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Questions tagged [electromagnetism]

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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Direction of Hall current

A Hall current arises when electric currents transverse to a magnetic field exist. In this figure (found online), the Faraday current appears to be going upwards due to a magnetic field pointing into ...
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20 views

Car remote stops working near gas station

Anywhere i go my car remote works perfectly. However when i park at my friend's place, very near a gas station with electrical systems and such, it doesn't work, never does, and when i leave it begins ...
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Good book for magnetism? [duplicate]

I'm just about to write an IA (short paper for school) and I want to go pretty deep into the theory of magnets. I was wondering if there are any good introductory books to electromagnetism (more ...
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Questions about Hall bar geometry

In preparation for an upcoming experiment, which goal is to measure the Hall voltage for different samples using the Drude model$^1$, something called Hall bar geometry was mentioned and accompanied ...
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Neodymium magnet pole reversal? [duplicate]

I watched this video which showed a Neodymium magnet being cut in half, what i expected to see was the two halves snap together due to aligned poles as shown in the image below, but what actually ...
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15 views

Wave Equations from Decoupling Maxwell's Equations in Bianisotropic Media

For several days now, I have been trying to decouple Maxwell's equations in bianisotropic media so that I end up with a form that involves only one variable (of E, D, B, H), i.e. a so-called 'wave ...
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What are the application if can predict turning point in random wave? [on hold]

What are the application in physics and computer science if can predict turning point in random wave? Is there more further can do after identify turning point?
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2answers
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Which Fresnel coefficients should be used at normal incidence?

There are two sets of Fresnel coefficients depending on the polarisation of the incident light. At normal incidence these equations converge except there is a phase factor of $\pm1$ For the reflection ...
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1answer
62 views

Do electromagnetic fields have inertia? Or, what sets the speed of light?

In all mechanical waves, there is a restoring force and an inertial influence. For example, a plucked string oscillates because the restoring force brings it back to being straight and then the string'...
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about calculation of current [on hold]

initially switch S1 is closed. After time t=t0 S1 is open and S2 is close then what will be the current at t=t0 and t=t0+ in circuit?
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1answer
24 views

What would be the material properties of a perfect reflector?

If I want to model a perfect reflecting material, what material parameters should I use? Specifically what refractive index or dielectric constant should I use? I know from the Fresnel equations that ...
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Low frequency em waves do pass through paper, light doesn't, gamma rays do. Why so? [duplicate]

If we talk about wave passing through paper, we mean that paper consists of atoms, which are ~90% empty space. Photons don't have scales, as well as position. When guys talk about the ability of em ...
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Refraction of a static electric field wavefront

When a static electric field is created, the edge of it propagates at the speed of light. Does this wavefront experience refraction when crossing refractive boundaries the same way light does? Does it ...
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1answer
39 views

Why doesn't shining light on a wire induce current in it?

If you accelerate magnet along a wire, an emf is induced in a wire because changing magnetic field induces changing electric field and thus electrons in wires are forced to form a current. So why ...
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2answers
61 views

Which provides the energy for induced current at the starting moment of the lenz's law

I am learning about magnetic fields, but I get confused with the way energy is transmitted in Lenz's law. As I read on the question Explaining Lenz's Law without conservation of energy: Let's ...
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1answer
23 views

Confusion about signs in the Dirac equation for an external electromagnetic field

I'm working through Maggiore's A Modern Introduction to Quantum Field Theory, and I'm studying the Dirac equation in an external electromagnetic field given by: $$ \left[\gamma^{\mu} \left(i\partial_{...
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3answers
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Atom is not neutral? [on hold]

The thing that always confused me, was how can atom be electrically neutral, if electrons are closer to observer. Well, okay, I started to read a quantum mechanics book, so to clarify: there is a big ...
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1answer
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Rest frame of massive photon in Meissner–Ochsenfeld effect

The Meissner–Ochsenfeld effect together with spontaneous symmetry breaking and the London Equation yields $(\Box+M^2)A^\mu=0$ and gives photon an effective mass $q\sqrt{\frac{n_c}{m_c}}$ Which is ...
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1answer
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Reversing magnet polarity to increase/decrease Eddy currents?

