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. Q

    Point charge at a boundary between dielectrics

    Homework Statement A point charge Q is at the boundary plane of two infi nite, homogeneous dielectrics with dielectric constants \epsilon_1 and \epsilon_2. Calculate the electric potential, the electric field and the displacement vector at any point in space. Homework Equations...
  2. B

    2 Dielectrics in a Parallel Plate Capacitor

    So, I know what happens with the first two cases, but what if the dielectrics are on a diagonal?
  3. P

    Maximum voltage in a capacitor with 2 dielectrics

    Homework Statement We have two infinite conductor plates, with two dielectrics (with permitivities K1 and K2) put together between them so that the capacitor may be taken as two capacitors connected in series. We know that the maximum electric field for the first dielectric is Er1, and we also...
  4. K

    Capacitor filled with 2 different dielectrics

    Homework Statement Hi there, I got a little problem with this one: plate capacitor is filled with 2 different dielectrics with permittivities \epsilon_1, \epsilon_2 (surrounding environment is \epsilon_0 ) and their respective thicknesses are d_1 and d_2 . The layers are parallel to the...
  5. K

    What distinguishes insulators from dielectrics?

    what is the difference between insulators and dielectrics?::confused:
  6. S

    Distorted orbital shell when E-field applied (Dielectrics)

    Homework Statement Єr = 3.0, atomic density = 1028 atoms/m3. The mag. of the E-field is 10,000 [V/m]. Two electrons in outer orbital shell will distort with an applied E-field. If both both electrons follow some orbital path as a pair, find spacing between center of nucleus and average...
  7. M

    2 dielectrics in a parrelle plate capacitor. (i dont need answer just the intuition)

    question: so here is what my problem is. there are two dielectrics between a parallel plate capacitor. distance between the two plates is '2s' and each dielectric is 's' long. each plate has a charge of \itshape \sigma (top being pos. and bottom being neg. and doesn't give an area) how would i...
  8. K

    Confusion about Dielectrics and Potential Difference in Capacitors

    I'm reading my physics textbook right now and it states that when you add a dielectric between two capacitors you are: 1. Increasing the potential difference between the two plates. 2. Increasing capacitance by decreasing V (Q/V=C) Isn't this contradictory? I thought that V in the equation...
  9. B

    Capacitance of a parallel plate capacitor with 2 dielectrics

    Homework Statement Find the capacitance of the parallel plate capacitor with 2 dielectrics below. Given that the parallel plate capacitor has area A = WL and the separation between plates is d. The Attempt at a Solution My method is to use integration. First solve for two small...
  10. W

    Dielectrics (cell membrane)

    Homework Statement Cell Membranes and Dielectrics Many cells in the body have a cell membrane whose inner and outer surfaces carry opposite charges, just like the plates of a parallel-plate capacitor. Suppose a typical cell membrane has a thickness of 8.0×10−9 , and its inner and outer...
  11. J

    Electrostatic Clamps Using Dielectrics

    b]1. Homework Statement [/b] Electrostatic clamps are used for holding workpieces while they are being machined, for holding silicon wafers during electron beam microfabrication, etc. They comprise an insulated conducting plate maintained at a potential of several thousand volts and covered...
  12. C

    What Determines Q(free) in Dielectrics?

    Hi. The chapter is electric potentials. In dielectrics, when solving for Q(bound), Q(free) is required. What is Q(free)? Is it Q with OR without the dielectric factored in? Or is C(knot) alone? Joben.
  13. A

    Question about capacitors with dielectrics

    Say i have a capacitor and i supply it with a voltage V and after that it has charge density sigmainitial on each plate. Now i remove the voltage source and then introduce a dilectric with area A that it equal to the area of one of the plates in the capacitor to the capacitor. But this...
  14. D

    Dielectrics Table: Reccomended Functions, Packages, Values & Ranges

    I could do with a table that's shows The meduim Reccomended Functions Pakages Polorised or not Capicitor values Tollerance ranges Anything near to that would be great Thanks
  15. S

    Dielectrics in Capacitors

    [b]1. A vertical parallel-plate capacitor is half filled with a dielectric for which the dielectric constant is 1.97 (Fig. P26.70a). When this capacitor is positioned horizontally, what percentage of it should be filled with the same dielectric (Fig. P26.70b) so that the two capacitors have...
  16. J

    Capacitors with multiple dielectrics

    Ok so I know that multiple dielectrics inserted into the space between two plates one on top of the other and not side by side should be treated as capacitors in series and the overall capacitance should be calculated this way but why? I can't find the theory behind this anywhere in my text.
  17. J

    Physics Homework problem: Dielectrics

    I cannot figure out this problem...can someone help me? A 3500 air-gap capacitor is connected to a 32 battery. If a piece of mica fills the space between the plates, how much charge will flow from the battery? Express your answer using two significant figures.
  18. M

    Why does adding a dielectric to a capacitor increase its charge storage?

    I was getting ready for a test in my physics class and have a question that I cannot figure out. Why does adding a dielectric to a capacitor cause the amount of charge that can be stored to increase. I understand what a dielectric is and how a capacitor works but am just not sure why this...
  19. K

    How Does a Dielectric Affect Capacitor Voltage for Equal Energy Storage?

