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

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20 views

solving an electromagnetic problem in the frequency domain

I study a course in electromagnetic fields and I don't understand why when I solve a problem in the frequency domain I lose the transient solution. can anyone show me mathematically why does it ...
4
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4answers
215 views

Does electrostatic fields really obey “action at a distance”?

In a Electromagnetic theory class, my professor introduced me the concept of "Action at a distance in Physics". He said that If two charges at some very large distance, and if any one of the charge ...
0
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0answers
15 views

How can electric and magnetic fields have any component in the direction of propagation of electromagnetic waves?

In case of waveguides we talk about E and H having non zero component in the direction of propagation of wave. But the entire basis of EMW is that E and H are perpendicular to the direction of ...
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1answer
40 views
-1
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0answers
45 views

Maxwell said the dimension of charge is $L^3 T^{-2}$ and of mass is $L^3 T^{-2}$, is he right? [on hold]

If his right then, from Lorentz magnetic force, $$F= BQV$$ where $F$ is force, $B$ is magnetic flux density, $Q$ is charge and $V$ is velocity. Therefore, $$M L T^{-2} = B Q V \, .$$ Substituting for ...
-3
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0answers
38 views

Is the proton mass to charge ratio equal to the plank mass?

Using a proton charge 1.602*10^-19 coulombs is equal to proton mass 1.673*10^-27 Kg. One coulomb = 1.673*10^-27 Kg divide by 1.602*10^-19 Therefore One coulomb is equal to 1.044*10^-8Kg. Therefore ...
-2
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2answers
54 views

Is gravity weak negative electric charge? [duplicate]

This could be true since the both have infinite range and other common properties. They both have fields.
0
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1answer
41 views

How is light slowing down in a medium thought of in the photon picture? [duplicate]

The speed of light in any medium besides vacuum is smaller than $c$. In a classical way, I just look at that as a wave that propagates less fast, the change in EM-field is passed on slower. How should ...
0
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0answers
63 views

Problems with Maxwell density Lagrangian [on hold]

I want to expand the right-hand side of $$\dfrac{1}{4} F_{\mu\nu}F^{\mu\nu} = \dfrac{1}{4}\left(\partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu}\right)\left(\partial^{\mu}A^{\nu} - ...
0
votes
1answer
19 views

Is internal resistance relevant in motional EMF?

When a conductor passes a magnetic field and connected to a circuit, the induced voltage is calculated via the motional EMF($\epsilon$): $$\epsilon=-vBL$$ Is the conductor's resistance (or internal ...
2
votes
1answer
61 views

How can radiation be a transverse wave? Does light really resemble a rope? How can a 3D field be a medium for non-spatial 1D waves? Need mental model

I understand longitudinal waves. For example, I've got a clear mental modal of air waves: a slice of air becomes overcompressed, then the slice next to it becomes overcompressed and the first slice ...
0
votes
1answer
61 views

Could electromagnetic charge curve something like spacetime in analogy with general relativity? [duplicate]

Newtonian gravity and electrostatics have the same form; this analogy is extended when we look at full dynamic electromagnetism, and correspondingly "gravitomagnetism". We are quite capable of ...
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0answers
26 views

Rotating cone magnetic field [on hold]

how to calculate the magnetic field of a rotating cone with a superficial charge distribution that varies with the altitude? It knows : height of the cone , truncated cone rays bases , there are ...
1
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0answers
42 views

Question about Elon Musk's Hyperloop Suspension [on hold]

So one of the proposed suspension systems that will be used on the hyperloop include the externally pressurised air cushions. These cushions lift (or atleast help lift) the capsule and reduce drag ...
1
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2answers
64 views

Physical meaning of wavelength of a EM Wave

The wavelength of a wave is defined as the spatial separation after which it repeats its shape. It is easy to visualize it for one dimension but if we consider a light wave/EM wave which is ...
1
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1answer
43 views

question about Gauss law

If I have an infinite plate with the surface charge of sigma. I know that my electric field is constant $2\pi\sigma$ (using Gauss's law). If I build the Gaussian surface above the plate the charge ...
1
vote
1answer
36 views

Force of electromagnet on a wire [on hold]

