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. D

    Dielectric constant of the materials, k

    Homework Statement C1 = 12uF, C2=20uF, and the capacitors are charged so that the voltage across each capacitor is 6V. When a dielectric material is inserted between the plates of C1, the charge on C2 changes by 32 uC. Calculate the dielectric constant of the material, k. (PS. C1 is parallel...
  2. E

    Is the Electric Field Inside a Hollow Dielectric Sphere Zero?

    Homework Statement I am asked to find if there exists an electric field of a hollow dielectric field at a sphere is 0 and proof it.Homework Equations The Attempt at a Solution I've drawn this picture: http://img19.imageshack.us/img19/2295/hollowp.th.jpg \omega \rightarrow 0 \delta q...
  3. E

    Electric field inside hollow dielectric field

    Homework Statement How do I proof that the Efield inside a hollow dielectric sphere is 0? Homework Equations The Attempt at a Solution
  4. J

    Electric Field inside and outside of Dielectric sphere

    Homework Statement A dielectric sphere of radius R has a uniform permanent polarisation P. Determine the electric field both inside and outside the sphere. (Hint: Since div P = 0 everywhere, the electrostatic potential satisfies Laplace's equation. Do not assume that the sphere is...
  5. G

    Calculating the Capacitance of a Semicircular Dielectric Capacitor

    Homework Statement http://nplq1.phyast.pitt.edu/res/westwolf/bookauthor/Capacitors/circle.jpg We use two circular metal plates of radius 0.55 m and thickness 8.7 mm to build a capacitor. We leave a gap of 2.5 mm between the plates and fill half of the space between the plates with a medium...
  6. S

    Dielectric constant for aliminium nitride

    I know that a dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space. It is an expression of the extent to which a material concentrates electric flux, and is the electrical equivalent of relative magnetic permeability. or in english terms: A...
  7. J

    The Relationship Between Dielectric Function and Joint Density of States

    Hi. I have been looking at some lecture notes. What is not so clear for me is, how the imaginary part of the dielectric function is related to the joint density of states. Is the "amplitude" of the epsilon2 directly proportional to JDOS? or is JDOS some kind of derivative of epsilon2? Thanks
  8. R

    How Does Inserting a Dielectric Affect Capacitor Voltage?

    Homework Statement An empty capacitor is connected to a 12.0-V battery and charged up. The capacitor is then disconnected from the battery, and a slab of dielectric material (K = 2.8) is inserted between the plates. Find the amount by which the potential difference across the plates changes...
  9. J

    Inhomogeneous Dielectric Question

    Homework Statement The space between two long coaxial conducting cylinders is filled with an inhomogeneous dielectric. Show that the E field can be made independent of position between the cylinders by an appropriate choice for the radial variation of the dielectric constant.Homework...
  10. C

    Leakage Current in Dielectric & Current-Temp Relation

    1. Is there any formula for calculating the leakage current carried by a dielectric in a capacitor? 2. A battery-powered light bulb has a tungsten filament. When the switch connecting the bulb to the battery is first turned on and the temperature of the bulb is 20 ^\circ {\rm C}, the current...
  11. N

    Electromagnetism question (Stump book) - Dielectric

    Ok this book is very common. It's the question number 6.5 A dielectric object that has a quasi-permanent polarization when the applied field is 0 is called an electret. Consider a uniformly polarized electret in the shape of a cylinder of height h and radius 10h. The polarization in the...
  12. A

    Can electrons deposit on a dielectric?

    Hi I have a question about the interaction of electrons with a dielectric matter; I am not sure if electrons can deposit on the SURFACE of the dilectric(specially ferroelectrics) matter or not (without penetrating into the matter).
  13. F

    A dielectric in side a spherical shell

    Assume that there is a spherical dielectric inside spherical shell. There is a vacuum between the dielectric and the shell. I found this configuration rather tricky. Any idea ? http://img117.imageshack.us/img117/5901/conductorly3.th.jpg...
  14. G

    Rotating dielectric sphere : Jackson 6.8

    Homework Statement I'm working at the exercise 6.8 of Jackson's Classical Electrodynamics. Here it is : We consider a dielectric sphere of dielectric constant \epsilon and of radius a located at the origin. There is a uniform applied electric field E_0 in the x direction. The sphere rotates...
  15. F

    Different dielectric material with different relative permittivity

    I am wondering how to different dielectric material with different relative permittivity behave when put together. Say i have two concentric sphere and the space between them is filled with a dielectric of relative permittivity A from the outer surface of the inner sphere to the mid point...
  16. E

    Bound charge inside and outside a dielectric

    Homework Statement A conducting wire of length a and charge density lambda is embedded inside a dielectric cylinder of radius b. To Show: a) Bound charge on the outer surface is equal in magnitude to the bound charge inside the surface. b) volume density of bound charge is 0 in the...
  17. F

    Bound and Free Charge in conductor and dielectric

    I am reading an electrodynamics book to grasp the concept of bound and free charge, esp in conductor and dielectric. I got lost with the text on the book. Can anyone please help me understand the concept well?
  18. Q

    Electric field with dielectric constant

    Homework Statement Two 5.0mm*5.0mm electrodes with a 0.10mm thick sheet of Mylar between them are attached to a 9.0 V battery. Without disconnecting the battery, the Mylar is withdrawn. (Very small spacers keep the electrode separation unchanged.) Dielectric constant for Mylar is k=3.1. What...
  19. I

    Potential of a Dielectric sphere and an exterior point charge.

