An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials, semiconductors and conductors conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors. The most common examples are non-metals.
A perfect insulator does not exist because even insulators contain small numbers of mobile charges (charge carriers) which can carry current. In addition, all insulators become electrically conductive when a sufficiently large voltage is applied that the electric field tears electrons away from the atoms. This is known as the breakdown voltage of an insulator. Some materials such as glass, paper and Teflon, which have high resistivity, are very good electrical insulators. A much larger class of materials, even though they may have lower bulk resistivity, are still good enough to prevent significant current from flowing at normally used voltages, and thus are employed as insulation for electrical wiring and cables. Examples include rubber-like polymers and most plastics which can be thermoset or thermoplastic in nature.
Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation. The term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers. They support the weight of the suspended wires without allowing the current to flow through the tower to ground.
Please explain what these things are for. I'm guessing they reduce the e-field strength at the end of the insulator while maintaining a long creepage path, maybe? Or something about reducing corona discharge?
What are they called? I can't seem to get a good search term.
If we have a small dielectric sphere and a point charge, they will experience an attractive force due to electrostatic induction. (From the elongation/rotation of charges bound to individual atoms).
Likewise, if we have a small metallic sphere and a point charge, they will experience an...
I have tried to write down the boundary conditions in this case and looked into them. As conditions i) and ii) were trivial, i looked into iii) and iv) for information that I could use. But all I got was that for the transmitted wave to have an angle, the reflective wave should also have an...
Hello! If I have some conductors in space, each at a certain potential (and assume everything is inside a conducting sphere, in order to have some well defined boundary conditions), we can calculate the potential everywhere (inside the sphere) by solving Laplace's equation. Hence a particle...
I am working on a project; a computer case made out of wood, most likely oak. I was wondering if two fans (one bringing air in, on taking air out) would be enough to keep the system at a stable temperature. I wasnt sure because i know most cases are made of thin metal which conducts and...
I have a question (more like a curiosity) related to three-dimensional topological insulators, which support Dirac-like states at their surfaces. From the theory, it is well known that these states are immune to scattering from non-magnetic impurities, i.e. impurities that do not break...
I found this paragraph from one of wiki article, "Mott considers a lattice model with just one electron per site. Without taking the interaction into account, each site could be occupied by two electrons, one with spin up and one with spin down. Due to the interaction the electrons would then...
Hello.
Do you know of any good material on topological insulators like books, review papers etc?
I would prefer something more oriented towards theoretical physics(because I know that there are reviews out there that are purely experimental).
Thank you!
Hello!
What are some good sources(preferably textbooks) to learn about Weyl semimetals?
I also want some sources to learn about topological insulators and anything containing the Integer Quantum Hall effect would be great.
As an aside, if you have any good book on theoretical condensed matter...
From what I've learned, excess charge on an insulator stays where it is but excess charge on a conductor spreads uniformly throughout its surface. Why does this happen? Can this be explained in terms of electrostatic potential?
I thought that insulators cannot be charged in the inside or the outside, so how can they have any charge density inside? I know that electric fields pass through a insulator, so is that why they can have charge density? I am currently reading about electric flux.
I just have a few conceptual questions:
Is it as difficult to remove electrons from an insulator as it is to add to it?
I understand insulators have a lower permittivity than conductors, and that they still allow charges to build upon the surface. However, I read that when you rub an insulator...
Hi everyone
Can anyone help me understanding the physical meaning for the complex dielectric constant?
Assuming a electromagnetic wave from air to a conductor, the following equation is valid
R= ((n-1)2+k2)/((n+1)2+k2) where K is the extinction coefficient (the complex part of the complex...
So a charged object can induce a charge on both conductors and insulators. For the conductor, (assuming a negative object is brought near it), all the negative charge would flow to one side creating a strong attractive force. For an insulator, what exactly happens? I understand there will be a...
I have been learning topological insulators recently, and I become more and more curious about the link between topological insulators and mathematical theory these days.
I know topological insulators have something to do with fiber bundles and K-theory. I have a relatively good background of...
So, I was watching PBS's Nazi Mega Weapons, and they were discussing the V-1 terror drone when they said something that made me scratch my head. They said that the Nazis initially had problems with the compass that facilitated navigation because of magnetic interference from the metal in the V-1...
A negatively charged plastic rod will negatively charge a pith ball when in contact. My understanding is that the extra electrons transfer from the rod to the ball, thus giving the pith ball a negative charge.
When an electrophorus is charged and the metal pan is put on top, it doesn't become...
So normally we explain transparency by saying that the band gap in insulators is too large for mere visible light photons to be absorbed by the electrons. But what about the classical EM explanation? I made an attempt at an explanation below. Feel free to correct mistakes.
Since Insulators lack...
First question i have is about the common glass rod-cloth experiment where the one gets plus charged and the other minus charged.The plus charged item how does it get back the electrons that it missed?If we touch it again with the other one or even through the air?And the minus charged how does...
I'm an apprentice electrician taking night courses. My question isn't a specific mathematical problem. It's a query about a concept. Please let me know if there's a better way/place I can ask it.
My text say that atoms can have a max of 32 electrons per shell, with 1-3 being ideal for...
Hello Guys!
I have been studying electromagnetic waves (EMW) interaction with matter lately and I just derived the results for the propagation of EMW inside linear media and perfect conductors. As it turns out, when a plane EMW changes medium (at a normal incidence) from air to (good)...
I'm used to problems which ask me to find the heat flux for when, for example I have a very long cylinder covered with an insulator, each with their respective conductivity coefficient. I'd use the formula \frac{\partial Q} {\partial t} =\int -k\vec{\nabla} T \vec {ds}. But now I have a...
