# 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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1answer
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### Obtaining a copy of R. W. O'Brien's PhD thesis

I have read lots of papers about high-contrast material, but lots of them cite the PhD thesis by R. W. O'Brien (see, for example Reference 2 here), but I couldn't find this dissertation. Can anyone ...
1answer
523 views

### Why does a half filled Brillouin zone result in conductivity?

As stated in the title, why does a half filled Brillouin zone result in an element being a conductor, or conversely, why does a filled Brillouin zone result in an insulator?
1answer
1k views

### Magnetic Wire Doesn't conduct Electricity

I recently bought a 22 and 30 gauge loop of magnetic wire from radio-shack. The loops of wire were colored differently (if this makes any difference) and on the package it noted how these wires were ...
0answers
48 views

### Insulation for magnetic fields [duplicate]

How can I insulate conductors independently one off the other, where they pass through a magnetic field? Are there a techniques or alloys? There is a issue how to insulate copper wire where current ...
4answers
4k views

### Measuring electric conductivity

My daughter is doing a science experiment on which metal (e.g., copper, silver, aluminum, iron) has maximum electric conductivity. We are assuming we can accomplish this by using different metal, 3 to ...
1answer
80 views

### Wave guide boundary conditions

Why only the normal component of Electric field and the parallel component of Magnetic field exist at the surface of a wave guide or any conductor?
2answers
579 views

### Charged dieletric/conductor in capacitor

It is a standard problem to consider a dielectric or a conductor between the parallel plates of a capacitor. But what happens to capacity, voltage, charge, inserting between the plates of an ideal ...
6answers
1k views

### What keeps electrons on a negatively-charged conductor from leaving?

Imagine a negatively charged conductor in a vacuum. The excess electrons will be spread out over the surface such that the net electric field inside the conductor is zero. What keeps these extra ...
4answers
2k views

### Rigorously prove that electric field is zero in a perfect conductor

I have ran into a problem while trying to prove that the electric field is zero in a perfect conductor My argument went something like this: We know that: $$\vec J = \sigma \vec E$$ In a ...
3answers
1k views

### Why does my measured I-V curve for a film of aluminum suggest high resistance?

I plotted the I-V curve between two points (few microns apart) on a thin aluminum film. I expected this metal to be a conductor and have a much lower resistance, but the slope suggests that it is ...
1answer
97 views

### What are the consequences of connecting a non-ideal conductor to a battery in open loop?

Suppose I have a battery with $\Delta V=5[\mathrm{V}]$. Now I connect a piece of a metal wire to the "+" side of the battery only. Let's assume that the ambient air is not conductive at all: Are ...
0answers
259 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 ...
1answer
454 views

1answer
543 views

### Image charge method to find electric field [closed]

The following is a question from my tutorial on boundary value problems and image charge method- A point charge +q is placed at (0, 0, d) above a grounded infinite conducting plane defined by z = 0. ...
2answers
791 views

### What causes the random movement of particles inside a conductor?

I'm reading about currents in electricity right now, and it was mentioned that even if there's no electric field inside a conductor, charged particles inside are still undergoing random movement. I ...
5answers
7k views

### Gauss Theorem:Electric field of an uniformly charged non-conducting spherical shell

I want to know the electric field of an uniformly charged non-conducting spherical shell. I know that in case of conductors(metals),the sphere can be shell or it can be solid,but in both the cases ,...
3answers
13k views

### When two spheres of equal charge make contact, why does the larger sphere gain more charge?

Suppose that two spheres, $S_1$ and $S_2,$ with radii $R_1$ and $R_2$ resp. have the same uniform charge $Q$ and $R_1 > R_2.$ After they are forced to come in contact, why does $S_1$ gain more ...
1answer
617 views

### Magnetic Force on a Ferromagenetic Material

I am currently working on a project involving solenoids, and I needed a force(Newtons, not a measure of magnetic field strength) equation. What I came up with after some digging around on the internet,...
6answers
8k views

### Do electrons flow only on the surface of a wire?

Since the $\vec{E}$ field inside a "perfect" conductor is zero, do the electrons(the current) flow only on the outer surface? This has bothered me since I studied electromagnetism. Thank you for ...
1answer
1k views

### Conducting sphere with a cavity

I have a conducting sphere which has a cavity in it. The cavity is not at the center of the sphere. If a charge $+q$ is placed inside the cavity (with the sphere remaining neutral as a whole), what ...
1answer
160 views

### Does charge distribute itself uniformly on a conductor?

An excerpt from a beginning E&M book [...] In other words, the surface of a conductor is an equipotential surface under static conditions. [...] Summarizing the boundary conditions at the ...
1answer
258 views

### Magnetic Field in the presence of a conductor

I am studying for my quals and came across an old question that reads like the following: There are two regions in space separated by an infinite conducting plane. Region 1 has a magnetic dipole ...
1answer
1k views

### Electric Field-Drift Velocity

Why is the net velocity of electrons (drift velocity) considered to be zero, before setting up any electric field? I mean in the derivation of the equation drift velocity: $$v =-\frac{Eet}{m}$$
2answers
280 views

