Skip to main content

Questions tagged [electromagnetism]

The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.

Filter by
Sorted by
Tagged with
1 vote
1 answer
41 views

Why does a charge need to have a velocity to experience force in a magnetic field?

While studying magnetism, I learned that force on a charged particle inside a magnetic field is $$F=q (vxB)$$ where all symbols have their usual meaning, which implies that a charged particle must be ...
Advait K's user avatar
0 votes
1 answer
32 views

Why does the electric field only depend on the rod?

In the following exercise: We are asked to calculate the electric field at a certain distance from an exis where a rod is located. Previously, we are asked to calculate the charge density a ...
MSU's user avatar
  • 1
0 votes
1 answer
17 views

Electric charge conveyor trap

Normally one cannot trap both positive and negative charge within the same region by using electrostatic confinement as one charge would be attracted and the other repelled. I was wondering is it ...
Girts's user avatar
  • 91
0 votes
0 answers
59 views

Is there a generalization of mode coupling theory?

I am currently reading a lecture on coupled-modes theory and have a question regarding the ansatz: $$E_\text{tot}=A(z)E_1(x,y,z) + B(z)E_2(x,y,z) \\ H_\text{tot}=A(z)H_1(x,y,z) + B(z)H_2(x,y,z)$$ and $...
Leopold's user avatar
1 vote
0 answers
30 views

How can the attraction of opposite electric charges be explained by the exchange of virtual photons? [duplicate]

Sometimes, the electric force between two electrically charged particles is explained by the analogy of two freely floating astronauts that start throwing a ball towards each other. In this analogy, ...
a_guest's user avatar
  • 260
0 votes
1 answer
41 views

Would we be able to see the superposition of two X-rays where the frequency of the modulation matches visible light?

Suppose I had the superposition of two electromagnetic waves whose angular frequency was in the X-ray region. Together they form a composite made of a carrier wave and a modulation wave where the ...
Hadi Khan's user avatar
  • 447
0 votes
0 answers
15 views

What is the physical meaning of the torque term involving the magnetic displacement force?

In Zangwill's Modern Electrodynamics the magnetic torque is derived in Eq. 12.63 to be \begin{equation} \mathbf{N}(\mathbf{r}_0) = \mathbf{m} \times \mathbf{B}(\mathbf{r}_0) + \mathbf{r}_0 \times \...
Marcus Aurelius's user avatar
0 votes
0 answers
19 views

Calculation of Capacitance Coefficients for Two Non-Concentric Spheres: Discrepancy with Jeffery's $C_{22}$ Value [closed]

I have calculated the capacitance coefficients $C_{11}$, $C_{12}$ and $C_{21}$, and they match the values found in the literature. However, I am having trouble with the coefficient $C_{22}$ as it does ...
Edward Henry Brenner's user avatar
1 vote
0 answers
36 views

Fourier transform of Light impulse [closed]

A function in the time domain and the frequency domain has inverse relationship in standard deviation. So the less standard deviation the function has in time domain the more spread out in the ...
Hello's user avatar
  • 25
0 votes
1 answer
43 views

Why doesn't increased permeability increase lorentz force on a wire? (or does it?)

Does increasing the relative permeability of a wire increase the force felt by the wire (given the current and H field remain the same)? The answer to this question seemed like an obvious "yes&...
Joseph Summerhays's user avatar
0 votes
0 answers
50 views

EM field of time dependent spherical current

A field of a time dependent rotating spherical current could be described by $\mathbf{J} = \sin \theta \; h(t) \delta(r-a) \hat{\boldsymbol{\phi}}$. First I related the current to the magnetisation. ...
Nitaa a's user avatar
  • 268
0 votes
1 answer
50 views

Why only two polarisation states of the EM wave in the Jeans cube are considered?

