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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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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0answers
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
240 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 ...
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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 ...
1
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1answer
58 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 $U(1)$?
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3answers
194 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 ...
2
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2answers
91 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 ...
1
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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 ...
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1answer
24 views

Co-ordinate rotations

I need help transforming a magnetic field vector from one co-ordinate system to another. I have the components of the Earth's magnetic field in a co-ordinate system with z facing radially into the ...
1
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1answer
36 views

Help understanding Diamagnetism

I need some help understanding Wikipedia description of diamagnetism https://en.m.wikipedia.org/wiki/Diamagnetism In the first sentence of the first paragraph, when said "...induced magnetic field ...
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0answers
21 views

Excitation spectrum of heisenberg model

I understand that ferromagnetic Heisenberg model (lattice of spin variables that can point in any direction) spectrum can be deduced by a $\lambda\phi^4$ theory with $\phi$ being complex. This model ...
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0answers
19 views

Approximate of self-inductance of a square wire coil

Imagine you have a square coil of wires with n turns. In order to calculate the self-inductance coefficient I should know the magnetic field. Is it acceptable to consider the 4 sides as infinitely ...
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0answers
25 views

EMF and Distance

As a professional underground service locator, EMF and Inductance are at the very core of what we do. Very few of us truly understand the detailed physics behind what makes it possible for us to ...
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0answers
10 views

what happens when a cylindrical diamagnetic rod is placed in a uniform magnetic field with the axis along the direction of the field?

When a cylindrical diamagnetic rod of lenght l is placed in a uniform magnetic field along the z axis with the axis of the rod along the same axis, what is the mathematical expression for the induced ...
0
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1answer
29 views

How does a magnet cause magnetic force and its magnitude/direction?

Magnetic fields are created due to electron spin in the magnet. But how exactly does an electron "spinning" create forces around the magnet? Also, the magnetic force on a charge moving in the magnetic ...
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1answer
33 views

Applying Biot-Savart to a circular loop along central axis

I'm trying to understand the solution to the magnetic field of a circular loop along its central axis. The solution I'm looking at is page 9 of this document: ...
3
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1answer
41 views

Would a solenoid move if a magnet went through it?

If you were to have a solenoid (0 current) floating still in space, and shot a magnet through it, would the solenoid move, or would it only create a DC current (what if it has a closed/open circuit)? ...
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0answers
14 views

Surface current density and infinite solenoid

I have an infinitely long cylinder with radius $R$ and axis lying on the $z-$axis, charged with volume density $\rho$ and surface density $\sigma$. The cylinder is spinning with angular velocity ...
0
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0answers
19 views

Force Between Two Solenoids

How does one calculate the magnetic force between two coaxial solenoids, placed in a way their currents are in the same sense? There is a simple way to treat both as dipoles and then calculate the ...
2
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0answers
39 views

How does lightning flip a car?

http://www.standard.co.uk/news/london/car-flips-into-air-after-being-struck-by-lightning-in-freak-electrical-storm-accident-10366208.html and a few others ...
3
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1answer
54 views

What force decays an oscillating charge?

Consider this scenario: We have a charge on a spring. As it oscillates, it loses energy to radiation. What force decays the oscillation? As far as I can see, the only forces in the scenario are ...
1
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1answer
68 views

Are non-atomic electrons scattered exactly like electrons in atoms?

Has the Compton effect ever been described in a beam of electrons in a Crookes tube or the like? All the references I found refer to electrons in atoms: In Compton's original experiment, the ...
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1answer
39 views

What is the strength of the magnetic field required to penetrate an average human body?

Introduction Suppose you are an experimental nanobot researcher trial-ling a new form of medication that involves activation and control of nanobots within the cells of the interior of the human body ...
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0answers
37 views

Magnetic field on axis of solenoid

So first I'd like to say that I have asked similar questions to this one. However, all the answers involve a level of calculus that I do not yet know. (Still on limits, going to spend the rest of ...
0
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2answers
50 views

Why are the formulas for magnetic or electric fluxes as such?

For electric flux, the formula is given by $$\Phi_E=EAcos\theta$$ For magnetic flux, the formula is similarly given by $$\Phi_M=BAcos\theta$$ But would it not make more sense to describe flux as the ...
0
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2answers
129 views

Induced EMF, additive to conductor's closed circuit?

