For questions that utilize the concept of electric fields (commonly denoted by the letter E), or for questions whose answers likely involve electric fields. More specific than the [tag:electricity], as questions about the phenomenon & theory of electricity do not necessarily involve the discussion ...

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Lightning sprites

Lightning usually occurs due to an electrostatic discharge between an electrically-charged cloud and the Earth's surface, or between clouds. There are also sprites, electrical discharges that occur ...
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140 views

Partition function of classical quadrupole in an electric field

The partition function of a dipole in an electric field is a well-known problem, analytical solvable (nice integral, can be calculated with pen and paper), for example in the Langevin treatment of ...
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196 views

Electric field of a capacitor in dielectric medium with weird size

I have been learning gauss's law in capacitor recently, recently I come up with this problem that I couldn't solve myself. If we have a capacitor,and a dielectric medium with half the volume between ...
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27 views

What is the meaning of the Fourier Transform of the electric field of a well guided mode in a dielectric waveguide?

I have been studying waveguiding in dielectrics for a while now; however, I cannot understand the meaning of the Fourier transformed electric field. I will first give some background information. ...
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24 views

Polarisation inside a sphere

Why is the electric field inside a uniformly polarised sphere not zero? I am confused because charge enclosed is zero and by Gauss' law electric field has to be zero.
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36 views

Method of image charges — Why is a *grounded* plate needed?

In the classic image charge problem of a charge $q$ above an infinite grounded plane, it is well known that the field lines essentially behave as though there were a negative charge behind it, and the ...
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53 views

Gauss' Law and Electric Field Close to a Ball

So I've learned about Gauss' law and I have something in my head. Why does electric field that is very close to a ball is not close to infinity. Take a look at this image: As we can see, if we make ...
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51 views

Van der pauw method for an isolated hole

Van der pauw method is a way to measure the resistivity of a material with arbitrary shape while it meets some specifications ( being homogeneous and ...). One of the conditions is that the sample ...
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31 views

Strongly Influencing Electric & Magnetic Field Forces:

Why is it easier to block electric field forces than magnetic field forces in close ranges to the source? What is the best way to block, redirect, and minimize the strength of half of the lines of ...
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52 views

Electric Field due a thin arc

I have been given to calculate electric field at the centre of thin arc with linear charge density as a function of $\cos\theta$ as $\lambda(\theta)= \lambda_0 \cos\theta$ How i approached: The angle ...
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107 views

If the field concept was invented by Faraday, then how did Newton interpret the $g$?

This is Newton's law of universal gravitation. $F=G\frac{m_1.m_2}{r^2}$ Gravitational field $g$ is derived from this formula $g=G\frac{m_1}{r^2}$ This is named gravitational "field" strength. If ...
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387 views

Calculating Electric Field from a Potential Difference w/o Charge

So here is my homework question: Two long cylindrical shells of metal (radii $r_1$ and $r_2$, $r_2 > r_1$) are arranged coaxially. The plates are maintained at the potential difference ...
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194 views

insulator based gauss law questions

My book is incredibly scarce on insulator based Gauss law questions. Conductors seem to handle themselves pretty simply. Here's a question I'm working on that isn't part of my book. where the radii ...
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33 views

Determine potential function given initial conditions?

Assuming a radially symmetric circular disk (let's say r=1). Given two simple initial conditions: Potential at the centre is 4 V Potential at the edges is 0 V How would I determine the potential ...
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21 views

Reversibility of uniqueness theorem

If we use uniqueness theorem then we know that if the boundary conditions and the charge distribution is same in 2 setups in a certain region then the electric field and potential in that region in ...
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41 views

Dielectric field in a homogenous electric field

I'm working through my workbook right now and currently am stuck on the chapter about dielectrics. The term $\vec{E}=\frac{3}{\epsilon_r +2}\vec{E_0}$ was introduced without a proper proof. Instead ...
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27 views

Imaging and the Electric Field

In this book (pg. 162), it mentioned that conventional lenses only focus propagating waves, thereby creating an imperfect image. In contrast, superlenses focus both propagating and evanescent waves, ...
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55 views

Calculating the amount of charges for an object that is electrostatically induced

Induction is one of the ways to get an object electrostatically charged. While positive charges accumulate on one side, negative charges accumulate on the other side for an object in an electric ...
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219 views

Why is the electric field operator normalized by a volume?