I understand that the centring of the Fermi energy at the Dirac point is a highly sought after property in Topological Insulators but I'm unsure as to exactly why? I see that the state at the conical intercept will be unique but I'm not sure of what is theorized to happen to the electrons...
It is well known that back-scattering of surface electrons in topological insulators is prohibited due to Kramer's degeneracy theorem as long as Time Reversal Symmetry is not broken by magnetic field or magnetic impurities.
I would like to know what effect this has on scattering length and...
Hello all,
I'm currently designing all the structure, equipment and grounding for a 230-115kV terminal substation, and for our dead end connections consisting porcelain ball & socket type suspension insulators we are given the number of insulators required for each voltage level. (i.e. 14 for...
Hi all!
I am currently reading stuff related to quantum hall effect and topological insulators, and have a couple of questions.
1. I read about that band insulators can be classified into two types: topological trivial insulators and topological non-trivial insulators. And there is a...
Hi I have been searching some papers online to find how practically we can approach for the fabrication of topological insulators.
Can somebody please help me regarding this by providing some web links or some insight on the fabrication of topolopgical insulators...
Hi,
I was curious if specific symmetries (or lack thereof) in crystal structure are necessary for the formation of topological insulators. Specifically, do we require that inversion symmetry (or inversion asymmetry) be present in the lattice in order to form the TI state?
Thanks,
Goalie33
In the literature on topological insulators and superconductors the 'bulk-boundary correspondence' features quite heavily. One version of this conjecture says roughly: "At an interface between two materials belonging to the same symmetry class with bulk invariants n and m, precisely |n-m|...
Homework Statement
From what we've learned, insulators are not able to allow electrons to pass through or exit through them (beside rubbing/friction). So if I have a negatively charged piece of cloth and move a negatively charged metal rod such that they touch, will they both become neutral...
I'm sorry if this is in the incorrect section, but can someone please explain what topological insulators are, the quantum hall effect, how you make a topological insulator and anything else that is relevant to the topic.
Thanks.
Hi PF,
I'm trying to come to grips with the work of Alexei Kitaev on applying notions from (topological) K-theory to the task of classifying phases of topological insulators and superconductors (paper here: http://arxiv.org/pdf/0901.2686v2.pdf). Despite having plenty of citations, I've yet to...
Hi everyone,
While reading about the BHZ model used to describe HgTe quantum well topological insulators, I read at many places that the effective Hamiltonian (which is a 4 x 4 matrix) can be written in block diagonal form and the lower 2x2 block can be derived from upper 2x2 block as...
Hello,
So a topological insulator can induce a magnetic field when an electric charge is near to it (I can give a reference if necessary), but the thing is, the paper interprets the origin of this magnetic field as being the hall currents on the surface of the topological insulator.
Now I...
It may be my imagination, but if I toast a fresh bagel it comes out of the toaster hotter than one that has been kicking around the kitchen for more than a week.
I tend to blob butter on it and let it melt before smoothing it over, rather than putting effort into 'spreading' cold butter...
Homework Statement
A cylindrical shell of radius 7.00 cm and length 240 cm has its charge uniformly distributed on its curved surface. The magnitude of the electric field at a point 19.0 cm ra- dially outward from its axis (measured from the midpoint of the shell) is 36.0 kN/C. Use approximate...
Hi, this is my first post here!
I've been studying about topological insulators, but still I can't understand why this materials are called topological, I've read about topological analogy between the donut and the coffee mug and the smooth changes on the Hamiltonian, but I can't get the full...
This is NOT a homework question.. It is just something that is bothering me...
1. If two neutral conductors are made to touch each other, no current will flow..
2. If a neutral conductor is made to touch with a positive conductor, the current will flow from the neutral to the positive...
Hi. I don't know if this is the correct place to ask this, but prefer you to suggest me where I should ask. I'm starting with numerical simulation and I've been playing with the finite differences method to solve the heat equation on 1D, 2D and 3D uniform grids. This was really simple. Now I...
Homework Statement
I have some hypothetical questions.
Question 1
There is a conductor with a single electron and proton inside of it. If we try to charge the conductor by induction, we might put a proton close to the conductor. The electron will go towards that proton while the proton in...
When we stack orbitals we get bands. Bands result in bonding and anti-bonding. Now for Na his s band is half full resulting in the top half to be conductive shell of anti-bonding orbitals.
Take Mg for instance. So his s band is completely full. Why does it conduct ? Because, as I learned, p...
What is work function of an insulating polymer (eg: Polystyrene ,PMMA etc..)? is it half of HOMO and LUMO? Do the ionization potential (IP) and Electron affinity (EA) change with work function?
IP= E(vacuum)-E(HOMO). So I guess this is always a constant. am I right?
But EA=E(Vacuum)-E(LUMO)...
Hi all,
I'am starting a Phd In Theoretical Condensed Matter Physics, and I would like to produce a thesis on the Topological Insulators topic. Unfortunately I don't have a background in Consensed Matter Physics (in my curriculum there are exams about General Relativity, Quantum Field Theory...
I've recently started learning about topological insulators. I've read a considerable amount of (review) papers on the subject, yet I still only have a phenomenological understanding of what a topological insulator is. I know for example, that the gapless surface states have to be there because...
Hi,
these days I have been trying to understand the essentials of the so-called topological insulators (TBI), such as Bi2Te3, which seem very hot in current research. As i understand, these materials should possesses at the same time gapped bulk bands but gapless surface bands, and spin-orbit...