Questions tagged [charge]
A fundamental property of matter which causes it to experience electromagnetic forces.
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What is the potential inside a hollow sphere with multipoles surrounding it?
If considering a hollow sphere with a surrounding uniform charge distribution, for example, it will have a constant and uniform potential throughout the inside of the hollow sphere because $\phi \sim ...
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0answers
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What is the second gravitational charge and second strong force charge? [on hold]
I have been watching documentaries and reading up on the 8 charge dimensions of Emergence Theory. In his Ted Talk (liked below) Garrett Lisi mentions 2 gravitational charge directions. Mass is ...
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1answer
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Conservation of bound charge?
It is intuitively obvious that free charge is conserved in vaccum. But when is bound charge conserved? I tried to find this by formula:
The charge conservation law in microscopic view (Assuming there ...
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1answer
50 views
Doubt on capacitors
Consider 4 capacitors connected in series
Now a +2Q and +4Q charges are given simultaneously at marked locations in figure. Ignore the points A and B.
My doubt is about the charge distribution that ...
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4answers
87 views
Is it possible to have non-integral multiple of $e$ as charge?
We have 2 similar balls. On one ball there is charge $e$ and on other no charge. I connect the balls using a metal wire. We know that the charge gets shared until they have the same charges. Thus we ...
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1answer
55 views
Can a free electron accelerating in a gravitational field absorb photons? [duplicate]
An 'free' electron accelerated in an electromagnetic field can both absorb and emit a photon. What about an election accelerating in a gravitational field?
Edit:
Some users have suggested that the ...
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1answer
85 views
Electric field at any point due to a continuous charge distribution
I am reading Purcell and Morin's Electricity and Magnetism 3rd Edition.
Equation ($1.22$):
$$\vec{E}(x,y,z)=\dfrac{1}{4 \pi \epsilon_0}
\int \dfrac{ρ\ (x^\prime, y^\prime, z^\prime)\ \hat{r}\ dx^\...
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Capacitance - Point charge inside Sphere with two layers of dielectric
A question in an exam was stated as follows:
A point charge $Q$ lies in the center of a dielectric sphere $\epsilon_1$ with radius $r_1$, which is itself cocentric with a dielectric sphere $\...
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1answer
60 views
Are positrons affected by electromagnetic fields?
I know positrons are anti-electrons. But electromagnetic fields aren't matter, and are pretty good for containing high energy particles, especially in something like a stellerator. So, would it be ...
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1answer
51 views
Charge accumulation in wire
I came across a question about charge accumulation. It states that if a steady current flows in a wire composed of a copper and iron wire of same area (see fig), will the charge accumulate on the ...
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1answer
27 views
How shall we compute the flux in this case?
I have a finite surface charge (in yellow) which cuts a Gaussian surface (in green).
Red points are the points of singularity on the Gaussian surface (i.e. where $\vec{E}$ is undefined).
Does this ...
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0answers
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Origin of the coulomb and ampere [migrated]
What is the historical origin of the size of the coulomb (and in turn, ampere)?
Currently (pardon the pun), the coulomb is defined in terms of the ampere. The ampere is in turn effectively defined by ...
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1answer
21 views
Doubt regarding direction of movement of electron wrt a field
An electron with an initial speed of $4.0 × 10^
6 m/s$
is brought to rest by an electric field. The mass and charge
of an electron are $9 × 10
^{-31} kg$ and $1.6 × 10
^{19}C$, respectively. Identify ...
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1answer
28 views
What happens if a positively charged object $+5q$ touches a negative charged object $-1q$? [closed]
What happens if a positively charged object +5q touches a negative charged object -1q?
Does the charge go from the negative object to the positive and they are left the first object with the charge +...
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0answers
31 views
Gauss's Law about excess charge on conductors, quantum mechanics, and doped semi-conductors
Does quantum mechanics predict that there is any probability of finding excess charge inside a conductor?
I've read an explanation about the distribution of excess charge placed on conductors. The ...
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2answers
60 views
How to plot the graph of this expression which involves Dirac delta function?
I was doing a problem on electrostatics which required finding the charge density from the given electric field and then plot a graph of the charge density. I was able to find the charge density which ...
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2answers
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How does Gauss's Law work with this charge density setup?
