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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378 views

Local explanation of the Aharonov-Bohm effect in terms of force fields

Here is an interesting paper for the Physics SE community: On the role of potentials in the Aharonov-Bohm effect. Lev Vaidman. Phys. Rev. A 86 no. 4, 040101 (R) (2012). arXiv:1110.6169 ...
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192 views

What different approximations yield Gravitoelectromagnetism and Weak Field Einstein Equations?

This question is inspired by this answer, which cites Gravitoelectromagnetism (GEM) as a valid approximation to the Einstein Field Equations (EFE). The wonted presentation of gravitational waves is ...
9
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325 views

Do intergalactic magnetic fields imply an Open Universe?

According to a recent paper on the arXiv, they do. How credible is this result? The abstract says: The detection of magnetic fields at high redshifts, and in empty intergalactic space, support ...
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119 views

How can I find the position of an image charge when the boundary is parabolic or hyperbolic?

If the position of some charge Q is known, the boundary condition is u=0 on some parabolic surface, and we know the image charge has its electric volume of Q', then how can I determine the position of ...
6
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72 views

Is the existence of electromagnetic standing waves dependent on the observers reference frame?

If I take two plane EM waves travelling in opposite direction e.g. $E = E_0 \sin(kx-\omega t)$ and $E=E_o \sin (kx + \omega t)$, they sum to give a standing wave with a time-averaged Poynting vector ...
6
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67 views

What is the intepretation of the electromagnetic tensor?

Let $A$ be the four-potential, then we know that we can form the electromagnetic tensor as $F=dA$. This is usually done as a way to have a better writing of Maxwell's equations. So, to simplify the ...
6
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75 views

Are there analogs to resistance, inductance, capacitance, and memristance connecting the weak force to electromagnetism?

A question was asked over at EE.SE recently which I tried to answer, but much of my answer was speculative. I'm hoping someone here can help my ignorance. In electronics design, there are four ...
6
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79 views

Is the uniqueness theorem correct in superconductivity?

There is an uniqueness theorem in electromagnetism. It says that the solution of Maxwell's Equations is determined uniquely by boundary conditions. We can treat superconductivity as a completely ...
6
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134 views

Materials with different gravitomagnetic permeability?

If you start with general relativity, and assume small perturbations around a nearly flat metric, it is possible to obtain linearized equations of gravity that look a lot like Maxwell's equations, ...
6
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206 views

Can I integrate out the fermion field that is not gapped?

This piece of argument has been repeated again and again by experts, that is Since the fermions are gapped, then I can integrate it out. but I have no idea of what will happen if the fermions ...
6
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247 views

1-form formulation of quantized electromagnetism

In a perpetual round of reformulations, I've put quantized electromagnetism into a 1-form notation. I'm looking for references that do anything similar, both to avoid reinventing the wheel and perhaps ...
5
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115 views

Why dimensionality of the Electric Charge varies with the spacetime dimensions?

The point is: We can find via dimensional analysis that the electric charge dimensionality varies with the dimension of space-time. $$[\text{charge}] = eV^{(3-D)/2}$$(You can see below the way I did ...
5
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108 views

Is it correct to sum over either index of the metric the same way?

I don't know if the following is correct, i want to compute the following derivative $$\frac{\partial }{\partial (\partial_{\mu}A_{\nu})}\left(\partial^{\alpha}A^{\beta}\partial_{\alpha}A_{\beta} ...
5
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98 views

Is the search for a Simple-group-based Electro-Weak theory over?

Just wondering: We know that, in its current form of the $SU(2)_L\times U(1)$, the electroweak theroy rides a wave of huge success. However, is it not possible that the correct simple group ...
5
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166 views

Does a rotating magnetic monopole have electric and magnetic moment in classical view?

Would a rotating sphere of magnetic monopole charge have electric moment ? In a duality transformation E->B.c etc. how is the magnetic moment translated m = I.S -> ? Mel = d/dt(-Qmag/c).S ? A more ...
5
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169 views

Semiclassical QED and long-range interaction

I'm interested in the (very) low energy limit of quantum electrodynamics. I've seen that taking this limit does not yield Maxwell equations, but a quantum corrected non-linear version of them. If ...
5
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250 views

Modified Coulomb potential

I'm working through Byron and Fuller's "Mathematics of Classical and Quantum Physics" and came across this problem: If the electric potential of a point charge were $\phi(r) = ...
4
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53 views

Is there any antenna with a single null?

