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Questions tagged [conductors]

For questions about materials which allow the flow of an electric charge (electrical conductors) or the transfer of heat (thermal conductors) through them.

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Skin effect fully explained by plane wave attenuation?

I went over the explanations of the skin effect in multiple sources. However, I still don't understand how the fact that this equation: \begin{equation} (\Delta - \mu_0\sigma\partial_t - \frac{1}{c^2}...
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733 views

How to calculate Hall coefficient in gold and silver?

BACKGROUND - Hall Effect Using the free-electron model, the Hall coefficient is calculated as $$R_H = \frac{1}{ne},$$ where $e$ is the elementary charge and $n$ is the carrier density. For a metal $X$...
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45 views

what is the current operator of an interacting electron gas?

If i have an electron gas with coulomb interactions, what would be the current, operator. I would write the Heisenberg equation of motion for the density operator, than write the continuity equation ...
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120 views

Van der pauw method for an isolated hole

Van der pauw method is a way to measure the resistivity of a material with arbitrary shape while it meets some specifications ( being homogeneous and ...). One of the conditions is that the sample ...
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248 views

Electric field in a “concave” conductor

I am aware that the electrons are distributed across charged conductor surface so that the areas with smaller radius of curvature have more charge per surface area. But what happens when the ...
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26 views

Exact distribution of electric field in conducting current carrying cylinder

Consider a conducting cylinder, whose place surfaces are connected to a battery. Now, if we assume electric field inside it is constant, and electric field just outside it is zero, then circulation of ...
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92 views

Confused about the Drude model

I was thinking about the Hall conductivity, when this question popped up. If there is a magnetic field and an electric field perpendicular to it, then a Hall current is generated since the ions have ...
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480 views

Semiconductors vs. Metals Conductivity at High Temperatures

For metals, I've been told that as temperature increases it's resistance increases, due to the lattice vibrating more, and thus there are more collisions with electrons (increasing resistance). ...
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66 views

Interference in electron conductance through e.g. single molecule or semiconductor?

Imagine attaching electrodes to a complex sample, e.g. a semi-conductor or a single chemical molecule, leading to some electric current. Can we decompose this electron flow into local flows? - like ...
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218 views

Why aren't all insulators transparent, since they have a large band gap?

According to Floris' answer in this link, diamonds are transparent as they have large band gaps while graphite is black as it is a conductor. As electrical insulators generally have a large band gap, ...
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1k views

How do excess charges move in an insulator?

I am currently studying intro into electrostatics and reading my notes from teacher that stated, "an insulator holds on tightly to its outer electrons and does not permit the flow of electric charges ...
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21 views

Why $d^{10}$ metals follow the free electron approx better than the other metals

The free electron gas model is surprisingly good at explaining the properties of the conduction electrons in metals, but it works better in some metals than others. In particular it works well for Au, ...
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613 views

Tap water conductivity differences between AC and DC

Direct current is often used in electrolysis and because of the alternating nature of AC, it's not great for electrolysis. Tap water, however, conducts AC really well. But why is that? Why does ...
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686 views

Is it a magnetic or an electric field that causes induction in the antenna?

wiki says that: The electric field (E, green arrows) of the incoming wave pushes the electrons in the rods back and forth, charging the ends alternately positive (+) and negative (−). but ...
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26 views

Determination of electrons flow through the crystal

Talking about doped semiconductors: Atoms outer shell extends and overlaps with another ones outer shell (the conduction band), right? So when electrical field is applied to a semiconductor bar (lets ...
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68 views

Difference in conduction in metals and semiconductors

According to Fermi-Dirac statistics, in a metal, only certain number of valence electrons take part in conduction when they acquire an energy equivalent to KT for some temperature. Now my questions ...
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647 views

How to calculate the Electric field near a 2-D charged square sheet of conducting material with finite area?

