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Charge conservation in ohmic material - Apparent paradox

As I understand it, the questioner's claim is that the equation $\frac{\partial Q}{\partial t}+\frac{\sigma}{\epsilon_0}Q=0$ is derived only from the standard Maxwell equations. As a result, $Q$ is ...
HEMMI's user avatar
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1 vote

Why don't positively charged metal ions (in a wire) move but electrons do?

The question is why the ions are localised and form a lattice, unlike the electrons. The reason is that they are typically 10000-100000 times heavier than electrons. Therefore they have very small, ...
my2cts's user avatar
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1 vote
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Why don't positively charged metal ions (in a wire) move but electrons do?

To answer this question, it is necessary to understand the structure of the metal at the atomic scale. A very simple way to see it is that the positively charged nuclei sit at fixed points in a ...
paulina's user avatar
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3 votes

Why don't positively charged metal ions (in a wire) move but electrons do?

It’s because the ions aren’t delocalized like the electrons are.
Hannah's user avatar
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3 votes
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Charge conservation in ohmic material - Apparent paradox

Differential problems are defined in a domain and require boundary conditions, and the solution to be "regular enough" for the differential equations to hold. If you're dealing with a body ...
basics's user avatar
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-1 votes

Dipoles as vectors

"why does it make sense that the resultant of those dipoles would give the same time period as of the original question" Your point is valid, it does feel and and seems misleading that the ...
Kyathallous's user avatar
2 votes

Dipoles as vectors

Rotational dynamics. The governing equation of the rotational dynamics of a system w.r.t. to its center of mass reads $$\frac{d \boldsymbol{\Gamma}_G}{dt} = \mathbf{M}_G^{ext} \ .$$ Considering only ...
basics's user avatar
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2 votes

Densities at a Point

It is a matter of approximation. Yes charges would not normally be concentrated into a point, but the specifics of charge distribution will normally contribute to second and third order effects. For ...
Cryo's user avatar
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1 vote

Why is the electric potential from a positive sphere not negative?

You have a really wonderful doubt. You did the calculations right, except for the dot product. It is a error easy to overlook.(Note: bold means vectors). Dot product E.dr is equal to Edrcos$\theta$. ...
EagerToLearn's user avatar
0 votes

Why is the electric potential from a positive sphere not negative?

The potential energy is the work done on the unit charge as it is moved from $\infty$ to $r$. That is, suppose you are pushing the charge inwards, then the change in PE is the work you do. That means ...
John Rennie's user avatar
3 votes

Densities at a Point

You are on the right track. Matter and charge are often treated as continuous. It is a good approximation. Air exerts a pressure on the walls. You think of it as a continuous fluid. In reality, the ...
mmesser314's user avatar
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0 votes

Surface charge density within a parallel plate capacitor on different voltages

Changing the potentials on the capacitor plates will not change the inside surface charges as long as the potential difference between the plates is constant. However, for a given potential difference ...
freecharly's user avatar
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1 vote

Divergence of Electric Field of Point Charge is always zero

You missed one point while calculation. Let me make calculation more easier by going towards spherical polar coordinates. Since $\vec E$ = $E_r \hat r + E_\theta \hat \theta + E_\phi \hat \phi$ = $\...
Chauhan's user avatar
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4 votes
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Divergence of Electric Field of Point Charge is always zero

Because this a point charge, the charge is 0 everywhere except the origin. This is consistent (everywhere except the origin) with your calculation that found the divergence to be 0. What you didn't ...
The Photon's user avatar
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3 votes

How many photons pass through us every second?

Say we have a beam of ordinary electromagnetic waves, with power $P$. Then the energy passing a plane, each second, is $P$. If it is monochromatic with frequency $\nu$ then the number of photons per ...
Andrew Steane's user avatar
3 votes

Is charge an intrinsic property of "all" the fundamental particles or an intrinsic property of "certain" fundamental particles?

The way we describe particles in quantum field theory is as states of a quantum field. For example there is an electron field that fills all of space. If we excite this field by adding energy to it ...
John Rennie's user avatar
1 vote

Is charge an intrinsic property of "all" the fundamental particles or an intrinsic property of "certain" fundamental particles?

Electrical charge is an intrinsic property of certain particles- not all of them. The ones that are charged are always charged- that is, there is no such thing as an uncharged electron.
niels nielsen's user avatar
5 votes

Why is the universe charge-neutral?

Charge conservation says that a universe which began charge-neutral would have remained charge-neutral. But why assume that it started out charge-neutral? A better way to ask the question is to ...
rob's user avatar
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6 votes

Why is the universe charge-neutral?

A nonzero net charge density is incompatible with the cosmological principle. Homogeneity implies a constant electromagnetic field, which implies via Gauss's law that the contained charge is zero. The ...
benrg's user avatar
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0 votes
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Why is the universe charge-neutral?

There is as of yet insufficient data to produce a meaningful answer. I would certainly love to tell you that the universe is charge-neutral, because that would imply I know enough about the Universe ...
controlgroup's user avatar
0 votes

Is it valid to write $\int{dq}$?

Yes, you can write $q=\int\mathrm dq$, even if the charge is discrete. To include discrete charges in continuous calculus, we use Dirac's "delta density distribution," defined by $$ \delta(x)...
rob's user avatar
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1 vote

Is it valid to write $\int{dq}$?

It is correct to suspect that something more fundamental is occurring when the integral is written with the quantity $\mathrm{d}q$. But consider the electric field created by a charge. How can one ...
Stephen Elliott's user avatar
8 votes
Accepted

Is it valid to write $\int{dq}$?

