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
3k views

Special designs to reduce the electrical resistance of a wire

The numerical simulation of this nerdy question shows that the resistance decreases with the number of nodes along longest side, and converges to a finite value when the # of nodes approaches ...
2
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1answer
372 views

Cherenkov radiation in nuclear bomb

Would Cherenkov radiation occur at the explosion of a nuclear bomb? Suppose it would not be occluded by smoke or anything else for that matter.
5
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2answers
387 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
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2answers
490 views

Is there an explicit angular momentum in Maxwell equations?

Electromagnetism implies special relativity and then the universal constant "c". And if we set c=1, the coupling constant has units of angular momentum (so in relativistic quantum mechanics we divide ...
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3answers
3k views

Visualizing Electromagnetic Waves in 3D Space [closed]

I did one module of physics for my GCSE one year ago which taught me about transverse EM waves & the EM spectrum, but since then, I do not understand how a wave would move in 3D space. Can someone ...
1
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1answer
636 views

Electrical eddy current visualization or simulation

Eddy currents are induced in a metal plate when it experiences a changing magnetic flux. Is there a realistic visualization or simulation of eddy currents available? The only picture I found, on ...
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4answers
1k views

When is the force null between parallel conducting wires?

Consider two long wire with negligible resistance closed at one end of the resistance R (say a light bulb), and the other end connected to a battery (DC voltage). Cross-sectional radius of each wire ...
19
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5answers
896 views

Should a neutron fall faster than a proton?

If you drop a proton and a neutron in a gravitational field, they both fall, but the proton has a charge and accelerating charges radiate energy, so that leaves less kinetic energy for the proton and ...
8
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3answers
2k views

Is the Abraham-Minkowski controversy resolved?

A paper was published in 2010 claiming to resolve the Abraham-Minkowski controversy. Is this paper viewed as definitive by physicists?
9
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4answers
3k views

How is a spherical electromagnetic wave emitted from an antenna described in terms of photons?

When an atenna transmits radiowaves isn't it true that the electromagnetic pulse is radiated away from the accelerating electron as a spherical wave in all directions simultaneously, and if so how can ...
6
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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
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2answers
876 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?
11
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4answers
6k views

Derivation of Maxwell's equations from field tensor lagrangian

I've started reading Peskin and Schroeder on my own time, and I'm a bit confused about how to obtain Maxwell's equations from the (source-free) lagrangian density $L = ...
6
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3answers
4k views

Do mirrors increase the amount of light in a room?

So if you have a light bulb in a room, and you had a tool to measure the amount of light that's in the room, then let's assume the amount of light only caused by the bulb is "1" If you place a mirror ...
2
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2answers
482 views

Software to calculate forces between magnets [duplicate]

I am working on a complex configuration of magnets and every time I make an experiment something unforseen happens. Now I believe I could speed up the development by sitting down and calculating the ...
3
votes
1answer
1k views

Impedance formula for an edge coupled differential stripline in an asymmetrical stackup?

I've been searching and have not been able to find a formula for calculating the impedance of differential lines on inner layers where the dielectric above and below it is not symmetrical. I've seen ...
7
votes
4answers
1k views

How does charge work if photons are neutral?

How can an electron distinguish between another electron and a positron? They use photons as exchange particles and photons are neutral, so how does it know to repel or attract?
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7answers
4k views

Is it theoretically possible to shield gravitational fields or waves?

Electromagnetic waves can be shielded by a perfect conductor. What about gravitational fields or waves?
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3answers
2k views

How is electromagnetic wave variation distributed in space?

Imagine an electromagnetic wave (a monochromatic one for example). The electric field amplitude and its variations travel in the propagation direction. So, if there really exists a propagation ...
10
votes
3answers
2k views

What is the symmetry which is responsible for preservation/conservation of electrical charges?

Another Noether's theorem question, this time about electrical charge. According to Noether's theorem, all conservation laws originate from invariance of a system to shifts in a certain space. For ...
4
votes
1answer
218 views

Ground-based anti-matter detector on the cheap?

