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.
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...
I am self-studying "Physics" (Volume 3) by Halliday, Resnick and Krane, and would like to ask some questions regarding the following example given in the book (with solution). I will copy the entire example here, with solution (translated from Portuguese, because I am using a Portuguese...
Homework Statement
The polarization charge in the surface of a spherical cavity is -\sigma_e \cos\theta ,at a point whose radius from the centre makes and angle \theta with a give axis Oz. Prove that the field strength at the centre is \frac{ \sigma_e}{3 \sigma_e} parallel to Oz.
If the...
Dear All,
I have a question that is afflicting me and I would be glad if you can give me an answer. I have a dipole in vacuum put at a certain distance from the surface of a dielectric material. I know the entity of the dipole, I know the distance from the surface and I know the interaction...
Homework Statement
a dielectric of dielectric constant 3 fills three fourth of the space between the plates of a parallel plate capacitor. What percentage of the energy is stored in the dielectric.
Homework Equations
U=CV2/2
= epsilon0AV2/d.2
The Attempt at a Solution
When...
I thought capacitance was a function of geometry. So how come when we put in a dielectric in between a parallel plate capacitor it increases the capacitance. Is this because we can increase the E field in between without worrying about dielectric breakdown. Or does it have something to do with...
Homework Statement
You have a co-axial cylindrical capacitor placed in vacuum. The two co-axial cylinder tubes are made of copper. The outside tube radius a1 and inside tube radius a2, with overlapping length L; both tubes have a thickness of t. Say, the capacitor was designed to withstand 5...
say you vaporized salt and threw it in the air. Would that be enough to turn that volume of air dielectric or would the minute pockets of fresh air in among the salt molecules still block low-med voltage
Why do materials like aluminum cut down the value of the B field?
Like suppose we had an infinite current carrying wire wrapped with a cylinder of aluminum.
To find the B field we would use amperes law and the magnetic susceptibility of aluminum.
For example, when a superconductor is...
Say we have an electromagnetic wave propagating inside a dielectric material. Of course physically this material will radiate, due to the little electrons being excited by the wave (their wiggling is also the physical cause of the \epsilon \neq \epsilon_0), and oscillating dipoles radiate. And...
Homework Statement
______|______
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_____________
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^ y
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|_ _ > x
This is supposed to be a capacitor with a dielectric in a form of a wedge in it.
Known data: area A of the plates, permitivity \epsilon_r
The...
Homework Statement
A long round dielectric cylinder is polarized so that the vector P = ar, where 'a' is a +ve constant & 'r' is the distance from the axis.find the space density rho` of bound charge as a function of distance r from the axis.
Homework Equations
Gauss Law.
The...
This may seem like a dumb question, but is a dielectric constant calculated from a measured capacitance normalized to thickness and electrode area, I’m having a brain fart.
Hey,
I have a question in how one can calculate the static dielectric constant, f, of NaCl. NaCl has density of 2170kg/m3, a lattice constant a= 5.6 A and a Young's modulus Y = 40GPa. the optical dielctric costant is 2.34. I couldn't find any formulas which connect these values together. We...
I'm trying to marry the concepts from my EM course with what I've been doing in my lab course. Correct me if I'm wrong, in a plain RC circuit, when closed with a DC source, the capacitor initially acts as a short (voltage is zero across the terminals, while I is max), until after a few...
Homework Statement
The dielectric permitivity need not be a constant. Typically one can find problems where the permitivity varies, but always does so in the direction of the field. I came up with a problem that may (or may not) be solvable without the use of numerical methods.
Consider a...
Homework Statement
Consider a horizontal square plate capacitor of area 1*1 m2, capacitance in vacuum 2 uF, which contains a dielectric material with dielectric constant K=5. The dielectric slides frictionlessly and is attached via a massless string and a massless pulley to a block of mass 2.5...
Homework Statement
When a certain air-filled parallel-plate capacitor is connected cross a battery, it acquires a charge (on each plate) of 130 μC. While the battery connection is maintained, a dielectric slab is inserted into and fills the region between the plates. This results in the...
Homework Statement
A prallel plate capacitor placed in air has a plate area A and a plate separation d. It is cahred to charge Q by connecting a constant foltage source across the plates. The voltage source is then disconnected and a slab of dielectric constant K and thickness h is inserted...
if in a capacitor ,the dielectric medium is replace by higher dielectric constant material the how does the capacitance of capacitor vary and why?
thanks.
Hi everyone, first time poster, long time reader (only because you're all so clever and I feel my contribution wouldn't be all that helpful haha).
Homework Statement
A dielectric (homogeneous, isotropic, with relative permativity \epsilon_{r}) is located in the region x<0.
An infinite line...
Can renormalization of QED really be interpreted as a dielectric shielding of the vacuum by electron/positron pairs that appear and disappear out of the vacuum?
I understand that's what the Feynman diagram for the QED vertex suggests, since it's the internal fermion lines that interact with a...
The energy density function for the electric field in vacuum is
u=\dfrac{\epsilon_0}{2}E^2
And the cited textbook result for the energy density inside a dielectric is:
u=\dfrac{\epsilon_0 \epsilon_r}{2}E^2
Now, one way to reach the upper formula is to look at the energy as...
1. Homework Statement
A di-electric slab of thickness d is between two differing dielectric media (u0,e0/u1,e1/u2,e2). What is the total reflection at the first interface and transmission through the second interface of the slab. The incident wave is in the x-z plane with an angle of...
I am having trouble with a homework problem assigned by my physics professor. An infinitely long cylinder of radius a and relative dielectric constant Er is immersed in a static electric field E=Eox where x is supposed to denote a unit vector in the x direction. The cylinder is alligned on the...
