The study of magnetic fields in systems where the currents are steady (not changing with time). It is the magnetic analogue of electrostatics, where the charges are stationary.
Questions tagged [magnetostatics]
375 questions
65
votes
7 answers
Is Biot-Savart law obtained empirically or can it be derived?
There's already a question like this here so that my question could be considered duplicate, but I'll try to make my point clear that this is a different question.
Is there a way to derive Biot-Savart law from the Lorentz' Force law or just from…
Gold
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Why is this vector field curl-free?
The curl in cylindrical coordinates is defined:
$$\nabla \times \vec{A}=\left({\frac {1}{\rho }}{\frac {\partial A_{z}}{\partial \varphi }}-{\frac {\partial A_{\varphi }}{\partial z}}\right){\hat {\boldsymbol {\rho }}}+\left({\frac {\partial A_{\rho…
forky40
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28
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Virtual photon description of $B$ and $E$ fields
I continue to find it amazing that something as “bulky” and macroscopic as a static magnetic or electric field is actually a manifestation of virtual photons.
So putting on your QFT spectacles, look closely at the space near the pole of a powerful…
Nigel Seel
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13
votes
3 answers
Magnetic scalar potential far above a magnetic film
The situation I am looking at is a magneto-static problem of a finite magnetic film with magnetization $\bf{M}$. I would like to find the the magnetic field far above the plate. My expectation is that far above the plate, the field should approach…
BeauGeste
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Deriving Biot-Savart Law from Maxwell's Equations
As an exercise, I've been trying to derive the Biot-Savart law from the second set of Maxwell's equations for steady-state current
$$\begin{align}&\nabla\cdot\mathbf{B}=0&&\nabla\times\mathbf{B}=\mu_0\mathbf{J}\end{align}$$
I've been able to do this…
JAustin
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10
votes
1 answer
Is Biot-Savart Law valid for time-varying currents unlike Ampere's law?
I have just finished learning the basics of magnetism, and it should be noted that I am not very familiar with Maxwell's equations.
Note:
In the question, when I say "Ampere's Law", I am referring to the equation without Maxwell's…
Newton
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9
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Why can't a static magnetic field have a local maximum?
Reading a brief on magnetic traps I've read that you can't have a local maximum in the magnetic field. I believe this is linked to the divergence of the B-field being zero in vacuum, but I don't see why one can have a local minimum but not a…
Klopmint
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8
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Interpretation of Poynting Vector
Short Version
How exaclty can the Poynting vector be physically interpreted for static electric and magnetic fields?
I know that it describes the magnitude and direction of energy flow in EM-waves. But how does this interpretation hold up when only…
Marc
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8
votes
3 answers
Are the field lines on a bar magnet diagram contour lines?
Following is the representation of magnetic field lines around a bar magnet.
The lines drawn, indicate the direction of magnetic field lines. Now I want to know that is this a contour mapping of the original space that is present around a magnet. I…
Samyak Marathe
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8
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Are there cases where $\nabla\cdot\iiint\frac{\mathbf{J}(\mathbf{x}')}{\left|\mathbf{x}-\mathbf{x'}\right|}\mathrm{d}V' \neq 0$?
In Jackson's Classical Electrodynamics, Section 5.4 (Vector Potential), the author seems to assume that because $\nabla\cdot\mathbf{J} = 0$, the following holds for the current density (where the integral is done over all…
Tob Ernack
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8
votes
1 answer
Current geometry and Ampere's law
Under the right circumstances, Ampere's law $\oint \vec H\cdot d\vec \ell=I_{encl}$ can be used to deduce the field $\vec H$ at a point from the current enclosed by the circuit which produces $\vec H$. This can be done when one can find a…
ZeroTheHero
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What is the importance of vector potential not being unique?
For a magnetic field we can have different solutions of its vector potential.
What is the physical aspect of this fact?
I mean, why the nature allows us not to have an unique vector potential of a field?
Priyadarshi Paul
- 301
8
votes
4 answers
How would you define electrostatics and magnetostatics starting from Maxwell's equations?
I'm reading Griffith's text, and he starts by defining Electrostatics as requiring the source charges don't move. I've seen a few slightly different definitions of electrostatics and magnetostatics. If you wanted to start from the full Maxwell…
user153582
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8
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Ampere's circuital law for finite current carrying wire
When I was studying about Ampere's circuital law. Then there comes a question in my mind that "whether this law is applicable for finite current carrying wire or not"
parth kamra
- 147
7
votes
5 answers
Wrong representation of the field of an axially magnetized ring magnet floating on the internet?
I always thought that the field of a short length axially magnetized ring magnet resembles this illustration here of Fig. 1 similar to the magnetic field of a single current loop:
Fig.1 Axial Ring Magnet Field (macroscopic far-field)
Red is the…
Markoul11
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