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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9 views

Low-altitude EMP

Can a low-altitude EMP exist from a detonated nuclear weapon or is the higher altitude required for propagation of the relevant fields necessary to induce destructive currents?
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39 views

What unit system puts a bunch of powers of ten in Maxwell's equations?

In what unit system can we get the Maxwell equation in the following form (section 1.2 from Lewin's book Advanced Theory of Waveguide) $$\nabla\times \vec E = -10^8\mu \frac{\partial \vec H} ...
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1answer
14 views

Electric Fields in a Neutral Object

A neutral object has no net charge since its positive and negative charges cancel each other. However, I’m wondering how, in terms of fields, they do cancel each other. Since fields are vectors, won’t ...
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0answers
17 views

What is the magnetic field formula for an arc?

I'm looking for the magnetic field of an arc. I'm looking for Bx, By and Bz at any arbitrary point. What I know for my arc : the radius and the angular length (or simply the angle). Is the only way ...
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1answer
68 views

Why can I put my hand through sand but not a table?

I've read in books that one can't put one's hand through a table because the table offers a "Normal Reaction" to the hand. And it is also stated that this force is electromagnetic in nature. But what ...
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2answers
47 views

Rotate a small wheel using magnets

I know this question already asked so much times. I tried to rotate a wheel by placing few magnets on it. And I used some powerful magnet and repel it using opposite poles in the magnets placed in a ...
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2answers
1k views

Is it possible to generalize the Maxwell equations to higher dimensions?

The usual Maxwell equations are for 3 spatial dimensions, right? Is it possible to generalize them to 2 spatial dimensions or 4 spatial dimensions?
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1answer
44 views

Is the sea of electrons in a metal at rest when the metal is in electrostatic equilibrium?

It is said that charges inside a metal in electrostatic equilibrium are at rest, and are stationary. However, don’t the electrons have their own thermal vibrations and whatnot? Aren’t they always ...
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0answers
22 views

Current density in covariant formulation [on hold]

I know that I have messed it up quite frankly, but don't know where- Why? $$qu_\alpha=J_\alpha$$ in covariant formulation.
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0answers
49 views

Is this idea practically possible? [duplicate]

I have to make a working model for my science exhibition. I have planned to make a wind turbine with some innovations. My model of wind turbine will consist of magnet it at the tip of every fan blade. ...
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1answer
60 views

Why doesn't the two poles of a u-shaped magnet attract each other?

Why doesn't the two poles of a u-shaped magnet attract each other? Since opposite poles attract each other why cant the north and south pole of a u-shaped magnet collapse by attracting each other?
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1answer
52 views

Magnetic field tangential surface integral

When deriving: $\vec{E}=-\frac{\partial\vec{A}}{\partial t}-\nabla\phi$ from Helmholtz decomposition of $\vec{E}$, It seems necessary to show: $$\iiint \nabla' \times \frac{\vec{B}(\vec{r')}}{|\vec{r} ...
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1answer
34 views

Coupling an electric charge to a gauge field. How is it done in this setup?

In page 9 of Tachikawa's N=2 susy dynamics for pedestrians it says that an electric particle with charge $n$ in the first quantised setup (in what sense first quantised?), Wick rotated to Euclidean ...
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0answers
25 views

Electromagnaetizma [on hold]

The figure shows a schematic diagram of a simple mass spectrometer, consisting of a velocity selector and a particle detector and being used to separate singly ionized atoms (q = +e = 1.602e-19 C) of ...
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4answers
205 views

Is Gauss' law valid for time-dependent electric fields?

The Maxwell's equation $\boldsymbol{\nabla}\cdot \textbf{E}(\textbf{r})=\frac{\rho(\textbf{r})}{\epsilon_0}$ is derived from the Gauss law in electrostatics (which is in turn derived from Coulomb's ...
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3answers
62 views

Is all of the energy dissipated in a magnetic core in the form of heat and can any of it be recovered?

