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Results tagged with electromagnetism
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user 31895
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.
22
votes
How is energy "stored in an electric field"?
The idea is that all energy, including kinetic energy and EM energy (such as that stored in the capacitor) is localized in space, i.e. given any region of space, one can assign net energy to it, and e …
- 41.2k
19
votes
Accepted
Does classical electrodynamics have a Lagrangian that gives both the Lorentz force and Maxwe...
Is there a combined Lagrangian that gives both the Lorentz force and Maxwell equations via the Euler-Lagrange equations?
Not sure about the continuous charge/current density case, but for point part …
- 41.2k
12
votes
Why do electrons and positrons exhibit opposite helical motion in a magnetic field?
But what we never seem to see is why the electron and positron move the way that they do. Saying "they move like they do because of the force on them" doesn't explain anything at all. It's a non-an …
- 41.2k
12
votes
Why do EM waves propagate forward in time rather than backward in time?
Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
Well, in most cases observed or measured, EM radiation do …
- 41.2k
10
votes
Accepted
How can there be a voltage across an inductor if the voltage through any conductor is zero?
This means the magnetic fields must produce electric fields inside the coil.
Yes, but this produced electric field, called induced electric field $\mathbf E_i$ , is only one component of total elect …
- 41.2k
9
votes
Accepted
Suspicious EMF equation
But if I want to use that equation I have to calculate couple of really tedious integrals. So I found some online source where some dude used this suspicious equation $$U_{ind} = \int (\textbf{v} \ti …
- 41.2k
9
votes
Recommended books for advanced undergraduate electrodynamics
W. K. H. Panofsky and M. Phillips, Classical electricity and magnetism, Addison Wesley, 2nd ed., 1962
Especially the first 14 chapters are very enjoyable yet carefully written study text about both b …
9
votes
Is an electron in an hydrogen atom being measured by the nucleus?
No. Effects of interaction are described by the Hamiltonian. Quantum measurements are not, they require some "projection", or "collapse" or "choice by hand".
- 41.2k
9
votes
Does Larmor radiation show that the fundamental laws are not necessarily time-reversible?
The Larmor formula for energy flow away from the particle is derived based on some assumptions, one of which is that field of the accelerated particle is given by the retarded solution to Maxwell's eq …
- 41.2k
8
votes
The energy stored in the electromagnetic field of an electron
How does the energy stored in the electric field of the electron relates to its rest mass?
It depends on whether we assume the electron has finite charge density everywhere or not.
In case the c …
- 41.2k
8
votes
Accepted
Does a time varying electric field always generate a Magnetic field?
The correct answer (magnetic field vanishing everywhere) can be reached on the high school level most simply by the argument using the central symmetry of the capacitor, or in a more complicated way, …
- 41.2k
7
votes
Accepted
The classical electrodynamic atom
The argument about collapse of the atom in Rutherford's model is originally, I think, due to Niels Bohr. It is, originally, not "rigorous", if that word means a mathematical proof.
Bohr's himself for …
- 41.2k
7
votes
What's the physical meaning of the statement that "photons don't have positions"?
The idea "photons do not have position operator" may have more meanings depending on who you ask.
To me, this statement means something very specific: EM radiation does not consist of particles that …
- 41.2k
7
votes
Faraday's law paradox during relative motion between conductor and magnet
If the ring I choose is not a physical ring, then in the magnets frame of reference, there is a moving imaginary ring... there are no charged particles in this ring, thus there is no magnetic lorentz …
- 41.2k
7
votes
Accepted
Does Kirchhoff's Law always hold?
...claiming Kirchhoff's Law doesn't always hold when magnetic fields are involved, and that two voltmeters attached to identical places in a circuit can give different readings. Is this the case?
It …
- 41.2k