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.
870
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Difference between electric field $\mathbf E$ and electric displacement field $\mathbf D$
$$\mathbf D = \varepsilon \mathbf E$$
I don't understand the difference between $\mathbf D$ and $\mathbf E$.
When I have a plate capacitor, a different medium inside will change $\mathbf D$, right?
$\...
- 919
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4
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What is the force between two charged objects when the space between them is partially filled by a dielectric medium?
I am given two charged particles of same charge at a distance of $r$. They initially apply force $F$.
Now an infinite dielectric (of dielectric constant $4$) of width $\frac{r}{2}$ is introduced ...
- 604
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3
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Why is there no permittivity-type constant for gravitation?
When I look at electric or magnetic fields, each of them has a constant that defines how a field affects or is affected by a medium. For example, electric fields in vacuum have a permittivity constant ...
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19
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How can the refractive index be below 1 in a dielectric?
Upon checking the optical properties of different dielectrics, I found the interesting case of $Al_2O_3$. It seems to be reported with a refractive index below 1 in the infrared range of $10 - 12~\mu ...
- 4,779
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2
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Why aren't all dielectrics transparent?
Conductors are opaque because, when hit by a Maxwellian wave, the free charges on their surface create another wave which destructively interferes with the former in the region of space beyond said ...
user115153
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2
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Charge distribution on a plate of Capacitor with Dielectrics .
I had this Homework Problem with a capacitor (parallel plate) that has a group of 3 dielectrics between it like so :
Now We were asked to find the equivalent capacitance and the distance of ...
- 950
14
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1
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How does $\epsilon \mu = 1/c_m^2$ change when $\mu$ or $\epsilon$ (permeability or permittivity) is a tensor?
I've read that in some materials, $\mu$ can be a tensor, not a mere scalar. (I haven't actually dealt with tensors before, but I'm assuming for my purposes here, it is synonymous with "matrix".)
I'...
- 4,141
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2
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What is the intuition behind Kramers-Kronig relations?
I have heard that Kramers-Kronig relations constrains the real and imaginary parts of complex permittivity $\varepsilon= \varepsilon^{'} + j\varepsilon^{''}$. What is the intuition behind this ...
- 475
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7
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How does current flow in a circuit with a capacitor?
When a capacitor is connected to a battery, current starts flowing in a circuit which charges the capacitor until the voltage between plates becomes equal to the voltage of the battery.
Since between ...
- 505
11
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1
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Why do oxides form amorphous films instead of crystalline films?
If I oxidize a metal at room temperature, say aluminum, why does it form an amorphous material instead of crystalline $\rm Al_2O_3$?
- 135
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How is bound charge and free charge possible?
I am studying Introduction to Electrodynamics by Griffiths and I came along a concept I cannot seem to understand properly. The concept of free charge AND bound charge. I do not understand how we can ...
- 215
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4
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What happens when you heat vodka in a microwave?
Since ethanol has a lower dielectric constant than water would the water heat up and boil before the ethanol? Would the water transfer heat to the ethanol and, since ethanol has a lower boiling point, ...
- 91
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3
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Electric field intensity in a dielectric inside a capacitor
In the question
A parallel plate capacitor is charged from a cell and then isolated
from it. A dielectric slab of dielectric constant $K$ is now introduced
in the left half region between the ...
- 388
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2
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What exactly is breakdown voltage of air?
Most of the online sources say that the breakdown voltage of air is 30kV/cm. I've made a Cockcroft Walton multiplier and I can see the air breaking in between 17-18kV/cm. Only in a discussion at one ...
- 191
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0
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Sphere half-submerged on a dielectric
This is a classic problem in electrostatics with a twist, so I thought it could be useful for others here. I did have a problem with the integration at the end, but on general I think the idea can ...
- 1,172
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1
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Does rubber insulate lightning more effectively than air?
Last week, an Ars Technica writer was struck by lightning. He says that the 911 operators were concerned about whether or not he was wearing shoes at the time, but he didn't think it would make much ...