    Consider a sphere of radius a with dielectric constant epsilon. A point charge q lies a distance d from the center of the sphere. Assume d > a, calculate the potential for all points inside the sphere, and outside the sphere. The problem is to be solved with an expansion of Legendre...
  20. S

    Effect of Dielectric Material on Electric Field in a Parallel Plate Capacitor

    Homework Statement A fully charged parallel plat capacitor remains connected to a battery while a dielectric is slid between. Does the electric field increase, decrease, or remain the same? The Attempt at a Solution Don't know this one or how to show it. I know that potential...
  21. C

    Dielectric constant and strength

    Hey all, I am currently working on a project with high voltage and wood. I have these values for dielectric constants of certain woods, but I can't seem to figure a way to convert this dielectric constant into dielectric strength. Anyone have a clue?
  22. J

    Capacitors With and Without Dielectric

    Homework Statement Two parallel-plate capacitors A and B are connected in parallel across a 620.0 V battery. Each plate has area 100 cm2 and the plate separations are 4.5 mm. Capacitor A is filled with air; capacitor B is filled with a dielectric of dielectric constant 2.2. A)Find the...
  23. M

    E (with dielectric) = E (w/o dielectric) – Ei =E/k

    1. E (with dielectric) = E (w/o dielectric) – Ei =E/k what is E then? Original Electric field? But I thought the original one was E without dielectric? Do these two both refer to the same electric field? 2. Whether it's "First the wave theory" or any questions relating to wave in high school...
  24. R

    Gauss Law: Dielectric Homework - Find Electric Field and Polarization Charge

    Homework Statement A positive charge q is in the center of an espheric hole of radius R inside a dielectric material with constant Ke. Find the electric field module inside the dielectric in a point very near to the hole surface and the polarization charge over the surface. Homework...
  25. A

    Capacitance - Dielectric Constant Relation?

    Hi, Does anyone know if there is a relation between a materials capacitance (C) and its dielectric constant (K)? Thanks,
  26. S

    Help to solve electric field lines in a dielectric

    Hi all, I am trying to solve numerically as well as model the electric field lines coming out of a electrode (not a point charge) in a dielectric medium. ANy suggestions would be greatly beneficial _________________________________________________ _ separated by d...
  27. S

    E-Field in Hollow Polarized Dielectric

    Homework Statement Determine the electric field intensity at the center of a small spherical cavity cut out of a large block of dielectric in which a polarization P exists. The Attempt at a Solution charge densitysurface = P(dot)n --> charge densitysurface = P(dot)r This is about as far as...
  28. K

    How does a dielectric increase capacitance, conceptually.

    Hi all, I'm a little stumped with how the dielectric increases capacitance. The general solutions all involve using the formulas, but don't really treat it conceptually. I realize that inserting a dielectric decreases field strength, and hence decreases the voltage across the capacitor. But...
  29. C

    Spherical Cavity in Dielectric Subject to Uniform Field

    Homework Statement The polarization charge on the surface of a spherical cavity is - \sigma_e cos(\theta) at a point whose radius vector from the centre makes an angle \theta with a given axis Oz. Prove that the field strength at the centre is \frac {\sigma_e}{3 \epsilon_o} parallel to...
  30. A

    Temperature Dependence of Dielectric Constants

    Does anyone have information on temperature dependence of dielectric constants? I haven't been able to find anything general enough on Google. I'm particularly interested in Polyethylene, Teflon, and Air but a general description would also be appreciated.
  31. F

    Longitudinal acoustic phonons: why does the dielectric function vanish?

    Hi everybody, In chapter 10 of Kittel's "Introduction to Solid State Physics" it is said that the zeros of the dielectric functions determine the frequency of the longitudinal modes of oscillation, \epsilon(\omega_L) = 0, Eq. (17). Am I missing something or this is actually an "unproved claim"...
  32. T

    Dielectric Compacitors Confirmation

    Dielectric compacitors can contain 1 or multiple dielectrics, if we say have a capacitor with 3 dielectrics between the two plates. We can model it as 3 capacitors in series. Since we know that Capacitors in series the equivalent is (1/Ceq) = (1/C1)+(1/C2)+(1/C3) Wouldnt the overall...
  33. A

