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Questions tagged [electrostatics]

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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21 views

E field within parallel plate capacitor with dielectric

I know that for an air-filled parallel plate capacitor with applied voltage, there exist the relation $E=V/d$, where d is the separation distance. Does this relation still hold when the parallel ...
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0answers
14 views

electrons moving poition in a conductor

I want to calculate how the charge density changes in the situation I have drawn. I figured charge density g = q/v. so I could say g(x)=q/v+dq. where dq is the new electrons that moved to position x ...
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1answer
27 views

Do charges in a metal group up a little in the middle?

Around the edges of a metal, the density of electrons is higher than the rest of the metal. I think this is because every electron is surrounded by neighbours pushing them away but once you get to the ...
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1answer
52 views

Do repelling charged objects reach a finite velocity?

Let's imagine I have 2 spheres made out of metal, each with a mass of exactly 1 kg. These spheres are sitting in a place in the universe devoid of any significant masses - meaning there is negligible ...
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0answers
13 views

Distribution of excess charges in conductors [on hold]

Consider a conducting hemisperical shell .Now on adding excess charge ,how will the excess charge distribute. 1)from Faraday's ice pail experiment the charges would reside on outer surface of ...
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1answer
51 views

Electric Potential of Non-Uniformly Charged Infinite Plane

A little background: I was tutoring an undergrad upperclassman when we came to a problem that he had been assigned which I couldn't make heads or tails of - at least in terms of what was being ...
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2answers
34 views

Induced charge according to method of images

If we place a charge +q at a distance a along the x-axis from a grounded plate, we can use the method of images to show the potential is $V(\textbf{r})=\frac{q}{4\pi \epsilon_0}(\frac{1}{r_1} -\frac{1}...
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5 views

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
20 views

Charging a parallel plate capacitor [on hold]

While charging a capacitor through a battery the electron taken away from one plate by the battery is not the electron which is put on the another plate (right). Then why we say that that $dq$ amount ...
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1answer
25 views

Electric field due to an infinite plane slab

So the solution says that in the x z plane, E = 0 by symmetry that is my problem, how is E = 0, maybe I can't visualize it correctly, however if I assume that that's really the case, I can continue ...
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0answers
7 views

Origin of electric flux and field lines [duplicate]

I wanted to know about the thoughtprocess which led to development of electric flux -Flux- I am aware of the fact that flux, on its own is a mathematical concept but how did it find its way into ...
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0answers
17 views

Electrostatic force between two grains of sand with unbalanced charge placed 30 meters apart

Quote from The Feynman Lectures on Physics Volume I: To give an idea of how much stronger electricity is than gravitation, consider two grains of sand, a millimeter across, thirty meters apart. ...
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2answers
50 views

Capacitor asymmetrically charged

Can a capacitor be asymmetrically charged? I mean, not to have equal and opposite charges on each plate, -Q and +Q, but two different charges of any sign, say, q1 and q2. I ask firstly if it's ...
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1answer
18 views

Charge in a solid conducting sphere [on hold]

Will a unit charge (–ve/+ve) experience any force when it is placed at the centre of a positively charged solid conducting sphere? If yes, which way will it go (please say about both the charges ...
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2answers
19 views

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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2answers
54 views

Can $E=\frac{q}{4\pi\epsilon_0 r^2}$ be directly derived from differential form of Maxwell equations?

The electric field of a point charge $q$ is well known to be $$\mathbf E=\frac{q}{4\pi\epsilon_0 |\mathbf r|^3}\hat{\mathbf r}$$ This can be derived easily from integral form of Gauss’s law. Taking $...
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1answer
29 views

Notion of flux and field lines

I am curious about the origin of electric flux and field lines. -Flux- I am aware of the fact that flux is a mathematical concept, but how did it find its way into physics? Was it just introduced ...
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1answer
44 views

Electric field inside a uniformly charged dielectric sphere

Every basic course and book on electrostatics has this problem, to find out the electric field inside a uniformly charged sphere. The result always is $\frac{\rho r}{3 \epsilon_0}$, obtained using ...
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1answer
45 views

Two electromagnetic fields [closed]

What happen if two electromagnetic field is neared? According to Faraday law, is it possible one can increase strength magnet or amplitude wave of other field?
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28 views

How to graph a function of force versus time for two charged objects? [closed]

Assuming you have two charged spheres with charges $Q1$ and $Q2$ and masses $m1$ and $m2$ witch start at a distance $r0$ from each other, what is the function $f(t)$ representing the force between the ...
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1answer
41 views

Static Electromagnetic fiels [closed]

What is the mathematical proof that static electric and magnetic fields are independent of each other?
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0answers
41 views

Van de Graaff generator with glass of water on top

I watched a video of Van de Graaff generator with a plastic bottle on top and lightning type sparks being produced in the bottle and was wondering if the same thing would occur if a person used a ...
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1answer
67 views

How to derive the $\frac{4\pi}{3}\vec{p}\delta^3(\vec{r})$ element for the dipole field, from its potential?

This might be a bit more general question about how to figure out what is the appropriate (delta) expression in singular points, but e.g. for the dipole, we can derive its potential by a taylor ...
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1answer
36 views

How do we generalise a specialised case in physics?

