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. C

    Dielectric Influence on Series and Parallel Capacitors

    Homework Statement http://img99.imageshack.us/img99/763/prob45.gif Fig. 1 and 2 show a dielectric slab being inserted between the plates of one of two identical capacitors, capacitor 2. Select the correct answer to each of the statements below (enter I for `increases', D for `decreases', or...
  2. T

    Inserting Dielectric and Direction of Force on It

    Homework Statement A slab of width d and dielectric constant K is inserted a distance x into square parallel capacitor plates of side L. Determine the magnitude and direction of the force on the slab (Assume V0 is constant. Homework Equations F= d/dx(U) U=1/2CV2 The Attempt at a...
  3. B

    Parallel plate capacitor with a dielectric?

    If you have a simple circuit with only a battery and a parallel plate capacitor with a dielectric, what exactly happens when the battery is turned on? Also, if the voltage of a capacitor with a dielectric is less than the EMF of the battery, what happens to the rest of the voltage? One...
  4. D

    Power of Wavefront Penetrating Dielectric Material

    Homework Statement How large proportion of wavefront's power penetrates dielectric material's surface in a perpendicular collision from air. The only parameter that I have is \varepsilon_r = 16 where \varepsilon_r is the relative permittivity.Homework Equations \varepsilon = \varepsilon_r...
  5. C

    Finding the work done to remove a dielectric slab.

    Homework Statement A 6.8-nF parallel plate capacitor with a sheet of Mylar (κ = 3.1) filling the space between the plates is charged to a potential difference of 160 V and is then disconnected. (The initial capacitance including the dielectric is 6.8 nF.) (a) How much work is required to...
  6. D

    Detecting resonance Q factor with a change in dielectric properties.

    I have seen some examples where a system has a resonance frequency, and, when the system changes, its Q factor also changes, and so the resonance frequency shifts, and this shift can be measured to detect the change in the system. An example I can think of is very sensitive mass measurement...
  7. K

    Paralell Plate Capacitors and Dielectric

    Homework Statement Two parallel plates, each having area A = 3118cm2 are connected to the terminals of a battery of voltage Vb = 6 V as shown. The plates are separated by a distance d = 0.35cm. You may assume (contrary to the drawing) that the separation between the plates is small compared...
  8. H

    Dielectric Resonators, Resonant Frequency, and Dielectric Constant?

    Hello, I have been trying to better understand the effects of dielectrics in resonant cavities. I read that the addition of a dielectric in a resonant cavity will reduce the resonant frequency of the cavity. My questions: Is there any relation to the reduction of the resonant...
  9. Z

    Conducting sphere surrounded by insulator with dielectric constant

    Homework Statement A conducting sphere of radius A has a charge +Q on it and is surrounded by an insulating material whose dielectric constant varies with radius according to εr = 2exp[-(r/a-1)]2. The dielectric has a spherical outer boundary B. Find the values of D, E, P, ρ as a function of...
  10. sunrah

    Dielectric sphere in constant E-field

    Homework Statement Given a dielectric sphere with relative permittivity = ε in a homogeneous E-field: \vec{E_{0}} = E \vec{e_{z}}. The E-field causes a homogeneous polarisation (dipole density) of \vec{p} = \frac{vec{P}}{V} with big P the dipole moment vector. The total electric field...
  11. E

    Force between capacitor plates, partially filled with dielectric

    So for just vacuum in between one could say F=q*E = (σA)*(σ/2ε0) = A*σ^2 / (2ε0) Alternatively, F = dU/dx, where x is the separation. U = 1/2 CV^2 = 1/2 QV = x*A*σ^2 / (2ε0). To get V, we just add up pieces of E-field*distance. But now let's say part of x is a dielectric of thickness t...
  12. Q

    Consider a long cylindrical dielectric shell of inner cross-sectional

    Homework Statement consider a long cylindrical dielectric shell of inner cross-sectional radius a , outer radius b, and constant volume charge density raw zero . THe potenials of the ineer and outer surfaces of the cylindrical shell are held at potentials 0 and V respectively as shown in the...
  13. M

    Calculating Dielectric Strength between plates

    I know that I should do my homework, but I lost all my notes because of the flood brought by "Sendong" a storm in the Philippines. I just need the equations to be used to solve the problem that was given to us. So here it is: A parallel plate capacitor has a capacitance of 7MF when filled...
  14. M

    Dielectric Function Explained Physically

    i was reading Random Phase Approximation and encouter with dielectric function ε(q,ω)= 1- v(q) ∏(q,ω) where v(q) is coulumb potential and ∏(q,ω) is density-density correlation function without coulumb interaction now i do not understand this dielctric...
  15. H

    Question about capacitor voltage and inner dielectric effects?

