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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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
37 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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1answer
272 views

Force due to combination of free space and dielectric

I will make a generalized form of my question. There are two point charges $q$, $x$ distance apart. And there is a dielectric slab of thickness $t$ and of dielectric constant $K$. Should the force ...
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1answer
346 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 ...
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3answers
35 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
5k 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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24 views

Electric potential of a uniform rod at coordinate beginning [on hold]

I was doing a problem in electrostatics and stumbled on an interesting potential question. The problem is stated as: Suppose there is a thin metal rod of length $2a$ placed in the origin as shown ...
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2answers
66 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
117 views

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

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
86 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
724 views

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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3answers
387 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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1answer
49 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
407 views

Finding Green function using eigenfunction expansion method

Given the Dirichlet boundary condition, I am to show that the functions that satisfy $$(\nabla ^2 + k_{lmn}^2) \psi_{lmn} (x,y,z) = 0$$ are given by $$\psi_{lmn} = (\frac{\pi}{2x})^{1/2} ...
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2answers
2k views

The electric field of a conductive sphere containing a charge - grounded vs not grounded

Let's suppose we have a sphere but unlike theoretical ones it'll have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge $q$ ...
2
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1answer
260 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
835 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
9 views

Electrical potential help? [on hold]

The electric potential increases from 72 V to 686 V from the bottom plate to the top parallel plate. What is the magnitude of the change in potential energy of a -3 X 10^-6 C charge from top to ...
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0answers
15 views

Conductor in electrostatic equilibrium

Consider the following capacitor: The upper conductor is charged by $Q$. There's a conductor on the middle with thickness $e$. The lower conductor is connected to the ground. All of them have area ...
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0answers
19 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
12 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
35 views

Charge between parallel plates given voltage

When you connect a parallel-plates capacitor to a voltage source, why is it assumed that the plates will have equal but opposite charge? According to the formula, the voltage only fixes the charge ...
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1answer
46 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
46 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
86 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
42 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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1answer
777 views

Electric field from conductive to dielectric media

I am interested in the main difference between transitions from electric fields from Conductive to Conductive/ Dielectric to Dielectric and Dielectric/Conductive media. What are the boundary ...
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3answers
428 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
60 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
12 views

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
91 views

Electric Potential Energy

When work is done on a positive test charge by an external force to move it from one location to another, does the potential energy increases or decreases, and does the electric potential increases or ...
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1answer
32 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
45 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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2answers
1k views

Meaning of boundary condition for steady current density?

Although I understand the derivation of boundary condition in case of steady electric current but I did not understand, that the electric field which is in direction of $J$ current density that is ...
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2answers
131 views

Two capacitor plates with equal positive charges $q$

I read in a book that if both the plates of a parallel plate capacitor are given equal positive charges $q$, then the charges on the facing surfaces will be zero and the charge on the outer surfaces ...
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4answers
2k views

A problem of missing energy when charging a second capacitor

A capacitor is charged. It is then connected to an identical uncharged capacitor using superconducting wires. Each capacitor has 1/2 the charge as the original, so 1/4 the energy - so we only have 1/2 ...
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0answers
13 views

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
64 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
55 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
209 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
63 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
773 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
28 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
23 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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1answer
53 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
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
142 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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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
89 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 $Q$, ...