The case for infinite sheets are simple enough, and also for a disk of finite size, which can be derived as in the picture. title edited to specify sheet is finite.
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962 views

What happens to metal when exposed to an electric current for an extended period of time?

I was wondering what happens to the actual metal (copper, aluminum, silver, gold) when electricity is ran through it for a long period of time. Say years like the wire in a house. Does the ...
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17 views

Are covalent crystal compounds with lone electron pairs electrically conductive?

In molecular compounds valence electrons can pair up and satisfy each other such as with carbon where the electron configuration is like the following but each electron is paired up with another ...
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58 views

Regarding the zero internal electric field in a conductor (electrostatic case)

Let's say we have a homogenous electric field in the $z$-direction. For computational simplicity let's say we have a thin sheet of metal covering entire the $x$-$y$ plane. The answer here is straight ...
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480 views

Why does AC Conductivty in Drude Theory have an Imaginary and a Real Part?

In the Drude Model the direct current (DC) conductivity is given by the following formula: $$\sigma_0=\frac{ne^2 \tau}{m}$$ where $\tau$ is the relaxation time. Furthermore, the AC conductivity in ...
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397 views

salt water conductivity

my book says the following on conductivity in water with ions. I am confused about why electrons from the zinc (anode) repel positive ions. Because zinc becomes negative, shouldn't it attract it? ...
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73 views

How to increase Resistance of a conductive material?

I'm working on a project that I should measure the resistance of conductive sample ( like brass ). But I've a problem. Resistance of conductive samples is too low which requires a miliohm meter to ...
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176 views

Azimuthally Symmetric Potential for a Spherical Conductor

I am trying to solve problem 2-13 from my textbook "Principles of Electrodynamics" (see image below). I believe that I should be solving the potential as $ \varphi(r,\theta) = \sum_{n=0}^\infty (...
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46 views

Do electrons move easier depending on the way a TIG tungsten head is grinded?

I'm in a TIG welding course, and during the course we (inevitably) messed up a few (suicidal) tungsten heads by grazing/suicide dive into the molten puddle during operation. Standard procedure is to ...
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120 views

Quantum master equation

In the framework of Redfield Quantum Master Equation, the popular approach is to use a tight-binding model linear conductor for the modeling of the Fermionic bath. Does someone can refer me to more ...
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154 views

Permittivity of an object

Is it possible that an object is a conductor and its permittivity is equal to the permittivity of vacuum? Is there any relationship between the permittivity and the conductivity?
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120 views

Electrical resistance of a metallic conductor in a gas

A long time ago I learned that the electrical resistance of a metallic conductor, when surrounded by a gas, varies with the pressure of said gas. • What is the name (if any) of the law involved? • ...
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29 views

Doubts on conductor and insulator

I read on Stephen Gray's discovery of conductor and insulator. From that I came across a question that how cork, wood, rope can act as conductor being an insulator but then I got the answer that it is ...
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22 views

Induced charges in Electrostatics

How to find the distribution of induced charge on conductor kept in a uniform electric field? Is there a particular method to do the same?
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18 views

On the Electric Field of conductor under Electrostatic Conditions

Let us take a hollow conductor which has a charge Q uniformly distributed on its surface. Now, we know that the Electric field inside the conductor must be ZERO. But what happens when I bring ...
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48 views

Is this a valid explanation for why charges in a conductor move to the outer surface?

This is a drawing of a spherical conductor with a hollow center. The black dots represent +ive charges, and the arrows represent their electric fields. I am assuming the black dots start on the inner ...
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25 views

Low energy electrons occupy holes

In Tipler's Physics it is said that for a temperature $T>0$ the only electrons that can gain energy from collisions are the ones with initial energy greater than $E_F-K_BT$. I understand that, ...
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19 views

Relation between potential and charge of a group of conductors

studying electrodynamics I encountered a few weeks ago this statement regarding a set of conductors in space with no free charges: I could not find an explicit proof of this in any book and I did not ...
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31 views

Does a superconductor conduct electricity at room temperature?