This question already has answers here and there. But none of them answers , why there are only two polarisation states for a mode in the Jeans cube ? I mean they only say that we take the two ...
CP of Physics 's user avatar
3 votes
1 answer
70 views

Effect of own magnetic field on stream of electrons (beam in vacuum and DC current in conductor)

Similar, but not the same as: Magnetic field inside a charged stream because I am interested in what happens inside a conductor, but the behaviour in a free beam can help clarifying what I am asking. ...
Peltio's user avatar
  • 756
1 vote
1 answer
62 views

Do twisted pair wires create a helical shaped magnetic field if parallel electrical currents are run through the two wires?

I would like to know if the shape of the magnetic field around twisted pair insulated wires will be a helical shaped magnetic field if both wires have parallel electrical current running through them. ...
user57467's user avatar
  • 472
1 vote
1 answer
18 views

When an element near the star surface absorbs the discrete frequency of star's em radiation do this absorbed photons ought to accumulate?

We all know about emittion lines that are empty from a discrete em freqency depending on the element that absorbs that frequency band near the star which we observe when looking at these astrophysical ...
Krešimir Bradvica's user avatar
-3 votes
0 answers
44 views

Maxwell's contribution to E&M [closed]

Is there a topological or geometric reason for why maxwell's correction term should be added to the equations so that the theory is consistent? Or it is the physics that requires this term and there ...
Amr Khaled's user avatar
0 votes
1 answer
28 views

Electric and magnetic field configuration that makes an electron trace the surface of a sphere

Can anyone suggest an electric and magnetic filed configuration that can make an electron trace the surface of a sphere? Has such a configuration been achieved experimentally?
Dr. user44690's user avatar
-1 votes
0 answers
38 views

This is a question about pendulum problem in electrodynamics [closed]

Question: When two particles $A$ (charge $q_{1}$, mass $m_{1}$) and $B$ (charge $q_{2}$, mass $m_{2}$) hang from a common point by insulating threads of lengths $l_{1}$ and $l_{2}$ respectively, the ...
sp nk's user avatar
  • 1
2 votes
0 answers
24 views

How can Fresnel's transmission coefficient be nonzero in Total Internal Reflection?

I'm working on a problem in which a wave is moving through a transparent medium of refractive constant $n_i$. It then reaches the interface of said medium with another one of refractive constant $n_t&...
Lagrangiano's user avatar
2 votes
0 answers
49 views

Time evolution of scalar potential using Huygens principle

Huygens principle states that every point in space acts as a source of spherical waves. The amplitude for potential (scalar and vector) will be given by $V(r,t)=f(t-r/c)/r,$ where $f$ is a function ...
Physics's user avatar
  • 63
1 vote
1 answer
58 views

Conservative and non-conservative electric field due to to changing magnetic flux

Consider this situation in which a uniform cross section conducting neutral ring is placed in a changing magnetic field which is given by $B=kt(-\hat{k})$ ($k$ is a constant and $t$ is time). The ...
FUSION X's user avatar
2 votes
0 answers
23 views

Capacitance coefficients of two enclosed spheres

I was reviewing G.B. Jeffery's work titled On a Form of the Solution of Laplace's Equation Suitable for Problems Relating to Two Spheres. To access the full text, you need to click "DOWNLOAD PDF&...
Edward Henry Brenner's user avatar
0 votes
1 answer
21 views

Why is the EMF zero in a conducting rod perpendicular to length

Consider a rod moving in uniform magnetic field with its length perpendicular to the field. My textbook says EMF induced is zero in this case, but why won’t there be a transverse electric field across ...
Kampann's user avatar
  • 157
0 votes
2 answers
98 views

Is the Lorentz force proportional to $B$-field in the wire or immediately outside of it?

When considering the force on a current carrying wire in a magnetic field, is $B$ in the Lorentz force $F=IlB$ the field inside the wire where the current is flowing, or is it the field immediately ...
Joseph Summerhays's user avatar
-1 votes
1 answer
22 views

Understanding of flux [closed]

Q1. The question: to find flux through a “half sphere with top cut off” (closed surface) with point charge at sphere’s center For this question- flux as I understand it is the number of field lines ...
12345X's user avatar
  • 1
0 votes
1 answer
45 views

Why the dielectric permitivity matrix of lossless media is symmetric?

