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.

133 questions with no upvoted or accepted answers
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3answers
391 views

Temperature distribution in a current carrying conductor

A rod of uniform cross section and composition is connected across a battery. Let the middle part of the rod(when divided into three equal parts) is heated uniformly. A book says that the temperature ...
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0answers
66 views

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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762 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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0answers
50 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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2answers
686 views

Why does Griffiths's book say that there can be no surface current since this would require an infinite electric field for an incident wave?

In sec. 9.4.2 Griffiths shows the well known boundary conditions for E and B fields, one of them is this: $$\frac{1}{\mu_{1}}\textbf{B}_{1}^{\parallel}-\frac{1}{\mu_{2}}\textbf{B}_{2}^{\parallel}=\...
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0answers
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 ...
2
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0answers
644 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 ...
2
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1answer
80 views

Do 2 conductors (1 grounded via resistor) reach equipotential, before surplus electrons drain to earth?

Case I: a negative conductor makes contact with a neutral conductor. Negative donates some electrons to neutral, until there is 0 potential difference. Then they both are slightly negative. This ...
2
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1answer
512 views

Location of mirror charges (method of images)

I was reading about method of images from Griffiths and I was thinking about a situation where a charge is kept inside a spherical cavity of a conducting shell rather than placing it outside a ...
2
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1answer
83 views

Magnetostatics or dynamics?

A spherical conductor, carrying a total charge $Q$, spins uniformly and very rapidly about an axis coinciding with one of its diameters. In the diagrams given below, the equilibrium charge density on ...
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2answers
92 views

Two balls are attached with a very long and thin conducting wire to two conducting plates. How does the capacitor react in this situation?

The question is as follows (taken from a previous exam): Two balls (conductors w/ Radius $R_1$ for left ball ball, $R_2$ for right) are attached with a very long and thin conducting wire to two ...
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0answers
121 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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0answers
264 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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2answers
65 views

On proving that charge is linearly proportional to potential for a conductor

In Mr. Purcell's Electricity and Magnetism, page 103, it is stated, An isolated conductor carrying a charge $Q$ has a certain potential $\phi _{0}$, with zero potential at infinity. $Q$ is ...
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1answer
36 views

Some confusion in Drude theory of metals

Discussion on the drude theory of metal usually begin with the case of zero magnetic field so that the force acting on the electrons is just the one from the electric field. But then, this electric ...
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29 views

“Conductors having excess charge can attain static equilibrium”, is this an empirical law?

Is the redistribution of excess charge in a conductor onto its surface, thereby reaching static equilibrium (a steady state), only an empirical observation? Or, equivalently, is it guaranteed, i.e. ...
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2answers
57 views

What is the exact mechanism of flow of electricity?

When a steady current flows through a conductor, the electrons in it move with a certain average ‘drift speed’. One can calculate this drift speed of electrons for a typical copper wire carrying a ...
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1answer
69 views

Does electric field vary with cross sectional area in a non uniform current carrying conductor?

Suoppose I have a non uniform conductor which is kept in a uniform electric field maintaining a constant potential difference across its ends.Both electric field and current density are a properties ...
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0answers
56 views

How to find the charge distribution of a conducting disc?

Generally,Poisson's equation can be solved with appropriate boundary conditions to get potential from which the surface charge densities can be obtained. Most textbooks on Classical electrodynamics ...
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0answers
24 views

Negative real part AC conductivity

I am reading this paper, where the authors are calculating the frequency dependence of the chiral magnetic effect, i.e., ${\bf J} = \sigma^{\text{CME}}(\omega) {\bf B}$. The authors find, see for ...
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0answers
37 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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2answers
80 views

Is the electric field within a cavity of a conductor affected only by other charges within the cavity?

The following exercise below confuses me: I don't understand why the answer is (A). I seem to be realizing empirically that the electric field at points inside a cavity in a conductor such as this is ...
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2answers
63 views

What is the voltage in electrical circuits?

I understand what the voltage is and I realize that the battery makes an electric field due to the accumulation of the charges in the anode and cathode this electric field causes electric potential ...
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4answers
503 views

Car hit by a lightning strike

In Griffiths' Introduction to Electrodynamics, at the Electrostatics chapter, in particular, in the conductors section, he says this after the stating that within an empty cavity surrounded by a ...
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2answers
429 views

Is there a way to make infrared pass through metals?

I am curious to know a way that will make infrared pass through metals. Metals are good reflectors of infrared,can we manipulate the wave in order to make them pass through metals?.
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1answer
38 views

Can the graphene's conductivity be explained using only orbitals?

I am trying to find a 'easier' or more 'intuitive' way to calculate the conductivity of graphene. I want do this by using atomic or molecular orbitals. Anyone have a clue about how this can be done? ...
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28 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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1answer
59 views

Where does the 2 come from in the force on the surface of a grounded sphere near a point charge?

In section 2.2 of the classical text on electrodynamics by John David Jackson the method of images is exemplified with a grounded sphere in the presence of a conductor. In the end of the section, he ...
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1answer
63 views

What's happening at a molecular level to the resistance when the temperature of salt water is increased?

What's happening to the electrical resistance at a molecular level when the temperature of a water with a bit of salt is increased? I noticed that the resistance decreases but in metals it is totally ...
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1answer
87 views

Problems with understanding conductors in electrostatic equilibrium

I watched a few videos on conductors in electrostatic equilibrium and all I understood is that the charges stick to the surface of the conductor. So does that mean if I have a copper wire with no ...
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0answers
97 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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1answer
586 views

How do insulators lose their charge?

Some theoretical questions that got me confused during physics lecture today. bringing a conducting balloon to a negatively charged rod close will allow the conducting balloon have positive charges ...
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0answers
553 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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0answers
67 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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3answers
529 views

Do charges move to the outer surface of a conductor to minimize the potential energy?

We can think the charges go to the outer surface of a conductor to minimize the electrostatic potential energy of the system. We can check this using a simple calculation using a charged sphere. A ...
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0answers
231 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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0answers
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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0answers
724 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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1answer
136 views

Is this the correct voltage graph of a conducting sphere in the presence of another charge?

This grading rubric show an example of an acceptable answer, however I wonder if the slopes at the surface of the second sphere are wrong. This is a previous AP Physics test question so I'm inclined ...
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1answer
230 views

Interaction of charged particles with a conducting or insulating surface

If I have a charged particle floating in a vacuum, and it strikes a conductor or insulator on its way, what would happen? Would the electron be taken into the conductor? or would it just bounce off ...
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2answers
412 views

Why doesn't a conductor between two wires affect the current wires?

When an aluminum plate is placed between two wires (lying parallel to each other), it doesn't change the repelling nor attracting force between the wires when a current is passing through them. But ...
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0answers
29 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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1answer
586 views

How do I calculate the surface potential of a conductor given a charge distribution?

I have tried the conventional definition but since there is a charge density at the point we want to calculate the potential at, it turns out to be infinity. Now, i dont know how to calculate the sum ...
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0answers
69 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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1answer
81 views

Electrostatic polarization of an axially symmetric conductor

A single point charge at the origin induces charge onto a grounded Z-axis symmetric conductor. The induced charge is given in cylindrical coordinates as $\sigma(r, z)$ since the Z symmetry means there ...
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0answers
710 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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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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0answers
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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0answers
59 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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532 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 ...