### Drude model: A concerning approach to $\tau$ hurts Ohm's Law

Here's the question. Between two points, $a$ and $b$, if an object is accelerated between them, it will cross the distance between them in time $t=\sqrt{2\frac{d}{a}}$. So, if the acceleration is ...
4answers
10k views

### Why does a short circuit generate fire?

When a short circuit occurs it's obvious that there is fire. How come electric energy turns out to be heat energy? What causes the conductors to get hot when short circuit is present.
2answers
1k views

### Two capacitor plates with equal positive charges $q$

I read in a book that if both the plates of a parallel plate capacitor are given equal positive charges $q$, then the charges on the facing surfaces will be zero and the charge on the outer surfaces ...
1answer
66 views

### Natural electricity in the atmosphere - lightning

If air is such a poor electrical conductor, how can lightning be produced that appears to travel through it?
4answers
8k views

### Why can x-rays pass and not radio waves?

If we stand in an elevator or other metal containers we lose radio signals etc the very same reason for which we cannot see across a block of metal that light cannot penetrate it. However x-rays and ...
0answers
160 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?
3answers
3k views

### Why the electric field inside a conductor is zero? [duplicate]

In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero.
1answer
251 views

### In Leyden Jars, how does the outer metal get charged?

In a Leyden jar, I have read that a charged object is brought in contact with the conductor in contact with the metal inside the jar, thus giving the inner metal a similar charge. And the metal ...
1answer
2k views

### Charge Distribution On Hollow Sphere

Say we have a hollow conducting sphere (with some finite thickness). If this object has an excess charge amounting to +Q coulomb, and there is no extra electric field in the surroundings (due to ...
3answers
673 views

### Gravitational doubt [duplicate]

If we can shield a charge from electrical forces by putting it inside a hollow conductor. Can we shield a body from gravitational influence of nearby matter by putting it inside a hollow sphere or by ...
9answers
47k views

### Does electricity flow on the surface of a wire or in the interior?

I was having a conversation with my father and father-in-law, both of whom are in electric related work, and we came to a point where none of us knew how to proceed. I was under the impression that ...
2answers
4k views

### Does the induced charge on a conductor stay at the surface?

My textbook says that when a conductor is placed in an electric field, the electrons in it realign so that the net electric field inside the conductor is zero. There isn't a proof for this. It merely ...
3answers
5k views

### Charge distribution on plates [closed]

$A,B,C$ are $3$ identical metallic plates. Initially, charges $Q$, $4Q$ and $2Q$ were given to $A$,$B$ and $C$ respectively. Find final charge distributions when $B$ was earthed and $A$ and $C$ were ...
3answers
16k views

### If the current is increased, is there more charge flowing or is it moving quicker?

Problem Current is the amount of charge that is flowing through a component per unit of time. For a given voltage, Ohm's law tells us that if we increase the resistance, then the current must ...
5answers
8k views

### Force on a point charge $q$ inside a cavity in an uncharged conductor

This is problem 2.40 from Introduction to Electrodynamics by D. J. Griffiths: A point charge $q$ is inside a cavity (not necessarily spherical or anything similarly regular) in an uncharged ...
0answers
69 views

### Earth as a conductor and emf produced? [closed]

Since about 73% of total surface of Earth is occupied by water, its internal is also occupied largely by hot molten mass.Let,the whole earth is considered a conductor.Sun is a source of gravitational ...
1answer
101 views

### Charging a capacitor

Below is an excerpt from a physics textbook: One common way to charge a capacitor is to connect these two wires to opposite terminals of a battery. Once the charges $Q$ and $-Q$ are established on ...
0answers
126 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? • ...
1answer
273 views

### How can electrons move along the conductive wire? ( seems to be a paradox )

Tangential components of the electric field across an interface between two media, with no impressed magnetic current densities along the boundary of the interface, are continuous. So: \$ n \times (E_2 ...
5answers
9k views

### Why is the electric field inside a conductor zero in equilibrium?

My textbook says the field inside a conductor must be zero in order for the system to be equilibrium and therefore there must be no excess charge inside. Their proof: 1) Place a gaussian surface ...
1answer
109 views

### Electric potential and movement of charges

If electric field is not present does that mean that charges achieve condition of electrostatics I.e, charges are stationary ? But we say that stationary charge can produce electric field. I read ...
0answers
164 views

### Field inside a conductor?

If the above image is a cross section of a conductor, the field at the point shown is not zero. So the field inside a conductor is not zero at all points. You could argue that the electrons would ...
2answers
867 views

### Migration of an ion in a non-conductive medium

Someone asked me why, when performing DNA electrophoresis we need to put the gel inside a conducting buffer. Couldn't we just run it in distilled water? My answer was that if we had distilled water ...
5answers
13k views

### Conductors and their charge?

Why does excess positive charge stay on the surface of a conductor? This is what I understood from: How does positive charge spread out in conductors? and other resources on the web: If there is a ...