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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2
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2answers
213 views

Two charged spheres connected with a conductor

I have a problem with a electrostatics problem: there are two spheres, each one of the same size carrying the same amount of charge, but of different sign. They are connected by a conducting wire, ...
0
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1answer
303 views

electric charges of metals in electrostatics

In electrostatics does metal gain electrons to be an ion or it conduct electrons in form of gaining them to have a negative electric charge
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1answer
725 views

Force per unit length between two long parallel wires, one of which is insulated

Suppose we have two very long parallel wires of radius $a$ and distance between their axes $d$ ($d>>a$). The first wire if is carrying charge of linear charge density $\alpha$ and is insulated ...
0
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1answer
45 views

Thomson problem vs. maximizing sum of distance

Given $N$ equally charged points lying on the unit sphere ("electrons"), the Thomson problem consists of finding the configuration of these points such that the electrostatic potential energy $$ U=...
3
votes
4answers
671 views

How would you define electrostatics and magnetostatics starting from Maxwell's equations?

I'm reading Griffith's text, and he starts by defining Electrostatics as requiring the source charges don't move. I've seen a few slightly different definitions of electrostatics and magnetostatics. ...
2
votes
1answer
80 views

Disturbing a line of infinite alternating charges

Consider a line of infinite number of alternating charges. All are point charges having charge of same magnitude and are placed in a line. Neglect the effect of gravity here. Consider one of the ...
1
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1answer
182 views

Finding the potential between two spherical shells [closed]

How to find the potential in region $a<r<b$ I know that the general solution for Laplace's equation is $$V(r,\theta)=\sum_{l=0} \left[A_l r^l +\frac{B_l}{r^{l+1}} \right]P_l(\cos{\theta}).$$ ...
0
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1answer
51 views

Why an undoped heterojunction causes potential barrier?

In this image (source) a potential double-barrier was created using GaAs and AlAs lattices (undoped). Why would any potential barrier be formed, if all the bonds are electrostatically balanced (i.e. ...
0
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1answer
120 views

Charge density on a plate of a realistic capacitor

Suppose we have a realistic capacitor,connected to a constant voltage source, with plates at some distance $d$ and a varying charge density across plate due to edge effects. Is it correct to assume ...
1
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1answer
3k views

Capacitance of two non parallel plates

What is the formula for capacitance of two non parallel plates at an angle with each other?If the plates were parallel then the value can be calculated as (PermittivityX area of one plate)/distance ...
0
votes
1answer
287 views

Want to know about divergence [duplicate]

Can anyone please explain how to know whether a vector field has divergence or not by seeing its diagram? I have read that a vector field must change for having divergence but why is divergence zero ...
13
votes
6answers
730 views

What keeps electrons on a negatively-charged conductor from leaving?

Imagine a negatively charged conductor in a vacuum. The excess electrons will be spread out over the surface such that the net electric field inside the conductor is zero. What keeps these extra ...
0
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1answer
945 views

Energy of a charge inside spherical conducting shell

A point charge $q$ is at the center of an uncharged conducting spherical shell of finite thickness, with inner and outer radii $a$ and $b$ respectively. Find the work done on the system when $q$ is ...
1
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1answer
227 views

Electric Potential-can anyone give the concept behind this?

Three points A, B and C lie in a uniform electric field (E) of 5 x 103 NC-1 as shown in the figure. Find the potential difference between A and C. I think there is some trick? How can the pd ...
0
votes
1answer
19 views

Electrostatic Potential-I tried many times ,but failed

A positive charge Q is placed at point O. Is the potential difference (Va-Vb) positive,negative,or zero,if Q is (i)positive,(ii)negative? Can anyone give the concept behind this?
5
votes
3answers
199 views

Is the charge distribution for an electric field unique?

If the electric field and boundary conditions are known exactly for a region of space, is it true that there exists only one charge distribution in that region of space that could have produced it? ...
0
votes
1answer
102 views

Derivation of a work done by forces on charge

Feynman claims is his lectures the following statement: Suppose we have two charges $q_1$ and $q_2$ separated by the distance $r_{12}$. There is some energy in the system, because a certain ...
0
votes
2answers
315 views

How does the force between two charges becomes zero?

