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. 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...
  2. J

    Dielectric Capacitance of Parallel Plate Cap

    Homework Statement A parallel plate cap of cross sectional area A and thickness d is filled with a dielectric material whose relative permittivity varies from \epsilon_r = 1 to \epsilon_r = 10 Find the capacitance. Homework Equations The Attempt at a Solution C = Q/V E = \sigma / e0...
  3. B

    Dielectric Help: Solving Parallel Plate Capacitor

    [SOLVED]Dielectric help Homework Statement To make a parallel plate capacitor, you have available two flat plates of aluminum (area = 180 cm2), a sheet of paper (thickness = 0.10 mm, k= 3.5), a sheet of glass (thickness = 2.0 mm, . k= 7.0), and a slab of paraffin (thickness = 10.0 mm, k=...
  4. L

    5. Energy of a Capacitor in the Presence of a Dielectric

    Homework Statement A dielectric-filled parallel-plate capacitor has plate area of 25.0 cm^2 and plate separation of 9.00 mm. The capacitor is connected to a battery that creates a constant voltage of 7.50 V. The dielectric constant is 2.00. Throughout the problem, use 8.85×10−12 C^2/N \cdot...
  5. B

    Gauss's Law with Dielectric: Deriving and Applying the Most General Form

    My textbook (high school level) derives an instance of Gauss's Law with Dielectric for the case in which the dielectric material fills the gap between a parallel-plate capacitor entirely. So you get surface int (D dot Area-vector) = q, where D = (dielectric constant)(epsilon_0)(Electric...
  6. M

    Electric Field of a Capacitor with asymmetric dielectric

    Hey guys, if an question regarding a capacitor. As seen in the picture there is a capacitor with an asymmetric dielectric e1 and e2. http://img129.imageshack.us/img129/5999/kondensatorti8.jpg My question: Who do I calculate the E-field of the capacitor? thanks in advamce, help is...
  7. V

    Energy of a Capacitor in the Presence of a Dielectric

    A dielectric-filled parallel-plate capacitor has plate area of 20.0 and plate separation of 5.00 . The capacitor is connected to a battery that creates a constant voltage of 7.50 . The dielectric constant is 2.00. Throughout the problem, use 8.85×10−12 . The dielectric plate is now slowly...
  8. S

    How can I simulate dielectric breakdown?

    Are there any programs around which will do this? I initially thought of Sonnet, but after some thought, I began to doubt that it would model dielectric breakdown. Any ideas at all? I've searched the web, and I can find some electrical (spice) models for it, but nothing geometric. Thanks...
  9. 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...
  10. 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...
  11. Repetit

    Light momentum inside a dielectric medium?

    Light in a vacuum has momentum \hbar k but when the light enters a dielectric medium, fx. glass, the momentum of the light is increased to \hbar\sqrt{\epsilon} k, where \epsilon is the dielectric constant of the dielectric. Where does the extra momentum come from? How can this be in accordance...
  12. S

    Does the Net Charge of a Dielectric Affect the External Electric Field?

    Let's say we have a sphere, radius R, which has a uniform volume charge density. Then we wrap it around with a dielectric with a frozen in polarizability of kz in the z direction. This dielectric goes from R to a radius A. The total surface bound charge on either surface of the dielectric is...
  13. J

    How to find the Dielectric Strength

    Hello, everyone! I have a question, and i don't know how to solve it... They ask me for the dielectric strength! How do i find it?
  14. S

    Linear dielectric in a capacitor

    Homework Statement Griffith's Problem 4.18 The space between the plates of a parallel-plate capacitor (in the figure) is filled with two slabs of linear dielectric material. Each slab has thickness a, so the total distance between the plates is 2a. Slab 1 has a dielectric constant of 2...
  15. Q

    Electric Field in Dielectric: Charge Distribution & Calculations

    Two identical, oppositely-charged, conducting plates of area 2.50cm² are separated by a dielectric 1.80 mm thick, with a dielectric constant of 3.60. The resultant electric field in the dielectric is 1.2*10^6 V/m. a)Compute the charge per unit area on the conducting plate. b)Compute the...
  16. A

    Question about capacitor and dielectric

    The problem is that I am complicated what the direction of the force between capacitor and dielectric is while inserting dielectric in capacitor, when the voltage of capacitor is constant. Also I want to know the direction of the force, when the charge of the capacitor is constant.
  17. I

    Does adding a dielectric to a capacitor increase the electric field?

    there is a capacitor with a constant potential difference of V in air. When a dielectric is completely inserted between the plates of the capacitor completely filling it, additional charge flows onto the positive plate. The additional charge should be Q=kCV-CV right? Would the induced charge...
  18. I

    Push the dielectric half way into the capacitor

    This is a general question because I cannot find any example problems to base this question off of. Suppose we have two parallel plate capacitors, what work is needed to push the dielectric half way into the capacitor and why does the slab feel a pull into the capacitor?
  19. A

    Dielectric Problem: Q&A to Calculate Electric Field & Induced Charge

    Homework Statement Two parallel plates have charges Q and -Q. When the space between the plates is devoid of matter, the electric field is 2.7E5 V/m. When the space is filled with a certain dielectric, the field is reduced to 1.3E5 V/m. What is the dielectric constant of the dielectric? I got...
  20. X

    A dielectric is inserted between the plates of a capacitor.

