# 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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### How do I apply Gauss's law to coaxial conducting cylinders?

$$\vert \vec E\vert =\frac{\lambda}{2\pi \varepsilon_0 r}$$ So I know this is the magnitude of the electric field of a line of charge using a cylindrical Gaussian surface. But, now let's say I have ...
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### What photoconducting materials/metamaterials reach full conductivity within 1/30th of a picosecond

I'm doing research on photoconducting materials/metamaterials but I'm having a hard time finding confirming how fast they reach full conuctivity, What photoconductors reach full conductivity and back ...
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### Point resistance

The resistance of a given object is expressed through: $$R=\rho\frac{l}{A}$$ I'm wondering if there is any quantity like resistance at a specific point. For example, $R$ for a copper wire with l=...
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### Electric field below conducting plane

In Griffiths introduction to Electrodynamics, the classic image problem is presented: There is a charge $q$, above a grounded conducting plane. Griffith says that the electric field below the plane is ...
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### Charge distribution in a hollow sphere [duplicate]

In electrostatics, why in the internal surface of a hollow charged sphere there aren't charges?
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### Entropy in Conductors

In Introduction to Electrodynamics by Griffiths, it is given that Like any other free dynamical system, the charge on the conductor will seek the configuration that minimises its potential energy. ...
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### 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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### Is it possible for a conductor to run out of free electrons?

For example, imagine I apply a high voltage to a piece of conductor (copper) and make the electrons jump out of it like a automotive spark plug. Can the copper after a prolonged period of time run out ...
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### Dielectric Grease on Electrical Connections

The electrical connection between my truck and our RV trailer was intermittent. When I wiggled the connection the errant light would go on and off, so I bought some electrical grease and problem ...
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### Doubt in electrostatics

I have studied that charges lie on the surface of a conductor i.e. no charges exist inside the body. Then why doesn't charges in a wire (through which electricity flows ) come to surface?
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### Why do charges move across wires in circuits if the voltage across them is zero?

Consider a simple circuit with a battery and a resistor, connected by wires. We usually treat the wires (excluding the resistor) as ideal conductors (no resistance). Therefore, we conclude that the ...
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### Difference between conduction current density & convection current density?

Could anyone please explain the difference between the conduction current density $J=σE$ and the convection current density $J=ρv$? I really appreciate any examples or applications to further ...
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### Speed of light vs speed of electricity

If I arranged an experiment where light raced electricity what would be the results? Let's say a red laser is fired at the same time a switch is closed that applies 110 volts to a 12 gauge loop of ...
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### Why do current carrying conductors need to be uncharged?

I’ve come across a lot of physics problems which ask of a current carrying wire has an electric field around it or will a current carrying conductor A induce charge on an adjacent grounded conductor ...
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### What is the potential variation inside solid conducting sphere? [duplicate]

The information on the internet is highly unreliable, these websites say that potential remains constant inside conducting solid sphere: Electric potential inside a conductor http://...
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### Why do metal valence electrons have low energies?

I know that metallic bonding happens because metal valence atoms have low energy so it can move free from atom to atom. But is there a reason why the have such low energies or is it just a fact that ...
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### Why don't insulators attract even if charged?

I understand that/ obviously, opposite charges will attract? However, I am still slightly confused about what happens if an insulator becomes charged. How come an insulator, which is charged, will ...
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### Does the surface charge density at the peak of a conical projection is smaller than that of on the peak of a conical hole?

The question is, A solid spherical conductor has a conical hole made at one end, ending in a point B and a small conical projection of same shape and size at the opposite end, ending in point A. If, ...
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### Electric field inside a conductor and induced charges

My textbook says two different things and I'm not sure how to reconcile these two: electric field inside a conductor is always 0. for a conductor with a cavity with a charge q inside it, the field ...
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### 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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### Ohm's law at high voltages [closed]

Ohm's law in its original form: The conductivity is constant for a given conductor at a given temperature.(Taken from H.C.Verma). My Question: When high voltages are impressed across a conductor, ...
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### How the current moves in the battery and outside the battery?

Does it move again to the negative terminal or stays at the positive terminal until the electrons all come .so the voltage will.be zero and current flow .I want simple clear explanation because i am ...
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### Electric Field of Perpendicular Charged Sheets

If we have two charged infinite sheets of charge density $\sigma$ and $-\sigma$ at right angles, how does the electric field look between them? By using Gauss's law to get that the field from one ...
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### If we remove all electrons from a conductor, how can the positive charge rearrange itself?

Explanations of conductors in electrostatics that I have encountered seem to describe positive charge spreading out, because you could say that lack of electrons can be thought of as abundance of ...
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### 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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### Does an electron physically flow? [duplicate]

In a DC current in a conductive wire, is it more accurate to think of one electron wiggling its way through a sea of electrons... or to think of one electron bumping into another, which bumps into ...
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### Gauss Law and Gauss surface [closed]

If we have hollow spherical conducting shell having no net charge. By placing positive point charge in the center of hollow conductor, negative charge will appear on inner face of conductor and ...
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### 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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### Why is the electric field in a conductor zero at equilibrium

This question has already been asked, but it has many answers and comments and I thought it would be tidyer not to add another discussion to it. In this forum and in many others, I find the following ...
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### continuity equation for uniform free charge distribution in electric field

Consider a neutral conductor with $n$ free carriers that are uniformly distributed inside the conductor when there is no electric field, $E_z = 0$. From the continuity equation, I can write down the ...
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### What is electric current? [closed]

I have been reading a book about electricity which states that: electric current is not the movement of electrons but the "impulse generated when free electrons orderly "jump" from one atom to the ...
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### 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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### Physics of throwing a power cord into a swimming pool

I saw a few questions related to swimming pools so I figured out I may ask here. If one takes a power cord that's plugged into a wall socket on one end and throws the other end in a bath, it may kill ...
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### Speed of electrons in a wire

What is the speed of electrons in a copper wire, used to charge a device? If there is a fixed speed, how is it determined?