Questions tagged [insulators]

Electrical insulators are materials through which electric charge does not flow freely. Insulators have high electrical resistivity.

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Explaining Valence Electrons

I want to explain the concept of free electrons in a conductor vs. an insulator as simple as possible for children that have not yet learned about valence electrons. Would it make sense if I explained ...
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Why do not all the semimetals turn into the excitonic insulators?

I want to know the condition for forming the excitonic insulator. When the binding energy of the exciton, $E_b$, overcomes the band gap, the system becomes the excitonic insulator. If so, all ...
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If a point charge is surrounded by an spherical insulator then according to the below diagram what will be the electric field at point A and point B

According to my observations, electric field strength depends on the relative permittivity of the medium. Different insulating materials can affect the overall strength of the electric field. If is it ...
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How does amorphous $\rm SiO_2$ crystallize?

I know crystalline $\rm SiO_2$ changes its crystalline structure depending on temperature, but what happens to amorphous $\rm SiO_2$ if you heat it up? I could find nothing on this topic. Is it ...
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Electric fields and intrinsic semiconductors

If we apply a electric field to a conductor the charges inside move close or away from the electric field which creates a electric field inside the conductor which cancels out the external electric ...
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Are there charge fluctuations in band insulators?

Consider a one-dimensional non-interacting Hubbard Hamiltonian: $$ H=-t\sum_{\langle i, j \rangle}\sum_{\sigma=\uparrow,\downarrow} \left(c_{i,\sigma}^\dagger c_{j,\sigma} +\mathrm{h.c.} \right) $$ ...
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How to derive the Clausius–Mossotti relation using Feynman diagrams?

The Clausius–Mossotti relation is usually derived by assuming that a molecular in a crystal is surrounded by a spherical hole, or by the $- \frac{1}{3k^2} \delta(\boldsymbol{R})$ term in the dyadic ...
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Why does the wave velocity of EM signals in a wire depend on the insulator's permittivity?

I'm in an electromagnetism class and struggling with a concept. The textbook derived several equations which state that the wave velocity of an electrical signal in a transmission line depends on the ...
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What is the role of insulators in the accumulation of static electricity?

The Wikipedia article for static electricity says A static electric charge can be created whenever two surfaces contact and have worn and separated, and at least one of the surfaces has a high ...
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What good reason to hang long cable carrying electric current high above the ground? [closed]

Assume no flooding or other natural disasters to damage the cable if it is laid beneath the ground, then what good reason for them to be suspended high above the ground? The cables are insulated and ...
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How to see that the trivial insulator is trivial?

I have been trying to better understand gapped phases of matter — which may be "topological" or "trivial" — and I have run into the problem that I don't really understand the ...
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Why is wood opaque?

Glass does not allow the flow of electrons through it, is transparent, and has higher skin depth. Similarly, wood has no free electrons and higher skin depth, but still it is opaque. Why?
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Can an insulator become a conductor at superconductive temperatures?

Can an insulator become a conductor at superconductive temperatures? As a part of electric resistivity is physical opposition to the stream of particles would an insulator having its nuclei inert in ...
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Is titanium chromium alloy an insulator or a conductor?

I want to get some copper parts made, and the maker of the parts says they can coat the parts with a PVD (physical vapor deposition) process using a coating of Titanium and Chromium. I need the parts ...
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Is there a solid insulator at room temperature that has a dielectric strength slightly less than that of air?

Ideally the material retains its properties after it breaks down with high voltage.
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Sharing of charges between two bodies

Why is charge shared between two insulating bodies till their charges are equal, while the charge is shared between two conductors till their potentials are equal?
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How defects can influence the electrical conductivity of ionic insulator, semiconductor and metals?

Does increasing defects increase the conductivity of the insulator? The band gap between the conduction band and valence band is large such that electrons cannot flow in-between. Shouldn't increasing ...
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Are ionic crystals, band insulators?

Ionic crystals are considered as electrical insulators. Is there a proof that they are insulators from the point of view of electronic band theory? In other words, is there a proof that ionic crystals ...
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Finding the charge of an insulated conductor using Green's Reciprocation Theorem

I am trying to work old E&M notes to prepare for a plasma physics class coming up but I'm getting stumped on using Green's reciprocation theorem. The problem is as follows: Consider two insulated ...
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Is making any material into wool transform it into a thermal insulator?

This questions originates from the existence of a number of wools made of different materials, such as glass or rock, that are used as thermal insulators for e.g. buildings. I wanted to ask a more ...
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Rubbers Shoes and Insulation

I know that rubber shoes indeed protect you from electrical current which may pass under your feet, and also hinder the completion of a circuit, say when one’s sustains a shock from a path, other than ...
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Why ferroelectric material needs to be insulating?

Is it necessary for a ferroelectric material to be insulating? Is it possible for a metal to be ferroelectric?
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Why can't excess charge built up in a conductor escape the object?

When you add electrons to an insulator the electrons stay where you place them and are unable to move whereas in a conductor they repel each other and move to the edges. Why don't the charges just ...
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When excess electrons are in an insulator they don't move. Why is this?

Let's say you have an insulator that is electrically neutral(has no net charge). Let's say you are able to add additional electrons into the same insulator resulting in the insulator having a net ...
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When you introduce excess charge into an insulator the charge stays still. Why is this?

