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 ...

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Can two electrons attract each other?

Due to electrostatic repulsion the two electrons will repel each other as they both possess similar charges, lets leave gravitational attractive force out of the picture my question is can there be ...
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electric field inside hollow conducting bodies

Let's say that there's a hollow conducting sphere placed in the presence of an external electric field and there's a + ve charge placed inside the sphere at a point other than the centre of the ...
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1answer
50 views

Force acting on a dipole placed in a non-uniform electric field

Why does the net force acts in the direction of increasing electric field when an electric dipole is placed in a non-uniform electric field?
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1answer
194 views

Electric field due to an electric dipole at a point on the equatorial line

According to [tamilnadu][1] textbook Electric field due to an electric dipole at a point on the equatorial line is given as The direction of E is along ...
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1answer
61 views

question about Gauss law

If I have an infinite plate with the surface charge of sigma. I know that my electric field is constant $2\pi\sigma$ (using Gauss's law). If I build the Gaussian surface above the plate the charge ...
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3answers
126 views

Electric field scalar quantiy or vector quantity

I cross referenced some website yahoo answers, wikipedia & some other websites. They were providing different answers. I know that electric field intensity is a vector quantity. But what abt ...
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2answers
6k views

Why is the electric field perpendicular to every point on the surface of a conductor?

I am reading Berkeley Physics Course, Volume 2 (Electricity and Magnetism by Edward M. Purcell). I am in chapter $3$, page $92$, and the book discusses conductors. The following is from the book: ...
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2answers
88 views

Confusion in understanding the proof of Uniqueness Theorem

I am having problems in comprehending the proof of contradiction used by Purcell in his book; ...We can now assert that $W^1$ must be zero at all points in space. For if it is not, it must have a ...
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1answer
129 views

How do you know when you need to use distributions to represent charge densities? [closed]

I tried to solve a problem using Gauss' law in the following way. Let's assume we have a spherical shell of radius $R$ with a charge $Q$ being homogenously distributed on its surface. I am trying to ...
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3answers
93 views

Can two charges with same sign atrract?

Can two charges with same sign (++/--) separated by some finite distance attract each other ?
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7answers
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Why do two ends of a long conducting wire have the same electric potential?

I am not seeing the "big picture" here. If I have two conducting spheres separated by a long conducting wire, why would the spheres share the same electric potential? I think of the spheres as point ...
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1answer
50 views

Doesn't Laplace's equation describe the local property of space?

$$\nabla^2 \phi = 0$$ is Laplace's equation used "wherever $\rho = 0$, that is in all parts of space where there is no electric charge.". However,how can Laplace's equation be used outside a conductor ...
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1answer
271 views

Boundary conditions for Laplace's equation

Given a grounded conducting sphere, $V=0$ and $\text{radius} = R$, centered at the origin with a pure electric dipole (dipole moment $\vec p$) situated at the origin and pointing along the positive ...
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4answers
873 views

Capacitance of two almost-touching hemispheres

This capacitor is composed of two half spherical shelled conductors both with radius $r$. There is a very small space between the two parts seeing to that no charge will exchange between them. So ...
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0answers
23 views

Variations in electric field of a light speed charged particle

From the question " Is there a travelling speed of for electric field? If yes, what is it?" I get to know electric field propagates at speed of light. What if a charged particle which creates this ...
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0answers
15 views

Giant dipole resonance

Could anyone explain in simple words what exactly is meant by GDR? What does giant imply? I have read about collective excitations and am also familiar with the multipolar form of the charge ...
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1answer
51 views

Why is the y-component of electric field of a uniformly-charged disk near its center the same as that of infinite sheet of charge?