    Homework Statement Two capacitors are identical, except that one is empty and the other is filled with a dielectric (κ = 3.20). The empty capacitor is connected to a 11.0-V battery. What must be the potential difference across the plates of the capacitor filled with a dielectric such that it...
  20. D

    Dielectrics influence on series/parallel

    Homework Statement 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 S for `stays the same')...
  21. R

    Solving Dielectric Field Problem: Infinite Charged Plane with Two Dielectrics

    Hi. I have a problem in trying to find the field \vec E in the following situation: I have an infinite charged plane, with charge density \sigma , and two dielectrics, like in picture: http://img53.imageshack.us/img53/2301/testrb0.jpg Now, if i think of \vec D being orthogonal to the...
  22. T

    Capacitor, Dielectrics and height movement

    Homework Statement Two long coaxial cylindrical metal tubes (inner radius a, outer radius b) stand vertically in a tank of (dielectric) oil (suceptibility X-e, mass density rho). the inner one is maintained at potential V, the outer one is grounded. to what height (h) does the oil rise...
  23. R

    Multiple dielectrics in one capacitor

    Hi guys, I'm absolutely, completely and utterly stumped with this one question I've been given.. Here is the exact question: Given that you possesses the following materials: (i) two sheets of copper of uniform thickness; (ii) one sheet of mica of uniform thickness 0.10 mm and dielectric...
  24. P

    What Happens to Free Electrons in a Vacuum When Used with Dielectric Materials?

    hi everyone, I've got a question. say i have two electrode plates placed pretty close together, with two pieces of a ceramic high dielectric constant material.. x7r class ceramics for instance, in between the two plates, with a gap in the middle of these two ceramic inserts, filled with...
  25. S

    Electrochemical capacitors/ ionic dielectrics ?

    I'm reading about electrochemical capacitors here: httpCOLON//electrochemDOTcwruDOTedu/ed/encycl/art-c03-elchem-cap.htm (Website won't let me post a URL until I've made 15 posts...) Do electro chemical capacitors actually store charge indefinitely ? Or do they deplete as soon as the charging...
  26. clope023

    Capacitors with partial dielectrics

    [SOLVED] Capacitors with partial dielectrics Homework Statement Consider two parallel-plate capacitors identical in shape, one aligned so that the plates are horizontal, and the other with the plates vertical horizontal: vertical: The horizontal capacitor is filled halfway...
  27. L

    How Do Dielectrics and Resistance Affect Capacitor Networks?

    Homework Statement For the capacitor network shown in the figure attached, the potential difference across ab is 220 V. Find the total charge stored in this network. Find the charge on each capacitor. Find the total energy stored in the network. Find the energy stored in each capacitor...
  28. S

    Force between charges and dielectrics

    suppose I have a charge q at (x=-d) and a charge q at (x=+d). the force between them is q^2/(4*pi*(eps_0)*4*d^2). now, I insert a dielectric (K) between (-d/2<x<d/2), and try to calculate the force now... it seems like it would be the same but it sounds strange... If I use the D field...
  29. P

    What are the Boundary Conditions for Dielectric Interfaces?

    Homework Statement Say I have a boundary between two dielectrics then it's easy to show using a gaussian pillarbox that: D(1)-D(2)=free surface charge density=s where D(1) is the component of the first medium normal to the surface. But suppose that there's nothing else apart from two...
  30. G

    Capacitors with Dielectrics

    For a capacitor not connected to a battery, why does the voltage decrease with the insertion of a dielectric. Would it be because the net electric field between the conductors is decreased?
  31. J

    Does the Presence of Conductors Affect Interface Dielectrics in a Coaxial Cable?

    Homework Statement A coaxial cable has a line charge running through it's center with a line charge density \lambda. There is a dielectric filled between the line charge and the first conducting shell cylinder and another dielectric between the outer cylindrical shell and the inner cylindrical...
  32. I

    Capacitance of a parallel plate capacitor with two dielectrics

    [SOLVED] Capacitor with 2 dielectrics Homework Statement A parallel plate capacitor of plate area A and spacing d is filled with two parallel slabs of dielectric of equal thickness with dielectric constants k1 and k2, respectively. What is the capacitance? Homework Equations You tell me. The...
  33. S

    Dielectrics and Maximum Potential Difference

    Homework Statement The radiation detector known as a Geiger Counter uses a closed hollow cylindrical tube with an insulated wire along its axis. Suppose a Geiger tube as its called has a 1.0mm diameter wire in a tube with a 25mm inner diameter. The tube is filled with a low pressure gas whose...
  34. P

    How Does a Dielectric Material Affect Capacitor Capacitance?