    Dielectric Sphere in Field of a Point Charge

    Hi, I have derived the electric potential equations inside and outside the sphere due to a point charge q placed a distance b way from the sphere's center. The potentials are given by: \Phi_{in}(r,\theta) = \sum^{\infty}_{n=0} A_{n}r^{n}P_{n}(cos\theta) and \Phi_{out}(r,\theta) =...
  34. A

    Dielectric Sphere in Electric Dipole

    Hi, I am aware that the effects of a dielectric sphere in a uniform electric field have been done in many introductory electromagnetism books. Is anyone ware of a similar problem where the uniform electric field is replaced by a dipole field? Would solving such a problem for the resultant...
  35. C

    Inserting a dielectric onto a capacitor and finding capacitance as a fxn of x

    I'm not too fond of writing the math down here, so I need only those who know their circuits to reply. Battery connection is maintained with one capacitor. du goes up as you insert a dielectric dc goes up dq goes up However, foe those who've done the thinking and solution...we find...
  36. L

    Understanding Dielectric Constants and Their Impact on Capacitance

    The higher the dielectric constant, the higher the capacitance right? I am reading that water has a dielectric constant of 80. This means the capacitance is 80 times greater (if there was water between the parallel plate capacitor) than if the capacitor was in vacuum. What is the...
  37. T

    Gas/Fluid Dielectric: Seeking EE Help for Variable Dielectric Constant

    Hi! First time poster seeking some EE help. I'm looking for a gas or a fluid that has a dielectric constant that can be varied by some sort of means(physical). Something in the area of changing the pressure. I will be sending microwaves in the 10-20Ghz range through this gas/fluid, so as...
  38. S

    Finding dielectric constant

    Homework Statement an air gap capacitor is charges with a 50 volt battery. the battery is then disconnected and oil is introduced between the plates. the potential difference between the plate drops 10 volts. a) what is the dielectric constant? b) what fraction of the original stored...
  39. S

    Parallel plate capacitor and dielectric

    Homework Statement a parallel-plate capacitor (2 plates) is filled with titanium dioxide which has a dielectric constant of 80. the area of each plate is 1 cm^2. a) what must be the spacing between the plates if one wishes to make a 10^-10 farad capacitor? b) if the dielectric strength...
  40. O

    Energy of a Capacitor in the Presence of a Dielectric

    An dielectric-filled parallel-plate capacitor has plate area A and plate separation d. The capacitor is connected to a battery that creates a constant voltage V. The dielectric constant is K. A. Find the energy U_1 of the dielectric-filled capacitor. The capacitor remains connected to the...
  41. S

    Capacitors with dielectric oil

    Homework Statement a 5 microfarad capactior and a 10 microfarad capacitor are connected in parallel across a 50 volt battery as shown. the battery is disconnected and the two capacitors are separated from one another without altering the charge on either one. oil with a dielectric constant of...
  42. A

    Capacitance of parallet plate with dielectric spheres in between

    I want to calculate the capacitance of a system consisting a parallel plate and dielectric spheres of different radius and dielectric strength in between the plates. please give some mathematical derivation. I really need to know it,my career depends on it. Please help me. :) thanks &...
  43. P

    Parallel-plate capacitor: Two dielectric materials

    [SOLVED] Parallel-plate capacitor: Two dielectric materials Homework Statement A parallel-plate capacitor with area A = 5.56 cm^2 and separation d = 5.56 mm has the left half of the gap filled with material of dielectric constant K1 = 7.00 and the right half filled with material of...
  44. S

    Dielectric and force between charges

    Homework Statement 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), what would be the force between the charges now? The attempt at a solution it seems like it...
  45. morrobay

    Index of refraction = sqrt dielectric constant

    Can someone explain in terms of electric fields how the index of refraction squared = the dielectric constant of the material ?
  46. T

    What is the physical explanation and results for a negative dielectric constant?

    Hi Guys, I was reading about plasmons on wikipedia and I found that there are some materials with negative dielectric constant, what I know is that there are complex dielectric and reflection coefficient constants due to reflection in metals, can we relate the the complex dielectric constants...
  47. S

    Dielectric with a parallel-plate capacitor finding minimum area

    The dielectric to be used in a parallel-plate capacitor has a dielectric constant of 3.70 and a dielectric strength of 1.90×10^7 V/m . The capacitor is to have a capacitance of 1.05×10^−9 F and must be able to withstand a maximum potential difference of 5600 V. What is the minimum area the...
  48. R

    More than one dielectric ibetween a parallel plate capacitor

    Hey, I am having some troubles with this question, the question asks me to calculate the capacitance of a parallel platecapacitor where the plates are separated by 3mm, and in between the are three layers of dielectric 1mm thick with different relative permitivities. Do I find the total by...
  49. I

    Water as a dielectric in capacitors

    "water" as a dielectric in capacitors Homework Statement Why do you think water is not commonly used as a dielectric in capacitors? K=80.4 *K=dielectric constant for water thx for any help
  50. 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...
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