The formula assumes a continuous charge distribution [1]. Such a thing may not actually exist. However, before you throw away the formula, pause to consider that the alternative you're proposing -- a ...
anon's user avatar
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0 votes

Uniqueness of charge distribution in conductor

If you assume that the charge is all distributed on the surface of the conductor then your boundary conditions (derived from Maxwell's equations) give you a relation for the surface charge density ...
QPhysl's user avatar
  • 145
0 votes

How do charges on two conductors charged by the same battery relate to each other?

I have a bit of a different take on this. The degree to which the two spheres will become "charged" will depend on the degree to which the spheres are physically isolated from one another. ...
Bob D's user avatar
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0 votes

How do charges on two conductors charged by the same battery relate to each other?

Assumption 2 is incorrect. You can't say you'll assume thin wires, and so neglect the charge. However thin the wires are, the electric field along the wires must be zero, which is what leads to each ...
BaddDadd's user avatar
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0 votes

How do charges on two conductors charged by the same battery relate to each other?

Not all of the assumptions that you have imposed can be satisfied. Let's look at All the elements are located at quite large distances from each other and $\dots$ we can neglect charges on these wires....
Farcher's user avatar
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8 votes
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Accumulated charge in conductors

(1) If your question is why the charge doesn't leave the metal, the answer is that there is an energy barrier (usually on the order of an electron volt) called work function which prevents the ...
freecharly's user avatar
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1 vote

Gauss's Law vs Image charges

You are confusing things. The method of images does not provide you with the potential inside a conductor; it only gives you the potential outside. The idea of the method is that you should look for a ...
QuantumBrachistochrone's user avatar
2 votes

Are there exceptions to Gauss's law?

The trick is that Gauss's law tells you about the flux of the Electric field through your surface, it doesn't actually tell you the electric field directly. So regardless of your charge distribution ...
Daniel Jensen's user avatar
0 votes

Total charge on a polarized neutral dielectric

In your question you mention that $\rho_\text{b}=0$ doesn't make sense. It is indeed not true that $\rho_\text{b} = 0$, but the integral of it over the volume of the dielectric is: $$ \int_V\mathrm{d}...
Jonathan Huang's user avatar
0 votes

Total charge on a polarized neutral dielectric

The total flux is only associated with free charges. It’s the flux density that increases inside the dielectric because dielectric medium offers less resistance to lines of electric field and these ...
Muhammad Amin's user avatar
0 votes

Why potential due to system of charges is scalar sum?

Consider a system if $n$ point charges (which I'll label from $1$ to $n$). We want to find the electric potential, $V$, at a certain position $\vec{r}$. This is defined as the electric potential ...
Anis Manuchehri-Ramirez's user avatar
1 vote

Potential on conducting shell without image charge

PS: The question's title was changed in an edit by OP, it previously didn't contain "without images", that's why this answer was valid. (And of course it gives the right numbers.) Since we ...
Jos Bergervoet's user avatar
0 votes

Induced charges due to uniform electric field

The previous answers have already addressed this question wrt the induced charges. But another way to look at it is by considering a charged isolated conductor that is then introduced into an electric ...
Nf23kdr's user avatar
  • 61
1 vote

A General Analysis of Charge Distribution inside conductors

A conductor is a body within which: Charge moves freely Charge cannot escape through the surface A corollary of the first point is that the net force on any infinitesimal volume of charge must be ...
Sam Gallagher's user avatar
3 votes

Dirac's quantisation condition and non-quantised charge

The identity $e g = 2\pi n$ (setting $\hbar=1$) has to hold for ALL electric and magnetic charges. Let $e_0$ be the smallest electric charge and let $g_0$ be the smallest magnetic charge (smallest in ...
Prahar's user avatar
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1 vote
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Induced charges due to uniform electric field

$\dots$ will it depend on the magnitude of the electric field? No electric field inside a conductor, when there is an external field, means that charges must move within the conductor (induced charges)...
Farcher's user avatar
  • 97.4k
2 votes

Induced charges due to uniform electric field

(1) When you put an isolated finite metallic object into an uniform electric field, there will be an equal amount of positive and negative charge induced. The total induced charge is thus zero. (2) If ...
freecharly's user avatar
  • 16.9k
0 votes

Is voltage a difference between two charged objects or two positions in a field?

"Like, one pole is positively charged, and the other is negatively charged. And if that is so, then I don't understand why we are not considering any object that is electrically neutral to be of ...
Philip Wood's user avatar
7 votes
Accepted

Is Coulomb's law wrong?

Coulomb's law only holds for static situations. It describes the force between particles that are always at rest with each other. The situation described in the question is not a static, as the ...
William Elderfield's user avatar
2 votes

Is Coulomb's law wrong?

You are making a beginner's misunderstanding, even though it confused all the great minds a few centuries back. Coulomb's law is correct, but it is not what you think it is doing, and you are using it ...
naturallyInconsistent's user avatar
1 vote

Is Coulomb's law wrong?

Electrostatic as well as electromagnetic force is transmitted with photons, so there is no contradiction. Any "immediate" change is immediate in terms of information travel speed. It cannot ...
Radek D's user avatar
  • 135
3 votes

Does QED explain why Moving charge produce magnetic field?

It's actually the other way round. Maxwell's equations explain why a moving charge produces a magnetic field, and we get quantum electrodynamics by quantising Maxwell's equations. The link between ...
John Rennie's user avatar
3 votes

Radiation from accelerated charged in a co-accelerated reference frame

It is quite easy, despite all the difficulties the comments are warning us about, to express this question in a mathematically tractable way: (and to actually answer it!) Solve the Maxwell equations ...
Jos Bergervoet's user avatar
-1 votes

Radiation from accelerated charged in a co-accelerated reference frame

if I sit on a accelerated charge particle I will not observe radiation since particle is at rest acc to me. If the particle is deflected in the magnetic field, for example, you either continue to ‘...
HolgerFiedler's user avatar

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