Questions tagged [electric-fields]

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 [electricity] tag, as questions about the phenomenon & theory of electricity do not necessarily involve the discussion of fields.

621 questions with no upvoted or accepted answers
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8
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0answers
636 views

Sphere half-submerged on a dielectric

This is a classic problem in electrostatics with a twist, so I thought it could be useful for others here. I did have a problem with the integration at the end, but on general I think the idea can ...
6
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3answers
467 views

Field Theory: Electric Field

I am a grade 12 student, and we are learning electric flux. We covered electrostatic forces and, now we are on electric flux. We defined electric flux as the total number of lines of force passing ...
5
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1answer
205 views

Black Holes and QED

So, in quantum electrodynamics (at least to my rudimentary knowledge), the electromagnetic force is mediated by photons. On the other hand, in classical general relativity, the Kerr Black Hole ...
4
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2answers
163 views

The Cause of lightning and charge distribution in clouds

I was going through this video about lightning and I couldn't understand some points . 1: What caused the water molecules in ice crystals to be arranged in that specific pattern i.e. having positive ...
4
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1answer
90 views

Does net charge on a conductor sit only on outer surfaces?

Suppose we had a hollow conducting sphere with a net charge q on it. There is no charge in the cavity; the conductor itself has a charge q. The idea is that this net charge would reside on the '...
4
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3answers
381 views

How does an electric dipole lose its energy while aligning with a uniform electric field?

How does an electric dipole lose its energy while aligning with a uniform electric field--through heat or light?
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1answer
1k views

How does the electric field produced by a simple circuit look?

I have not seen anywhere a description of how the electric field looks inside and around a simple circuit. For example let's say we have the circuit shown below. One DC voltage source, two resistors, ...
4
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1answer
392 views

Is it possible to create arbitrary shapes of magnetic fields?

I've been reading about Transcranial Magnetic Stimulation (TMS) which can activate neurons using a magnetic field, which got me thinking... what if we can pick and choose exactly which neurons to ...
3
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0answers
105 views

Physical meaning of a mathematical identity

I have found this mathematical identity which is related to the Caderon identities and I want to understand its physical meaning. Let $S$ be a closed surface with unit normal vector $\mathbf n$ and ...
3
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0answers
44 views

Infinite sum of transmitted parallel light fields

I'm currently studying optics and came across the possibility of retrieving the original electric (light field) from a pair of partially reflecting mirrors, but I am confused by several ...
3
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0answers
38 views

How are the equiliberium points of the electric potential characterized?

I am interested in information about the points where the force per charge of a classical electrostatic potential is exactly zero. Loosely speaking, that is to say, if $$ V(\vec{r};\vec{r}_1,\cdots,\...
3
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0answers
25 views

Reason for phase change in the electric field oscillations, not the magnetic field oscillations?

Wikipedia states that when an EM wave undergoes reflection, there is a phase change only in the electric field oscillations, not the magnetic field oscillations. It also suggests that the opposite is ...
3
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1answer
580 views

Question on Gauss's law

This question is from Griffiths' Electrodynamics, Chapter 2, question 49, part e). The question is as follows: Problem 2.49 Imagine that new and extraordinarily precise measurements have revealed ...
3
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0answers
122 views

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 ...
3
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1answer
61 views

Meaning of potential in a discharging capacitor

I am dealing with this thing I cannot figure out. When a capacitor is discharging, the electric field inside it varies with time so we cannot perform the line integral to determine the potential ...
3
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0answers
161 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 ...
3
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0answers
384 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 ...
3
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0answers
313 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 ...
2
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0answers
105 views

Why the any point has same magnitude of electric line of force?

The $n~$ point charges have been placed on the same straight line. $\theta_{i}:=\text{angle between 2 line segments of point A like shown as the above diagram.}$ We want to deduce the below equation ...
2
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1answer
34 views

Newton's 3rd Law Coil in Magnetic Field

When a current-carrying rectangular loop is placed in a magnetic field, the forces acting on either side of the loop which is perpendicular to the field provides a torque which rotates the loop. ...
2
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0answers
75 views

Mathematically proving that field in a conductor is zero for equilibrium condition using Lagrange multipliers

I was reading this article here and near the half of it, the author discusses a way to prove that potential is a body is constant is the state which minimizes potential of a body. I was able to follow ...
2
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1answer
59 views

What is causing the acceleration of charges in an ideal TEM transmission line?

As I understand, in an ideal TEM transmission line we can set up the telegrapher equations and solve to show that the line propagates voltage and current waves. My confusion arises when we recognize ...
2
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0answers
50 views

Are there two groups of charges associated in an alternating current half wave?

Edit: to better express the problem: As alternating current passes along a wire: Individual current charges produce a magnetic field after zig zagging rapidly locally with a small resultant vector. ...
2
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0answers
23 views

How can I calculate the $D$ field when all the free charge is on a conductor embedded in a dielectric?

Let $K$ be a bounded piece of conductor, embedded in an isotropic, homogeneous, uniform dielectric of permittivity $\epsilon$. Let $ \vec r$ be a point in the exterior of the conductor. Let $\rho_f$ ...
2
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0answers
31 views

Lossy electromagnetic wave and reactive power

Consider an electromagnetic wave in a lossy medium. This medium has a complex permittivity $\varepsilon_r=\varepsilon_r' +j \varepsilon_r''$ and a wave impedance given by $$Z=\frac{E}{H}=\sqrt{\frac{\...
2
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1answer
69 views

Why is the impedance of an electromagnetic wave written as a ratio between the electric and magnetic fields, $E/H$?