My friend and I are self-studying electrodynamics. In Griffiths, Introduction to Electrodynamics (1999), the concept of divergence is introduced mathematically and the following vector field is drawn.
...
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1answer
28 views
Force of electric charges
For the image below, lets say the top charge is 5C and the bottom 1C.
And consider this observation frozen at $t=0$, consider an imaginary horizontal line between the 2 charges denoting the centre of ...
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1answer
44 views
Electric potential - Batygin, Toptygin book
I found in Batygin and Toptygin problems in electrodynamics a particular problem:
Density of charge is $$\rho = \rho_{0}\cos{\alpha x} \cos{\beta y} \cos{\gamma z}$$ in whole space. Find electric ...
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0answers
14 views
Does a moving charged particle experience a force due to the magnetic dipole moment it produces interacting with external magnetic fields? [duplicate]
I have feeling that the force on a moving charged particle from an external field is due to the interaction of the external magnetic field with the magnetic field produced by the charged particle. ...
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2answers
41 views
Gain in electric potential energy or loss?
When a unit positive charge (say A) is in the field of a unit negative charge (B) , it attracts A towards it. But when it moves towards B its potential energy changes to kinetic energy and by the time ...
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1answer
23 views
How can a get the lambda in the electric field of an infinite filament formula?
This is the formula that i have to apply in the problem. Is the lambda a constant?
$$E=2K_o\frac{\lambda}{r}$$
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1answer
23 views
Total charge in an insulated dielectric
Is it trivial that the total charge in an insulated polarized dielectric is zero??
My T.A. mentioned it in class but I didn't quite got how the "insulated" part of the affirmation could lead to this ...
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2answers
32 views
Can an electrostatic field itself be insulated, as opposed to creating resistance to a current?
Is it possible to insulate an electrostatic field itself, as opposed to preventing electrons from moving by creating resistance?
Specifically, if we position an isolated charge on one side of a ...
9
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1answer
767 views
Is it a coincidence that quarks have exactly -1/3 or 2/3 the electron's charge? [duplicate]
I have read these questions:
Why do quarks have a fractional charge?
Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges?
Hypercharge for $U(1)$ ...
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Derivation of the formula for the electrostatic force with a dielectric in the middle
In the answer by user JohnRennie on the post "What is the force in the presence of a dielectric?", it says:
If the dielectric constant is $K$ and the thickness of the dielectric is $t$, then for ...
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3answers
58 views
Gauss law with two infinite planes
The electric field of an infinite plane above its surface is $E=\frac{\rho}{2\epsilon_0}$, where $\rho$ is the surface charge density and $\epsilon$ is the permittivity of free space. If we have two ...
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How is the charge density on the surface of a PEC wedge $\rho=- \frac{\nu C_2\varepsilon_0}{r^{1-\nu}}$ given by the electric and magnetic fields?
For a perfectly conducting wedge the components $E_z/H_z$ (parallel) and $E_t/H_z$ (tangential) of the electrical and magnetic fields are given by
\begin{align}
E_z & = j\omega \mu_0 C_1 r^v (\nu \...
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1answer
25 views
Does “charge density” account for all charges, or only negative charges, and do opposite charges cancel each other or add?
if I had 10 electrons and 8 protons in a meter cubed would the charge density be 2 or 10 or 18? I suspect 10, but I don't see why charge density only takes into account the negative charges.
another ...
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0answers
33 views
Fusion & vaporization of a solid
The values for electric dipoles in a salt (gas phase) are huge respect to organic molecules. The following seems a reasonable question (although it might be wrong):
Is it possible to consider ...
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2answers
22 views
Is the charge density of a polarised object, 0 or negative?
if I place a negative point charge above a metal plate so that the metal plate polarizes completely with all the electrons on the bottom and a bunch of ions on top, would the charge density on the top ...
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1answer
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DC Battery Charging Question
I have a 7.4v LiIon that hold 1450ma. I have a variable DC bench power supply that I can crank up or down and adjust as needed. I want to quickly charge the battery and noticed if I adjust the ...
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Can someone explain how charge stability diagrams work?
Sorry I'm relatively new to this area. I keep seeing figures like the one shown here
and I'm unsure how to interpret what it means. What do the numbers (0,0), (1,0) etc. come from, and what causes ...