In case of Coulombs law, $$ F=k\frac{q_1q_2}{d^2} $$ So, if $F=0$, then $q_1q_2$ must be 0. Is this true?
2
votes
1answer
171 views

Laplace equation vs Gauss theorem

Two concentric conducting spherical shells of radii $a_1$ and $a_2$ ($a_2>a_1$), are charged to potentials $φ_1$ and $φ_2$, respectively. Determine the electric potential and field in the ...
2
votes
1answer
123 views

Usage of Poisson's equation?

I revisited electrostatics and I am now wondering what the big fuzz about Poisson's equation $$\nabla^2 \phi = -\frac{\rho}{\varepsilon_0}$$ is. Wiki says One of the cornerstones of electrostatics ...
0
votes
1answer
25 views

How does the dieletric displacement change among two dieletric materials?

Here's a question I am working on. "A sphere of linear dielectric material with permittivity $\epsilon_1$ and radius $a$ is surrounded by an infinite region of linear permittivity $\epsilon_2$. In the ...
4
votes
1answer
293 views

Flashing a fluorescent light bulb with high voltage

My son and I built a Wimshurst machine (our second try) over the last couple of weekends. It works -- not terribly well, as it only makes 2cm sparks with 20 cm disks (something like 60 kVolt when it ...
0
votes
0answers
22 views

electrostatic force vs gravitational force [duplicate]

I have question regarding the forces caused by electrostatic charges and gravity. From the explanation here in the link just by existing an object with mass distorts space-time. Will there be a ...
0
votes
1answer
63 views

Finding energy stored in a capacitor

i am given a voltage time graph for a capacitor circuit. How to find energy stored in that capacitor at various time instants? Can we just calculate by using $\frac{1}{2}CV^2$ We are given capacitance ...
0
votes
2answers
158 views

Relation between electric field and dipole moment

I want to show the following equality $$\int_{\left|\vec{r}\right|<R}d^3r\vec{E}\left(\vec{r}\right)=-\frac{\vec{p}}{3\epsilon_0}$$ where $\vec{p}$ is the dipole moment of a charge distribution $\...
2
votes
1answer
226 views

How is the electostatic field propagated by the vacuum? How does a charge feel the presence of another charge when there is NOTHING between them?

Is the word "vacuum" equal to "nothing"? Imagine two charges of opposite sign, far from one another in vacuum, and moving with constant velocity - s.t. none radiates energy, none emits photons. At ...
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3answers
1k views

Polarization vector of dielectric electrostatics

I know two laws for Polarization vector of a dielectric material $$\vec P = N q \vec{\Delta L}$$ Where $N$ is the number of dipoles per meter cube, $\vec{\Delta L}$ is the vector that represents the ...
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votes
4answers
176 views

Electrostatics and two electric charges [closed]

How can two identical metallic objects have the same but opposite charges (one loses electrons and one gains electrons) when we know that metals have the ability to lose electrons only?
1
vote
1answer
243 views

Charge distribution on a doughnut shaped conductor

In a spherical solid conductor the charge is always on the outer surface. Even if the sphere has a cavity, the surface of the inner cavity can not carry a charge due to Gauss's Law. What would be ...
0
votes
3answers
536 views

Explaining the current flow of the positive shunt clipper (diodes)

I am currently studying clippers or parallel limiters in the Navy and I was wondering if someone could clear up a few things for me. Here is a picture that fits my description: A clipper has a ...
0
votes
1answer
57 views

Tranverse electromagnetic waves

TEM waves do not exist in waveguide. Is this the correct explanation- Both curl and divergence of TEM are zero inside the waveguide and because of the boundary conditions (electric field zero at every ...
1
vote
1answer
2k views

What is the force between two charged objects when the space between them is partially filled by a dielectric medium?

I am given two charged particles of same charge at a distance of $r$. They initially apply force $F$. Now an infinite dielectric (of dielectric constant $4$) of width $\frac{r}{2}$ is introduced ...
1
vote
1answer
65 views

What are the consequences of connecting a non-ideal conductor to a battery in open loop?