    A capacitor is connected to a HVDC power supply which provides a minimal current. When the volage reaches the capacitor plates the dielectric material in the capacitor polarizes. Now, if there existed a barrier between the dielectric and the capacitor plate the capacitor could theoretically...
  16. T

    Dielectric constant refractive index relationship

    hi, i have seen on another topic here that the refractive index equals the square root of the dielectric constant. from datasheet values we have... water refractive index = 1.333 dielectric constant = 80.1 Without even doing the calculation its obvious that the square root of 80.1 is not...
  17. 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...
  18. H

    AC Applied to a capacitor and dielectric effects?

    Hi all, An electrolytic capacitor has 2 AC sources connected to it, 1 at each plate. The AC sources are 180 degrees out of phase and have a high impedance which limits current in the nA range. Even though each plate should have AC on it which is 180 out of phase the voltage at each plate...
  19. H

    Dielectric Polarization and leakage effects?

    When the dielectric in a capacitor polarizes does it effect the leakage current through the dielectric? Just wondering, if you had a capacitor with a lossy dielectric and you were able to polarize the dielectric would the leakage current drop? Can anyone give me any links for further...
  20. F

    Dielectric materials in Optical Traps

    Why are optical traps constructed using beads that are made of dielectric materials? What property of dielectrics is being employed here? Would a non-dielectric material still experience radiation force from photons? Thanks!
  21. I

    Infinite sheet of dielectric

    Here is the problem from I.E.Irodov's Basic laws of electromagnetism. An infinitely large plate made of homogeneous linear isotropic dielectric with dielectric constant \epsilon is uniformly charged by an extraneous charge (see footnote) with volume density \rho > 0.The thickness of the...
  22. T

    Force on a dielectric inside a capacitor and conservation of energy

    The problem is as follows: Two long coaxial cylindrical metal tubes (inner radius a, outer radius b) stand vertically in a tank of dielectric oil (susceptibility χe, density ρ). The inner one is maintained a potential V, and the outer one is grounded. To what height (h) does the oil rise in the...
  23. M

    Why Does Voltage Drop When a Dielectric Is Inserted in a Capacitor?

    Homework Statement This was done on my Physics II class, ans the Professor has'nt want to explain it to usA 2 Circular Metallic Plate Capacitor, maybe of a diameter of 15cm, was connected to a constant sourch of DC voltage until it was charge to 10Volt, after this the source was DISCONNECTED...
  24. E

    Dual plate capacitor with two dielectric slabs

    Homework Statement Dual plate capacitor with two dielectric slabs placed between the capacitors and a battery supply's a voltage across the capacitors. The slabs are not equal in dielectric permeability. What is the charge at the interface of the two slabs? Homework Equations The...
  25. B

    Lorentz model and dielectric

    Hi I read in text for calculation dielectric constant in Lorentz model, we only regard electric field that coupled with each oscillator. So the magnetic field of input wave has no effect in calculation of dielectric constant in this model?
  26. M

    Metal Sphere surrounded by dielectric

    It is Example 4.5 in Griffiths intro to Electrodynamics. A metal sphere of radius a carries a charge Q. It is surrounded, out to radius b, by linear dielectric material of permittivity epsilon ... He goes on to say that E = P = D = 0 inside the sphere. I understand that D = 0 inside, but...
  27. E

    Capacitor separated by a dielectric

    Homework Statement REFER TO ATTACHED SCREEN SHOT Homework Equations The Attempt at a Solution My discrepancy is with the last question labeled "Exercise" (What is the maximum energy that can be stored in the capacitor?). Since the max voltage is 16000V = 16000 J/C, why is...
  28. Telemachus

    Concentrical conducting spheres with charge distribution and dielectric

    Hi. I have this problem, which I must solve. It says: two concentric conducting spherical shells, of radius a and b (a<b), are charged at Q and -Q respectively. The space between the spheres is filled at its half by an hemisphere of dielectric with dielectric constante ε. a)Find the field for...
  29. J

    Variable dielectric capacitors

    Good day All: How can I prove that a linear relationship exist between the displacement (d) and the capacitance(C) of a Variable dielectric capacitor? I know that the equation for a capacitor's capacitance is: C= εA/d
  30. 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...
  31. 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...
  32. M

    Magnetism dielectric crystals

    What is origin of magnetism in dielectric crystals?
  33. B

    Resolving an Infinite Sheet of Charge in Dielectric Material

    Hi everybody, I am getting confused by a very simple problem: let's take an infinite sheet electrically charged with a surface density σ. Because the sheet is infinite, we can first determine that the electrical field on both side contains only components normal to the sheet. If the plate is...
  34. S

    Removal of dielectric from a charged capacitor.