This is an excerpt from Edward M. Purcell's Electricity & Magnetism: As $y$ approaches zero from the positive side, $E_y$ approaches $\dfrac{\sigma}{2\epsilon_0}$. On in the negative side of ...
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2answers
62 views

Electric potential between two infinite plates

Below is a solved exercise from Griffiths' Electrodynamics. I don't understand why it's directly assumed that the configuration is independent of $z$. Shouldn't there be a contribution from it since ...
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2answers
3k views

Electric field at the centre of a charged disc of uniform charge density

The electric field at any point at a finite distance z from the centre of a charged disc of uniform charge density along the axis of the disc is given by the equation: $$E= \int dE=\dfrac{\sigma ...
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2answers
97 views

Why is energy associated with the electric field given as $U = \dfrac{\epsilon_0}{2} \int E^2 dv$?

This is an excerpt from Edward M. Purcell's Electricity & magnetism: Suppose a spherical shell of charge is compressed slightly, from an initial radius of $r_0$ to a smaller radius. This ...
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2answers
63 views

Force on a layer of charge: How can electric field impart force on the charges which created the field?

This is an excerpt from Berkeley Physics: Electricity & Magnetism by Edward M. Purcell: The Force on layer of charge: The sphere has charge distributed over its surface with uniform ...
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3answers
497 views

Why the electric field $\vec{E}$ is constant (=position independent) for an infinite 2D sheet of constant charge?

So I'm reading a text on electricity and it talks about using the integral to compute the total charge of a collection of points, which I mostly understand. But then we get to finding the electric ...
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3answers
63 views

Why doesn't $\vec{E} =\dfrac{1}{4\pi\epsilon_0} \int\dfrac{\rho \hat{r}dxdydz}{r^2}$ blow up at $r=0$, when $\rho$ is finite?

Electric field at $(x,y,z)$ produced by a continuous distribution of charges is given by:$$\vec{E}(x,y,z) =\dfrac{1}{4\pi\epsilon_0} \int\dfrac{\rho(x',y',z') \hat{r} dx'dy'dz'}{r^2}$$. Now, as Edward ...
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0answers
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How would a closed conductor with only 1 layer of (atoms/molecules) behave if a charge is placed inside it?

I have quite a few questions actually related to this . Is it possible to have such a situation practically? If theoretically possible, how would the system behave?
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1answer
34 views

Proving assumptions used in 'method of image charges'

While studying the method of images for an infinite grounded plate, I came upon two assumption I can't seem to find the logic for: The test charge doesn't induce a charge density on the plate which ...
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1answer
52 views

What does multiplying of charges means?

Today I learned Coulomb's law, and I didn't get what does this multiplication $q_1 * q_2$ gives? I want to understand this visually.
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0answers
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Distribution of fragments in fission reactions

What decides the mass and charge distribution of fission fragments? are these factors decided at or before the saddle point? and how? Why does the valley in the distribution function become shallow on ...
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1answer
81 views

Can lightning actually weld fillings in your teeth?

So, I remember sometime in my childhood, someone was teaching me about lightning safety, and they explained that it was important to crouch low but keep as little contact with the ground as possible, ...
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2answers
59 views

“Rotating any system of charges causes a corresponding rotation of the electric field.”- What is the proof?

While I was reading 'symmetry' from wikipedia, then I came to this statement: ...For example, an electric field due to a wire is said to exhibit cylindrical symmetry, because the electric field ...
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2answers
216 views

What is meant by “unique direction” in most of the arguments in application of Gauss' Law?

This term is really bothering me a lot. While explaining the radial direction of electric field of a uniformly charged sphere, my book writes: Notice the use of argument of symmetry. There is no ...
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1answer
76 views

How to prove using symmetry that electrostatic force acting parallel to the line joining two charges?

The unit vector $\hat{r}_{21}$ shows that the force is parallel to the line joing the charges. It could be otherwise unless space itself has some built-in directional property. . . This can be ...
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2answers
825 views

How do I express the interaction energy between two charged spheres?

Consider two identical insulating spheres each with radius $R$ and uniform charge $Q$ through their volume. They are separated from their centers by a distance of $d>2R$. Here is my general ...
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1answer
48 views

Gauss' law and external electric flux through a cube: net flux is not zero while the interior charge is 0. What have I done wrong?

