Electrostatics is concerned with the electrical fields and scalar potentials of stationary electrical charges and charge distributions. Use this for questions about electromagnetic situations in which currents and magnetic fields are absent, otherwise use [tag:electromagnetism] and/or [tag:magnetic-...

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Problem from Purcell and Morin's Electricity and Magnetism: Holding the charge in place

This is the problem given in Purcell and Morin's electricity and magnetism book. (Problem 3.2 If you have the book) Figure: I was able to figure out that the charges on A,B,C,D cant be held ...
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46 views

Why is the susceptibility $\chi(t)$ real?

So my question is quite simple I suppose, and perhaps trivial. It is known that the frequency domain susceptbility $\chi(\omega)$ is complex, and that the two parts can be related with the Kramers-...
3
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3answers
116 views

What does the Dirac delta function physically do while deriving Gauss Law form Coulomb's law?

While doing this derivation, the the source coordinates are mentioned as "$s$" and the coordinate of the point at which field is to be calculated is mentioned as "$r$". Kindly follow this Wikipedia ...
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0answers
101 views

Electric field due to charged disc, on the plane of the disc [closed]

A standard problem in finding the field is that of a uniformly charged disc, on its axis, but for this problem I'm supposed to find the potential and the field on the edge of the disc, i.e. in the ...
3
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3answers
296 views

Difference between $E$ field configuration, sheet of charge: infinite sheet of charge, conducting vs. non-conducting

This is a very easy question, but I often confused myself. Perhaps someone could explain this concept again: A non-conducting infinite sheet of charge has the electric field configuration \begin{...
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0answers
31 views

Scale-covariant decomposition of capacitance

I'm wondering if there is any good insight of how to evaluate a given capacitive geometry in such a way that it would be expressed as a function that depends only on two components: as a geometric ...
3
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1answer
123 views

Interpretation of a term in the Maxwell stress tensor

With no magnetism, the $xx$ component of the Maxwell stress tensor $T$ is $$T_{xx} = \frac{1}{2}(E_x^2 - E_y^2 - E_z^2)$$ I can see why there should be a $+E_x^2$ term, but intuitively I don't see why ...
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0answers
37 views

Why charge density is higher in the sharp edges of conductor? [duplicate]

If we have a conductor which is in electrostatic equilibrium, then the charge distribution over this surface $\sigma$ is greatest at the sharp edges of that surface. Why is this the case? It is ...
3
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2answers
791 views

Why can't charge be in a stable equilibrium in electrostatic field?

I am reading Feynman's Lectures volume_II where he discussed the impossibility of the presence of stable equilibrium in an electrostatic field. There are no points of stable equilibrium in any ...
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2answers
3k views

Electric potential inside a conductor

I just began studying electrostatics in university, and I didn't understand completely why the electric potential due to a conducting sphere is $$ V(\vec{r})=\begin{cases} \dfrac{1}{4\pi\...
3
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2answers
164 views

Question regarding Van De Graff generator Belt

I have made a VDG generator with a rubber band as the belt and a glass roller. It doesnt seem to work because I think the rubber band may be conductive. I was thinking of using other materials for ...
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0answers
75 views

What would be the charge distribution in a Klein bottle?

We know that for any conductor the charge lies on the outer surface at electrostatic equilibrium. What would happen if a Klein bottle is made up of a conductor and a charge is placed on it?
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1answer
662 views

Boundary conditions in Electrostatics

If I have a grounded conducting material, then I know that $\phi=0$ inside this material, no matter what the electric configuration in the surrounding will be. Now I have a conducting material that ...
3
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0answers
88 views

What are the parameters for Pauli's repulsion pseudo-force?

I have found the following formula for the repulsion potential due to the overlap of the electron clouds arising from Pauli's exclusion principle: $$V = A\exp(-r/\phi)$$ where r is the distance ...
3
votes
1answer
145 views

Electricity from lightning

According to the internet, a lightning strike contains about 5 billion joules or 5 GJ. How was this calculated? Another thing: Once the lightning strike a metal grounded rod, a current will flow. ...
3
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1answer
155 views

Is the system of equations of electrostatics underdetermined or overdetermined? [duplicate]

The following equations are equations of electrostatics: $$\nabla \times \vec E=0$$ $$\nabla\cdot\vec E=\dfrac{\rho}{\epsilon_0}.$$ These are 4 independent equations, while $\vec E$ has only 3 ...
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4answers
681 views

Does an object's movement affect the likelihood of being struck by lightning?