I am studying optics and I met a strange statement in the section 2.3.4 (page 34) of Fundamentals of Nonlinear Optics by Peter E. Powers and Joseph W. Haus. The relationship between $\vec{D},\ \vec{E}$...
Hsu Bill's user avatar
  • 388
0 votes
3 answers
84 views

Edited: longitudinal view of different modes of electromagnetic waves

We have a single, polarized $TEM_{00}$ and the same for a $TEM_{01}$/or any other. mode relative to the z-axe. Reformulated questions: In classical mechanics we have a standing wave. When we look from ...
plantpot's user avatar
2 votes
0 answers
42 views

How can auroras be visible at lower latitudes when a strong solar wind hits Earth?

Auroras are a product of electrically charged particles hitting Earth's atmosphere at the poles, where the geomagnetic field is weaker (where magnetic lines originate). How can a strong solar wind ...
jack_O'Dim's user avatar
1 vote
1 answer
42 views

Ambiguities in optical waveguide modes

While studying concept of slab waveguide mode, I got stuck on some problems. In textbook(Yariv chapter 3 pg 112), for guided TE modes it tells that the mode function is taken as which means that the ...
photonics2024's user avatar
1 vote
0 answers
27 views

What is the reletive permeability of structual steel?

Help, i need to know what the reletive permeability is of a few materials (listed below) but i can not find the data on the internet. Does annybody know the data or where i can find it? -s235jr -...
laurent's user avatar
  • 11
0 votes
1 answer
50 views

Can an oscillatory field produced by a time-dependent charge distribution fall off faster than $1/r$?

An electric charge has a field that decays at large distances like $1/r^2$. A charge distribution with total charge zero, but with a nonvanishing dipole moment, has a field that decays at large ...
user196574's user avatar
  • 2,122
2 votes
1 answer
77 views

Utilization of Hertz potentials in calculations

Electrodynamics textbooks, like Zangwill's Modern Electrodynamics, introduce the Hertz potentials $\boldsymbol{\Pi}_m$ and $\boldsymbol{\Pi}_e$(see Chapter 20 of the fore-mentioned book). While they ...
2 votes
0 answers
29 views

What is the physical interpretation of the eigenvalues of the Maxwell stress tensor?

The Wikipedia page on Maxwell stress tensor has a section on the eigenvalues of the Maxwell stress tensor, which is given by $$ \mathrm{Eig}\{\mathbf{T}\} = \left\{ -\left(\frac{\epsilon_0}{2}E^2+\...
Jono94's user avatar
  • 631
2 votes
3 answers
65 views

Current density and units

I have a question about current densities. My understanding is that there are 3, volumic $(\vec{J})$ , surface $(\vec{K})$ and linear $(\vec{\lambda})$. The first question is, that if J is volumetric, ...
JL14's user avatar
  • 59
0 votes
0 answers
17 views

Resolution of current in solenoid in order to analyze magnetic field?

So i came across this question in one of my tests, it asked something appearing very easy,It actually asked "If radius of solenoid is R and that of wire wrapped on it is r then comment about the ...
Vansh Pandey's user avatar
2 votes
4 answers
184 views

Why electrons do not emit electromagnetic radiation when they "jump" to an excited state?

According to electromagnetism, accelerating charges emit electromagnetic (EM) radiation. However, according to quantum mechanics, electrons do not emit EM radiation while they "orbit" around ...
MrDoppler's user avatar
1 vote
1 answer
43 views

Potential on concentric shells not making sense?

Suppose you have 2 concentric spherical shells, radius $A$ (inner) and $B$ (outer). Now suppose the inner shell has $+Q$ charge and the outer one has $-Q$ charge. Through integration, we get that the ...
AankNum's user avatar
  • 11
18 votes
5 answers
3k views

Does a time varying electric field always generate a Magnetic field?