    A dielectric is inserted between the plates of a capacitor. The system is charged and the dielectric is removed. The electrostatic energy stored in the capacitor is 1. greater than 2. the same as 3. smaller than it would have been if the dielectric were left in place. U= 1/2 (K)EAd E^2 K=...
  21. M

    Does a.c. pass through a dielectric in a capacitor?

    Hi all My teacher says an a.c. passes through the dielectric of a capacitor. She says that the dielectric filters the a.c. passing through it. My book has no views on this. It just states that E lags behind the current I by a phase angle of 90 degrees. No comments on whether the a.c. is...
  22. W

    Find Change in Charge of Identical Capacitors w/ Dielectric Insertion

    Homework Statement Two identical capacitors and of capacitance 1.20 F are connected in series across a FIXED total potential of 650 V. A dielectric slab of dielectric constant 3.70 can fill and is slowly inserted into that capacitor. 1. What is the change in charge, , on when the...
  23. Q

    Dielectric sphere - Find the electric field

    Consider a dielectric sphere of radius R and dielectric constant e_r. The sphere contains free charges that have been uniformly distributed with density rho. (a) Show that electric field inside the sphere is given by E = [rho*r /(3*e_0*e_r)]* r hat where r hat is the unit vector pointing...
  24. Repetit

    Light hitting a dielectric, increase of momentum

    When light propagates in a dielectric its wavevector is given by: k = \frac{\omega n}{c} where n is the refractive index. If light propagates in vacuum n=1 the momentum is \omega / c but if light propagates in a dielectric of for example n=1.33 the momentum is increased beyond the...
  25. 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.
  26. M

    Does Inserting a Dielectric Affect Voltage and Ground Resistivity?

    1) When we insert dielectric between plates, plates can "hold" a greater quantity of charge since capacitance is increased. But when capacitance increases, does it require that voltage decreases? (From the formula C = Q/V, capacitance and charge could increase while voltage remains...
  27. S

    Dielectric Function: Relation to Frequency & Wavevector

    Hi guys: Could someone kindly explain the relation between dielectric funciton (e) and frequency, wavevetor? What is the condition for wavevector e(k=0, w), e(k, w=0) and why? Thanks a lot :smile:
  28. M

    Pleeeease Help Why a dielectric absorbs only a certain amt of field

    Pleeeease Help! Why a dielectric absorbs only a certain amt of field Hello Everyone! I am a new member in this forum.:cool: What we learn at school regarding dielectrics is: When you apply an electric field on a dielectric, the molecules of the dielectrics polarize and stretch (the...
  29. P

    Tunneling electrons through a magnetic dielectric

    Hello, I am trying to learn something about how experimental physics is done. I am very new at it and am looking for experienced guidance. A friend of mine (zapperz) suggested that a good way to measure the effect of a magnetic field on electrons in the tunneling state is to have the...
  30. D

    Capacitance Dielectric Problem

    Homework Statement A parallel plate capacitor is constructed by placing square metal sheets of side length 30 cm on either side of a sheet of polythene which is 2mm thick If the permeability of the polythene is 2.2 *10^-11 F m^-1, what is the capacitance of the system (ii)If a 50V power...
  31. L

    Dielectric material becomes conductive at High Frequency?

    Dear colleagues, I have a question related with dielectrics and their conductivity when High Frequency signals are applied. Is it possible to become conductive a dielectric material if sufficiently High Frequency signals are applied? When a high frequency signal is applied to a...
  32. A

    Searching for Dielectric Constants

    hi everybody...:cool: I'm looking for materials with dielectric constant 10,94 and 32,8... Please help me.. if you want to respect me, please send email to: alexz_lib3rty@yahoo.com Thanx...Gbu all
  33. 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...
  34. I

    Electric field inside a charged dielectric

    I've been thinking about this problem a while and can't seem to get anywhere. A charged dielectric plate of thickness t has permittivity e. The 2 surfaces each have a surface charge density +s. Obtain an expression for the electric field inside the dielectric. I think the answer is be that...
  35. D

    Parallel-plate capacitor with two dielectric between them

    Homework Statement The upper and the lower conducting plates of a large parallel-plate capacitor are separated by a distance d and maintained at potentials V0 and 0, respectively. A dielectric slab bof dielectric constant 6.0 and uniform thickness 0.8d is placed over the lower plate. Assuming...
  36. C

    How Is Work Calculated When Removing a Dielectric from a Charged Capacitor?

