Questions tagged [dielectric]

This tag is for questions relating to a non-conducting material called dielectric (or dielectric material). Dielectrics are very much important to explain various phenomena in various fields of physics like solid-state physics, optics, electronics, cell biophysics, etc.

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27 views

Confusion from Griffith's Electrodynamics

In Griffith's Electrodynamics chapter 4: Electric Field in Matter - when he derives the Gauss's Law for dielectric he just ignores the surface-bound charge and gives the reason for doing it as It may ...
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1answer
28 views

Surface charge on dielectric interface

What I have in mind is a system that consists of a capacitor filled with two dielectric materials, one of them with dielectric constant $\kappa_1$ and the other with $\kappa_2$. The capacitor is ...
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15 views

Transmission through a smoothly varying medium

I'm looking for references regarding the transmission of EM waves through objects whose optical parameters vary smoothly. I know how to solve the equations, but I'm looking for physical intuition ...
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1answer
42 views

How is dielectric constant both $E_{net}/E_o$ and $ε/ε_o$?

The questions asks that, given the (surface) charge density (σ) on the plates of a parallel plate capacitor and dielectric constant (k), what would be the magnitude of induced charge density on the ...
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29 views

Why do Green functions show up in treating dielectric media microscopically?

I'm reading the treatment of Thomas-Fermi screening in Ashcroft and Mermin (ch. 17). They write some strange equations which I've never seen before, anywhere. First of all, they write the usual local ...
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17 views

Electrostatic Induction Metal vs Insulator

If we have a small dielectric sphere and a point charge, they will experience an attractive force due to electrostatic induction. Likewise, if we have a small metallic sphere and a point charge, they ...
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Visualizing the dielectric profile between a conductor and an dielectric during wave equation derivation

I was deriving the wave equation for a conductor and a dielectric medium. While solving it considered the dielectric constant with negligible variation over distances on the order of one optical ...
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2answers
39 views

Confusion about Electric Permittivity

I have learned about electric permittivity in two contexts: How much a medium reduces the strength of the electric field (Like if I have a charged ball inside a vat of oil, the oil will polarize and ...
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1answer
46 views

Electric field lines definition question

I have a question about the definition of electric field lines. Do they refer to $\mathbf E$ or $\mathbf D$, where $\mathbf D = ε_0 \mathbf E + \mathbf P$ ? So when I'm plotting an electric field's ...
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14 views

How does the dielectric breakdown of air change with Temperature, Humidity and Pressure?

I've done a lot of online research but the results I've found are't great, and sometimes even contradict each other. Are you aware of any paper describing this change? Starting from wiki, that ...
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9 views

Pressure increment in the gap between two parallel plate capacitors

What is the pressure increment in the gap between two parallel plate capacitors when they are immersed in water horizontally with a constant voltage of 500? Take dielectric constant = 81, distance ...
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1answer
25 views

Do surface charges exist when EM wave gets reflected by dielectric boundary?

If both the materials on a boundary are dielectric then do surface charge exists. While soving for reflection coeffecient it wass sufficient to satisfy tangential componenta, I was solving using ...
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1answer
341 views

A question about electronic polarizability [closed]

I am having trouble with this question. The question is: Carbon tetrachloride contains 74 electrons in its molecule. Its relative permittivity is 2.26 when its density is 1.6810^3 kg/m^3. If the field ...
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24 views

Electric Field Outside a Conductor and Dielectric

I know that an electric field just outside of a conductor is E = local surface charge density / epsilon_0. If the surroundings of the conductor is a dielectric with permitivitty epsilon_1, does the ...
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1answer
66 views

Find electric field $\vec{E}$ on the axis of a uniformly polarized cylinder

I have a uniformly polarized infinite cylinder of radius $a$ whose axis lies along the $z$ axis with polarization vector $\vec{P} = P \vec{u_x}$, where $\vec{u_x}$ is the unit vector towards the $x$ ...
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7 views

Set the boundary conditions for the electric field at the separation surface between a dielectric and an ideal conductor?