    A capacitor has a capacitance of 50 pF, which increases to 150 pF when a dielectric material is between its plates. What is the dielectric constant of the material? C = 150 pF and Co = 50 pF Therefore Dielectric constant K = C/Co = 150 pF/ 50 pF = 3
  35. J

    Dielectrics scattering electromagnetic waves

    Hello everyone, First and foremost I would like to see if everyone's having a good day? (assuming you respond yes) Awsome! Secondly I was hoping someone would be able to help me understand how dielectrics work. I don't need to know everything about dielectrics. I only need to know how...
  36. R

    Why Is My Calculation of the Dielectric Constant Incorrect?

    the answer i keep getting is wrong ... help? Homework Statement Two parallel plates of area 110 cm2 are given charges of equal magnitudes 9.6 × 10-7 C but opposite signs. The electric field within the dielectric material filling the space between the plates is 4.2 × 106 V/m. (a)...
  37. M

    Capacitor with two dielectrics

    Homework Statement An air-insulated parallel-plate capacitor of capacitance C_0 is charged to voltage V_0 and then disconnected from the charging battery. A slab of material with dielectric constant \kappa, whose thickness is essentially equal to the capacitor spacing, is then inserted...
  38. N

    Confused by E=ρ/ε0 in Conductors and Dielectrics?

    A little bit of confusion: Is it not correct to write ▼. E=ρ/ε0 inside a dielectric body. As far as I know we should write ε instead of ε0.[where ε=εr*ε0] Then why do we write ▼. E=ρ/ε0 inside a conductor?
  39. B

    Attenuation constant (low-loss dielectrics)

    \alpha =\frac {\omega \epsilon \prime \prime} {2} \sqrt {\mu \epsilon \prime} My question is what exactly does the \epsilon \prime \prime term signify?? I see sections of my notes that say \epsilon \prime \prime << \epsilon , but what is it? I mean when I am trying to find the attenuation...
  40. quasar987

    Are Monochromatic Plane Wave Solutions Possible in Dielectrics with Non-Zero Conductivity?

    Let's see if I understand this correctly... In an isotropic material of conductivity \sigma \neq 0 (and charge density \rho=0, the 4th Maxwell equation has a non-null current term \vec{J}=\sigma \vec{E} so the resulting wave equations for \vec{E} and \vec{H} take the form \nabla...
  41. V

    Capacitor and dielectrics help

    This is a conceptial problem. A slab of dielectric, with a dielectric constant K between an isolated parallel-plate capacitor, is removed. The two plates of the capacitor have charges Q and -Q, which do not change when the slab is removed. Is the energy stored in the capacitor more, less, or...
  42. V

    Microdischarges in solid dielectrics

    Hi all, I'm looking for information/theories/data/phenomenology about micro discharges in dielectrics (and surfaces). I'll explain the problem: we have some conductors under a potential of ~2500V which are (of course) in contact with solid dielectrics (types of plastic, ceramics...), and...
  43. S

    Capacitors and Dielectrics of a circuit

    Two capacitors are identical, except that one is empty and the other is filled with a dielectric ( k= 5.00). The empty capacitor is connected to a 6.0 V battery. What must be the potential difference across the plates of the capacitor filled with a dielectric such that it stores the same amount...
  44. D

    Help with dielectrics, capacitors, batteries, etc

    1. can someone please explain the idea of a dielectric to me (or at least give me a link that explains it in laymans terms) - all i understand is that its placed between two capacitors and it increases their capacitance (by the factor of K). what does it do to the voltage? and the charge...
  45. K

    Capacitors and dielectrics

    I am having problems with these two questions - Two capacitors are identical, except that one is empty and the other is filled with a dielectric ( = 3.70). The empty capacitor is connected to a 18.0 V battery. What must be the potential difference across the plates of the capacitor filled...
  46. M

    How Does a Cavity and Geometry Affect Electric Fields in Linear Dielectrics?

    Here's the problem: http://img41.imageshack.us/my.php?image=efield3od.png Can anyone give me a push in the right direction? I'm really stuck on two things - how does the cavity affect the problem (the hint doesn't really help me), and what does the geometry of the problem (since I'm giving...
  47. G

    Capacitors, Electric Fields, and Dielectrics

    I have a question that is confusing me perhaps one of you can help me. If I hook up a constant potential difference to a capacitor and place a dielectric inside of it, will the electric field decrease even if the plate separation remains constant? I think that the capacitance will increase as...
  48. C

    Capacitors, Electric fields and dielectrics

    I have a nasty problem here which I have been working at for a while but keep getting rubbish answers. I have tried using: E = surface charge density/(dielectric constant * Epsilon0 (8.85*10^-12) but I get a dielectric material which has a lower dielectric constant than air. I really...
  49. J

    Gauss' Law in Dielectrics Part II

    OK I just want to start from the beginning and try to get the first part of this problem so I can get what is going on in my head and understand it. Here's the problem: A point charge q is imbedded in a solid material of dielectric constant K. A) Use Gauss's law as stated in equation...
  50. J

    How Does Gauss's Law Apply to Dielectrics with Embedded Point Charges?

    This problem is also giving me a lots and lots of trouble, and I don't even know where to begin. A point charge q is imbedded in a solid material of dielectric constant K. A) Use Gauss's law as stated in equation \oint{K \vec{E} \cdot \vec{A}} \;=\; \frac{Q_{free}}{\epsilon_{0}} to find...
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