What is Dielectrics: Definition and 154 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. Destroxia

    Parallel-plate capacitor with 2 dielectrics?

    Homework Statement [/B] The figure shows a parallel-plate capacitor with a plate area A = 5.29 cm^2 and plate separation d = 8.10 mm. The left half of the gap is filled with material of dielectric constant κ1 = 6.50; the right half is filled with material of dielectric constant κ2 = 11.4. What...
  2. V

    How Much Charge Can a Capacitor Hold Before Failure?

    Homework Statement You are building a parallel plate capacitor out of two square metal plates with side lengths of L and a thin piece of dielectric of thickness d and dielectric strength of Eb. The piece of dielectric will act as a means of separating the two metal plates. In terms of l...
  3. O

    Dielectric effects confined inside the dielectric material?

    Hi all, I am wondering how is it possible that the polarization effects of a dielectric material remain confined inside the material itself. That is: for a LIH dielectric, the equations state that the electric field inside the material is reduced by \epsilon_r. But outside the material, no...
  4. S

    Electric Fields through dielectrics

    My question is simple; yet, I can not find the answer. In the picture below, all variables are identical; the plate separations, surface area, etc. The only difference is the fact that example 1 has 2 different dielectrics. Better yet, it has a dielectric that doesn't extend the entire distance...
  5. L

    Potential of coaxial with two dielectrics?

    The question asks to find the potential of the ungrounded outer conducting sheath of a coaxial cable when the inner conductor has a voltage of \frac{220}{\sqrt{3}} kV. Coaxial conditions: i) Central copper conductor of diameter 4.8 cm. ii) Insulating layer of XPLE of thickness 2.3 cm and...
  6. J

    Normal electric field across the interface

    Dear all: The boundary condition of electric field is well know for us which illustrates that the normal component of the electric field will not be continuous across the interface between 2 dielectric material with different dielectric functions. (There is no extra fixed charge on the...
  7. A

    Electric charge in parallel plate capacitor with 2 parallel dielectrics

    Homework Statement My question is: If we have a parallel plate capacitor with 2 parallel dielectrics both taking A/2 of the complete surface, is the total electric charge equal to sum of the electrical charges in the first dielectric and the second dielectric, i.e is qtotal=q1+q2=σ1*A/2+σ2*A/2...
  8. almarpa

    Understanding the Derivation of Energy in Dielectric Systems

    Hello all. I have a doubt about the derivation of energy in dielectrics formula (Griffiths pages 191 - 192). In a certain step of the formula derivation, we encounter the following operation: (view formula below). I do not undertand that operation. Can someone help me?
  9. ShayanJ

    Parallel plate capacitor with layers of dielectrics in between

    Consider a parallel plate capacitor with layers of dielectric between its plates somehow that the interfaces between them are parallel to the plates of the capacitor. If the surface charge density on the plates of the capacitors be \sigma , gauss's law gives D=\sigma which is the same inside...
  10. STEMucator

    Capacitors in series with dielectrics

    Homework Statement A ##240 nF## capacitor and a ##4.0 \mu F## capacitor are connected in series with a ##240 V## potential difference. The ##4.0 \mu F## capacitor has a parallel plate configuration, with a surface area of ##110 cm^2## and a dielectric material between the plates. The...
  11. O

    Differential form of Gauss' theorem with dielectrics

    Hi all, I'm stuck on this incompatibility within the differential form of Gauss' thearem (or Maxwell's first equation) with dielectrics. \vec{\nabla}\cdot\vec{E}=\frac{\rho_{free}+\rho_{bound}}{\epsilon_{0}} \rho_{bound}=-\vec{\nabla}\cdot\vec{P} But with a linear, homogeneous...
  12. J

    Question about dielectrics in capacitors

    How come an insulator is put in between two capacitors? I realize it is to polarize the atoms and create a smaller electric field and hence smaller electric pressure/voltage and increase the capacitance. But why not use a conductor? Pretty much all the charge would cancel. OR am I missing a...
  13. F

    Electrostatic boundary value problem with radial dielectrics

    Homework Statement A unit sphere at the origin contains no free charge or conductors in its interior or on its boundary. It is, however, embedded in a dielectric medium. The dielectric is linear, but the permitivity varies by angle about the origin. It is constant along any radial direction...
  14. P

    What's the Difference Between Prolate and Oblate Holes?

