Questions tagged [electromagnetism]
The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.
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Recovering energy from a modern, magnetic-levitated flywheel
A modern flywheel rotor is suspended in a vacuum by magnetic bearings. This means that nothing touches the rotor as it spins. When time comes that we need to recover that stored kinetic energy, how do ...
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Relativistic charged particles in a constant uniform magnetic field
How can i derive the dynamic of a relativistic charged particle in a uniform magnetic field $B=(0,0,B)$?
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What is the density of virtual photons around a unit charge?
It seems that virtual photons also exist in vacuum. So the precise question is:
What is the additional virtual photon density due to the electric field of a unit charge?
Or: How many virtual photons ...
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Magnetic moment of relativistic rotating ring
Let's consider rotating charged ring. Theoretically mass of this ring has no limit as rotation speed increases. So what about magnetic moment of the ring? Is it limited by the value of speed of light?...
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Is it possible/correct to describe electromagnetism using curved space(-time)? [duplicate]
Comparing the simples form of the forces of both phenomena: the law of Newton for gravitation $V\propto \frac{1}{r}$, and the Coulomb law for electrostatics $V\propto \frac{1}{r}$, one might think ...
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Relationship between magnetic resonance linewidth and spin relaxation
First of all, what is the mathematical relationship between measured linewidth (usually in units of magnetic field) and spin relaxation time? I see papers talk about spin relaxation times in terms of ...
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meaning of an integral in the continuity equation
This is about continuity equation. What does the last integral mean?
$$\frac{\mathrm{d}Q_V}{\mathrm{d}t}=\iiint_V \mathrm{d}^3x \,\frac{\partial\rho}{\partial t}=-\iiint_V\! \mathrm{d}^3x\,\...
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Amount of free energy in the Earth-ionosphere waveguide
How much free energy is there in the Earth-ionosphere waveguide resulting from the constant bombardment of lightning strikes all over the Earth, and how do you go about calculating an estimate for it?
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What is the medium that allows magnetic fields *or any forcefield* to exist?
Magnetic fields are obvious distortions.. of.. something, but what exactly are they distortions of? Massive objects produce curvatures/gradients in space-time resulting in what we observe as gravity.....
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Does van Eck phreaking really work, or is it an urban myth?
Van Eck phreaking, the ability to reconstruct distally the text on a CRT or LCD screen using the leaking em from the target computer, was in the news about five to ten years ago. It is talked about as ...
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What is the effect of ice on an antenna?
A local FM radio station transmitting at 89.3 MHz recently announced that it would be running at 50% power due to freezing weather and a forecast of ice accumulation, as "when ice is forecast ... it ...
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Einstein's Field equations and impulse-energy tensor
I premise that I haven't yet studied General Relativity, but in Relativistic Electrodymaics I have knowed impulse-energy tensor of Electromagnetic Field.
I know in Einstein's equations there is ...
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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.
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Studying electrodynamics problems
Suppose an advanced undergraduate student has reached a moderate level of understanding on electrodynamics.
Where should he focus on, to sharpen his problem-solving skills?
Practicing integrals and/...
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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 ...
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Does bunching reduce synchrotron radiation?
A continuous charge distribution flowing as a constant current in a closed loop doesn't radiate. Is it therefore true that as you increase the number of proton bunches in the LHC, while keeping the ...
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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 ...
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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 ...
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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 ...
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"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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 of ...
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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 ...
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What does an atom radiate: a wave packet or a single photon?
What does an atom radiate: a wave packet or a single photon?
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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 ...
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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 ...
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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 \...
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