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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2answers
679 views

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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1answer
22 views

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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1answer
360 views

Infinite conductor plane near a point charge

If i have an infinite conductor plane near a point charge ( that is the configuration of the common "Method of images" example), if i calculate the conductor's inducted charged density as $$\sigma =-\...
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3answers
304 views

Why is the electric field across a perfect wire zero?

I’ve looked at the answers given to the previous times this question has been asked, but I still don’t seem to understand how this holds in the case of a closed circuit. Here’s an explanation given ...
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1answer
564 views

The charge surface distribution of a conductor with a non centered charge

A point like charge Q is placed inside the cavity of a spherical conductor of an internal radius R1 and external radius R2 initially neutral(uncharged) (see the figure), the question is how is the ...
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1answer
98 views

Electrons close to Fermi-Conductivity

As a student of electrical and computer engineering solid state physics is not my thing so I might have fundamental blanks here and there. I really like this course and I try to gain as much as ...
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1answer
173 views

Why the electric field inside a capacitor isn't nul?

I have a doubt regarding this point, i know that the electric field inside a conductor is null, and the capacitor is made by two conducting plates, so what s the point here?
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1answer
1k views

Can you conduct electricity through a banana peel?

While grabbing a banana for breakfast today I got zapped due to static electricity building up while I was moving on my chair, but the conductor I was grabbing was said banana. Is it possible to ...
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1answer
382 views

A point charge near an infinite conducting plane

I want to calculate (with Poisson's equation) the electric field in the region containing a point charge near an infinite conducting plane with 0 potential. My textbook uses V(x,y,z)= 0 for every x,y,...
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1answer
65 views

Replacing an equipotential surface with a conductor

If i replace an equipotential surface generated by a charge distribution with a conductor (i already know that the conductor has an equipotential surface), what assures me that the original charge ...
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3answers
5k views

Tree vs lightning rod: why does one burn and the other not?

I have this simple question, but I cannot find the answer. I saw this video about a plane getting hit by lightning. In it, Captain Joe explains why people do not get electrocuted. This has a simple ...
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2answers
258 views

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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1answer
47 views

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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2answers
636 views

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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2answers
430 views

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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1answer
67 views

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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0answers
495 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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3answers
204 views

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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1answer
674 views

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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1answer
89 views

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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3answers
148 views

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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2answers
2k views

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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5answers
22k views

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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3answers
601 views

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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2answers
852 views

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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1answer
258 views

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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1answer
277 views

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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2answers
456 views

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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2answers
4k views

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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0answers
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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1answer
92 views

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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1answer
178 views

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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1answer
363 views

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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3answers
3k views

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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3answers
493 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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2answers
511 views

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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2answers
505 views

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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0answers
223 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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1answer
43 views

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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1answer
142 views

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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1answer
146 views

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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2answers
369 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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0answers
34 views

Two conductors in free space [closed]

In free space there are two masses: Metallic sphere of mass $M$, radius $R$ and total charge equal to 0. It has also a resistivity $\rho$. Metallic sphere of mass $m$, radius $r$ and charge $...
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0answers
142 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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2answers
364 views

If energy delivered to the resistor is not the kinetic energy of the electrons then how is it delivered? [duplicate]

In a help session by Walter Lewin he says that the energy delivered to the resistor is not the kinetic energy of the electrons. If not how is energy delivered. The video link is https://youtu.be/...
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0answers
79 views

Potential near a strip - conformal maps [closed]

I need to solve this problem: An infinitly long wire(at $y=h,x=0$) placed (symmetrically) next to a semi-infinite conducting strip ($y<0$ and $|x|<a/2$). Find the potential in all space. ...
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1answer
310 views

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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1answer
414 views

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?
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2answers
256 views

What will happen to the charges if we dig a hole in a hollow charged conductor(example a hollow conducting sphere)?

I am confused about how will the charges on outer surface of a hollow charged conductor would distribute themselves to make electric field zero inside after we dig a hole in the hollow conductor going ...
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2answers
2k views

Do electrons move around a circuit?

We could imagine a simple electronic circuit composed by a power source and a resistor. It is usual find descriptions as "The moving charged particles in an electric current are called charge ...