Does the state of whether an object if moving or stationary affect the likelihood of it being struck by lightning? I suppose some things that could be considered would be: Whether the movement ...
3
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0answers
125 views

Electrodynamics and induced EMF question [closed]

A very long straight wire carries a current I. A plane rectangular coil of high resistance, with sides of length $a$ and $b$, is coplanar with the wire. One of the sides of length $a$ is parallel to ...
3
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0answers
288 views

How to set up Schrodinger's equation for an electron (as a charge distribution) under its own electrostatic field

After reading about the hydrogen atom and understanding how Schrodinger's equation explains most part of the atomic spectrum of an hydrogen atom, and also came to know that, it explains most of the ...
3
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0answers
68 views

Modeling the formation of a stellar system and matter accretion

I am trying to figure out what do I need to know to properly simulate the creation of a solar system from a particle cloud with random distribution of hydrogen atoms. Being more of a programming ...
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0answers
50 views

Nature of electricity [duplicate]

Suppose a lightning strikes and there is an iron rod and a coconut tree. How does the electricity know that rod is the least resistant path before hand.
3
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2answers
866 views

Electrostatics:Basic question on electric current

I've got two questions for you. Electric current is the flow of electrons across a conductor.Why has it always got to do with electrons and not with protons? (I know neutrons are not eligible for ...
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3answers
549 views

Why capacitance is given as constant value in Farads, and not as max charge in Coulombs?

The equation for capacitance is $Q=CV$ or $V={1\over C}Q$. I don't understand what is the physical meaning of this "$C$": Does the charge in a system changes linearly with voltage under all ...
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4answers
2k views

Electric Field due to a disk of charge. (Problem in derivation)

This might be a really silly question, but I don't understand it. In finding the electric field due to a thin disk of charge, we use the known result of the field due to a ring of charge and then ...
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4answers
531 views

Is Gauss' law valid for time-dependent electric fields?

The Maxwell's equation $\boldsymbol{\nabla}\cdot \textbf{E}(\textbf{r})=\frac{\rho(\textbf{r})}{\epsilon_0}$ is derived from the Gauss law in electrostatics (which is in turn derived from Coulomb's ...
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4answers
11k views

Why are there dust particles on TV screens?

My professor gave us the following reason: The screen is positively charged. When dust particles fly near it, the positive charges in the screen induce a charge in the dust particle, pulling the ...
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2answers
3k views

Highest man-made voltage

What was the highest voltage achieved and was it produced by electrostatic means or just some transformers and multipliers? What are the limitations when it comes to producing voltage using ...
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2answers
6k views

Is a charged particle at rest affected by magnetic field?

It is known that particles such as electrons and protons bear electric charge, but not a magnetic charge. When these particles are at rest, are they somehow affected by magnetic field? The similar ...
2
votes
4answers
618 views

Gauss' law - changes in the magnitude of E field inside the closed surface

Gauss's law says that the flux through a closed surface which contains neither a sink nor a source will be zero. It's quite clear that all field lines will have to exit somehow, but the strength of ...
2
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3answers
177 views

Laplacian of 1/r satisfies laplacian equation?

We know that $$ \nabla^2 \left( \frac{1}{r} \right) = -4 \pi \delta(r) \tag{1}$$ and that the general solution to the laplace equation $\nabla^2\Psi = 0$ may be expanded as $$\Psi=\sum_l \left(A_lr^l+...
2
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1answer
274 views

How to approximate trajectories and movement of two oppositely charged particles?

Imagine a single, stationary charged atomic ion, say a Lithium anion or cation (Li+ or Li-). Now imagine another a single free, oppositely charged particle--perhaps an electron or Hydrogen ion (H+)--...
2
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1answer
1k views

Is there a difference between Electric and Electrostatic Field?

Is there a difference between Electric and Electrostatic Field? All I know is that they both represented with same law suppose we have a Charge placed at the Origin: $$E=\frac{1}{4\pi\epsilon_0}\...
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3answers
3k views

Can we have negative Electrostatic potential

What does it mean to have a negative electric potential? not talking about potential difference or voltage.
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3answers
170 views

How come we talk about gravitational potential energy and not gravitational potential?