The 'impedance of free space is written like this, too, as the absolute value of the $E$-field over the absolute value of the $H$-field. What does the ratio of the strengths of the two fields of an ...
2
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0answers
43 views

Is there any dependence between the shape and dynamics of the electric field produced by an electron and 'shape' of its wave function?

In classical electromagnetism the electron is described by a point charge that generates an electric field with spherical symmetry when the electron is static but at the quantum level the electron is ...
2
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0answers
269 views

What is the highest electric field value known?

What is the highest electric field known in nature? To add clarity, as requested: an electric field is measured in V/m, Volt per meter. What is highest value that has been measured or observed? What ...
2
votes
1answer
224 views

Angle between dipole moment and Electric field

I was learning the potential energy of a dipole because of torque from Halliday Resnick. In the given diagram, it said that if we move the system anticlockwise then the amount the Work that was done ...
2
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0answers
175 views

Relations between symmetries in sources and fields

I've edited this question way more times that I like to admit. I'll do my best Relation between highly symetric charge distributions and $\nabla\times\mathbf{D}$: In electrostatics, for some charge ...
2
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0answers
42 views

Position of the electric field induced by a magnetic field

I've been told that a cylindrical time-varying magnetic field induces a non-conservative electric field shaped like circles centred at the axis of the cylindrical magnetic field. I suppose it's an ...
2
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1answer
57 views

Discontinuities in electric fields

I'm a mathematician self-studying physics for fun and I'm trying to wrap my head around a simple concept, which is a consequence of approximations. Basically, by Coulomb's law, if I have a point ...
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0answers
51 views

Integrand discontinuity of surface integral of electric field of dielectrics

I am reading an article here on dielectrics Equation $(4.10)$ is: $$\Phi(\mathbf{r})=\dfrac{1}{4\pi \epsilon_0}\int_{V} \dfrac{d^3r'}{|\mathbf{r}-\mathbf{r'}|} [\rho (\mathbf{r'})\ -\nabla'.\mathbf{...
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0answers
58 views

Time Reversal of electric field in Euclidean signature (Wick Rotation)

This is a follow up to this question: How to Perform Wick Rotation in the Lagrangian of a Gauge Theory (like QCD)? I am wondering if their (6), using that $E^i_M = F^{0i}_M = i F^{0i}_E = i E^i_E$, ...
2
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1answer
42 views

Dielectrics and capacitors

Does the electric field after passing through the dielectric reduce. What I mean is If there is a dielectric which is in between the plates ( but NOT IN contact with them ) Suppose field begins from ...
2
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3answers
593 views

How is the $E$-field getting canceled between outer and inner surface of a neutral conducting spherical shell?

I am reading Purcell's E&M book and in one of the example questions, it shows that there is no E field between outer and inner surface after a a point charge is located at an arbitrary position ...
2
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0answers
145 views

Proof that true passive linear memristors don't exist

This is a sequel to the following (now irrelevent) question: My attempt to implement linear memristor Assume the "conceptual symmetry" of the fundamental passive circuit elements holds: ...
2
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1answer
837 views

How to measure a static electric field?

I looked up google but didn't find any design for measuring electric field that doesn't vary with time. My own idea is to use two parallel plates (like a capacitor but without the dielectric). In an ...
2
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1answer
993 views

How do insulators lose their charge?

Some theoretical questions that got me confused during physics lecture today. Bringing a conducting balloon to a negatively charged rod close will allow the conducting balloon to have positive ...
2
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1answer
229 views

Does $\sigma_f=\epsilon\sigma$ when $\vec{P}=\chi_e \vec{E}$?

(I am working in c.g.s) The electric displacement is defined to be $\vec{D}=\vec{E}+4\pi\vec{P}$. In an isotropic material we have $\vec{P}=\chi_e \vec{E}$, yielding $\vec{D}=\epsilon \vec{E}$ where ...
2
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0answers
53 views

Zero point energy and volume integral of the expected value of intensity

In his article "The concept of the photon" Scully and Sargent say that the zero point energy of the quantized electromagnetic field $\hbar\omega/2$ is given by the volume integral of $\langle 0|E^2|0\...
2
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1answer
77 views

what is difference between region around a charge and region out of it?

Basically I want to know what makes a region around a charge particle so affective that another charge will have energy when brought in this region or it will experience a force when enters into this ...
2
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0answers
150 views

Eletrical field Mobius strip

I had this question in my mind for months, is there a way to calculate the Electric Field ( Gravitational field as well) generated from a non orientabile Surface ?
2
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0answers
76 views

Linear Dependence of Stark Effect on Energy Level

I'm trying to get intuitive understanding of the well-known Stark Effect in QM. Pauli has found that the splitting of the levels depends linearly on $n$, the principal quantum number of the hydrogen ...
2
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0answers
406 views

How does the energy transfer in the near field of an antenna work?

Answering the question What is the relation between electromagnetic wave and photon? I wrote The EM radiation of an antenna is measurable and it was found out that the nearfield of an antenna has ...
2
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0answers
563 views

electric field energy density for an electron

I am currently reading a chapter in a physics book covering the electric energy stored in a parallel plate capacitor. The author derives the formula for the energy density: $u = 1/2 \epsilon E^2 $ and ...
2
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1answer
958 views

Measurement of electrostatic induction

How is it with the electrostatic induction measurement? Everywhere you can read about the effect of electrostatic induction but I still can't found any detailed explanations or quantitative ...
2
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0answers
469 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. ...
2
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0answers
122 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.
2
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1answer
613 views

Surface bound charge density in dielectric displacement

In Griffiths, it derived that the electric potential caused by Polarization $\bf {P}$ is written $$V({\bf r}) = \frac{1}{4\pi \epsilon_0} \int_{\mathcal{V}} \frac{\hat{\gamma} \cdot {\bf P}{({\bf r'})...

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