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0answers
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Bound Surface Charge Density and Polarisation
Here's what I read in Introduction to Electrodynamics by D.J.Griffiths:
Given the polarisation vector $\vec P$ and the unit vector normal to the surface $\vec n$, we can find the surface bound charge ...
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1answer
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The effects of particles with complex electromagnetic charges on current physics
I've just had a crazy idea, and I need some input on it. It is entirely theoretical, and maybe I don't understand much about how electromagnetism works, but what if particles could have complex ...
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2answers
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Electrostatics: Charge Distribution and Energy - Confusion
Consider the following situation:
Between two metallic plates, are two dielectrics of dielectric constants $K$1 and $K$2. The surface charge density on the upper metallic plate is $\sigma$, and that ...
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1answer
57 views
Gauge transformations with varying phase give us conservation of the charge density. Hence charged particles cannot move?
I stumbled upon the following paragraph in Quark confinement and Topology of gauge theories by Polyakov
"Gauge invariance with constant phase $\Psi \to e^{i \alpha}$ lead to conservation of the
...
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2answers
58 views
“why is current the derivative of charge and not integral of charge?”
Current is defined as the amount of charge passing a given point per unit time. The word amount throws me off. sorry if this question seems dumb, but
why can current not be equal to integral of ...
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Differential Symmetry Between Matter & Charge
Baryonic matter and anti matter represent halves of a symmetry (broken, to all appearances) that balances the net value of energy in the universe.
Charge (positive and negative) also represent a ...
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42 views
How much energy is stored in the charge when electron and positron are created?
I had asked "The energy of electron formation becomes mass, charge, spin and momentum. How much becomes the charge? We know how much becomes mass: E = mc^2. What is the equation for the charge?". ...
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4answers
85 views
Why is electric field of an infinite plate constant at all points?
I know from Gauss law, it is $\vec{E}=\dfrac{\sigma}{2 \epsilon_0}(\hat{n})$ at all points. But it doesn't make sense because of the inverse square nature of electric field which suggests if you move ...
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1answer
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Motion of an electron near a proton [closed]
Statement of the problem:
Consider an electron and a proton that are initially at rest separated $a$ meters. Do not take into account the movement of the proton, because its mass is much greater ...
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1answer
52 views
Change in electric potential energy after sphere splits in two
The problem:
Consider a uniformly charged sphere of radius $R$ and charge $Q$ and then they separate into two spherical halves of equal volume and charge, and both get to stabilize. Determine the ...
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1answer
39 views
Why is electric field inside a charge distribution not infinite?
Let's consider electric field due to a charge distribution at a point $P$ inside the charge distribution. Due to inverse square nature of electric field, electric field due to an element volume charge ...
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0answers
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Two dimensional hyperbolic potential has no charge density but a surface charge density?
I am learning about electric potential, and I am confused about what exactly is going on in the following situation:
Say we have a potential $V =- V_0 \frac{xy}{a^2}$
This means that $\nabla^2V=0$.
...
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1answer
50 views
In charge renormalization equation, $e=e_{0}^{2}\left[1-e_{0}^{2}A\right]$, how can an infinite $e_{0}$ and $A$ give finite $e$ in any limit?
In Griffiths elementary particle book (chapter 7, 'Quantum electrodynamics', equation 7.188), one gets the following equation for the vacuum polarization calculated to one loop correction.
$$\frac{e_{...
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1answer
28 views
Quantifying electrical energy stored in a plasma
The energy stored in the electric field in a medium is given by $U = \frac{1}{2} \epsilon E^2$, where $\epsilon$ is the permittivity in the medium and $E$ is the electric field. When considering a ...
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3answers
85 views
Lorentz invariance of charge in classical electrodynamics - What volumes to look at?
There is an (plausible claim) that the charge is a lorentz invariant quantity (best example would be that the electron as a point charge has the same charge in every frame of reference).
I'm trying ...
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2answers
42 views
Force between charges
Let us take two opposite charges are moving away from each other in directly opposite direction ......it's obvious that kinetic energy of both of them will decrease as both of them are attracting each ...
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3answers
2k views
Can the center of charge and center of mass of an electron differ in quantum mechanics?
Traditionally for a free electron, we presume the expectation of its location (place of the center of mass) and the center of charge at the same place. Although this seemed to be reasonable for a ...
