Electrostatics is concerned with the field and potential of stationary electrical charges and electric charge distributions. Problems are this type are almost exclusively concerned with mathematics of geometries using the inverse-square law.

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What is the net charge of the Earth?

This question arose in a seminar today about the solar wind... This is my vagueish understanding of the problem - please correct if you see errors! The 'classical' picture of atmospheric electricity ...
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4answers
338 views

Distribution of point charges on a line of finite length

How will $N$ freely moving charges confined to a line with length $L$ be distributed? What are their equilibrium positions?
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4answers
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Will a charged capacitor discharge if one lead is connected to ground?

If I charge a capacitor and connect one lead to ground keeping the other lead floating, will the capacitor discharge ? ...
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178 views

What happens to 5 electrons on a sphere?

Let's suppose we put 5 electrons on a perfectly conducting (no resistance at all) sphere. There's no equilibrium configuration with 5 (though there is with 2, 3, 4 or 6). So will they keep moving on ...
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2answers
349 views

Gauss' law and an external charge

Gauss' law states that the net outward normal electric flux through a closed surface is equal to $q_{total, inside}/\epsilon_0$. However, I'm a bit confused of why the presence of an external charge ...
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2answers
303 views

Shape of electric charges on sphere in equilibrium state

When electric charges of equal magnitude and sign are released on a regular sphere (and assume that they stick to the surface of the sphere, but they are free to move along its surface), what is the ...
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Is this really how a capacitor works? Why doesn't it behave like a resistor?

My book says a capacitor is two conducts being connected by an insulator. Now let's take a parallel plate capacitor to simplify the problem I have. Suppose I got two parallel plate capacitor in ...
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1answer
499 views

Why doesn't a gaussian surface pass through discrete charges?

I have read that Gaussian surface cannot pass through discrete charges. Why is it so? I have even seen in application of Gauss' Law when we imagine a Gaussian Surface passing through a charge ...
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7answers
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Electric field lines density

When we're dealing with problems in electrostatics (especially when we use Gauss' law) we often refer to electric field lines density which is inversely proportional to radius in case of a single ...
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5answers
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Why a glass rod when rubbed with silk cloth aquire positive charge and not negative charge?

I have read many times in the topic of induction that a glass rod when rubbed against a silk cloth acquires a positive charge. Why does it acquire positive charge only, why not negative charge? It ...
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1answer
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What is the penetration length of static electric field into conducting metals?

How large is the penetration length for static electric field into good conductors? I have two versions: (1) few atomic spacings $$a\sim n_{e}^{-1/3},$$ and (2) Debye length computed by Fermi ...
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2answers
90 views

Does a AAA battery have a dipole moment?

Does a AAA or D battery have an electric dipole moment? Why don't the opposite poles of two batteries attract each other like that of magnet's?
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1answer
205 views

Density of repulsive particles on a disk?

NB: the external circle (where particle or water is in it) is fixed ! It's a 2D theoretical problem (just for understand something in particular). Here, no gravity, no temperature. I put in a disk a ...
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3answers
237 views

Is it true that $\vec{E}\neq 0$ inside a 1- or 2-dimensional conductor?

It is known that when a conductor is placed in an electric field, the charges redistribute themselves such that $E=0$ inside the conductor. I was also told that the same is NOT true for the 2D and 1D ...
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4answers
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Infinitely charged wire and Differential form of Gauss' Law

I have tried calculating the potential of a charged wire the direct way. If lambda is the charge density of the wire, then I get $$\phi(r) = \frac{\lambda}{4 \pi \epsilon_0 r} \int_{-\infty}^\infty ...
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2answers
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How can a conductor be grounded yet there are induced charges on it?

A classic example for the method of images is the following, quoted from Griffiths's Introduction to Electrodynamics, page 121: "Suppose a point charge $q$ is held a distance $d$ above an infinite ...
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2answers
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Electric Field One-Form

I know for instance that we can interpret the electric field as the one-form that given a vector gives the change in potential in the direction of the vector, however I'm very unsure about how to ...
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4answers
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How does positive charge spread out in conductors?

