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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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Why do electrons accumulate on the surface of a wire (along its length) when a voltage source is applied across the wire cross section?

When I was going through how electric fields are transmitted long distances through a wire, I read that there was accumulation of charges along the surface of the conductor to drive the fields to long ...
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Electric field inside and outside a hollow spherical shell

If a charge(+q) is placed at distance away from a hollow spherical conducting shell , would the net electric field inside the hollow portion remain zero? If the +q charge was placed anywhere inside ...
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Why doesn't shell theorem work here?

I think I have a misunderstanding about the shell theorem regarding electrostatics here. Since we have a conducting spherical shell, and we are looking for the $E$ field, shouldn't it be 0 within ...
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366 views

Charged Cavity in conductor

Problem: Suppose we have an isolated spherical conductor and a cavity that is not concentric. Then, a charge is placed at the center of the cavity. What can we say about the distribution ...
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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
1k views

Electron holes in metals

For semiconductors, conductivity is given by $$\sigma=n|e|\mu_e+p|e|\mu_h$$ where $\sigma$ is conductivity, $n$ is the concentration of electrons, $e$ is the elementary charge, $p$ is the ...
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230 views

Electrostatics and electric field inside conductor

I have tried for a while finding an answer to this question. Similar ones have been explained earlier by using Gauss law. However I am wondering about the physical change happening to the conductor in ...
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603 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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53 views

Why Electrical conductivity tensor is symmetric? Or is it not always symmetric?

How to show that the electrical conductivity tensor is symmetric? (or it's not always symmetric?)
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Equipotentiality of the conductor surface with extra charges sprinkled and Poisson's equation

The electrostatic potential $\phi(x,y,z)$ everywhere on the surface of a conductor/metal is the same. For a quick reference see this post. Hence, any derivative of $\phi(x,y,z)$ must be zero on the ...
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Is it possible to use Ampere's law to calculate vector B around short straight line conductor?

Maybe this question sounds easy, but I would really be grateful if someone could give me an explanation if it's true or not. I'm not sure if I understand it good enough.
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Ohm's Law in a conductor

Assume steady-state conditions and a homogeneous conductor. Then dp/dt = 0 where p is volume the charge density. If ohm's law apply in the conductor, then $${\rm div}\ \bar{J} = {\rm div}\ \bar{E} = ...
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How to show that the electrons responsible for a current have an energy within $k_BT$ of the Fermi energy?

It is commonly written in textbooks that in metals the electrons responsible for an electric current are the ones that have an energy about $E_F$ and a few $k_BT$ around that energy. See for example ...
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Why can't free electron flow in water to conduct electricity?

This question is related to how batteries work. In a battery, the electrons can only flow in conductors, because they can't flow in the solution. my own thoughts on the matter: I believe it is ...
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1answer
18 views

Confusion in least action in the following situation

I understand that when electric field is applied normal to the surface of a conductor the net electric field inside the conductor is zero. But as shown in the diagram above, if electric field is not ...
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2answers
630 views

Speed of Signals in a Wire vs Fiber Optic Cable

How much faster is the transmission of a signal in a fiber optic cable than in a copper wire? I would assume fiber optic cables transmit signals at the speed of light (this begs the question, are ...
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How does electric current continue to flow in a circuit despite there being zero potential difference?

Consider a conductor connected to a battery by conducting wires. When wires are connected then after a very small amount of time steady state is achieved and voltage across conductor becomes equal to ...
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Why do liquid metals conduct electric current?

This is a question I wanted to ask for some time now. You learn in solid state theory that the free electron model is the reason for metals conducting electric current. The electron orbitals ...
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1answer
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Is electric force constant all over the surface of a conductor?

This question was asked in IIT JEE 2010. I know that the electrostatic pressure is equal to (1/2)∈(E)² and if we multiply this with the projected area then we would get the force acting on an object ...
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46 views

Why should there be electrostatic equilibrium inside a conductor? [duplicate]

I have been trying to understand why the net electric field inside a conductor is zero regardless of the exterbal electric field. But why should equilibrium ever be attained?
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Hydrogen: Whether it's a metal or non-metal

I know hydrogen is a non metal, but when I just study about some introductory elementary band theory I find the band structure of hydrogen has a half filled valence band just like alkali metals, and ...
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1answer
701 views

How to calculate flux density in a toroidal CT that has an electrical line pass through the center?

