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.

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8
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839 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 ...
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3answers
529 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 ...
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1answer
219 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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1answer
142 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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1answer
675 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 ...
4
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1answer
427 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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1answer
47 views

How can the surface of the system consisting of two spheres and wire be equipotential, if the potential function is defined NOT for the net force?

Potential is a function defined for conservative force(s). Now consider what happens when we connect two metallic spheres with a conducting wire. The whole system will act like a big metallic thing ...
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0answers
76 views

Force due to a concentric hemisphere on a sphere of smaller radius

Recently while revisiting electrostatics I found a question now I know that a sphere imitates the electric field behavior of a charge, so to calculate the force on the hemisphere due to charge I ...
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0answers
106 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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45 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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1answer
71 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 ...
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,\...
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0answers
151 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: ...
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126 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
62 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 ...
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400 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
324 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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0answers
55 views

Equation of path traced by a charged particle in time varying magnetic field

Is there anyway to figure out the equation for trajectory of a charged particle in a magnetic field(which varies with time) increasing inside the plane of the screen, the particle is outside the ...
2
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0answers
59 views

Electrical conductivity/resistance of gas or vapor in an electrostatic field at normal temperature and pressure

For liquids (e.g. liquid metal and water), I could find their electrical conductivities (unit in S m$^{-1}$) or resistances in the CRC handbook. Also, I noted that equations for calculating the ...
2
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7answers
120 views

How can current flow without voltage?

The following is an image from my school textbook How do electrons travel from E to F is voltage (or the J per C of charge) is zero? I think my issue is a deeper misunderstanding of the nature of ...
2
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0answers
29 views

Energy of dipole using the electrostatic energy of all of space

I was watching my online lecs, and we were considering the electrostatic energy of a dipole. First, doing the torque-in-uniform-field calculations, and derived that $U_{rot}= - \vec{p} \cdot \vec{E}$. ...
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33 views

Why is coherence time the integral over (negative) infinite delay time?

Let $\vec{E_{1}}$ be a wave of the some profile. To observe the interference between these two waves, of the same profile, at different times, $t$ and $t + \tau$, the autocorrelation function $ \xi(t) ...
2
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1answer
76 views

How gauss law is not applicable here?

I am a high school student and I am very confused in how to use Gauss law, when we have to calculate electric field due to infinite sheet or wire, and for spherical surfaces, I know how we do that, we ...
2
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0answers
128 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
82 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. ...
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0answers
80 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 ...
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0answers
52 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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2answers
234 views

Electric field in a DC circuit

I have a power source connected to a resistor in series. I am asked, "what is the electromagnetic field in the circuit?" I know there is a magnetic field due to the moving current but is ...
2
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0answers
30 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 $\rho_f$ ...
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0answers
40 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
106 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 ...
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0answers
48 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
188 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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0answers
27 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 ...
2
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1answer
70 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
59 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
62 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
44 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
792 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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1answer
68 views

Where does the 2 come from in the force on the surface of a grounded sphere near a point charge?

In section 2.2 of the classical text on electrodynamics by John David Jackson the method of images is exemplified with a grounded sphere in the presence of a conductor. In the end of the section, he ...
2
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1answer
1k 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 ...
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2answers
1k 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
247 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 ...
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0answers
55 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
87 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
159 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
79 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
418 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 ...

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