When you add charge to an insulator the electrons stay in the same place whereas in a conductor they spread apart. Why is this? What force is making the excess charge stay in one place in an insulator?...
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Why can't excess charge travel through an insulator?

Lets say you have a closed circuit connected to a battery made of copper wire. Lets say that at one point of the copper wire there is plastic. The electrons can't flow through the insulator and back ...
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How does having free electrons make something a conductor?

My question is how does having free electrons make something a conductor? I know that the flow or movement of electrons create a current but can't you just add free electrons (such as a battery) to an ...
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Why can't an insulator let electricity pass?

I have read about this: Essentially in an insulators there is a big energy gap between the (valence) and the conduction band which is why there aren't many free electrons in a insulator. How does ...
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What makes a conductor able to pass electricity?

My question is what makes a conductor able to pass electricity? I know that conductors have free electrons where as insulators don't have as many but can't you just add free electrons to the insulator ...
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Why are non-metallic elements with partially filled valence bands not conductors?

Throughout this whole question, I will be referring solely to single element solids. According to band theory, ns and np bands are close enough in energy to overlap and create one band with 8N states ...
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Insulator or conductor with different boundary conditions

I'm studying the 1-D SSH model. It's a toy model for a topological insulator. Here's the reference I'm using. If the hopping amplitudes $v$ and $w$ are equal, then with periodic boundary conditions we ...
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Charging Insulators

Can insulators like plastics be charged with the help of conduction? What happens when such materials are brought in contact with charged bodies that might be conductor or insulator?
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Heat capacity for real insulator

In the Debye model, for temperatures $T \ll T_D \equiv \frac{\hbar\omega_D}{k_B}$, the molar heat capacity $c_V$ can be calculated as follows: $$c_V = \frac{12\pi^{4}}{5}R \left(\frac{T}{T_D}\right)^3$...
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Why don't we use tubes of vacuum as insulator in houses? [closed]

If vacuum is a good insulator, why don't we use tubes of it as insulator in houses?
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Why is electric field in an insulator non zero?

I had read from several sources that electric field inside a conductor is zero. This is attributed to the fact that the electrons are loosely bound to the nuclei and they are free to rearrange ...
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Does the Mott metal-insulator transition occur with increasing or decreasing density of valence electrons?

When reading about the Mott metal-insulator transition, it has not become clear to me if the transition from a metal to an insulator occurs with increasing or decreasing density of valence electrons. ...
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Metal-insulator transition (material properties)

When studying about metal-insulator transitions, I was wondering which material properties can give direct information about this phenomena. Also, what information can be derived from these properties....
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Gauss's law and electric field inside spheres and shells

I have a question regarding the electric field inside a sphere and shell and I know the result but don't really understand why it is what it is. Lets say there is a shell with radius $R$ and that has ...
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Conductors and Insulators from the point of view of Quantum Mechanics

So, I was watching this lecture of MIT 8.04 Quantum Mechanics course and at around 38:00, the instructor starts discussing periodic potentials to predict the properties of conductors and insulators. ...
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Can a conductor be uniformly charged?

I have been reading in books that charges on a conductor resides on its surface and that for a body to be uniformly charged it has to be an insulator.Is it true?If yes does it mean we can consider a ...
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Does the Mott insulator exist?

The Mott insulator is a system that, due to strong electron-electron interactions, is an insulator but is expected to be a metal by formal charge counting of electrons in the unit cell. Often, the ...
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Joining two insulators at different potentials with a conductor

If two insulators are connected by a conducting wire, will the charges flow if they are different potentials? According to me, as the charges can't enter the insulators, charges only get distributed ...
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Comparing energy band diagram for metals, semiconductors and insulators

The energy band diagram is a model for describing why an insulator is not a good conductor compared to a semiconductor: in the first case, electrons would need to pass a very large band gap in order ...
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How do that charge gets transferred while rubbing?

We all have studied that on rubbing a glass rod with silk or human hair, the two get charged with opposite polarities. What confuses me is that since both glass and silk(or hair) are insulators, they ...
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What does the subindex $x$ in $\text{Bi}_{1-x}\text{Sb}_{x}$ mean?

I am currently reworking our condensed matter lecture. We shortly discussed topologic insulaters at the example of $$\text{Bi}_{1-x}\text{Sb}_{x}$$ I am not sure what the $x$ stands for. Normally ...
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Wiedemann-Franz law generalized to quantum Hall effects in electronic systems

Wiedemann-Franz law states a relation in a conductor between the thermal and electric conductivities by their ratio as $\kappa/\sigma=LT$ where $T$ is the temperature and $L$ is the Lorenz number ...
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Grounded Conductors and Charge

Not HW, just something that popped up in my mind during a shower XD Consider a configuration consisting of an insulator that has been charged negatively by friction, and a conductor placed nearby. ...
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What makes electrons 'more free or less free' to move around?

I understand that conductors allow electron flow because their valence electrons are 'free' to move around.. But what exactly determines this 'freeness' and the lack thereof that separates conductors ...
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What exactly happens when a charged conductor comes into contact with an electric insulator?

Let us say we have a negatively charged conducting sphere: If we put an insulator into contact with the sphere: Would the negative charges located in the contact region transfer from the surface of ...
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Does an insulator always contain the Fermi surface in the 1st BZ

I'm looking for a clarification about the classification of metals and insulators; is it correct to state that if the Fermi surface is contained into the first BZ, then the material is an insulator, ...
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