I know that when there are excess positive charges in a conductor, for example, a metal sphere, the positive charges will spread out over its surface. However, I am confused about how this excess ...
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2answers
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Electric field and electric potential of a point charge in 2D and 1D

in 3D, electric field of a piont charge is inversely proportional to the square of distance while the potential is inversely proportional to distance. We can derive it from Coulomb's law. however, I ...
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1answer
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Is the electric field at the edge of a uniformly charged disk infinite?

Consider a disk with a radius $R$ (I'll use $R=1$ at various points here) that has a constant surface charge density $\sigma$. Unlike the similar problem of the field in the vicinity of a infinitely ...
2
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1answer
88 views

How to find the equillibrium points using Jacobian and Hessian?

Given that I have Jacobian and Hessian matrices of three particles interacting with each other in a harmonic trap through Coulomb's law in a 2D plane, how do I find the equilibrium points of them (I ...
2
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1answer
377 views

Two electron beams exert different forces on each other depending on frame of reference?

I am sure there is a simple explanation for my confusion, but I am a little puzzled: We are dealing with two parallel electron cannons that each produces a straight beam of electrons. They are placed ...
2
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2answers
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Dirichlet and Neumann Boundary condition: physical example

Can anybody tell me some practical/physical example where we use Dirichlet and Neumann Boundary condition. Is it possible to use both conditions together at the same region? If we have a cylindrical ...
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4answers
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How does instant charging of one plate affect the potential of the other plate of a floating capacitor?

If I have an uncharged floating capacitor and I instantaneously connect one plate to some potential, then that plate will acquire some charge. In practice, the other floating plate will ...
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3answers
616 views

Is there is any difference between Electric Flux ($\Psi$) and Total number of Electric Field lines ($E\times$Area)?

Is there is any difference between Electric Flux ($\Psi$) and Total number of Electric Field lines ($E\times$Area)? $\psi = \Sigma Q$, and $\phi$ = Electric field intensity $\times$ Area where Area ...
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1answer
207 views

Can a super-extremal charged black hole be made out of electrons only?

In a previous Question it was argued that it would be impossible to add enough charge to a black hole to make it pass the extremal black hole limit since adding charge would increase the mass of the ...
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1answer
115 views

Weird consequence of Gauss's law

According to Gauss's Law, the electric field at a surface is the function of only the charge enclosed inside it. But that doesn't make sense. I mean, if I put the surface in an electric field, won't ...
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1answer
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What defines the maximum charge a capacitor can store?

The formula for a capacitor discharging is $Q=Q_0e^{-\frac{t}{RC}}$ Where $Q_0$ is the maximum charge. But what property defines the maximum charge a capacitor can store? If it depends on ...
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5answers
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How can I prevent being zapped by static electricity every time I touch a doorknob or handle in the office?

I don't know what it is about this office, but it seems everything I touch (doorknob, bathroom faucet, edge of kitchen sink in the break room), I get zapped by static electricity. It's getting old. ...
4
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1answer
124 views

How do aspherical gravitational monopoles look like?

I was recently pointed by laboussoleestmonpays to a beautiful paper from some time ago, Aspherical gravitational monopoles. Alain Connes, Thibault Damour and Pierre Fayet. Nucl. Phys. B 490 no. ...
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1answer
880 views

Trying to understand Laplace's equation

I'm struggling here so please excuse if I'm writing nonsense. I understand that the gravitational potential field, a scalar field, is given by $$\phi=\frac{-Gm}{r}$$ where $\phi$ is the ...
3
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1answer
412 views

Why does Hauksbee's electrostatic machine produce light?

I'm reading on the history of the discovery of electricity and the electron, and I've went from reading about Rutherford's gold leaf experiment all the way back to Francis Hauksbee's spinning glass ...
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2answers
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When I connect in series two floating capacitors, one charged and the other not charged, does current flow?