    So I was thinking about similarities in the nature between these two which could justify similarity in the nomenclature. So, diamagnetic materials are those whose atoms do not have permanent magnetic dipols, so when you apply magnetic force on them, they create local dipole oriented...
  15. Kelsi_Jade

    Dielectrics, heat capacity and polarization

    Consider a dielecrtic with polarization P=(a+b/T)\epsilon and heat capactiy C\epsilon=A+B\epsilon, where a and b are constants. Show that B=2bV/T2 and find the isothermal dielectric constant \kappael. Use properties of G(T,\epsilon) I'm really not sure where to start with this one. Any help...
  16. M

    Capacitance 3 dielectrics sandwiched between two conductors.

    Find that capacitance of the system consisting of 3 dielectrics w/ length, l=1.0m, width, w= 1.0m and depth, d= 1.0 CM. ##k_1=1.5, k_2=2, k_3=2.5## *dimensions of conducting plates not given* Equations: Capacitance, ##C= Q/{\delta}V## Field in the dielectrics...
  17. mishima

    D and E at boundary (dielectrics)

    Homework Statement Electromagnetics, Kraus, 4th edition problem 4.7.3 The y-z plane is the boundary between 2 dielectrics of relative permittivities εr = 2 and εr = 5. For negative values of x, E = (3,0,2) V/m. Find D (magnitude and direction) for positive values of x. Homework Equations...
  18. S

    Calculate Capacitance with Dielectrics

    Hi, I need help with this. A non-conducting slab of thickness t, area A and dielectric constant κe is inserted into the space between the plates of a parallel-plate capacitor with spacing d, charge Q and area A, as shown in Figure 7.7.5(a). The slab is not necessarily halfway between the...
  19. M

    Multiple dielectrics inserted in capacitor

    Homework Statement A parallel-plate capacitor is constructed by filling the space between two square plates with blocks of three dielectric materials, as in Figure P26.61. You may assume that l >> d. (a) Find an expression for the capacitance of the device in terms of the plate area A and...
  20. fluidistic

    Capacitance of a parallel plate capacitor with dielectrics

    Homework Statement I'm asked to find 1)The capacitance 2)The electric field 3)The surface charge density 4)The polarization charge at the interface between the dielectrics. Of 2 set ups. The first one is a parallel plate capacitor which is half filled with a dielectric ##\varepsilon _1## and...
  21. C

    Dielectrics and Capacitance

    Homework Statement A parallel plate capacitor with plate area A and plate separation d=5mm is connected to a 120 Volt power supply and allowed to fully charge. A) Calculate the capacitance, stored charge, electric field midway between the plates and potential energy stored. The...
  22. R

    Electromagnetism (Dielectrics)

    Homework Statement A dielectric slab with a susceptibility ##\chi_e## rests on a conducting plate whose upper surface carries a free surface charge density ##\sigma##. Show that the polarization surface charge density ##\sigma_{pol}## on the lower face of the dialectic slab is: ##\sigma_{pol}...
  23. K

    Dielectrics Attracted to Capacitors

    I have two questions: 1) Is it in general assumed that the parallel plates of a capacitor are fixed to some surface or is there a force that counteracts the attractive force between the plates whenever one considers a typical problem involving capacitors? 2) Consider a dielectric of length L...
  24. D

    Calculating capacitance of capacitor filled with 2 dielectrics

    Homework Statement A capacitor is formed by 2 square metal plates of edge a and separated by distance d. Dielectrics of dielectrics constants K1 and K2 are filled in the gap as shown. 2. The attempt at a solution This was my initial approach: I integrated the parallel combination of...
  25. P