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Real and imaginary parts of dielectric constant vs refractive index?
So for a complex dielectric constant $\epsilon = \epsilon_a + i\epsilon_b$, the wave vector and index of refraction are related to it through $k = \frac{\omega}{c}n$ and $n = \sqrt{\frac{\mu \epsilon}{...
- 2,883
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To what direction will a compass in a magnetic medium points? The direction of $B$-field or that of the $H$-field?
Question in title.
To avoid "same direction" answers, let's assume the B and H are pointing in different direction, i.e., the magnetic permeability is not a diagonal matrix. What direction ...
8
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1
answer
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Charge over 2 layer dielectric, image method
If I have a charge $Q$ located over a 2 layer dielectric as represented:
According to the image method: the charge $Q'1$ will be located at a distance $h_1$ under the first interface and the $Q'2$ ...
7
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2
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What would be electric potential due to induced charge sphere?
We know that the potential at the center of the charged sphere (if it is conductor) would be
$$V_o = \frac{1}{4\pi E_0}\frac{+q}{x}$$
If the distance between charges is x from their center of the ...
- 1,840
7
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1
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Will a circular Gaussian beam reflected at a dielectric interface become elliptical?
I remember reading a really elegant paper many years ago about the Fresnel reflection of a narrow Gaussian beam from a dielectric interface. The paper showed mathematically that since reflection from ...
- 6,307
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2
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Microwave oven + water: dielectric heating or ion drag?
When you place a water or food in a microwave oven, it heats.
Which process commits more energy to that: dielectric heating, or ion drag i.e. resistive heating?
AFAIK, in distilled water (which is a ...
- 359
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2
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Main cause of self-charging of unshorted capacitors?
In the lab, we keep all of the high voltage capacitors shorted when not in use, and rightfully so. They tend to spontaneously charge when left for some time and become extremely dangerous. while the ...
- 2,827
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How much blue sky comes from each altitude; dependence of atmosphere's dielectric constant and isothermal compressibility with altitude?
Background
left: from this answer to Moon during the day with bright blue sky light right: from Why does Unity look transparent? below: from this answer
note Unity is the bit in the middle.
I'm ...
- 6,307
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2
answers
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How London dispersion forces come into existence out of nowhere?
I was revisiting the chapter on states of matter and one thing that bothered me was a section on London dispersion forces. This is what the textbook says:
Atoms and nonpolar molecules are ...
user249968
6
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6
answers
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Why is water not used as a dielectric in the condenser?
The dielectric constant of water is very high. Then why is it not used as a dielectric in the condenser?
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2
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Refractive index of dielectric in different frames of reference
The setup
A transparent isotropic dielectric medium moving in the negative $x'$ direction at speed $v$ in frame $S'$ is stationary in frame $S$, where it has refractive index $n$. In other words, ...
- 6,375
6
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2
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Looking for help justifying a factor of $1/2$ in Jackson's formulation of electrostatic energy in dielectric media
Electrostatic Energy in Dielectric Media
In Section 1.11 we discussed the energy of a system of charges in free space. The result obtained there,
$$W=\frac{1}{2}\int \rho(\mathbf{x})\Phi(\...
- 71
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2
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Coulomb force between two point charges in a dielectric medium
In a dielectric medium with relative dielectric constant $\epsilon_r$, what is the Coulomb force between two free point charges $q_1$ and $q_2$ at distance $r$? Is it equal to the Coulomb force in ...
- 586
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Understanding the Susceptibility Tensor
When an electric field passes through a dielectric medium, it causes polarization for the medium, and we define the electric susceptibility $\chi_e$ at some point in the dielectric as:$$\vec{P}=\...
- 2,661
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4
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Energy density with complex permittivity?
Question
What is the correct form of the energy density when we have a complex permittivity (such as in a dielectric)?
Additional information
A complex permittivity means that we have:
$$\vec ...
6
votes
1
answer
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Why is $\textbf{D}$ the response to $\textbf{E}$?