Given today's revelation of the detection of terrestrial gammay-ray flashes (TGF) produced by thunderstorms and the associated pair production of an electron and a positron, how feasible is it to set ...
2
votes
7answers
779 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
1k 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, ...
3
votes
1answer
253 views

Physically induced latency in internet connections

As a trade I am a software architect. It does happen that I have to design sites where the servers are located in different parts of the world. Now an essential parameter to consider is latency: that ...
18
votes
1answer
2k 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 ...
14
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3answers
1k views

Shine a light into a superconductor

A type-I superconductor can expel almost all magnetic flux (below some critical value $H_c$) from its interior when superconducting. Light as we know is an electromagnetic wave. So what would happen ...
4
votes
2answers
214 views

Dynamic ferrofluid sculptures [duplicate]

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
2answers
160 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 ...
11
votes
2answers
593 views

What's the explanation for the Giant Magnetoresistance effect?

I've been reading this review on Giant Magnetoresistance, and something about it is bothering me. The basic effect is that, using a special "stack" of layers (alternating between ferromagnetic and not ...
14
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3answers
4k views

The exchange of photons gives rise to the electromagnetic force

Pardon me for my stubborn classical/semiclassical brain. But I bet I am not the only one finding such description confusing. If EM force is caused by the exchange of photons, does that mean only when ...
3
votes
1answer
855 views

How does an electron microscope work?

I am a physics novice. Google tells me that electron microscopes work much like their optical counterparts -- but the analogy falls apart for me when I think about what I'm "viewing." Obviously, you ...
12
votes
3answers
21k views

Can magnets rotate infinitely?

There are many videos on youtube in which people arranged magnets in circle and rotated one placing in middle of that circle on a shaft, and the magnet (magnet motor) starts madly and continues its ...
1
vote
1answer
206 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 ...
6
votes
3answers
350 views

Controllable faster-than-light phase velocity

This is not another question about faster-than-light travel or superluminal communication. I totally appreciate the speed limit capped by physical laws (or theories.) Just curious, since there is no ...
8
votes
3answers
3k views

Can I levitate an object without using an electromagnet?

I know that it's possible to make an object levitate using an electromagnet to hold it up. But is it also possible to do this with regular magnets? Is there a special kind of magnet I need in order ...
7
votes
3answers
6k views

Is it safe to use any wireless device during a lightning storm?

I need "educated" reasons whether it is safe to use any wireless device during a lightning storm. Most people said don't use it but they cannot explain why.
11
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1answer
528 views

Formulation of Transformation optics using a Material Manifold

Dear Community, recently, Transformation optics celebrates some sort of scientific revival due to its (possible) applications for cloaking, see e.g. Broadband Invisibility by Non-Euclidean Cloaking ...
7
votes
2answers
442 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 ...
17
votes
1answer
5k views

Kubo Formula for Quantum Hall Effect

I'm trying to understand the Kubo Formula for the electrical conductivity in the context of the Quantum Hall Effect. My problem is that several papers, for instance the famous TKNN (1982) paper, or ...
7
votes
2answers
541 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 ...
17
votes
5answers
2k views

Home experiments using wireless LAN or mobile phones about electromagnetism?

Are there any nice experiments using wireless LAN access points or routers or mobile phones to demonstrate physical features of electromagnetic fields, especially em-waves? More precisely I am ...
5
votes
2answers
1k views

What does an atom radiate: a wave packet or a single photon?

What does an atom radiate: a wave packet or a single photon?
2
votes
1answer
2k 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 ...
6
votes
6answers
645 views

Interaction ranges in the Standard Model - Electrodynamics vs QCD

as you might know, the Standard Model of physics can be seen as a $U(1)\times SU(2)\times SU(3)$ gauge theory where each symmetry group accounts for different force fields. The behaviour for the ...
6
votes
5answers
4k views

Is there a travelling speed of for electric field? If yes, what is it?

Consider two circuits containing a battery, bulb, switch and conducting wires but of length 1 meter in one case and 1000KM in other. When switched on at the same time both the bulbs glow ...
2
votes
1answer
473 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 ...
14
votes
2answers
2k views

Deriving the speed of the propagation of a change in the Electromagnetic Field from Maxwell's Equations

I've been told that, from Maxwell's equations, one can find that the propagation of change in the Electromagnetic Field travels at a speed $\frac{1}{\sqrt{\mu_0 \epsilon_0}}$ (the values of which can ...
1
vote
2answers
349 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 ...
1
vote
2answers
496 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? ...
13
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4answers
826 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 ...