In an AC motor where you use a laminated magnetic core to shield the induction process from eddy currents, the field lines that run through it result in core loss through heat. Is all of the energy ...
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1answer
21 views

Why does normal incidence eliminate the photocarrier effect radiation in this experiment?

Here's a paper in which they use GaAs crystals at a few orientations to produce THz radiation, by means of Optical Rectification (OR). That's actually not what this question is about, though. They ...
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2answers
63 views

What is induced current? [on hold]

Can someone please provide me with a detailed, elementary explanation about the principle of induced current in electromagnetism.
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1answer
25 views

Already integrated formula of magnetic field for a finite line?

I was looking for a formula to simulate a magnetic field due to a straight finite line. The closest to what I wanted to find was in these lecture notes (formula 9.11.2 page 9-50), \begin{align} ...
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0answers
57 views

What empirical evidence is there for displacement current?

I wonder what more or less direct measurements of the displacement current exist. I know that the existence of em waves demonstrates its existence, though somewhat indirectly. I also know that there ...
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1answer
144 views

Is there any other solution to this ray tracing problem? [on hold]

We have the following scene: We can see that in this scene, there are places which are very bright and there are places which are dark(shadows). I want to know which theory other than classical ...
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3answers
70 views

In terms of the Ampere-Maxwell law, why is $\vec {E}=0$ in a wire of a capacitor circuit?

I'm currently studying from "Introduction to Electromagnetics" by D.J. Griffiths. In the book the significance of the displacement current term is explained by looking a non-steady capacitor circuit ...
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1answer
31 views

Can light (electromagnetic radiation) cause electromagnetic induction in a wire?

Can light, as an electromagnetic wave, cause electromagnetic induction in a wire by passing near the wire? Does a moving electromagnetic wave cause a varying magnetic field in the region near the ...
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0answers
36 views

How to achieve vertical lift using magnets [duplicate]

Is there a way to create vertical lift using magnets which are aligned with same facing polarity?
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1answer
34 views

Eddy currents on a conductors surface, and induced current flow in a circuit coexist?

The title seems confusing, because Eddy currents are induced currents... however, let me explain. Assume the following closed loop passing a uniform magnetic field like so: Now, this loop would ...
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1answer
21 views

EMF Induced in a solenoid

When is the emf induced in a solenoid higher,when making or breaking the circuit? Isn't it the same magnitude since change in flux is same in both rhe cases?
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1answer
39 views

Will this system of magnets rotate?

A system of four magnets are placed as shown in the figure. As per the application of Maglev, a stationary magnet produces electro motive force with the magnets in motion. Note That the point O is ...
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2answers
165 views

Is light moving because of self induction? [duplicate]

Light is made by an electric field wave and a magnetic field wave. Induction laws state that a variation in the electric field creates a magnetic field and vice versa. Therefore can it be said that ...
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0answers
38 views

How to model radio wave attenuation by seawater?

From the very limited literature I can find regarding radio waves in saline-water solutions (as in seawater), I have been able to find very few corroborating models of radio wave propagation through ...
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0answers
18 views

Single slit diffraction treated as a differential equation

I want to find the values of electromagnetic fields that result from single slit diffraction. This should be possible by solving maxwell's equations for appropriate boundary conditions. But I'm not ...
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0answers
19 views

Coordinate Systems Transformation(Rectangular to Cylindrical) [closed]

I am new to this subject: Cartesian, Cylindrical and Spherical coordinate system. Coordinate System Transformation I have this example problem that I cant get the right answer. Transform to ...
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1answer
71 views

Can a train with magnets attached move with less fuel?

For a train, if we attach magnets ( big ones ) such that, for each compartment north faces front and south faces back, can that train move. So if this is right, we can move a train by just moving the ...
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0answers
24 views

How does the hendo hoverboard achieve omni-directional movement?

An older thread already gave away the wonderful details of how the Hendo hoverboard achieves levitation, but how does it achieve its form of omni-directional control and movement? My idea was that ...
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1answer
53 views

Could a magnetic field repel electromagnetic waves?