Assume the following conductor, with current flowing, powered from a source $S$: Now, I've introduced a magnetic field($B) to the conductor covering a small area of it like so: The change in ...
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1answer
31 views

Magnetic field re-routing

Can a magnetic field be directed in a particular direction, that is re-route it, such that the magnetic field comes out in only one direction?
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4answers
47 views

Why are excess charges in a conductor at the surface?

I’ve been told that coulomb repulsion pushes excess electrons to the surface of a conductor (i.e. sphere) electrostatic equilibrium, and this symmetry causes the net electric field inside to be zero. ...
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0answers
19 views

How to describe frequency spectrum with samples?

I posted this same question in math, but nobody is answering, so I thought I'd give a try here too... To me the question is pretty straightforward, but nevertheless I have to explain its background ...
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0answers
33 views

Why do Superconductors make Magnetic Fields Bend Away

When superconductors reach their "threshold temperature" their electrical resistance turns 0. This makes the magnetic field lines not pass through the superconductor but instead bend itself around it ...
0
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1answer
51 views

What are the interpretations of ampere's circuital law for a single moving electron?

I understand from Ampere's circuital law that when a current passes though any open surface with a boundary (a circular boundary, for simplicity), then limit of summation of the scalar products of ...
0
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0answers
30 views

Gravitomagnetic railgun

Would a gravitomagnetic analogue of a railgun work as expected, in theory? Consider replacing the electric currents on each rail with mass currents. Then place a mass between the rails, moving with ...
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1answer
19 views

An electric motor that does not reverse current flow

If an electric motor did not reverse the direction of its current every half-turn, what would be observed in the armature? Would it spin from left to right clockwise, then spin back anti-clockwise ...
-4
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1answer
45 views

is it possible to get an object to travel over 200 mph with magnets [closed]

Is it possible by magnetic forces to cause a certain material to travel at speeds over 5000 mph<>?
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1answer
70 views

Why is magnetic field perpendicular to that plane?

Magnetic field is perpendicular to the plane containing direction of flow of current in a straight wire and radius vector.What I have been told is that,to explain lorentz force magnetic field was ...
1
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1answer
59 views

The truest/most general Maxwell's equations in isotropic, linear, inhomogeneous media with sources

Sources use $\mu H=B$ and $\epsilon E= D$, assuming homogeneous media. Obviously if $\mu$ is space varying, $\nabla . (\mu H)$ need not be equal to $\nabla . B$ What is the most general form for ...
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0answers
20 views

Correlation of magnetic field range to induced current?

If a magnetic field($B$) is increased in range(size of coverage,or flux area is larger)at the same strength, would there be higher output of current if there is a conductor with velocity($v$) passing ...
0
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0answers
14 views

Poisson Spot vs. Shadows

In textbooks, whenever I read about the Poisson spot, it involves a disk, and having light waves diffract around it and interfere constructively in the center. At the same time, when I read about ...
-4
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1answer
56 views

Can the fundamental dimension of Electric Charge be Mass only? [closed]

After solving dimensions of electrical equations, I found out that the fundamental dimension of Electric charge is mass only. This also leads to the derivation of dimensions of other Electrical units ...
5
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4answers
219 views

Method of calculating eddy currents of a conductor, is this correct?

I have a conductor with volume $V$, passing a magnetic field($B$) with velocity($v$): I'm trying to calculate the Eddy currents to figure out the magnitude of the drag force($F_d$) generated the ...
0
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0answers
30 views

Developing an analytic equation set for a complicated solenoid

So, I'm a bit stumped by this. I've been asked to develop an analytic function for the magnetic field of a complicated axisymmetric solenoid with free parameters to be determined by making a fit ...
0
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0answers
19 views

Electromagnetic transfer function

In a paper on the superlens, I came across the term of "transfer function". I understand that the transfer function relates the output to a given input, but I've been unable to find a formula for the ...
3
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1answer
41 views

The role of amplitude, frequency, and intensity in mechanical vs. EM waves

As far as I know (correct me if I’m wrong), for a mechanical wave (e.g. sound), the frequency determines the pitch, the amplitude determines the loudness, and the amplitude is proportional to the ...