I'm trying to produce an equation for the force produced by an electromagnet on a wire. I'm very aware I don't know any vector calculus but I think as it's the special case (Perpendicular) I can just ...
0
votes
0answers
23 views

Energy distribution for a monochromatic plane wave [on hold]

the task it to examine the energy distribution over the spectral components of a monochromatic plane wave averaged over time. To do this, I need to prove: There are no other clues! How do I ...
1
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0answers
43 views

How did Weyl's 1918 paper; Gravitation and Electricity, influence classical physics? [migrated]

The main-stream view seems to be that Weyl's 1918 paper Gravitation and Electricity was initially considered a failure for reasons first pointed out by Einstein. But these initial ideas were reapplied ...
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0answers
40 views

Maxwell's equation; electromagnetism [closed]

I'm just curious about this, but I want to know about Maxwell's equation? What its use? Please define it in a simple way.
1
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1answer
62 views

Electric Motors: why do they draw more current when stalled, and less when moving? [duplicate]

I'm familiar with how an electric motor works, and also familiar with what stall current and free current refers to in an electric motor. I'm also somehow familiar with the notions of energy being ...
2
votes
1answer
93 views

Resource for mass-charge interaction

My GR professor mentioned that trajectories of charged particles in GR are not the same as those of non-charged particles (i.e. charged particles don't move on geodesics). As I understood it, the ...
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5answers
543 views
+100

Can you depict the electron's electromagetic field?

I've had a number of discussions with individuals about electromagnetism. A recurring issue concerns the distinction between field and force, and seems to be associated with the lack of unification in ...
1
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1answer
46 views

Why doesn't light vibrate in-situ?

Light always moves in a straight geodesic path (shortest distance between 2 points in flat space where gravity is homogeneous) across 3 dimensions of space and 1 dimension of time. It is consists of a ...
0
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1answer
28 views

Reducing eddy currents, changes the property of the conductor & circuit?

In an attempt of reducing the eddy currents in a conductor, such as having gaps to break the induced eddy currents, would that by any chance change the conductor's orientation from series to parallel? ...
2
votes
1answer
61 views

Why do high voltage transmission line workers need a Faraday cage suit?

In this video the high voltage transmission line workers are wearing a Faraday cage suit. Why is this needed? Without the Faraday cage, the resistance of the human would be very high compared to the ...
0
votes
1answer
62 views

Cylindrical capacitor in an electric circuit

I've come across a tricky question and would appreciate some hints or explanations as to why the given solution is the way it is. The question reads as follows: A coaxial cable consists of a wire ...
1
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0answers
39 views

Lack of symmetry in Poynting vector

I've noticed that there's a lack of symmetry in the definition of the Poynting vector, being defined as: $$S=E\times H$$ meaning, using the electric field cross the magnetizing field instead of the ...
0
votes
1answer
76 views

How to write the Lagrangian in terms of a projection

We know that $$ L=\frac{1}{2}\left(\partial_{\mu} A_{\nu} \partial^{\mu} A^{\nu}-\partial_{\mu} A_{\nu} \partial^{\nu} A^{\mu}\right) $$ But how do we write the Lagrangian in the following way: ...
0
votes
1answer
39 views

Fringing effect of electric current

We know the what is the fringing effect of electric field in capacitor, of magnetic field in some in some solenoid or magnetic field in through joint of some metal. But is there is something similar ...
0
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0answers
25 views

A magnet floating due to Meissner effect

If a magnet is floating due to the Meissner effect, can the magnet rotate freely under influence of external field in spite of the presence of north and south pole in it ?
1
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1answer
50 views

Derivation of magnetic force for a charge in motion relative to a wire (M. Purcell's Electricity and Magnetism)

I have a question regarding the derivation of magnetic force in M. Purcell and David Morin's Electricity and Magnetism. In the first part, they derived the force first by assuming that a charge q is ...
0
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0answers
29 views

About Michelson-Morley experiment

Can you please explain it to me. As far as I know, we have a monochromatic and coherent em source and we getting an interference picture (because we clearly couldn't make the splitted beams travel ...
0
votes
1answer
31 views

Border conditions on the separation surface (Electromagnetism & Optics)