Suppose I have a battery with $\Delta V=5[\mathrm{V}]$. Now I connect a piece of a metal wire to the "+" side of the battery only. Let's assume that the ambient air is not conductive at all: Are ...
2
votes
3answers
544 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 ...
1
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1answer
1k views

Why does energy rise in a constant voltage capacitor after inserting a dielectric?

For example from this link: http://te.fisica.edu.uy/fuerza_en_Capacitor.pdf we can deduce, that the work the electric field inside a constant-voltage capacitor does during the insertion of a ...
1
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1answer
78 views

Find quantity of electricity of two circular faces

So, there are two circular conductive sheets with quantities of electricity of Q and -Q. If I know that the distance d between them is 0.002 meters and their radius is 0.1m and the voltage between ...
1
vote
2answers
153 views

Using Coulomb's law to solve for a continuous charge distribution [closed]

I have been trying to evaluate this specific integral and have been completely stuck. $$\frac{1}{4\pi \epsilon_0} \int^L_0 \frac{2\lambda z}{(x^2+z^2)^\frac{3}{2}}dx.$$ I am a freshman and have been ...
0
votes
1answer
23 views

discharging static

Quick question, if you have a buildup of static charge causing sheets of paper to stick together, can you have a grounding foil touching the paper to dissipate the charge to prevent pages from ...
1
vote
0answers
67 views

Electric field at a point [closed]

We consider a thin disk whose center is $O$ and radius is $R$, which has an electric surface charge density of $\sigma$. We want to find the expression of the electric field $\vec{E}$ at a point $M$ ...
0
votes
1answer
126 views

Electric field and potential between two charges [closed]

There are two point charges on the $x$ axis and $x'$ is a place where the potential, relative to infinity, is the biggest. Why is the electric field zero at this point?
2
votes
0answers
101 views

Electric field in a “concave” conductor

I am aware that the electrons are distributed across charged conductor surface so that the areas with smaller radius of curvature have more charge per surface area. But what happens when the ...
0
votes
0answers
42 views

Addition of forces in dielectric material

In this paper (page 2 of document) it is said that: Because this calculated force was comparable to the gravitational force, they assumed that the same would be true for the forces on a ...
2
votes
3answers
628 views

Calculate the flux of a point charge with Gauss's law

I know from my class that to calculate the flux of a point charge with Gauss's law, I have to make a surface that intersects with all of the flux lines resulting from the charge, and then make this ...
0
votes
1answer
42 views

Finding voltage between two points in space

If electric field vector is defines as : $\vec{E} = \frac{V_0x^2}{a^3} \vec{i_x} + \frac{V_0y}{a^2} \vec{i_y} $ where $V_0 $ and $a$ are known constants, $\vec{i_x}$ and $\vec{i_y}$ unit vectors of ...
-1
votes
1answer
142 views

The “classical radius” of the electron [closed]

According to one theory, the mass m of the electron arises simply as a consequence of the electrostatic energy of its electric field, through Einstein's famous expression ε=mc^2, where ε is the field ...
0
votes
1answer
171 views

Net Electric Field of Multiple Charges [closed]

Question: Four charges, each of magnitude +Q are placed at the corners of a square of side a. Obtain an expression for the electric potential at the centre of the square and at the mid point of one ...
2
votes
1answer
239 views

How does EM radiation depend on the reference frame?

In special relativity, magnetism is electrostatics in a different reference frame. This is how we explain the magnetic field being produced by moving charges (aka currents). Charges that move produce ...
1
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1answer
44 views

Show the equivalence of two electrostatic energy

$$U = \frac{1}{2}\iint_{all space}^{ } \frac{\rho(1)\rho(2)}{4\pi\epsilon_{0}r_{12}}dV_{1}dV_{2} $$ and $$U = \frac{\epsilon_{0}}{2}\int_{allspace}^{ } \vec{E} \cdot \vec{E} dV.$$ In the left ...
1
vote
1answer
2k views

Relationship between polarization density and electric field

Imagine I have an electric field $E$ created due to some free charges. Then I introduce a dielectric material somewhere. What confuses me is the polarization field $P$, which is now proportional to ...
0
votes
1answer
445 views

Why does the earth suck both positive and negative charges?

If the earth is a bit negatively charged, it is understood that it can take away the positive charges of a positively charged body when grounded. Why does it take away the extra electrons of a ...