With regards to gravity the equation learned is $$U=-\frac{GMm}{r}$$ And the relationship to force is $$F=-\frac{dU}{dr}$$ In electrostatics we instead talk about electric field and electric ...
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2answers
1k views

Is there really no meaning in potential energy and potential?

I have been told all my physics life that potential energy between two mass/charge has no meaning and only their difference has meaning. The same goes for electric potential, only the difference ...
2
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2answers
408 views

Maximum limit of charging a capacitor

We say that we can charge a capacitor in proportion to the potential difference we apply across its plates and the maximum potential difference depends on the dielectric strength of the medium. Now ...
2
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1answer
115 views

Coulomb's law with an $r^3$, not $r^2$, in the denominator [duplicate]

I am reading an older physics book that my professor gave me. It is going over Coulomb's law and Gauss' theorem. However, the book gives both equations with an $r^3$, not $r^2$, in the denominator. ...
2
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5answers
994 views

If the electrostatic potential is zero, why doesn't the electric field have to be zero?

I thought the relation between the electrostatic field $\vec E$ and the electrostatic potential $V$ is as follows: $$\vec E = - \nabla V$$ Thus, when $V$ is zero, $\vec E$ is also zero.
2
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2answers
504 views

Why do electric field lines start and end at 90 degree at the surface of a conductor? [duplicate]

There is one property of electric lines of forces which states that: Electric field lines start and end at 90 degree at the surface of the conductor. But why is that so? Is there any proof for ...
2
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2answers
66 views

Basic of Capacitor

I've 2 capacitors; plate area, difference between plates and dielectric is same. Only thing is that the metal used in plates is different. Since the formula $\displaystyle C=\frac{\varepsilon A}{d}$ ...
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3answers
6k views

Why the electric potential of earth is zero?

For a localized charge distribution the potential is set to zero far away from the charge distribution (at infinity) Now, when grounding a conductor, i.e. connecting it to Earth, it is said that we ...
2
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2answers
237 views

My conundrum with Gauss’ law in electrostatics

If I use Gauss’ law to calculate the electric field outside of a charged (conducting or insulating) sphere or a point charge, the fields are the same. However, as a test approaches a point charge, the ...
2
votes
2answers
7k views

Why potential energy of a dipole in an electric field has a negative sign?

In the following equation $$V = -\mathbf{P}\cdot \mathbf{E}$$ why I have to take Potential Energy as negative. Is there any simple reason behind this ? I am preparing for my high school examination....
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6answers
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Is voltage electric potential or electric potential difference?

On Wikipedia, voltage is defined to be the electric potential difference. However, I am still not certain as to whether voltage is the electric potential ($PE/q$) or electric potential change ($\...
2
votes
2answers
193 views

Determination of auxiliary scale in dimensional regularization

My questions are in italics. In the article [1] a dimensional regularization is presented on an electrostatic example of an infinite wire with constant linear charge density $\lambda$. It is shown ...
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2answers
2k views

Electric potential due to a point charge in Gaussian/CGS units

I learned electrostatics in SI units. In SI, the electrostatic potential due to a point charge $q$ located at $\textbf{r}$ is given by $\Phi(\textbf{r}) = \frac{q}{4 \pi \epsilon_0 |\textbf{r}|}$. ...
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2answers
502 views

Where is the flaw in deriving Gauss's law in its differential form?

From the divergence theorem for any vector field E, $\displaystyle\oint E\cdot da=\int (\nabla\cdot E) ~d\tau$ and from Gauss's law $\displaystyle\oint E\cdot da=\frac{Q_{enclosed}}{\epsilon_0}=\...
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2answers
539 views

Gauss' law giving zero field where field is not zero?

Two plastic sheets with charged densities as shown: I'm trying to find the field at $B$. I obtained the correct answer by adding up the fields created by each charge density. But I realized that ...
2
votes
3answers
357 views

Electric field or static electric field around a plugged-in lamp cord (when lamp is not turned on)?

When an electrical cord from, say, a lamp, is plugged into an AC wall socket, I'm aware that an electric field forms around the entire length of the cord and even before the lamp switch is flipped on. ...
2
votes
1answer
56 views

Physical meaning of the separation constants in Laplace's Equation for Electrostatics

In Electrostatics, if we consider a region without charges the electrostatic potential $V$ obeys Laplace's Equation $\nabla^2 V = 0$. We can tackle this with separation of variables. In cartesian ...