In an ideal conductor (sigma goes toward the infinite), there can be no electric field within it. But neither can there be a tangential component on its surface. Based on this, set the boundary ...
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16 views

Variation of dielectric constant (relative permittivity) of air with humidity or rain days

I would like to know a value of the air dielectric constant on a rainy day or the relationship of its variation to humidity. Thank you.
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3answers
47 views

Is free space a 'dielectric'?

The physical constant $\epsilon_0$ is usually called "permittivity of free space" or "vacuum permittivity". Griffiths says: I dislike the term, for it suggests that the vacuum is ...
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1answer
21 views

About the electric field in a dielectric and the capacitor plate

Why is the electric field caused by the induced surface charges in the dielectric less than the electric field caused by the conductor plates in a capacitor?
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36 views

Feynman diagram

I am having trouble understanding how the Feynman diagram represents the dielectric medium and its interference on the screen of the charge of the electron. The diagrams are as follow: Could you ...
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18 views

Why can't all plastics form electrets?

What property should a dielectric need to become an electret? At first, I though polar dielectrics formed electrets, but non polar dielectrics like polypropylene also form electrets. So what property ...
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10 views

Inconsistency in the Energy of polarized linear dielectric

There is apparent inconsistency in Griffiths' interpretation of the energy of polarized dielectric. Griifiths says there is some extra energy contained in the "springs" that hold the dipoles....
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1answer
138 views

Average field inside a sphere

Griffiths, problem 3.47: show that the average field inside a sphere of radius R, due to all the charge within the sphere, is $$\langle {\bf E} \rangle = - {1 \over 4 \pi \epsilon_0} {\bf p_{\tt tot}\...
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1answer
45 views

Uniformly polarized sphere

The electric field produced inside a uniformly polarized sphere of radius R is equal to: $$ \bf E = - {\bf P \over \rm 3 \epsilon_0}$$ It doesn't depend on the sphere radius. Does that mean... as long ...
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1answer
42 views

Conductivity from dielectric permittivity

If I have a typical Drude dielectric permittivity: $$\epsilon(\omega) = \epsilon_{\infty} - \frac{\omega_p^2 \tau}{\omega^2\tau + i\omega}$$ Now, decomposing $\Re{(\epsilon(\omega))}$ and $\Im{(\...
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1answer
36 views

Permittivity-Conductivity relationship sign problem

I have asked this question a number of times and am still uneasy with it. I want to know how somebody can derive the equation (also see above, picture from a publication): $$\epsilon(\omega)=\...
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19 views

Why in non-uniform polarisation of dielectric we take net charge density to represent charge inside the dielectric?

I have two doubts, First is why we use term net charge flow out of volume instead of positive charge like in case of uniform polarization and the charge $Q$ in eq 10.21 is net charge of volume element ...
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26 views

Does surface charge contribute in polarization of the dielectrics? [closed]

If yes, exactly how does the surface charge contribute in the dielectric polarization?
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34 views

Potential of a polarized dielectric [duplicate]

As Griffiths says: Suppose we have a piece of polarized material - that is, an object containing a lot of microscopic dipoles lined up. The dipole moment per unit volume P is given. What is the ...
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1answer
53 views

Are electric fields constant in the dielectric materials of a parallel plate capacitor?

For every example I've seen this was an assumption I have made. However with this example, I am unsure. Either the electric field is constant through the e1 dielectric meaning e2 and e3 must be equal, ...
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1answer
28 views

How is Coulomb’s constant affected when it is not in a vacuum permittivity?

How is Coulomb’s constant affected when it is not in a vacuum permittivity? And how do you determine the new value?
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21 views

How can I calculate the $D$ field when all the free charge is on a conductor embedded in a dielectric?

Let $K$ be a bounded piece of conductor, embedded in an isotropic, homogeneous, uniform dielectric of permittivity $\epsilon$. Let $ \vec r$ be a point in the exterior of the conductor. Let $\rho_f$ ...
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2answers
245 views

Griffiths on Averaging and the Macroscopic Electric Field

I am self-studying Griffiths's Introduction to Electrodynamics (4th edition) and all has been smooth sailing except for section 4.2.3 in which Griffiths argues for why we can compute (at least at the ...
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35 views

What is the magnitude of the curl of a electric field? and in general from a vectorial field?