I came across the following definition of the electric field operator: But I am not sure what this $V$, the "volume of a box", is about. It seems to enter the discussion in order to have standing ...
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121 views

How does non-constant conductivity change surface charge on a wire?

Current density is equal to conductivity times electric field. Therefore flux through a cross section of a wire is equal to current over conductivity. Current has to be constant along a wire. This ...
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47 views

Fresnel equations of S and T waves and Isofrequecy Curves: Feeling confused

First of all sorry for my (probably) bad english. I've been studying propagation of light in anisotropic media from the Born and Wolf and from Landau "electrodynamics in continuous media" and I'm ...
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39 views

Can electromagnetic fields be measured from a distance?

I know that direct measurements of electromagnetic fields can only tell information about the field near the probes, but I am curious if there is a way to measure the electromagnetic field in a not ...
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23 views

What makes an insulator good for polarizing?

Water in an electric field become polarized easily, since the natural dipoles twist and turn to align with the field. In non-polar insulating materials, a redistribution of charge can happen in the ...
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91 views

Sign error in calculating the electric field of point charge

I have to determine the electric field of a point charge, I get a true result except for a sign. Here is my passages. $$\nabla \cdot e = \frac{\rho}{\epsilon}$$ $$e = - \nabla u$$ $$\nabla^2 u = - ...
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191 views

Electric field produced by a charged ring

I have a question I couldn't find an answer for anywhere. There is a ring of radius $R$ which is charged uniformly with linear density $\lambda$, and I have to find the electric field on any point of ...
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743 views

Electric potential on a uniformly charged tube

A hollow cylinder, with no top or bottom, of radius $R$ and length $L$ is uniformly charged with density $\sigma>0$. I have to find the point on space where a point charge $q>0$ has to be drawn ...
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629 views

Complex polarizability of a dielectric sphere in a homohenious electric field

It is well known that complex polarizability of uniform dielectric sphere with radius $r$ and complex permittivity $\hat\epsilon_{in}(\omega)$ placed in a medium with complex permittivity ...
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566 views

Properties of electric field

I have the following vector field: $E=E_0(-sin(\phi),cos(\phi),0)^T$ and $E_0$ is some constant. Does anybody here have an idea what this electric field does to a metallic sphere that is in it? ...
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39 views

Potentials in Helmoholtz Theorem

I read about Helmholtz theorem on the Griffiths (Introduction to electrodynamics) and in the appendix B it shows how to use the Helmholtz theorem to determine the field F starting from the potential. ...
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723 views

What is a boundary condition for capacitors/dielectrics?

I am extremely confused about what boundary conditions are. One minute ago I was solving easy capacitor questions and the next minute I am being asked boundary condition questions and there is no such ...
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251 views

What is the electric field part of an EM wave? Radiation field or the induction field?

Look at this image: I wonder if the electric field is from the induction field from a vibrating electron or the radiation field? If it is from the radiation field, as I suppose, than can someone ...
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314 views

How to find the electric field at a point based on a uniformly charged surface

What is the general solution to finding the electric field at a point based on some (or multiple) charged surfaces. I know that we can perform a line/surface integral if a charge is close to a wire or ...
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21 views

Grounding system of conducting plates

So, I always make mistakes on problems such as this (the grounding part), so I'm hoping someone could really explain to me how the process works . There are n large parallel plate conductors carrying ...
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20 views

Electric field of an infinite plane (with and without an infinite conductor)