    A parallel-plate capacitor filled with dielectric K=3.4 is connected to a 100 V battery. After charging, the dielectric is removed and the battery remains connected. What would be the work required to remove the dielectric.I've done a problem similar to the one above, however, the battery was...
  37. M

    Lagrangian density for the EM field in a dielectric medium

    Why does the Lagrangian density for the EM field in a dielectric medium take the form d^3 \bf x \left[ \epsilon \bf E^2 - \bf B^2 \right]? I can see that the expression for Lagrangian density has units of energy per unit volume as you would expect but that's about it. Much appreciated.
  38. M

    The action integral for the EM field in a dielectric medium

    Show that the action integral for the electromagnetic field in a matter with dielectric constant \epsilon is given by S_m=\frac{1}{8 \pi} \int dt d^3 \bf x \left[ \epsilon \bf E^2 - \bf B^2 \right] where the standard expressions for the E field and B field E=-\frac{1}{c}\partial_t \bf A -...
  39. B

    Complex Dielectric Permittivity

    Complex Dielectric Permittivity! Homework Statement Calculate the power dissipated per unit cycle in a dielectric medium per unit volume in terms of the dielectric loss and the strength of the electric field The previous question was: Why does the dielectric permittivity of a material in...
  40. F

    Paralle plate capacitor (with dielectric)

    EDIT: I figured it out.Homework Statement A parallel-plate capacitor of width 2w , length L and separation d is partially filled with dielectric material of \epsilon_0 \epsilon_r . A voltage V_0 is applied. 1. Find \vec D , \vec E , \rho_S [/itex] ================ -------...
  41. S

    Energy to make a dielectric explode?

    i'm working through a homework problem. it has us jump through a few hoops. the premise is that a bunch of electrons are injected into a block of lucite (relative permittivity is supplied). the electrons are all concentrated in a given volume within the block. it asks us for the volume...
  42. N

    Formic acid and glycerin as dielectric substances

    Hello everybody I have tried to obtain but I have not been successful the dielectric strength or breakdown voltage values of following materials... these are: FORMIC ACID and GLYCERIN. (to room temperature) I need to know these values... thank you again. Norbert
  43. quasar987

    Induced charge density by non-uniform dipole density in dielectric?

    In chapter 10 section 3 volume 2 of the Feynman lectures on physics, there is a passage that I can't force myself to agree with. He says, talking about the polarization vector of dielectrics, Can someone explain this perhaps differently? I really don't see how a non-uniform polarisation...
  44. T

    Dielectric Constants from solids to pellets

    Hi, Could someone explain why when comparing a materials dielectric constant in solid form it is sometimes higher in pellet form and sometimes lower for other materials. For example, Polypropylene has a dk = 1.5 when in a solid (lump) block. This then becomes dk ~ 1.5 - 1.8 when in pellet...
  45. T

    Dielectric Cube in a uniform electric field

    Hi. Those of you familiar with the classic problem in Jackson, where a dielectric sphere (diel const = k) is placed in a uniform electric field E_0, may recall the simple expressions for the field inside of the sphere: E_in = 3/(2+k) E_out. The solution tells us that the field...
  46. 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)...
  47. T

    Aluminium Oxide as a dielectric

    Hi, I have been doing some experimentation with parallel plate capacitors, see https://www.physicsforums.com/showthread.php?t=124150" For one arrangement of aluminium plates (air as the dielectric) I was expecting the measured capacitance to be approx. 7.9pF and what I measured was 65pF...
  48. A

    Dielectric Constants & Breakdown of Various Materials

    I need a huge table of the dielectric consant and breakdown of various materials... I have looked all over the net but can only find small tables with 5-10 materials...
  49. S

    Anisotropic dielectric medium

    we have a non magnetic but anisotropic dielectric medium which has the following relationships between D and E Dx = k1*Ex, Dy = k2*Ey, Dz = k3*Ez we have to show that waves propogate in the z-dir'n at one speed only. I can't get the wave eq'n to fall out. Usually you just use...
  50. R

    Could we use flowing air as a capacitor dielectric?

    I wanted to use air as the dielectric for a capacitor for energy storage for aircraft. My thinking was that we could charge the capacitor on the ground and leave the capicitor open to the flowing air in flight. As long as the density of the flowing air remained the same, the capacitance would...
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