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.

learn more… | top users | synonyms (5)

5
votes
2answers
355 views

What would the electromagnetic field of a massless electron look like

The Standard Model gives non-zero mass to the electron via the coupling to the Higgs field. Issues of renormalizability aside, this is fundamentally unrelated to the fact that the electron couples to ...
1
vote
2answers
676 views

Can an insulator have magnetic poles?

Is it possible to make an insulator have two poles like a magnet? If yes, how to make it?
6
votes
1answer
1k views

Is the force carrier of the magnetism in a common household magnet a photon?

As I have understood it, the Standard Model includes particles that carry the different forces, e.g. the electromagnetic (EM) force, the gravitational (G) force. When talking about EM fields such as ...
1
vote
2answers
157 views

EM irradiament and multipoles

Why in the irradiament mulipoles of Lienard-Wiechert's potential we say that electric quadrupole give a contribute of the same order of the magnetic dipole? How can we see it from their equations? And ...
2
votes
7answers
650 views

“Magnetic mnemonics”

Over and over I'm getting into the same trouble, so I'd like to ask for some help. I need to solve some basic electrodynamics problem, involving magnetic fields, moving charges or currents. But I ...
4
votes
1answer
844 views

Self induction: Why is induced voltage smaller than the applied voltage?

Imagine a circuit with a voltage source, a switch and an inductivity all connected in series. First, the switch is open and there's no current and no magnetic field around. If we close the switch, ...
17
votes
1answer
1k views

Flux through a Mobius strip

I was sent here from mathoverflow, hoping for a complete answer to this: === A friend of mine asked me what is the flux of the electric field (or any vector field like $$ \vec r=(x,y,z)\mapsto ...
4
votes
2answers
189 views

Dynamic ferrofluid sculptures

http://www.youtube.com/watch?v=UJJuq_pcyIQ What exactly is going on in the video example? I understand the phenomena occurs because of magnetism but I am trying to figure out the mechanics behind ...
1
vote
1answer
197 views

Electromagnetic weapons: power?

I essentially have three questions concerning weapons based on EM waves or more generally. Focusing on the weapons using radio-waves and/or micro-waves, what power do these types of weapons need to ...
2
votes
1answer
450 views

What is the pressure between two electric dipole sheets of finite extent?

I have recently become curious about modeling the repulsion of everyday objects in contact with one another. By repulsion I mean as you attempt to walk through a wall, the pain in your nose suddenly ...
12
votes
4answers
685 views

Nonlinear optics as gauge theory

the widely used approach to nonlinear optics is a Taylor expansion of the dielectric displacement field $\mathbf{D} = \epsilon_0\cdot\mathbf{E} + \mathbf{P}$ in a Fourier representation of the ...
9
votes
3answers
1k views

Electromagnetic Field as a Connection in a Vector Bundle

I would like to know more about Ehresmann connections in vector bundles and how they relate to the electromagnetic field and the electron in quantum mechanics. Background: The Schrödinger equation ...
7
votes
2answers
402 views

Why is the ground state of the ferromagnetic tetrahedron threefold degenerate?

I'm preparing a presentation on Spin-Ice, but something's been bugging me for a while. On the Wikipedia page for Geometrical Frustration, it says the following about easy spins on a tetrahedron with ...
6
votes
2answers
519 views

Navy's new Mach 7 Rail Gun Photo

There have been a few articles about the Navy's new Mach 7 33 Megajoule railgun. As a physics teacher, I have a couple of questions about this, and was hoping for some help. Is the kinetic energy ...
6
votes
2answers
366 views

Notation for Sections of Vector Bundles

(Reformulation of part 1 of Electromagnetic Field as a Connection in a Vector Bundle) I am looking for a good notation for sections of vector bundles that is both invariant and references bundle ...
4
votes
2answers
1k views
2
votes
1answer
1k views

Current from induced emf

If the induced emf in a circuit is negative, and current from this emf is the emf over the resistance, what happens to the negative sign in the induced emf when solving for the current? Surely there's ...
0
votes
2answers
360 views

Magnetism-Related Terminology

A few questions about a magnet and a paperclip: What do you call a material that attracts another material via magnetism? (i.e. the magnet) What do you call the material that is attracted in #1? ...
1
vote
2answers
295 views

Creation of the Electromagnetic Spectrum [closed]

After seeing this image: http://mynasadata.larc.nasa.gov/images/EM_Spectrum3-new.jpg And reading this: "The long wavelength limit is the size of the universe itself, while it is thought that the ...
2
votes
2answers
151 views

Utility of displacements potentials in geophysics

In the elasticity theory, you can derive a wave equation from the fundamental equation of motion for an elastic linear homogeneous isotropic medium: $\rho \partial^2_t \overline{u} = \mu \nabla^2 ...
1
vote
1answer
6k views

Is there a name for the derivative of current with respect to time, or the second derivative of charge with respect to time?

This measurement comes up a lot in my E&M class, in regards to inductance and inductors. Is there really no conventional term for this? If not, is there some historical reason for this omission? ...
0
votes
2answers
729 views

How is electrical energy transmitted?

My original question was in an effort to understand the electrical analogy to Markov chains, which is explained in Snell's article. There are some neat parallels that involve taking a Markov chain ...
2
votes
2answers
294 views

Why isn't the ISS electrically charged?

If metal moves in a magnetic field It creates a current so when the ISS or any other satellite/object charged so that if you connected a light/ put it in a circuit/ it would light up? also why doesn't ...
6
votes
2answers
553 views

Modified Maxwell's equations

In 1985, Harmuth wrote that Maxwell's equations are incompatible with causality, and overcame the problem by adding a term for magnetic dipole currents, and as a consequence the problem of infinite ...
5
votes
1answer
1k views

Wi-Fi in the presence of very strong magnets?

A friend of mine claims to have been able to surf the Internet without fuss on a Wi-Fi connection while performing NMR on samples he was analyzing. I would have thought the strong magnets needed for ...
0
votes
1answer
570 views

Heim Theory and FTL [closed]

Years ago there was some hype around a theory that would supposedly allow for FTL. But I have since heard nothing of this. Is anything happening with the theory? How would a magnetic field allow us ...
4
votes
2answers
537 views

Alkali atom - photon interaction in zero magnetic field

An alkali atom has a single outer electron that interacts with incoming photons of the right wavelength (for alkalies it's in the visible & IR range). If there is an external magnetic field, the ...
10
votes
1answer
340 views

How many atoms per light year does light encounter when traversing interstellar space?

Interstellar space is pretty empty but there a small number of of atoms (mostly hydrogen?) floating around. How many atoms per light year would a photon encounter while traversing interstellar space?
1
vote
2answers
280 views

Notation of plane waves

Consider a monochromatic plane wave (I am using bold to represent vectors) $$ \mathbf{E}(\mathbf{r},t) = \mathbf{E}_0(\mathbf{r})e^{i(\mathbf{k} \cdot \mathbf{r} - \omega t)}, $$ $$ ...
1
vote
2answers
335 views

Maxwell equations: how to know the behavior of charge and current?

In school-level tasks, when (almost) all substances are linear, homogeneous and isotropic, we have $D=\epsilon E$, $H=B/\mu$ and thus Maxwell "in material" equations (1) say how $E$ and $B$ depend on ...
7
votes
2answers
1k views

Would a magnet attract a paperclip indefinitely?

Let's say we have a magnet stuck to a metal bar, suspended above the ground. If I attach a paperclip to the magnet, where is the energy to hold the paperclip coming from (against the force of ...