Suppose we have an infinite and uniformly charged (of surface charge density $\sigma \gt 0$) plane at $z = 0$. We can find the electric field at any point $(x, y, z)$ by computing an integral all ...
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23 views

Charge Magnitude Based on Isoline Spacing

Suppose we have two positive charges of unknown magnitudes. We are given the isoline map (the equipotential lines) for the two-charge system. One has isolines more "squashed together" (more closely ...
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16 views

Which way does the force due to current point

The current is towards the right. The particle with charge $-q$ is going with velocity towards the right. How does one find the force due to the current on $-q$? (The RHR doesn't do anything here). ...
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26 views

Macroscopic electric field

How does the integral over potentials due to dipoles equal the macroscopic field as given in Griffiths page 174. Does that mean macroscopic electric field is numerically equal to the potential?
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36 views

electrostatic shielding in paradox

We have electric field in side a sphere with formula E=q×r\4π€R^2 But according to electrostatic shielding electric field inside a conductor is zero. How to solve the paradox. In the above equation r ...
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14 views

Why does a 2-sided propagating EM wave become 1-sided if B is made proportional to E?

If you simulate the propagation of an electromagnetic wave in 1D free space (no charges or currents) with initial conditions of $E\neq0$ and $B=0$, and you look at a movie of $E$ vs time, then after ...
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29 views

How do we calculate electric field on the axis of a disc using gauss law and the concept of solid angle?

We can easily find the electric field at the axis of the disc by considering a differential ring and then integrating it to form a disc, but I was searching for rather a bit simplified proof using ...
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25 views

Would a spinning carbon steel (high magnetic permeability) sphere become magnetized?

Would a spinning carbon steel (high magnetic permeability) sphere "falling" through Earth's magnetic field become magnetized? Would a spinning, evenly charged sphere generate a magnetic field?
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21 views

Choosing between a parallel-plate and spherical capacitor model

This problem is solved in the solutions manual by making reference to equations for the parallel-plate capacitor. I have some basic understanding of why this is the case (the local curvature is small ...
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0answers
35 views

Electric field of a non-uniformly charged quarter circle

I was studying for my Electromagnetism test when I stumbled upon this problem and haven't been quite able to do it correctly, mostly because I can't find any symmetry for me to calculate the Electric ...
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0answers
22 views

Electric field intensity near to a small conducting plate?

I know the electric field intensity near a infinite charged conducting plate. when the plate is very large we assume that there is a symmetry and take the electric field intensity as same as for ...
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0answers
12 views

Constant electric background field from theta-term in QCD?

The theta-term of $1+1$ dimensional QED corresponds to a constant electric background field. Does the theta-term of QCD also induce a constant electric background field, which could be measurable in ...
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42 views

When deriving potential between plates of parallel plate capacitor, why isn't the charge distributed on the top *and* bottom of both plates?

Let's say we have a canonical parallel plate capacitor with area $A$ and separation $d$ where $A>> d^2$. A charge of $+Q$ is placed on the top plate and $-Q$ is placed on the bottom plate. We ...
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21 views

Null point (vector) between n point charges

I have derived the result for 2 positive charges, and for one positive one negative can be obtained by using the minus sign correctly. But I was unable to extend it or solve for n charges. Is my ...
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39 views

How do pulse properties relate to the pulse's peak power?

Let's say we know the temporal shape of an optical pulse, which is $E(t) = E_0 \cdot f(t)$, where $E(t)$ is the electric field, $E_0$ its amplitude and $f(t)$ the shape function (e.g. $sech^2$, ...
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78 views

Electric field at centre of two different hemispheres

I have a sphere separated into two hemispheres which are insulated from each other the bottom half is earthed and the top half has potential $V$. Radius=$a$. I am trying to find the Electric ...
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17 views

Voltage drop along electron beam

A focused electron beam represents a current and unless the charges (electrons) meet no resistance to their movement there should be a voltage drop along the length of the beam. So, assuming the beam ...