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I'm trying to use the liftgarbagez equation to compute the Casimir-Liftgarbagez force between two different surfaces immersed in ethanol at a certain distance apart.
I've never used or studied this equation before, and there are some things I...
Homework Statement
Re‐write the formula E = Eo cos (k• r −ωt) for each of the three waves, in
terms of the angles θi, θr and θt and the dielectric constants ni and nt
(for the materials on the left and the right) in place of k
The incident wave is in the xy plane only as is therefore...
Homework Statement
A typical AAA battery has stored energy of about 3400 J. (Battery capacity is typically listed as 625 mA h, meaning that much charge can be delivered at approximately 1.5 V.) Suppose you want to build a parallel plate capacitor to store this amount of energy, using a plate...
While designing a microstrip, how do I calculate the effective dielectric constant if the microstrip is laid on FR4 PCB(er=4).
Whats the formula for calculating effective er?
Homework Statement
A cylindrical distribution of charge [tex]\rho=\frac{\alpha}{\sqrt{r}}[\tex]
where [ tex ]\alpha = \frac{2\muC}{m^\frac{5}{2}} [ \tex ] extends from 0 cm to 8.2 cm. Concentric with this is a dielectric shell with 4.08 of inner radius 16 cm and other radius 26 cm. What is...
Homework Statement
A parallel plate capacitor has rectangular plates measuring 44.0 cm by 30.0 cm, and can be charged to 1600 V maximum ΔV without electrical breakdown. The gap between the plates is fulled with mylar dielectric (κ=3.2). Find the thickness of the dielectric.Homework Equations...
Homework Statement
A 4.0-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 120 V and is then disconnected. (The initial capacitance including the dielectric is 4.0 nF.)
(i) How much work is required to...
Hi All,
I want help to solve a problem:
A point charge is placed at a distance 'L' from the surface of an infinite dielectric slab (permittivity: k1 and thickness 'd'). The entire region of space (outside the slab has a permittivity k2).
First, I need to solve for the energy of the system...
If I have some increased electric charge in some material which is surrounded by dielectric,
what could be a way to discharge it?Let`s say, I can`t penetrate a dielectric with grounded metal probe.
Hi All,
I want help to solve a problem:
A point charge is placed at a distance 'L' from the surface of an infinite dielectric slab (permittivity: k1 and thickness 'd'). The entire region of space (outside the slab has a permittivity k2).
First, I need to solve for the energy of the system...
Homework Statement
[PLAIN]http://img97.imageshack.us/img97/6749/kappam.jpg
Homework Equations
U = (1/2)CV2
V = V0/k
The Attempt at a Solution
(1) \Delta V_0= \Delta V <==== Electrical potential difference is constant since the battery was never removed.
(2) \kappa Q_0 = Q <=== Since the...
Can someone please explain the concept of optical losses and its correlation with the imaginary part of the dielectric function in elementary terms. I am confused.
Hey all,
I'm studying laser-matter interactions and was wondering: Is there any physical meaning to a non-vanishing polarization field with non-trivial constitutive relation but vanishing divergence? (By non-trivial I mean the constitutive equation does not stipulate that the polarization and...
Homework Statement
Ideal dielectric gas is in a container closed by a movable piston and in thermal contact with its surroundings, so is kept at constant tempertaure T_0 and pressure p_0. Inside there is a capacitor with fixed voltage and total electric field E. The gas has permittivity...
Consider having a hollow silicone tube of 7 mm diameter and a wall thickness of 1.5 mm. There are two copper foil plates that are both 64 mm^2 in area. Will a fluid, such as distilled water, passing through said tube have an measurable influence on producing a change in capacitance?
Note: k =...
Homework Statement
It is actually not a problem, but a formulation of the electric potential energy in a dielectric medium present in a book, which seems to me as inconsistent with the way it is usually defined in electromagnetism books. I can't see it as a typo or a mistake because the author...
I have a powerpoint presentation and I don't really understand this topic . I have looked up for vacuum and dielectric materials individually and separately but still there is no success.
I found one website very useful but I am not sure is this a same thing. Please help ...
I thought if it`s possible to create a device which would be a something average between
capacitor and solar cell.In solar cell we are getting non-uniform charge separation which is then used to produce current with help of low voltage electric field.Current which could be acheived in solar...
Nonlinear Dielectric Heating and more!
Hello all,
Here is an interesting query for some work I am trying to figure out. Everyone knows about dielectric heating, which is the principle on which microwave ovens operate. Without deriving the formula for the power dissipated into an object...
Homework Statement
A point charge Q is imbedded in a linear, isotropic, homogeneous dielectric medium of susceptibility X_{e}.
a.) What is the free charge enclosed by a sphere of radius R centered at Q.
b.) What is the bound charge enclosed by the sphere? How does the result vary with R? Do...
In my high school calculus-based electricity class two students and I are trying to create a demo where we set up a parallel plate capacitor and have some dielectric material inside it that we can pull out slightly, and have it oscillate into and out of the capacitor.
Some ideas we have...
Hi Everyone,
I'm told that the following formula represents Kirchhoff's current law
g_1 E_{1 n}+\varepsilon_1 \frac{\partial E_{1 n}}{\partial t}=g_2 E_{2 n}+\varepsilon_2 \frac{\partial E_{2 n}}{\partial t}
where the first term on each side is Ohm's law and the conductive current
and...
Homework Statement
I am trying to find the force acting on a charge placed a distance r0 from the center of a spherical cavity of radius a. The entire cavity is immersed in a dielectric material, epsilon2.
Homework Equations
The Attempt at a Solution
Here's my quandary: I can find the...
We derived a formula to calculate the dielectric constant for some materials. It works well for gases and some liquids. But, water has a extraordinary dielectric constant of ~80. I tried googling it up but couldn't find any place which explains (mathematically) why it's so big. The professor...