    There is a parallel plate capacitor having capacity C. It initially has got no charge on it. Now we insert a dielectric material of dielectric constant K between its plates (it still has no charge). Now we connect this capacitor (with dielectric) to a d.c source of potential difference V. Now...
  35. jegues

    Dielectric Sphere with Free Volume Charge

    Homework Statement See figure attached. Homework Equations The Attempt at a Solution I'm confused as to how they got their D(r) Using Gauss' Law, For r < or = a \oint_{S} \vec{D} \cdot \hat{n} dS = \int_{v} \rho dv D(4 \pi r^{2}) = \frac{\rho 4 \pi r^{3}}{3}...
  36. D

    Electrostatic force between point charge and dielectric ball.

    At a certain distance from a point charge q there is small, dielectric ball. How would change the value of electrostatic force acting on the ball, if the value of a point charge would be doubled? According to F=k[(q1*q1)/r^2] there would be no force on the dielectric ball, because his resultant...
  37. K

    Finding Electric Field of Charged Dielectric Sphere

    Homework Statement There is a charged dielectric sphere of radius R. I center it at the origin of an x,y,z cartesian system. It has a charge density rho=3Qcos(theta)/4*Pi*R^3. Q and R are given. I need to find the Electric field at a point that is outside the sphere. Homework...
  38. 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...
  39. M

    Infinitesimally small dielectric layers in a capacitor

    I have a parallel plate capacitor with a dielectric inside whose relative permittivity varies as εr = βexp(\alphax) [a theoretical calculation, I have not measured this directly] Eventually I want to calculate the capacitance of the system. First I need to calculate the \overline{D}...
  40. E

    Anisotropic Dielectric Media Transition

    Hey, I was going over my electromagnetics course material and I realized we didn't learn much about anisotropic mediums (and still we had some homework questions about them). I'm trying to find some information about transition between anisotropic mediums, or even to be more specific -...
  41. M

    Capacitance of a capacitor with dielectric of variable dimensions and constant volume

    Homework Statement Homework Equations \int\vec{E}\cdot\vec{dA}=\frac{Q_{enc}}{\epsilon_{0}} \int\vec{E}\cdot\vec{dA}=\frac{Q_{enc}}{k\epsilon_{0}} V=\int\vec{E}\cdot\vec{dS} C=\frac{q}{V} C_{eq}=C_{1}+C_{2}+... \frac{1}{C_{eq}}=\frac{1}{C_{1}}+\frac{1}{C_{2}}+... The Attempt at...
  42. C

    One dimensional medium with 2 different dielectric constants

    I just got this question on a classical mechanics assignment... and unfortunately I know NOTHING about dielectric materials (never been introduced to me for some reason >.<). I don't even know why this is on my classical mechanics assignment but it is anyway. And btw there is a disclaimer on the...
  43. A

    Perturbation of a uniform electrostatic field by a dielectric cube

    Hi, Is there any way to analytically calculate the perturbation of a uniform electrostatic field by a dielectric cube. I know a solution exists for dielectric spheres but I haven't been able to come across the solution, when dealing with a cube. Ohh.. and I'm assuming the simplest case...
  44. C

    Measurement of capacitance of dielectric film using front contants

    Hi, I have deposited a film of dielectric on SiO2 substrate. Then, deposited metal dots on the top of dielectric film to measure electrical properties. I want to measure capacitance using metal dots on the top of dielectric. Since I have SiO2 as a substrate, I can not make a parallel plate...
  45. C

    Measurement of capacitance of dielectric film using front contants

    Hi, I have deposited a film of dielectric on SiO2 substrate. Then, deposited metal dots on the top of dielectric film to measure electrical properties. I want to measure capacitance using metal dots on the top of dielectric. Since I have SiO2 as a substrate, I can not make a parallel...
  46. 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
  47. F

    Free Charges in a Dielectric Sphere

    Why is it that a dielectric sphere containing free charges, uniformly distributed throughout, has a net electric field? If the sphere is electrically neutral, then all the charges should cancel out, and since the free charges are uniformly distributed, I don't understand why there should be an...
  48. S

    Dielectric objects in electric field

    Hello, This is simple question, but I didnt find the clear answer e.g. on the web pages: How Faraday cage works in electric field is clear. 1. The metal blown sphere = faraday cage in electric field - inside the sphere is not electric field. 2. But how is it when the blown sphere is...
  49. J

    How Can I Calculate the Dielectric Susceptibility of Silicon Correctly?

    Hi everybody, i'm trying to calculate the dielectric susceptibility of Silicon (Si) using the formula \chi_{\vec g}=S(\vec g)(-\frac{\omega_p^2}{\omega^2})\frac{F(\vec g)}{Z}e^{-M} where S(\vec g) is the structure factor, \omega_p is the plasma frequency, \omega is the frequency...
  50. X

    Understanding Dipole Behavior in a Dielectric Medium

    Homework Statement A dipole p is situated at thecentre of a spherical cavity of radius a in an infiite medium of relative permitivity \epsilon_r . show that the potential in the dielectric medium is the same as would be produced by a dipole p' immersed in a continuous dielectric, where...
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