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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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 ...
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 ...
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 ...
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 '...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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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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 $E^i_M = F^{0i}_M = i F^{0i}_E = i E^i_E$, ...
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 ...
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 ...
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 ...
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 ...
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 ...
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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 ...