Suppose I energize one capacitor by connecting it across a battery, allowing it to achieve some potential difference V0 across its plates, then disconnect it and allow both of its leads to float in ...
3
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3answers
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How does an object regains its neutrality after being charged by rubbing?

Objects (like comb) can be charged by rubbing as charged particles, particularly electrons, are transferred from one object to other. This can be seen as the object (comb) attracts small bits of ...
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3answers
106 views

Calculating the Potential from the E-Field

I find that often times I'll be tripped up by questioning whether or not I can do something mathematically, and be unable to come up with a satisfying answer. This is, unfortunately, one of those ...
2
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1answer
241 views

Coulomb interaction as virtual particles exchange?

I've been reading about virtual particle exchanges in physics books and in Physics SA posts, where a particle interpretation of gravity and Coulomb interaction is established. The Feynman Diagram ...
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2answers
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Electric Field Between Two Parallel Infinite Plates of Positive Charge and a Gaussian Cylinder

Is the electric field between two positively charged parallel infinite plates one with a charge density twice the other effect the electric field on the outside of the plates? I am thinking no, ...
2
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2answers
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Calculating the field of an infinite flat sheet of charge using the superposition principle

I am trying to calculate the field of an infinite flat sheet of charge (a plain with uniform charge density $\sigma$) using the superposition principle. I know that the field of an infinite line ...
2
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3answers
535 views

Potential Inside Conducting Cube

A cubical box with sides of length L consists of six metal plates. Five sides of the box { the plates at $x=0, x=L, y=0, y=L, z=0$ - are grounded. The top of the box (at z = L) is made of a separate ...
2
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1answer
179 views

Electrostatic charge leakage

What are the ways electrostatic charged objects leak charge in humid conditions? Can airborne particles pick up charge by contact, then be repelled hence removing charge? If so would it be a ...
2
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1answer
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Minimizing potential energy of a dipole in an electric field

My test paper asked me which way a dipole should be orientated in an electric field to minimize its potential energy. My answer was that the dipole should lie parallel to the electric field with the ...
2
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1answer
412 views

What is the energy of interaction between a point charge and an infinite cylinder?

I don't remember enough from my electromagnetism course and I can't find any simple, full example on this subject. I know, that I can consider the cylinder as a wire with the same charge density ...
2
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1answer
145 views

electrostatic potential, analytic properties

An electrostatic potential associated with some delocalized charge $\int \rho(\mathbf{r}) d{\mathbf{r}}$ is given by: $$v_H(\mathbf{r}) = \int ...
2
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2answers
834 views

Electric potential of sphere

(a) I am a little confused about this part. The point at A to B isn't radial. The electric field is radially outward, but if I look at the integral $$\int_{a}^{b}\mathbf{E}\cdot d\mathbf{s} = ...
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4answers
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If something has zero resistance, does it have infinite amperage?

If amps = volts / ohms, and ohms is 0, then what is x volts / 0 ohms?
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1answer
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How to find the electric field of a charged tube?

Let's say there is a charged tube(cylinder with no top or bottom) with radius $a$, length $l$ and charge $q$ and a point which is collinear with the centre of the charged tube. Anyway, since we can ...
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0answers
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How to calculate the electrostatic force between two dielectric rings of charge?

Let's say there is a dielectric ring of charge with radius $a$ and charge $q_1$. I could calculate the electrostatic force applied on a point charge with charge $q_2$ and which is collinear with the ...
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3answers
120 views

How can the potential on a cube's surface replicate the potential of a point particle?

If i have a cube (either hollow, or an insulating solid) and i want its surface have a potential such that it looks like a point particle outside of the box does that mean the exact potential on the ...
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1answer
130 views

Charging the plates before making the capacitor

Basically, a simple capacitor will consist of 2 plates and a dielectric material between them, what if i took 2 plates, charged one with a +ve charge and the other with equal -ve charge, then i put ...
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2answers
76 views

Can a liquid insulator be electrically charged by touching a charged conductor?

Can a liquid insulator be electrically charged by touching a charged conductor? I understand that solid insulator will only be charge on the surface where it is touch, but the case is different ...