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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Opacity/transparency of conductive meshes to charged particles (electrons/ions)
When using a conductive (metal) mesh, effectively a metallic woven fabric, in vacuum applications as a "grid" for charged particle optics, how does one calculate (or at least estimate) the opacity or ...
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Motion of a magnet inside a solenoid
I have a homework problem where a bar magnet is placed halfway inside a horizontal solenoid. A cut away shows that the magnet's north pole points to the left of the page and the south pole is outside ...
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Conformal mapping and van der Pauw
I'm trying to understand the van der Pauw methods with my limited mathematical understanding. If any of my steps are wrong, please correct me.
As far as I understood from a textbook (Mahan, Gerald D. ...
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Maxwell stress tensor on a capacitor late given a dielectric
Given a capacitor with large plates (area $A$) separated by a dielectric with relative permittivity $\varepsilon_r$ and thickness $g$, I believe the Maxwell stress tensor states that the force on each ...
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How to derive magnetic moment for integrated circuit level?
Imagine we have a circuit on the xy-plane, with a random geometry (it just need to be closed). I want to calculate the magnetic moment of this setup:
$$\vec{m} = \frac{1}{2} \int_V d^3 x' \vec{x}' \...
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About the notation for TEM waves
I just came across this article where the term "$\mathrm{TE}_{101}$ microwave mode" is mentioned. Other than the basics of TEM waves which I learned in Griffiths, this is the first time I ...
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What's the coordinate of the Landau tube?
The Hamiltonian of a three-dimensional electron gas in a static magnetic field $\vec{B}$ is :
$$\hat{H}=\frac{(\hat{\vec{p}}+e\hat{\vec{A}})^2}{2m}$$
If choosing $\vec{B}=B\vec{e_z}$ and using Landau ...
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How is the index notation for the electromagnetic potentials defined?
I don't understand, how the $\vec{A}$ potential is defined in the covariant formulation of the Maxwell-Equations.
I am using the metric $(+,-,-,-)$.
The electric field (SI-Units) is defined as:
$$
\...
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Lenz law - Direction of induced current
I understand the Lenz Law is such that it tells us that the induced current must be in a direction that makes the end of the solenoid facing the magnet behave as a North Pole to repel the magnet’s ...
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How do I find the wavelength of an EM wave derived from an accelerating electron, given its acceleration?
I understand the Larmors formula, but I can't find any material regarding wavelength of a single photon.
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How to solve Relativistic Lorentz Force equation if $\gamma$ is not constant?
I am trying to numerically obtain the trajectory of an electron inside a periodic magnetic field $\mathbf{B}$, taking into account that the relativistic factor $\gamma$ is not a constant (the electron ...
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Motor Effect Experiment
I recently saw an demonstration (image below) where the motor effect was being shown. They used the fact that forces come in pairs (Newton's third law) and so when current goes through the copper rod, ...
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A question on perturbed flux function
Given a magnetic field $\mathbf{B}=B_{0}\left(\dfrac{xz}{z_{s}^{2}},\dfrac{yz}{z_{s}^{2}}, 1-2\left( \dfrac{x^{2}}{r_{s}^{2}}+\dfrac{y^{2}}{r_{s}^{2}}\right) -\dfrac{z^{2}}{z_{s}^{2}}\right)$ with the ...
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Materials to complement "Interacting Electrons and Quantum Magnetism" by Assa Auerbach
Does anyone know of any material, such as lecture notes from a university, that can complement the sometimes brief chapters of the book "Interacting Electrons and Quantum Magnetism" by Assa Auerbach?
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How does changing the angular frequency ω of the generator affect the current flowing in the circuit and the power transferred to the electric motor?
When an electric motor is used with an electric generator, the situation can be viewed as an RLC circuit where the generator is an AC power source. The source produces a sinusoidal AC voltage with an ...
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Eddy current brake with superconductor
There are eddy current brakes used with metal plates to stop trains. It converts kinetic energy of the metal plate to heat via eddy current on it. So what if we have a superconducting metal plate and ...
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What's the difference between conduction current density and source (impressed) current density in an $RC$ circuit?
My electromagnetics textbook has a picture of an $RC$ circuit with a current source.
As you can see, there are three current density vectors, $J_i$, $J_c$, and $J_d$. The book labels them as follows:
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What is the impressed current density? [duplicate]
I don't have a too solid background for physics and am reading some engineering books of electromagnetics. What is the impressed current density here? I think it is Ohm's law but couldn't find its ...
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Comparing Electric Potential Energy of two Charges
I do not know what I am missing here and would appreciate a little help in figuring out the flaw in my logic. I have a row of positive charges and a row of negative charges as shown in the image above....
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Effects of Localized Medium Changes on Field Propagation
I've studied various theories related to fields. These theories often include equations describing how the activity of a source is transmitted to other locations. The properties of the medium ...
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Velocity gained as a metal object approaches a magnet
I need to find the Kinetic Energy gained as a steel bearing ball approaches a Neodymium magnet. I have the value for the magnetic flux density of the magnet, now I need to find a way to calculate the ...
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Why the $T_1$ recovery & $T_2$ decay are independent?
In MRI, I was thinking that the decrease in transverse magnetization results in the recovery of longitudinal magnetization.
However, recently, I found it was wrong. I saw a diagram
(McRobbie 2014. ...
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How do you convert from Townsend Unit $\rm Td$ to $\rm kV/(cm bar)$?
I have found a conversion online which says 1Td = 2.829 V/(cm Torr) and 1Torr = 0.001332 bar and with this;
1Td = 0.3768 V/(cm bar)
However from literature for SF6;
362Td = 86.3 kV/(cm bar) where they ...
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Most generic form of refractive index tensors
The refractive index of a material is in general a $3x3$ tensor (as in the case of birefringent crystals). From literature, it seems that in the case of transparent crystals, this tensor is in general ...
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Rotating Tank of Charged Liquid
Consider a long rectangular tank of dimensions a×b, where a≫b, that is rotating at a constant angular velocity and filled with an incompressible charged fluid. How would one find an equation ...
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Can a satellite generate electricity by using a planet's magnetic field? [duplicate]
I am entering AP Physics E&M and don't have much knowledge about electricity but always had an idea based on my limited knowledge.
If a satellite had a metal coil inside of it, wouldn't it have an ...
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Straight wire in moving uniform magnetic field induced emf
My question is a follow-up to this one.
The green dotted line is the arbitrary loop which is constructed in the calculation of emf in the wire of length L. x is a variable which can be changed to ...
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Doppler Cone: What exactly is it?
I'm trying to understand Synthetic Aperture Radar (SAR). It appears that it makes use of what's called a "Doppler cone". I understand Doppler frequency shifts of light, but I'm not sure what the cone ...
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What is the net macroscopic electric field at any point inside a dielectric?
This question is based on section 4.2.3 of Introduction to Electrodynamics by David J. Griffiths (Third Edition).
Consider a point $\vec{r}$ inside a dielectric where we are interested in finding the ...
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Induced electrical field of infinite straight current carrying wire
I'm kinda confused about the law of induction of a straight wire.
Suppose I have an infinite (infinitely long and thin) wire along the z-axis with current $I=I_0 \cos(\omega t) \, e_z$. The magnetic ...
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