If I understand magnetism correctly, then two magnetic fields with opposing directions would repel each other. Could this same affect happen to electromagnetic waves? And if so, could it be reproduced ...
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2answers
34 views

Electric Potential Between Two Like Charges

At the point horizontally across and equidistant from the centers of the two charges (also oriented horizontally), what is the electric potential? At that point, the electric field of the first charge ...
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2answers
40 views

Do permanent magnets have an electric current surrounding them?

Permanent magnets seems to have different properties to electromagnets, such that electromagnets can be used for induction and energy transfer if a conductor is placed within their changing magnetic ...
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41 views

Are Landau levels always degenerate?

Solving the Landau problem, namely the quantum mechanical problem of a particle in a magnetic field leads to degenerate energy states, the famous Landau levels. My question consists of two parts. ...
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1answer
58 views

Electromagnetic waves in detail

So I have read many things on electromagnetism and I have competed in the IPhO lf 2015, got an honorable mention. That is my level of physics. Now, I have been reading many topics again, this time ...
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0answers
37 views

What is the electric field of a diffraction grating?

I'm trying to follow the equations in "Introduction to Modern Optics" by Fowles. He starts out with equation for a single slit of length $L$ and width $b$: $ U_p = C \int \int e^{ikr} dA $ where $U$ ...
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0answers
10 views

Wave propagation in 2D metal cavity

I would like to know there is an analytic solution for the propagation of electromagnetic waves in metals in a 2D case. The 1D case is well known to lead to a traveling wave with exponential decay ...
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3answers
101 views

Is this a Lorentz-scalar? How do I tell?

I'm struggling to identify whether a scalar is a Lorentz-scalar. E.g: $$\partial_i A^i \quad i \in {1,2,3}.$$ How do I determine if this is a Lorentz-scalar or not? If got the same problem with ...
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0answers
27 views

Motion of electrons in electric field

If an electron is allowed to pass through two parallel horizontal plates in a strong electric field such that the electron takes a parabolic path between the parallel plates. Will the electron stick ...
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0answers
27 views

What are some of the failed experiments to determine electron's position? [closed]

One that I could think of is trying to observe it with the help of electromagnetic radiation which could tear apart the atom. I asked this because I want to know what sort of methods are used to ...
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4answers
238 views

What is the *cause* of the Lorentz Force

Is it possible to explain what actually causes the force on a current carrying conductor in a magnetic field. I have read that this is due to the magnetic fields 'interacting' in some way. This ...
3
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1answer
49 views

Interpretation of a term in the Maxwell stress tensor

With no magnetism, the $xx$ component of the Maxwell stress tensor $T$ is $$T_{xx} = \frac{1}{2}(E_x^2 - E_y^2 - E_z^2)$$ I can see why there should be a $+E_x^2$ term, but intuitively I don't see why ...
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1answer
26 views

Connection between Polarization and Coherence in optics

It is not completely clear to me how the notions of polarization and coherence, in optics, work together! I quite understand both of them but it's still hard to grasp their deep connection. I'm quite ...
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1answer
56 views

Is EM interpreted in a principal or vector bundle?

I've read in a few places that EM is a $U(1)$-principal bundle; but is this correct? Isn't it rather an associated vector bundle using the adjoint representation of $U(1)$?
4
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3answers
193 views

Energy-Momentum Tensor for Electromagnetism in Curved Space

$\newcommand{\l}{\mathcal L} \newcommand{\g}{\sqrt{-g}}$$\newcommand{\fdv}[2]{\frac{\delta #1}{\delta #2}}$I want to calculate the energy-momentum tensor in curved free space by functional ...
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2answers
90 views

Does special relativity explains working of an electromagnet?

I heard that special relativity could be used to explain the working of electromagnet, but couldn't dig anything out of it. Can somebody give some explanation of the above? I also heard that it is ...
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2answers
102 views

How does the conductor knows which side is outside?

For a electrostatic equilibrium state, we know charges only stay on the outer surface of the conductor. But, how does the conductor know which side is outside? If it's about the curvature, then ...