In the text Wooten, equation 2.69 shows $\textbf{D}$ being the response to $\textbf{E}$ with $\epsilon$ as the response function:
$$
\textbf{D}(\textbf{r},t) = \int d\textbf{r}^{\prime} \int dt^{\...
- 87
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9
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What is the dielectric constant of a pure conductor?
Dielectric constant is the ratio of permittivity of a medium to the permittivity of free space. How to find dielectric constant of a conductor?
- 239
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3
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What force creates electronegativity?
Electric charge is used to describe the behavior of electrons which seek to counterbalance the positive charge of protons.
But I have read about other forces which also attract electrons to atoms, ...
- 904
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2
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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 ...
- 1,065
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How is a Lichtenberg figure created?
Related: Breakdown voltage of a dielectric
When I think of the dielectric breakdown of air, an electric field of $3×10^6$ V/m is enough to accelerate initially ionized electrons created primarily ...
- 4,598
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4
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Why is capacitance increased with a dielectric rather than reduced?
So conceptually, if a capacitor is connected to a voltage source, and if you decrease the distance between two plates, the electric field in between the plates increases. This means that you can hold ...
- 525
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1
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Force on a dielectric
Why is a dielectric slab repelled when inserted between the plates of a parallel plate capacitor which is connected to a battery of constant emf?
I think that it should get repelled as when the ...
- 199
5
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1
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Vacuum permittivity and vacuum polarization
Is vacuum permittivity an effect of vacuum polarization, or are these unrelated phenomena? A more detailed way to ask this might be, is the vacuum analagous to a dielectric in that electron-positron ...
- 71
5
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1
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Energy in Dielectric Material
The total work done to build up the free charge from zero to the final configuration in the presence of a dielectric material is: $$W = \frac{1}{2}\int \vec{D} \cdot \vec{E} d\tau.$$ We got this by ...
user100411
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1
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What is the linear momentum of an EM wave in a medium?
In free space, the linear momentum density of an EM wave is given by the Poynting vector $\vec S$ over the speed of light squared, $\vec g=\frac{\vec S}{c^2}$.
In a medium, $S$ is generally not ...
- 467
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Green's function for a dielectric with a charge [closed]
Suppose there are two infinite planes, one in $z=a$ and the other in $z=b$, with $a<b$. Between the planes, there is a dielectric medium with constant $\epsilon_1$. The differential equation for ...
- 178
4
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5
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Permittivity of free space [closed]
Free space is a region in which there is no matter and no electromagnetic or gravitational field. Which means that the resistance in free space is zero, because there is no resisting force and as far ...
- 83
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4
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Why does a dielectric have a frequency dependent resistivity?
This question has come about because of my discussion with Steve B in the link below.
Related: Why is glass much more transparent than water?
For conductors, I can clearly see how resistivity $\rho\...
- 4,598
4
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3
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2k
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4
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1
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Does the Coulomb's force depend on the configuration of the medium?
I know that when two charges are placed in a dielectric medium (say water) then the force between the charges get reduced and the force equation is given by :-
$$F=\frac{q_1q_2}{(4π \epsilon_o \...
- 8,206
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2
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Can relative permittivity be less than 1?
Relative permittivity shows that force of interaction in some media is 3 times less than in vacuum ($\varepsilon = 3$) for example. When looking tables of permittivity I never saw a value less than 1.
...
- 255
4
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2
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Inserting dielectric slab into a capacitor
I studied that inserting the slab into a capacitor which is connected to a battery is difficult and we have to do the work, and inserting the slab into a disconnected capacitor is easy and we don't ...
4
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2
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Intuitive meaning of the permittivity and the permeability in Electromagnetism
I wonder what the correct way to intuitively understand the concepts of electrical permittivity and magnetic permeability would be.
The electric permittivity $\varepsilon$ of a medium is defined as a ...
- 964
4
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2
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What happens to the electric field at the boundary of a dielectric?
The question in the title is a broader one, but for now, I want to confine myself to the following problem.
I have the task to find the potential difference between points A and B shown in the ...
- 735