit volume. Find E, D and P as functions of z. Homework Equations P = εoXeE D = εrεoE ∇×P=εoXe(∇×E) = 0...
  30. N

    Force on dielectric in parallel plate capicitor

    Force act on dielectric slab on inserting between the parallel plate = [8.85 * 10^-12]b(k-1)(V^2)/2d where b = width of the plate , d = distance b/w the plates , V is the constant potential difference across the plates and k = dielectric constant Which force is acting on dielectric...
  31. C

    Capacitors with different dielectric constants

    Two capacitors have the same plate separation, but one has square plates and the other has circular plates. The square plates are a length L on each side, and the diameter of the circular plate is L. The capacitors have the same capacitance because they contain different dielectric materials...
  32. B

    Cylindrical capacitor with varying dielectric

    Homework Statement Consider a long cylindrical coaxial capacitor with an inner conductor of radius a, and outer conductor of radius b, and a dielectric with a relative electric permittivity or dielectric ε(r), varying with the cylindrical radius. The capacitor is charged to the voltage V...
  33. T

    Capacitor dielectric question?

    How does the voltage on a capacitor vary if the dielectric is an ionised gas?
  34. E

    EM wave at a plane dielectric boundary

    i was studying incidence of EM wave at a plane dielectric boundary and encountered equations in the attachment . I just want to know if n2 > n1 then electric field amplitude at the boundary increases . So from where does this extra value comes ? n1 and n2 are intrinsic impedances of 1st and...
  35. A

    Two Dielectric Materials in Capacitor

    Homework Statement A capacitor consisting of two parallel plates of area A = 7.3 m2 and spacing d = 0.150 m is filled with two parallel slabs of dielectric material of equal thickness and with dielectric constants 1 = 3.20 and 2 = 7.50, respectively. What is the total capacitance? k1 fills...
  36. O

    Coaxial coils in dielectric material

    Hi everyone I have a problem to solve, I already simulated it with FEMM, but I wonder if it is possible to find an analytical solution. Let's say that there's a small coil (100 turns) around a pipe (2in diameter), the pipe is filled with air. This pipe is located inside a bigger pipe...
  37. T

    Free and bound charge in a dielectric

    Homework Statement I'm just trying to understand better what happens at the interface between a conductor and a dielectric, particularly with regard to free and bound charge. I would like to know: - under what conditions can a dielectric acquire free charge, and how this free charge...
  38. N

    Calculating Capacitance With Dielectric

    Lets say There is a capacitor with the are of Plates A and the distance between the plates say is 5m if a dielectric of similar dimensions except the width is 3m is filled between the Capacitor plates how to calculate the new Capacitance ??
  39. T

    Parallel plate capacitor with two dielectric materials?

    Homework Statement Use Gauss' law to find an expression for the electric field within a charged parallel plate capacitor with two layers of dielectric materials (?r1 and ?r2). (See attached image, this is for question 2a). The Attempt at a Solution My approach would be to split the...
  40. H

    Solving Dielectric Lens Electric Field Equation

    Homework Statement In the figure the left surface of a dielectric lens is that of a circular cylinder, and the right surface is a plane. If E1 at point P(r,45,z) in region 1 is 5\hat{a}_{r}-3\hat{a}_{\phi }, what must be the dielectric constant of the lens if the electric field in the...
  41. K

    Dielectric slab in between plates of capacitor

    i'm reposting this question as nobody answered it previously. please answer it this time. in given type of arrangement we normally take it equivalent to two capacitors(plate 1 and surface 2) and (surface 2 and plate 3) in series. My question is that a capacitor is formed with two plates of...
  42. K

    Dielectric slab in some space between a capacitor

    when we place a dielectric slab between two plates of a capacitor(size small as compared to space between plates), we take it equivalent to 2 capacitors in series- one plate of capacitor and surface of dielectric and other plate of capacitor and surface of dielectric. My question is that a...
  43. M

    Capacitor with a dielectric: studying for an exam

    Okay so I have a parallel-plate capactior k=5.5 Area= .034m^2 Plate Separation= 2mm If the Electric Field falls short, the capacitor will burn up if exceeding 200kN/C. It's asking for the max energy stored by the capacitor. My attempt was lame. I tried using C= (ε0)A/d and...
  44. C

    Dielectric Barrier Discharge Plasma Discharge Circuit

    To anyone that can help me, Hello everyone. I am student from Mechanical Engineering and I am very new to electronic field. I currently doing my final year project which is developing the high voltage discharge circuit for the DBD plasma. The middle electronic elements is the representative...
  45. D

    Calculate dielectric constants at an angle

    Homework Statement For an application you require a thin wafer of dielectric with dielectric constant = 12 perpendicular to the wafer. You have available a tetragonal crystal of dielectric ceramic with relative dielectric constants εx = εy = 18. and εz = 10. At what angle to the z axis...
  46. V

    Dielectric constants in different directions - does this make sense?

    Dielectric constants in different directions -- does this make sense? So I'm trying to analyze a scenario in which I have a plane wave incident (from, say, some medium with permittivity and permeability ε_1 and μ_1), on a plane of a dielectric material that has an anisotropic permittivity: in...
  47. J

    Coulomb force if dielectric is placed in between them

    Homework Statement two charges q1 and q2 are palced at a distance r. A slab of thickness t is placed between the two cahrges having dielectic constant k. Find coulomb force between the charges. Homework Equations Well F = q1q2 / 4∏ε°k - this would have been the force if the slab was...
  48. V

    Dipole embedded in dielectric sphere is this the best way to do this?

    Homework Statement Hey all, I want to find the potential due to a point-like (mathematical, not physical) dipole inside and outside of a sphere made of dielectric material with dielectric ε. It's of radius R. Outside the sphere is vacuum.Homework Equations The Attempt at a Solution Inside...
  49. S

    Does Dielectric Polarization Affect AC Transmission or Is It the Frequency?

    I had always thought that a capacitor with a dielectric transmits AC precisely because it polarizes in response to the applied field. To tell you the truth, I realize now that I had two different views on how this process works: One: the AC is oscillating on both sides of the dielectric...
  50. D

    Dielectric Breakdown and Capacitance

    If a capacitor's dielectric partially breaks down, as in some of the material has ionized and acted as a conductor, will there still be a capacitance to the component? Say its a high frequency AC signal on a capacitor with a small part of its dielectric material in a breakdown state. My...
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