I have come across this problem from 200 Puzzling physics problems A charged spherical capacitor slowly discharges as a result of the slight conductivity of the dielectric between its concentric ...
Rishikesh's user avatar
  • 333
-1 votes
0 answers
36 views

How magnetic field with it s rotational effect emerges from movement of the particule? and why is it perpendeculare to the electric field in EM wave? [closed]

Is there an intuitive way without deliving in to math to answer this circulare effect and the perpendecularity of the magnetic on the electric field in the EM wave? Why it depends on velocity? When a ...
user402553's user avatar
0 votes
0 answers
28 views

Force on an iron ball in a homogeneous magnetic field [duplicate]

Just a simple question. If I have a homogeneous magnetic field and I put an iron ball into this field, it would be attracted to the source of the magnetic field. But how do I calculate the force that ...
Mo711's user avatar
  • 61
1 vote
2 answers
47 views

Does diffusion current "consume" thermal energy?

My (possibly erroneous) understanding of solid state physic has led me to the belief that diffusion current may "consume" thermal energy. Here is my (possibly erroneous) understanding. When ...
Math Keeps Me Busy's user avatar
5 votes
2 answers
629 views

Theorem in mechanics relating energy flow and momentum

In Feynman's Lecture 27 on Vol. II it is written that There is an important theorem in mechanics which is this: whenever there is a flow of energy in any circumstance at all (field energy or any ...
lalala's user avatar
  • 1,831
0 votes
2 answers
93 views

Why In an electromagnetic wave both electric and magnetic waves are in sync and perpendeculare? if one makes the other shouldnt there be a delay? [closed]

Why are electric and magnetic waves in phase if one induces the other? Shouldn't there be a delay, similar to how potential energy converts to kinetic energy and vice versa? Additionally, why are ...
user402553's user avatar
0 votes
0 answers
42 views

Landau Classical Theory of Fields. Chapter 5 [closed]

I'm studying Landau's book on classical field theory, and specifically the end of chapter 5 has given me some doubts. Can you help me understand some of the demonstration steps and how he defines some ...
Sergio's user avatar
  • 1
0 votes
1 answer
25 views

Magnetic object affected by electromagnetic wave

If a dipole antenna is strong enough, can it make a compass needle oscillate?
Simon Lin's user avatar
  • 156
0 votes
2 answers
64 views

Understanding time reversal symmetry in Classical Physics

By looking at Newton's second law, we can immediately infer said equation is symmetric in time: $$m\frac{d^2\vec{r}}{dt^2}=\vec{F}(\vec{r},t)$$ since we can change $t\to -t$ and everything remains ...
Lagrangiano's user avatar
0 votes
1 answer
36 views

Laplace equation boundary condition

I'm reading a paper and seeing that the boundary condition for solving Laplace equation is set to $ \frac{\partial V}{\partial y} = 0 $ just because there is no charge at that boundary. Does this ...
user207787's user avatar
3 votes
0 answers
50 views

Question about Fourier-coefficients in Griffith's Problem 3.15 (Electrodynamics) [closed]

I am having some trouble with problem 3.15 from Griffith's Electrodynamics. It states the following: A rectangular pipe, running parallel to the $z$-axis (from $-\infty$ to $+\infty$), has three ...
want2know's user avatar
0 votes
1 answer
123 views
+50

How do I calculate change in flux in an augmented rail accelerator without violating conservation of energy?

Suppose I have two rails and a wire connecting them I'd like to accelerate. Then $\frac{d\phi}{dt}=Bvl$, where $B$ is the magnetic field strength where the wire is, $v$ is the velocity, and $l$ is the ...
Joseph Summerhays's user avatar
-1 votes
0 answers
31 views

How to Solve the Schrödinger equation for a System with Dipole-Dipole Interaction Potential? [duplicate]

I am currently working on a project where I need to solve the schrödingel equation for a system characterized by electric dipole-dipole interaction potential. So my associated potential is $ U = \frac{...
Hakan Akgün's user avatar

1
2 3 4 5
364