    Capacitors, Capacitance and Dielectrics

    Hi, So I am learning about parallel-plate capacitors. The way my book puts it is that it is basically two parallel plates of opposite polarities, separated by a distance d. In order to establish that distance, work must be done and the energy is stored as electric potential energy. From...
  26. V

    Boundary conditions with dielectrics question

    Hi all, I'm doing what should be a pretty simple problem, but some theory is giving me trouble. Basically, in this problem I have a conducting sphere, surrounded by a thick insulating layer, and then vacuum outside that. I'm attempting to solve for the potential in the insulating layer by...
  27. R

    Electromagnetism Problem (conductors, dielectrics)

    Homework Statement http://img209.imageshack.us/img209/1508/problemhd.jpg Homework Equations The Ampere law: \oint_C \vec{B} \cdot d\vec{l} = \mu_0 I_{enc} The field and flux is proportional to the current: \Phi = LI The Attempt at a Solution (a) \oint_C \vec{B} \cdot d\vec{l} = \vec{B}...
  28. A

    Solving Linear Dielectric Eqns for E & P

    Say we have a linear dielectric with electric susceptibility χe a certain free charge density ρ. By using the fact that ∫D\cdotda = Qfree-enclosed you can find the resulting electric field, because D = εE , where ε = ε0(1+χe). The above is very weird for me. It seems to me that you are...
  29. A

    What is Gauss' Law for Dielectrics and How Does it Account for Polarization?

    Inside a dielectric we have: ∇\cdotε0E = ρbound + ρfree , where ρbound refers to the fact that these charges come from polarization. We can write this as: ∇\cdotε0E = -∇\cdotP + ρfree where P is the polarization of the material. And combing the two divergence terms...
  30. H

    Information about High Frequency Dielectrics

    I have a project about High Frequency Dielectrics and I am searching everywhere but nothing found. Please I need your help to find some information that would help me in my project.
  31. M

    Understanding the Effects of Dielectrics on Capacitors

    Homework Statement When a dielectric is inserted in a capacitor, why does the charge remain unchanged while the potential decreases and capacitance increase? Homework Equations The Attempt at a Solution i'm not really about this one, but is it because the charges accumulate on the surface area...
  32. S

    A few quick conceptual questions about capacitators and dielectrics

    Homework Statement So my question is conceptual. I am trying to figure out in what direction an electron will move if it starts between two plates of a parallel plate capacitator. One of the plates is at 0V and the other is at 50V. Also, would placing a dielectric in a charged, isolated...
  33. W

    How Does Adding Different Dielectrics Affect a Capacitor's Performance?

    Homework Statement A parallel plate capacitor of area 2 cm^2 is filled with three dielectrics with constants k1=3.5, k2=1.7 and k3=8.5. The dielectrics are placed as shown in the figure, each occupying half the total area, while the volume of the first double of the other two. If the...
  34. C

    Dielectrics: What You Need to Know

    just kidding
  35. C

    Incident wave of boundary between two different dielectrics

    http://imageupload.org/getfile.php?id=171120&a=a955b8cf905480ad89ee96abfea140da&t=4f27421f&o=36BBD6199C49C981F6CC7562A37DC69B664D4F14FBA06DFCF24E9B24875233233B2BA7CB1980&n=%E6%9C%AA%E5%91%BD%E5%90%8D.png&i=1 I have just been given the question without much support so I can't even get a...
  36. T

    The two media are lossless dielectrics with n1>n2

    Homework Statement The two media are lossless dielectrics with n1>n2. If θ exceeds thtee critical angle, state how b affects the amplitude and phase of the reflected wave, and give a physical reason for your statement θ:angle between incident wave and normal line b:distance between...
  37. I

    What are the Different Types of Dielectrics?

