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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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
774 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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29 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
54 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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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
143 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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12 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
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 $Q$, ...
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1answer
182 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
32 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
175 views

How do electrons distribute themselves along a wire attached to one pole of a battery?

Let's assume we have an electrochemical cell, like an AA battery. We attach a long straight wire to the negative terminus of the battery, the other end of the wire extends right away from the battery ...
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1answer
366 views

Apply Gauss' law to find electric field around nonconducting plastic sheets

The question: Two very large, nonconducting plastic sheets, each 10.0 cm thick, carry uniform charge densities $\sigma_1$,$\sigma_2$,$\sigma_3$ and $\sigma_4$ on their surfaces, as shown in the ...
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1answer
211 views

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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6answers
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electric field inside a conductor?

We have studied so far that electric field inside a conductor if no charge is placed inside is zero. But we know that every conductor has only a limited number of electrons. What happens when ALL the ...
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2answers
99 views

Two different electrostatic charges in rotation

It's a theoretical problem. I mean I drawn a circle and I consider this circle exist. I would like to understand how works this device composed of a circle and two charges: Two charges fixed on a ...
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1answer
39 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 ...
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1answer
26 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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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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1answer
29 views

Is capacitor plate length assumed to be finite? [duplicate]

infinte length plate won't have any zero potential point (not even at infinty ) and hence we can never find out absolute potential. When we say that potential on the plate to be $V$, we can think that ...
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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
45 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 ...
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0answers
49 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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1answer
409 views

How can one explain the Kelvin Water drop experiment without assuming the container to already possess a positive charge?

Kelvin Water Dropper experiment refers to the electrostatic generator invented by Lord Kelvin, which uses falling water to generate a voltage by electrostatic induction occurring between ...
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0answers
33 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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1answer
140 views

Static electricty and fields inside of the conductor?

I have a few related questions about static electricity and conductors. 1. when we say static electric field inside a conductor is zero, let us take an example of two concentric conductors, outer one ...
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1answer
45 views

Capacitance of spherical capacitor when earthed

The capacitance of a spherical capacitor is given by $$C=\frac{4\pi \varepsilon_{0}}{\left ( \frac{1}{a}-\frac{1}{b} \right )}$$ How can I find out the capacitance of the capacitor when The ...
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0answers
11 views

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
57 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 ...
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2answers
111 views

Help understanding the solution to a problem regarding kinetic energy of a group of point charges

The problem provided by my professor goes as follows: "Now consider a situation in which all charges are equal to q and they simultaneously become "unglued". What speed will each charge have when a ...
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2answers
88 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, ...
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1answer
24 views

Electrostatic potential due to two charge system

When we calculate electric potential energy of a two particle system, say first I bring $+q_1$ and then I bring $+q_2$ against $q_1$'s electric field. Say I get that $q_2$ charge to a point $r$ ...
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2answers
144 views

Will the electrostatic force between two charges change if we place a metal plate between them?

If a thin metal plate is placed between two charges $+q$ and $+q$, will this cause a change in the electrostatic force acting on one charge due to another? What is the concept behind this? What will ...
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2answers
62 views

Why is the Electric Field Zero at this point?

In a Phet Lab simulation, which is all I have at the moment to do my learning on electric field forces, the point represented as colored on the diagram below is shown to have an electric field ...
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2answers
90 views

Electric field and flux through a spherical surface inside an uneven hollow charge distribution

Consider a uniformly charged shell and two concentric spherical Gaussian surfaces $S_1$ and $S_2$. ($S_1$ radius is greater than charged shell and $S_2$ radius is less than that of charged shell.) We ...
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2answers
215 views

Numerically solving 2D poisson equation by FFT, proper units

The 2D Poisson equation is: (1)$$\frac{d^2\varphi(x,y)}{dx^2}+\frac{d^2\varphi(x,y)}{dy^2}=-\frac{\varrho(x,y)}{\epsilon_0\epsilon}$$ And in $k$-space it is in form of: (2)$$(k_x^2+k_y^2) ...
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2answers
230 views

Electric force between charges in two different media

As far as I know, Coulomb's law of electrostatic force is applicable on two different charges situated in same medium. But if two individual charges are in different media (say one charge on a iron ...
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1answer
39 views

How can a point hold mass or charge where it doesn't tell anything except position? [duplicate]

In geometry point is a dimension less quantity as it doesn't have length, breath or height. But when we define columbs law in electrostatics, we define points holding charges or Newton's law of ...
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3answers
86 views

Electrostatics and two electric charges

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?
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1answer
37 views

Why charge distribution is greatest at pointy edges of a surface? [duplicate]

If we have a conductor which is in electrostatic equilibrium, then the charge distribution over this surface $\sigma$ is greatest at the sharp edges of that surface. Why is this the case? I want ...
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1answer
24 views

can a power supply with high voltage value and some current be split into multiple small voltages of same current?

For example: if I have a source that can give an output of 10,000 Volts with some unknown current value, now, can i make that 10,000 Volts to 50 (need not be 50 exactly but maybe more than 30) of 200 ...
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0answers
28 views

Non-parallel-plate Capacitor

Imagine you start with a parallel plate capacitor with square plates of side $s$ and gap $p$. Turning one of the plates slightly results in a small increase and decrease in gap separation $d$ at the ...
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0answers
17 views

How can I have a voltage in hall effect with zero magnetic field?

How can we obtain a voltage with no magnetic field is applied to the semiconductor? They told me that if the points where I measure the potential difference are not at the same level I would obtain a ...
2
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1answer
174 views

How to approximate trajectories and movement of two oppositely charged particles?

Imagine a single, stationary charged atomic ion, say a Lithium anion or cation (Li+ or Li-). Now imagine another a single free, oppositely charged particle--perhaps an electron or Hydrogen ion ...
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13 views

Charge Distribution Across A System Of Metallic Parallel Plates

While calculating the charge distribution across a system of metallic plates, (taught as a prequel to the parallel plate capacitor), we say that the electric field inside each plate must be zero. We ...
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0answers
54 views

Sphere of electric charge revisited

I am thinking about a sphere of homogeneous charge distribution (see Electric field due to a solid sphere of charge, for example). Here we use a Gaussian surface (blue area) to find the electric ...
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1answer
103 views

Earnshaw Theorem for ionic solids

Is a single molecule of sodium chloride (say) or a cluster of molecules of NaCl unstable, although macroscopically NaCl is in fact, stable? How can I reason this based on Earnshaw's theorem?
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What is the cause of the time-varying electric and magnetic near-fields around a wire with a 60Hz AC current?

I know that it's the accelerating electrons in an AC current that are the cause of far field effects. But, what about the reactive near field close to a wire that has a 60Hz AC current? What is the ...
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3answers
867 views

How can I find the potential created by spherical capacitor with dielectric material?

If we have a spherical capacitor with inner radius or r1 and outer radius of r2, with charges (+/-)q on them and there is a dielectric material (with constant e) in between them with. What kind of a ...
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2answers
41 views

What happens to half of the energy in a circuit with a capacitor?

For a simple circuit with a battery supplying a voltage V to a capacitor, let us assume that the charge on the capacitor is Q. Now, the work done by the battery or the energy supplied is given by the ...