If we designate the origin (the reference point from which all displacement vectors are measured) $\vec{0}$, and If we consider a sphere $\mathbb{B}\left(\vec{0},\mathcal{R}\right)$ of radius ...
4
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112 views

Reaction-at-a-distance: Do charged plates immediately repel each other?

Imagine that we have a pair of parallel plates, $A$ and $B$, separated by some distance as in Fig. $1$ above. At time $t_1$ we simultaneously charge both the plates. This could be done by ...
4
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182 views

Why are magnetic field lines perpendicular to the surface of a ferromagnetic material?

It is known that magnetic field lines become nearly perpendicular to the surface of a ferromagnetic material. The quantitative proof which uses the boundary condition requires that magnetization at ...
4
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344 views

Gauge invariance and Feynman path-integrals

Let me look at the Hamiltonian of a charged particle in a plane in a constant magnetic field ($\vec{B}$) pointing upwards - then in usual notation it is, $$\hat{H} = \frac{1}{2m}\biggl(\hat{p} + ...
3
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43 views

Electric field in a sphere with a cylindrical hole drilled through it

Suppose that you have a sphere of radius $R$ and uniform charge density $\rho$; a cylindrical hole with radius $a$ ($a\ll R$) is drilled through the center of the sphere, leaving it like a "necklace ...
3
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29 views

Photomagnetic effect

I just saw an article on wikipedia: http://en.wikipedia.org/wiki/Photomagnetic_effect "This article appears to contain unverifiable speculation and unjustified claims. Information must be verifiable ...
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27 views

Are magnetic hysteresis losses relevant to alternating currents flowing in a wire?

Say we have an AC in a magnetically lossy material, like iron. Because of iron's relatively high permeability, skin effect will be more pronounced than it is in say, copper, so this iron wire isn't so ...
3
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101 views

What is the more fundamental quantity? The electromagnetic field F or the potential A?

Read somewhere that potential is a more fundamental quantity than EM field because if the latter is more fundamental then gauge transformation will reduce to nothing more than a mathematical trick. I ...
3
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50 views

Charge distribution and potential in a 1-dimensional quasistatic system

Suppose you have an 1-dimensional system with a charge distribution $\rho(x)$ (not given) moving with an speed $v(x)$ (not given), calculate the potential $\phi(x)$ and the charge distribution ...
3
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89 views

Are there any models that explain the cause of the dual symmetry-breaking of the in electrodynamics?

Source-free Maxwell eqautions a dual symmetry between electric and magnetic fields is obvious. But in the presence of electric charge, such symmetry is broken. Recover it possible by an introduction ...
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58 views

Do primary first class constraints change the electric field in the Hamiltonian form of Maxwell's theory?

In my understanding of Dirac's theory of constrained Hamiltonians, the primary (and also the secondary) first class constraints are generators of canonical transformations that do not change the ...
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81 views

Accelerated electromagnetic system leads to divergent calculation?

Consider the above system comprising a pair of oppositely charged parallel plates, connected by a rigid rod of length $r$, constrained to move in the x-direction. The forces on the plates from the ...
3
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153 views

Angular momentum of particle in dipole magnetic field

Basically I'm just trying to find the expression for the angular momentum of a particle of mass $m$ and charge $q$ in a dipole magnetic field. In cylindrical coordinates, ...
3
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0answers
67 views

Quantum Cyclotron Frequency - Why is it off by a factor of 2?

Say you have a magnetic field $\vec{B}=(0,0,B_0)$. Then the Schrodinger Equation Hamiltonian for a spin-2 particle of charge $e$ moving in this field is: $$H = ...
3
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0answers
158 views

Finding the terminal velocity of a magnet dropped in a solenoid

We have to find proportionality of the terminal velocity with the factors of the system: Plot: a small dipole(mass $m$) with dipole moment $\mu$ is dropped in a long solenoid (radius $r$, ...
3
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159 views

Theoretically speaking what are the limits for super-capacitors in terms of their storage capability?