I have come across this sort of thing a lot of times in my textbook. I give the examples below- Eg.1- In the case of a capacitor connected across an alternating current generator, we find $V_c=...
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3answers
38 views

What happens when a super large charge is brought close to a conductor with limited supply of charges?

Imagine the following induction scenario: a super large charge +Q is brought close to a real conductor with limited supply of charges; that is, the total charge of all electrons inside this conductor ...
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0answers
33 views

Partial capacitances of a system of conductors - conductor acting as a shield

I have a small question about the following problem. The figure represents the cross-section of a three-conductor system comprising a communications coaxial cable of length l running parallel to a ...
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1answer
35 views

Electrostatics: Potentials and Minus signs

I've got a simple question regarding electric potentials in electrostatics. My book defines electric potential V as $$ V(b) = -\int_a^b \mathbf{E}\cdot d\mathbf{l} $$ where A is defined as where ...
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0answers
22 views

Property of surface Green function in electrostatic field

Let's consider a 2D-square with 4 equal subsquares containing different dielectrics. Inside the square domain, the unknown electric potential function $\Phi$ satisfies the Laplace equation: $$\nabla^...
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1answer
49 views

Dual finite parallel disk capacitor; estimating mathematically that the potential or field or distribution is nearly uniform from first principles

Working through Purcell. In particular, doing my best to put everything on a firm footing, mathematically, so that I can understand it. But, I have struggled all week in establishing from first ...
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4answers
75 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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2answers
65 views

Electric Field between two parallel plans of opposite charge density

So considering two infinite parallel plans of opposite charge density let's say +σ for the left plan and -σ for the right plan Why is the electric field calculated this way : $$ E = σ/2εo + σ/2εo ...
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1answer
27 views

Electric flux through gauss law

Why is it that objects kept in uniform electric field have net flux through them when gauss law says that net flux through a surface is q/epsilon.I mean the net charge will be zero if a gausian ...
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1answer
25 views

Solving dynamics of two oppositely charged particles without using energy conservation

Two charges, each $+q$, are separated by distance $d$. One of the charges is fixed, and the other is free to move under the influence of the force from the first. The second particle is initially at ...
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0answers
33 views

How to arrange charges on a 1d line so that the electric field along the line far away is r^-6? [closed]

My question is simple: How to arrange charges on a 1d line so that the electric field along the line far away is r^-6?e.g., we can make field falling as r^-3 by two charges(dipole field). This type ...
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4answers
86 views

Is the vacuum permittivity a result of defining other units first?

From Coulomb's law $$F=\frac{1}{4\pi\epsilon_0}\frac{q_1q_2}{r^2}$$ If instead we defined the charge of a coulomb to be $\sqrt{\epsilon_0}$ times it is now, the force would be exactly the ...
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2answers
49 views

Gauss Law For Electrostatics [duplicate]

In Gauss Law for Electrostatics, Electric flux term contains Electric field due to charges that are both inside and outside the Gaussian surface. If we use Gauss Law to calculate electric field at a ...
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1answer
23 views

Capacitor, stored energy versus reactive power

When an AC voltage U is put onto a loss less capacitor C the capacitor will require a certain reactive power Q (current 90 degress out of phase with the voltage): $Q=UI = \omega C U^2$ in VAr (Only ...
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0answers
28 views

Electric flux over a closed surface when point charge lies on the surface

What will be the electric flux over a closed surface when point charge lies on the surface, that is neither inside nor outside? I ask this question because electric field at that point will be ...
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1answer
51 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
33 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
26 views

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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2answers
54 views

Definition of Voltage using integral: minus sign?

So I'm studying electrostatics and I came across to two different definitions of potential difference/voltage (because we're in stationary regimes) and I'm having trouble understanding how the ...
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1answer
27 views

Why do the field line asymptotes in this diagram bend?

If there is a +1 charge and another +1 charge the field lines have a vertical and horizontal asymptote. However, when the charges are uneven, the vertical asymptote is curved leftwards: I don't ...
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1answer
69 views

Electric field from a quadrupole

In the following problem, I have already solved for the value of the potential, and I would like to tackle the extra exercise, which asks for the electric field of a point quadrupole: At every ...
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1answer
67 views

Average electric field calculated from average potential

In a Griffiths problem (3.4) I'm asked to find the average electric field over the surface of a sphere due to point charges inside/outside the surface. The calculation is done in his solutions ...
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1answer
42 views

Electric potential everywhere around an infinite slab

The problem: Consider an infinite slab with uniform charge density $\rho$ between two planes $z=\frac{d}{2}$ and $z=-\frac{d}{2}$. Find the electric potential $V$ in the entire space and plot $V$ ...
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2answers
37 views

What is the physical significance of Dipole moment?

What does dipole moment physically signify? I know it is the product of 2 charges and distance between them. Like momentum is the product of mass and velocity, but physically it shows the quantity of ...
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0answers
27 views

Using Poissons equation to find the potential between two parallel metal plates?

Problem information/statements: Two metal plates with distance $d=1$cm has a evenly charge density $\rho_v=-10^{-5}\frac{C}{m^3}$ between them. And it has a relative permitivity $\epsilon_r=1$. One ...
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1answer
31 views

Showing that the exterior surface charge density of two parallel plates with thickness are equal

I have some problems with the next exercise. It states: Two infinite conducting parallel plates I and II, with thickness $t_1$ and $t_2$ respectively are separated by a distance $L$ from its nearer ...