    Hi I have some comments/questions about the terminology used for dielectrics in physics textbooks. Linear dielectric means that components of \vec{P} are linear combination of the components of \vec{E}. Homogeneous dielectric means that dielectric constant is not the function of...
  38. J

    Tough Concentric Spheres with mixed Dielectrics and a air-gap Problem

    1. Homework Statement 1. Homework Statement I have concentric spheres with mixed dielectrics. There is an air-gap between the spheres which consist of a permittivity ε0. The radius' are a, b and c and the permittivities of the dielectric portions are ε1 and ε2. An image is attached! What...
  39. J

    Tough Concentric Spheres with mixed Dielectrics and a air-gap Problem

    Homework Statement I have concentric spheres with mixed dielectrics. There is an air-gap between the spheres which consist of a permittivity ε0. The radius' are a, b and c and the permittivities of the dielectric portions are ε1 and ε2. An image is attached! What are the potentials in the 4...
  40. D

    Capacitance with Non-Uniform Dielectrics

    Homework Statement 1. A parallel plate capacitor, with plates of area A, and spacing d, is filled with a non-uniform dielectric, with a permitivity that varies as ε = ε0 + ax where a is a constant, and x is the distance from one plate Homework Equations C = Q/V I'm...
  41. L

    Spherical capacitor with 2 dielectrics.

    Homework Statement The problem is on page 40 of this PDF: http://web.mit.edu/8.02t/www/802TEAL3D/visualizations/coursenotes/modules/guide05.pdf Find the capacitance of a spherical capacitor with 2 different homogeneous dielectrics arranged concentrically.The Attempt at a Solution In that...
  42. L

    Capacitor with two dielectrics.

    Homework Statement A parallel-plate capacitor contains two dielectrics of different electric permitivities and conductivities 1 and 2, respectively (they are separated by a line with the horizontal). A voltage V is applied to the terminals, find: The free and polarization charge densities. The...
  43. Y

    Dielectrics: Guass Law & Polarization Charge Density

    here is the thing, I have understood this in dielectrics, and I know that we have a new vector field instead of E, the displacement that is not neccessarily conservative. what I was thinking is that all these books, when they want to drag this law out of the info we already had, just try to make...
  44. T

    Polarisation in dielectrics, anyone?

    I have been studying polarization in dielectrics recently. I got stuck after coming to Claussius Mossoti equation. I can't understand it's importance. I read that it is used to determine molecular structure but how exactly? I've just joined this forum, hope someone can help. :) TIA P.S: Sorry...
  45. P

    Dielectrics, Varying Reflectivity, and Polarization

    I am very curious as to why dielectrics such as water have a varying level of reflectivity depending on what angle they are viewed at. For a lake of water, what angle yields 100% (or near 100%) reflectivity? Is this angle the same as the Brewster angle? Also, why exactly is it that metals do...
  46. F

    Does a Dielectric Rod Alter the Force Between Electric Charges?

    Homework Statement Does placing a dielectric rod between two electric charges increase or decrease the total force exerted on any of the charges? Homework Equations Not really algebraic, only conceptual. The Attempt at a Solution
  47. S

    Capacitors with dielectrics

    A coaxial cable used in a transmission line has an inner radius of 0.10 mm and an outer radius of 0.60 mm. Calculate the capacitance per meter for the cable. Assume that the space between the conductors is filled with polystyrene. Kappa for polystyrene is 2.6 I have no clue how to start or...
  48. R

    Dielectrics and Capacitors, Very confused.

    Homework Statement A 25pF parallel plate capacitor with an air gap b/w the plates is connected to a 100v battery. A Teflon slab is then inserted b/w the plates and completely fills the gap. What is the change in charge on the positive plate when the Teflon is inserted? Homework Equations...
  49. Z

    Electric displacement field across dielectrics

    So suppose we have two dielectrics in contact and we want to know how \mathbf{D} varies across them, then we can use the fact that since \nabla \cdot \mathbf{D} = \rho_f and we have no "free" charges at the boundary then \mathbf{D} is continuous across it. So my question is, in Grant & Philips...
  50. S

    Calculating Oil Height Between Coaxial Tubes with Dielectric Homework

    Homework Statement Two coaxial metal tubes (placed vertically) have an inner radius a and outer radius b. They are placed vertically between a dielectric oil (with susceptibility X and mass density p). The inner tube has potential V and the outer one is grounded (V=0). How high will the oil...
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