According to wikipedia, commercially available super-capacitors in 2010 can store 30Wh/kg, with 85Wh/kg achieved in a lab in 2011. Have any theoretical calculations been done to show what can be ...
3
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116 views

Bandgap Spacing in Photonic Crystals

I am doing some self-study on photonics and have encountered the following question: We know that amorphous electronic crystals such as amorphous silicon have a bandgap. Can amorphous photonic ...
3
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208 views

Question about laws of conservation in electrodynamics

One way of deriving laws of energy, impulse and angular momentum of electromagnetic field conservation is following: Introduce two values below: $$ \mathbf P = \frac{c}{4 \pi}[\mathbf E \times ...
3
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0answers
108 views

Can you safely draw sparks from the nose of an electrified boy?

From Purcell's Electricity and Magnetism A spectacular conclusion of one of the popular exhibitions of the time was likely to be the electrification of a boy suspended by many silk threads ...
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345 views

I lost a factor of two in the electromagnetic field tensor

I apologize for this simple question, but I lost a factor of 2 and can't find it anymore, so now I'm looking on the internet, perhaps one of you has some information about its whereabouts. :-) ...
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32 views

Is polarization of a wave just a description of its motion in three dimensions?

Since a polarization of the wave is described by complex numbers, we can try to give that mathematical formalism geometrical meaning. With having two different axes, one imaginary and other real, it ...
2
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0answers
31 views

Lorentz force in rotating frame

This is the common problem of a charged particle moving in a static electric and magnetic field. Say $\textbf{E}=(E_x,0,0)$ and $\textbf{B}=(0,0,B_z)$. In the inertial frame of reference, the ...
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27 views

What are the parameters for Pauli's repulsion pseudo-force?

I have found the following formula for the repulsion potential due to the overlap of the electron clouds arising from Pauli's exclusion principle: $$V = A\exp(-r/\phi)$$ where r is the distance ...
2
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67 views

Can the two electromagnetic field tensors be combined into a more general tensor?

Given the electromagnetic field tensor $$\begin{align} F_{\mu\nu} = \begin{pmatrix} 0 & -E_{x} & -E_{y} & -E_{z} \\ E_{x} & 0 & B_{z} & -B_{y} \\ E_{y} & -B_{z} & 0 ...
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0answers
25 views

How to calculate the force acting on a magnet due to a solenoid

Can I assume both magnet and solenoid as magnetic dipole and use coulombs law to find the force acting the magnet?
2
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0answers
94 views

Huggins Displacement Theory and Retrocausality

I was looking at the Wikipedia entries on Time Travel and the Grandfather paradox and noticed a paragraph on the so-called Huggins Displacement Theory. I haven't been able to find the source although ...
2
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0answers
31 views

Electric field of a capacitor in dielectric medium with weird size

I have been learning gauss's law in capacitor recently, recently I come up with this problem that I couldn't solve myself. If we have a capacitor,and a dielectric medium with half the volume between ...
2
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0answers
42 views

Physical distribution of salt anions and cations during electrophoresis

If I have a volume of $L$ liters of salt water at a concentration of $\approx N$ mM NaCl and I pour it into an electrophoretic apparatus (like this one: ). Once we turn the apparatus on, and set the ...
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95 views

Maxwell equations and symmetry

Do the full inhomogeneous Maxwell equations obey parity (P) and time reversal (T) symmetry separately or only the full CPT symmetry? I believe the homogeneous Maxwell equations obey parity and time ...
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48 views

Hidden momentum

I'm trying to learn about hidden momentum. After reading what I could find with a google search, I understand that it is equal to the momentum carried by radiation, calculated with the Poynting ...
2
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0answers
152 views

What is the minimum physical distance between two electrons?

If electrons repel, then it seems to me that energy is required to decrease the distance between two electrons. Since energy and mass are equivalent, adding energy to a system also adds some mass. ...
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39 views

Help Understanding Equation for Characteristic Time of Induced Magnetic Field

I am reading this book, the part in particular about Eddy-current separation starting at Page 246, in it there is an equation for calculating the "characteristic time with which the induced magnetic ...
2
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0answers
109 views

Hall effect with similar positive and negative carriers?

The Hall effect includes the transverse (to the flow of current) electric field set up by the charges which accumulate on the edges, to counter the magnetic component of the Lorentz force acting on ...