Consider a cube with side length $L$ and with its sides parallel to the basis vectors $\vec{i}$, $\vec{j}$ and $\vec{k}$. The $X$ axis goes right through the center of two of its faces. The closest ...
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1answer
36 views

Capacitance of three plates

I'm sorry if this has been asked before, but here it goes. Consider three parallel plane conducting plates (they can be infinite) and suppose the middle plate has some thickness $\delta$ and the other ...
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2answers
6k views

What are the units or dimensions of the Dirac delta function?

In three dimensions, the Dirac delta function $\delta^3 (\textbf{r}) = \delta(x) \delta(y) \delta(z)$ is defined by the volume integral: $$\int_{\text{all space}} \delta^3 (\textbf{r}) \, dV = ...
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1answer
152 views

Electrostatics problem concerning induction by a point charge inside a conducting shell

Consider two independent conducting shells (not thin shells! i.e., their internal and external surfaces do not overlap.) whose shapes of external surfaces are identical but internal surfaces are not ...
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0answers
16 views

Validity of Poisson Boltzmann in a thin channel between charged plates

I'm trying to find the pressure between two charged infinite plates either side of a solution of ions but I'm having a little trouble justifying the use of the Poisson Boltzmann equation which is used ...
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1answer
123 views

Method of image charges [closed]

In an attempt to understand the Method of image charges, I'll try to calculate the total charge on grounded conducting plane - with electric dipole & point charge. Given: Point charge $Q$, ...
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1answer
249 views

Charge present at the centroid of equilateral triangle

Three equal charges +Q each are placed on the vertices of an equilateral triangle. A charge +q is initially placed at the centre of the triangle. If this charge (+q) is slightly displaced towards a ...
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1answer
54 views

What is meant by 'a perfect dipole'?

Question What is meant by a perfect (electric) dipole? Additional information I came across the term in this question Force from point charge on perfect dipole and also in a textbook (which does ...
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1answer
58 views

Why is this electric field due to one plate of a capacitor $\sigma / 2 \epsilon_0$ when the capacitor plates are finite?

We know that electric field due to an INFINTE large sheet is constant and at INFINTY the electric field is not zero. But say if I take a finite sheet of length l and width w. Then the electric field ...
0
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1answer
31 views

Potential at the surface of a conducting sphere near a dipole

An ideal conducting solid sphere of radius $R$ and center $O$ is brought near a dipole with a dipole moment of magnitude $p$. Let the center of the dipole be called point $C$, and let the tangent from ...
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0answers
9 views

Corona discharge v pressure in air

Does anyone have any information on how a corona discharge between two electrodes changes as pressure is reduced from atmospheric to below 1mB? I am assuming current limited. Also, what I am looking ...
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0answers
17 views

How does one start drawing electric fields? [duplicate]

How does one start drawing electric fields.you are given two charge.now there are infinite electric field lines so how do you show greater electric field by drawing denser lines.After all there can be ...
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2answers
55 views

Please give your valuable opinion in this capacitor problem! [closed]

The plates of a parallel capacitor are given charges +4Q and -2QThe capacitor is then connected across an uncharged capacitor of same capacitance C. What is the final potential difference between ...
2
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0answers
63 views

Current Density Boundary Conditions and its Implications

According to Ohm's Law, one can say $ \overline{J} =\sigma \overline{E} $ if the field is in a conductor, and $ \overline{J} =0 $ if it's in empty space. Now if we take the surface of a conductor and ...
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0answers
40 views

Multipole expansion of Woods-Saxon potential?

When can a distribution be expanded in multipoles? What is the basic requirement? Can it be done for a potential like the Woods-Saxon form?
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0answers
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Analytical Calculations For a Stable Electret in Motion in Interplanetary Space. Determining the magnetic field

We know that a charging capacitor has, associated with the increasing E-field, a magnetic field. Now please consider the case of a very strong dipole or E field produced in an electret. Let us say ...
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2answers
82 views

Gauss' Law and area vector

Recently I've been doing some physics exercises on electric and magnetic fields and read up somewhere that the vector area of a closed surface is equal to zero. That made me wonder why, when using ...