I found the following result in a book: but I do not understand what is the meaning of the magnitude of the curl of a vectorial field? and how is this related with the amount of spatial oscillations.
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36 views

Dielectric constant or permitivity of copper

I'm trying to simulate a capacitor made of copper plates in comsol multiphysics. What is the value that I should use for the dielectric constant or permittivity of the copper plates? I've read that ...
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29 views

Dipole moment in primary polarization mechanism in a dielectric

The question I have is regarding material from an old University book I am currently reading, Chapter 13, "The Solid State", Third Edition, H.M Rosenburg. And it states that the first ...
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6 views

Are rough dielectric surfaces (for purposes of scattering) always a collection of specular surfaces?

When an EM-wave (e.g. radar $\lambda$=1cm) is incident on an extended specular surface (e.g. glass), the angular distribution of the scattering is a delta-function. That is to say, angle of reflection ...
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2answers
48 views

Why does force between plate capacitors not change when dielectric is inserted between them?

I was told in my physics class that the force does not change between the two plates but wouldnt the electric field not change between them bc it gets divided by the dielectric constant?Hence the ...
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23 views

Equation for the work done to bring in an small amount of free charge in a dielectric

Griffiths says: Suppose the dielectric material is fixed in position, and we bring in the free charge, a bit at a time. As $\rho_{f}$ increased by an amount $\triangle \rho_{f}$, the polarization ...
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3answers
75 views

Will the free charge density on a disconnected capacitor plate change if I insert a dielectric?

We have a disconnected capacitor having charge density $\sigma_{1}$ on its positive plate. Now we fill it with a dielectric as shown. Will the free charge density( the mobile charges on the ...
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1answer
26 views

Intuitive explanation for the formula of bound surface charge in a dielectric

The bound surface charge in a dielectric is given as $\sigma_{b}=\vec{P} \cdot \hat{n}$. Where $\vec{P}$ is the polarisation and $\hat{n}$ is the surface normal. Could anyone please give me a ...
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1answer
25 views

Reflectivity coefficients at dielectric interface

In the book Principles of Lasers by Orazio Svelto, at chapter 4.3 "Wave Reflection and Transmission at a Dielectric Interface", the author tells that If the wave is initially in the medium ...
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32 views

Electric field of a capacitor with a non-linear dielectric

Let's consider a parallel plate capacitor with a non-linear dielectric: The electric field between the plates will be equal to: $$E = V/d$$ where d is the distance and V the voltage between the ...
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1answer
23 views

Anisotropic dielectric media and collinearity between polarization and electric field

I am trying to understand the definition of an anisotropic dielectric media. I think I understand the definition in terms of the susceptibility tensor: $$ \begin{pmatrix} P_{x}\\ P_{y} \\ P_{z} \end{...
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34 views

Extraordinary wave [closed]

In anisotropic media, for extraordinary wave, I don't understand how can the power flow not be in the same direction as the propagation. I can't find a physical intuition for it.
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1answer
20 views

Adding dipole contribution and charge contribution to find electric potential

I'm reading a book called Teoria do electromagnetismo by Kleber-Daum-Machado Volume 1. More especifically a section about the effect of electric fields in dielectric materials, in there he describes a ...
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21 views

Dispacement current value through dielectric

Will the displacement current be multiplied by K when a dielectric is placed between the plates of a capacitor. Will its value then be K times the value without dielectric. Will it be still equal to ...
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1answer
26 views

Whats the frequency of the modes in a waveguide?

I have been able to confuse myself: I am studying the form of the modes in a rectangular waveguide: I understand that each mode has a different spatial distribution, but what I dont understand is if ...
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1answer
35 views

Dielectric material in a Waveguide

I'm in the middle of an experiment and before my final measurement I want to find out the electic properties of the material i'm working with. The question is: If I have a metallic waveguide and I ...
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36 views

Derivation of applied electric field from polarized and free charge

According to my physics book, the polarization is a consequence of the applied electric field E0. It is said that the field which produces polarization can be derived from free charges and ...

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