I know you need to cool a superconductor below a certain temperature for it to exhibit superconductivity, but do superconductors, specifically YBCO superconductors, conduct electricity normally at ...
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32 views

Do conductors reflect Wifi signals? If so why?

I know electric field can't pass through conductors, but I have seen people surround their wifi router by soda can (not entirely) for better signal strength. I want to know what really happens there.
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24 views

Why is there an accumulation of charges at the junction of 2 rods of different metals joined together?

Let two similar rods of different metals ( say copper and iron ) are joined together and some current is let to flow . Is there a charge accumulation at the junction? 1. If so what is the cause of it ...
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49 views

Paradox in conservation of energy

Let us assume there is a constant electric field in an interested region (finite volume)and a non-conducting object is thrown into it with speed $v$ and now take the second scenario with the same ...
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257 views

Capacitance of spherical capacitor when inner sphere is earthed

Consider the following derivation: (Source: http://www.ncert.nic.in/html/learning_basket/electricity/electricity/electrostatics/inner_sphere.htm) If a charge of $+Q$ coulombs is given to the outer ...
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98 views

Is the electrostatic condition $\vec{E} = \vec{0}$ in a conductor something to be accepted?

The usual explanation goes as follows. Charge flows until the applied electric field is canceled by the induced field, giving a total field $\vec{E} = \vec{0}$. This is reasonable if one gives as an ...
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195 views

Charge distribution on Spherical conducting shells

For example we have very thin conducting spherical shells of radius R and 2R. Initially the smaller shell has Q and other shell has q charge of their own, now there will be charge induction in them ...
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103 views

Kubo formula derivation

In the derivation of the Kubo formula for conductivty we write the total hamiltonian as $$H_{\text{tot}}=H_0+H_{\text{ext}}$$ where $$H_{\text{tot}}=H(A_0+A_{\text{ext}}),$$ $$H_0=H(A_0)$$ and $$H_{\...
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126 views

Relation of carrier density to number of valence electrons in metals

In the classical Drude model, we find that the electrical conductivity of a metal is given by $$\sigma = \frac{ne^2\tau}{m} $$ where $\tau$ is the relaxation time, $m$ is the electron mass and $n$ is ...
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318 views

How to prove that the induced surface charge on a conductor is univocally determined?

Suppose we have a conductor $\Omega$ and a charge distribution $\rho$ outside said conductor in free space. Elementary electrostatics tells us that $\rho$ will cause the free charges inside $\Omega$ ...
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139 views

Why do vinyl gloves work on my touch screen, while other objects don't?

If I use a rubber or plastic object on the screen of my smartphone (Galaxy S5), the digitizer does not register the contact. According to my understanding, the reason it registers fingers but not ...
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53 views

Poissons Equation to calculate potentials

How can I use the poissons equation to determine the potential due to a charge placed near a conducting sphere. I think the boundary conditions are potential at r =a and the potential at infinity is 0....
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222 views

Where does the energy to accelerate particle in an electric field come from?

Consider a hollow conducting tube with a highly positively charged object close to one of its ends. The medium between the conducting tube and the charged object is strong enough to prevent an ...
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155 views

Halved conducting spherical shell with uniform electric field

I am troubling with physical reason of behavior. If I apply the uniform electric field on two halved conducting sphere shell, by calculation using stress tensor, I will get the force that is pulling ...
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30 views

How am I obtaining silicon with resistivity proportional to the number of conduction electrons?

The resistivity of silicon is given by $$\large\rho=\rho_0e^{\Large{{\frac{E_g}{2k_BT}}}}$$ and the number of conduction electrons in a semiconductor conduction band is $$\large n_{\text{...
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298 views

Why is the electric field zero outside this sphere?

The inside of a grounded spherical metal shell of radius $R$ is filled with a charge density $\rho$. Find the electric field outside the sphere. The answer is zero, but I don't understand why. What ...