I have seen the Biot–Savart equation, but I don't know how to apply it. Does the conductor length need to be considered finite and equal to the core length, or will the calculation be for a conductor ...
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4answers
675 views

Electric field due to uniformly charged infinite plane sheet

For getting the electric field in this case we use the Gauss's law. we get the equation $$ 2EA = pA/\epsilon_0 $$ here $E$ is electric field, $A$ is the cross sectional area, $p$ is the uniform ...
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377 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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1answer
222 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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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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1answer
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Energy Loss during Sharing of Charge between two Capacitors

It is fairly easy to show that there is always a loss energy when two capacitors share their charge to attain the same common potential, but is it with the same ease that one can explain why it ...
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1answer
224 views

Reason for gold being the most malleable and ductile of metals

I understand how fcc structure enables plastic deformation in metals, but why is gold, in particular, the most malleable and ductile of fcc metals? Is there something about the electronic structure ...
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1answer
71 views

Non-Hermitian Hamiltonian for electron conductance in electric field?

Electron conductance in a solid state is usually driven by electric field - making some direction of jumps more likely. It makes (e.g. Hubbard's) Hamiltonian no longer self-adjoint, how to simulate ...
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2answers
63 views

When to use Poisson's equation in electrostatics

When does when elect to use Laplace's equation when dealing with charge distributions. For example, if I had a metallic sphere of radius $R$ and charge $Q$, then $$\mathbf E = \begin{cases} 0, & ...
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1answer
486 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 ...
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3answers
50 views

Thermal Energy in a Conductor

We know that thermal energy developed in a current-carrying resistor is given by $U=I^2Rt$ and also $U=VIt$. So my question is- Should we say that $U$ is proportional to $I$ or $I^2$
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1answer
445 views

Point charge inside a electrically neutral cavity in conductor placed eccentrically, and effect of external electric field if switched on

bear with me, but i would like a definite answer, now, starting off the external charge density on the outer surface of sphere WILL be uniform by unique solution of Laplace equation and letting the ...
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36 views

Electric Fields 'passing' through conductor material

I've been reading Chapter 3.2 and 3.3 of Purcell's Electricity and Magnetism, 3rd ed, and found that I don't really understand a few ideas that Purcell makes about electric fields and conducting ...
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Potential at the surface of a conducting sphere near a dipole

An ideal conducting solid sphere of radius $R$ and center $O$ is brought near a dipole with a dipole moment of magnitude $p$. Let the center of the dipole be called point $C$, and let the tangent from ...
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Gauss law electric field inside a conductor [closed]

Can you mathematically prove that if there is a cavity in a conductor and no charge is placed in it, the field at all points in the cavity will be zero?
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68 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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Prove: “If a cavity surrounded by conducting material is itself empty of charge, then the field within the cavity is zero.” [closed]

Prove: "If a cavity surrounded by conducting material is itself empty of charge, then the field within the cavity is zero." My attempt: Take a Gaussian surface that lies completely inside the cavity....
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2answers
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Why is the electric field zero inside a hollow conducting sphere?

If you have a conducting hollow sphere with a uniform charge on its surface, then will the electric field at every point inside the shell be 0. The reason the electric field is 0 at the center is ...
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1answer
39 views

When can charge reside on the inner surface of a conductor?

My confusion stems from the following exercise: I've written sloppily: "Why are charges not induced on at least that portion of the inner surface?". As I ask, I don't see how the charge density on ...
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1answer
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Plane of charge versus plane of charge on surface of conductor

The exercise below aiming to test my understanding has me confused: Why is the answer $(B)$? To me, I can envision for infinite planes of charge that its electric field lines are leaving normal to ...
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Charge density on inner surface of conducting shell

The following exercise has brought to my mind something that confuses me: Here, I don't see why there isn't positive charge residing on the inner surface of the conductor at $r=a$. The way I see it,...
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1answer
180 views

Neutral conductor and charged insulator brought near each other

What happens when a charged insulator is placed near an uncharged neutral metallic conductor? I know it attracts each other because of charging by induction (electrons redistribute). But would the ...
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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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1answer
263 views

Conduction and Ionic Conduction

How the ionic conduction is different from normal conduction ? Does the electrons that leave atoms completely conduct in ionic conduction while in normal conduction the conduction takes place through ...
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What is “surface potential” of a conductor?

If there exists a charged conductor, the surface has a potential. This potential at a point on the surface is created by the charge distribution of all the other points on the surface. This means that ...
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1answer
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How does charge develop inside a spherical shell (with non-negligible thickness)?

I read that if there were a charge $+q \ $ kept inside a spherical conducting shell of thickness $t$, a charge of $-q \ $ would develop on the inner surface of the shell. Not more, not less. Why is ...
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1answer
562 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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Why Electric field inside the spherical shell is zero? [duplicate]

electric field in and out of the spherical shell Why the field inside the conducting spherical shell is zero? Professor Lewin said and I quote," there is NO charge inside the conductor because any ...
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Why can an insulator send charges to a conductor via conduction, and not upon an insulator via conduction?

Suppose we have an ebonite rod (insulator). This rod has a negative charge, and once it touches a neutral pith ball, charges are distributed amongst the pith ball. However, why doesn't the same happen ...