My teacher taught me that we can consider the following equation: $$E_{1t}=E_{2t}$$ to the descontinuity of the electric field tangent component on the separation surface of two means with ...
1
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2answers
78 views

Electric field energy of two parallel moving charges at relativity speeds

Assume two particles of the same charge $q$ moving in parallel trajectories on the x,y plane. The distance between them is $d$ and it's defined in the y axon. The problem is to calculate the energy of ...
2
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0answers
19 views

Motion decomposition (Relativistic case)

When an electron moves at very close at $c$ (speed of light), is it physical to decompose the motion in two other directions (like what we do in classical case). If so, the motion in each direction ...
1
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0answers
35 views

Electric field from time varying charge density

Inside a cylinder of infinite length in $z$ axis, there is charge density $ ρ = cos(βz -ωt)$. I want to find the electric field and as far as i can understand we will get a radial component of $E$. ...
0
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2answers
46 views

Electric potential between two infinite plates

Below is a solved exercise from Griffiths' Electrodynamics. I don't understand why it's directly assumed that the configuration is independent of $z$. Shouldn't there be a contribution from it since ...
0
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0answers
49 views

$E$-field from changing current in straight wire

A very long insulated wire oriented along the $z$ axis of a cylindrical coordinate system is carrying current that is defined by the following function: $$I(t) =Io + k⋅t$$ (current increases linearly ...
2
votes
2answers
51 views

Why is the introduction of a quantization volume necessary for quantization of the EM field

I have been working through the quantization of the electromagnetic field, and every source I find introduces a quantization volume with periodic boundary conditions in the process, in which we fit ...
0
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0answers
16 views

Ratio E/B and power in rectangular cavity

I would like to know if the relation $E=B*c$ still holds in a rectangular cavity Let's consider this rectangular cavity where the wave is travelling along the z direction ...
0
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0answers
28 views

Reactor for electrical energy design base assumption inefficient?

Im no physicist or engineer but as I observe our methods to obtain electrical energy I noticed a pattern where we cause a exothermic reaction, the resulting energy heats water, that turns into vapor, ...
0
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0answers
39 views

Regarding Ampere's Circuital Law

If I am to show that Ampere's Circuital law holds true for any arbitrary closed loop in a plane normal to the straight wire, with its validity already established for the closed loop being a circle of ...
1
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0answers
11 views

Coordinate Transformation across different media

I have an arrangement that is as follows : (1) inner cylinder(radius r1) filled with water (2) outer cylinder(concentric, radius r2>r1) made of glass I have a sensor S1 at radius r(r1) at angle beta. ...
0
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0answers
23 views

How is the electromagnetic tensor expanded?

The electromagnetic tensor is given by $F_{\mu \nu} = \partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu}$, and it appears in the Lagrangian as $L = -\frac{1}{4}F_{\mu\nu}^2 - A_{\mu}J_{\mu}$. The text I'm ...
0
votes
1answer
16 views

$H$ field from corresponding $E$ field (antenna)

The $E$ field at $kr >> 1$ due to a short dipole oriented in the $z$-direction and located at the origin is: $$E_0 = \frac{10^3e^{-jkr}}{r}\sin\theta\space\space(V/m)$$ Can I just solve for the ...
0
votes
1answer
25 views

what is the meaning of spatial function of Ex?

I came across this while i was studying Resonant cavities. Consider the component of $E_x $ of $ E $. Within the cavity $$ E_x = E_x(x,y,z) $$ Why should we take $E_x $ in all three directions?
2
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0answers
48 views

Spectroscopy from a classical light wave or photon only?

In chemistry we mostly regard light/electromagnetic radiation as a beam of particles or photons. This is a very useful model to explain molecular excitations and ionisations from quantum interactions. ...
0
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1answer
39 views

Apparent discrepancy between Lagrange field equation and Maxwell equation [closed]

I am deriving Maxwell's equations from a Lagrange field equation and have come across something I can not figure out no matter how hard I try. The problem is in the signs. If we take the Lagrange ...
0
votes
1answer
63 views

What is the recent most important discovery and study about magnets? [closed]

I believe that magnetism is a very powerful tool to do various things.It can make amazing machines.What is the recent most important piece of study that has been done of magnetism. The study that can ...