I have a cast iron wheel with magnets around the inner radius as a braking mechanism. If I were to add additional magnets around the outer radius, would the amount of Eddy currents increase or crease ...
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Is this integral setup correct? If so, how would you solve the question since there is a cos(theta)? [on hold]

In part c of the problem, is my surface integral setup correct? If so, how would you solve it since theta is not known? I converted the vector from spherical form to cartesian using the conversion ...
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1answer
56 views

Derivation of curl of magnetic field [on hold]

I am having trouble in one part of derivation of curl of magnetic field, from Biot-Savart law. The attached picture is from Griffiths - Introduction to Electrodynamics. I got all the parts, but only ...
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0answers
40 views

S-matrix and Green's function

I'm considering one paper about electron recombination and there is an expression for S-matrix that confuses me $${S_{fi}} = i\mathop {\lim }\limits_{t' \to \infty \atop t \to - \infty } \left\langle ...
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Can induction of Vortexing Electromagnetic fields be a precursor to nuclear fusion? [on hold]

I have come across a phenomenon that involves a device that produces a stand alone vortex of electromagnetic energy resonance, threw my observation It seems as though, electromagnetism can hold ...
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1answer
26 views

Why do the field line asymptotes in this diagram bend?

If there is a +1 charge and another +1 charge the field lines have a vertical and horizontal asymptote. However, when the charges are uneven, the vertical asymptote is curved leftwards: I don't ...
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2answers
32 views

forces on moving charges in a magnetic field

When a conductor is moving relative to a magnetic field (for example a magnet falling in copper pipe, or a Eddy current brake in a train) , it is considered that the conductor moves, the conductor ...
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2answers
44 views

Why does a voltage appears between $A$ and $C$ when this coil is rotated?

Find the voltage between the points $A$ and $C$ when a wire is conecting $A$ and $D$. We know that there is a magnetic field $B$ perpendicular and entering in the papers plane, the semicircular metal ...
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Stress on a hollow conducting cylinder due to current [on hold]

Can anyone provide the calculation of stress on a hollow conducting cylinder (in the shape of a pop can) with a current $I$ flowing through it, where $l$ is the length of the can, and $r$ is its ...
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What concept to apply in order to understand infrared reflectance of materials such as walls and trees?

I know some concepts about the optical reflectance of molecules and phonons. But at the macroscopic level, I don't know which one to use because we know for sure there is reflectance due to molecules ...
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46 views

How do you measure and distinguish between E and D fields, and B and H fields

I’m pretty familiar with maxwells equations, light waves, fields and materials etc, but I’m not clear on how the the various fields are actually measured. How is this typically done? Can the fields ...
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33 views

Why does changing magnetic flux induce an emf? [duplicate]

What happen to charges when we change magnetic field? What is the real reason behind it?
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1answer
46 views

Liquid water has no rotational spectrum but does absorb in the microwave region

I came across a wikipedia page and it states "Liquid water has no rotational spectrum but does absorb in the microwave region" water molecules rotates while in transit which causes friction so it's ...
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1answer
56 views

Explaining Magnetism using Relativity if a point charge is not moving parallel to a wire with current

There are many explanations of magnetism in one reference frame turning into a electric force in another. However almost all references are relative to a case of a point charge moving parallel to a ...
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1answer
39 views

Electric potential everywhere around an infinite slab

The problem: Consider an infinite slab with uniform charge density $\rho$ between two planes $z=\frac{d}{2}$ and $z=-\frac{d}{2}$. Find the electric potential $V$ in the entire space and plot $V$ ...
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Magnetic monopoles imaged through neutron scattering experiment

I am writing a report about a magnetic monopoles, in the report I am trying to write about the observations made during an experiment using a neutron scattering technique. The experiment mean that the ...
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22 views

Electric quadrupole moment traceless or not?

Are Second rank tensors always expressible as dyadic? I am specifically asking about the electric quadrupole moment which can be defined traceless or not!?
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2answers
58 views

Ferrofluid between glass plates: what’s going on?

There’s a phenomenon I ran across recently and I’m trying to understand what’s going on with it. When you have a thin layer of ferrofluid between two glass plates and move a magnet closer and farther ...
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2answers
90 views

Why atom has the straight discrete energy levels? [duplicate]

Interaction between a nucleus and electrons is in gravity(not considering) and electrostatics. Due to electrostatics nucleus attracts electrons. The force that describes this process is $$F=k\dfrac{...
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1answer
26 views

What is the difference between phonon-infrared scattering and molecular-infrared scattering?

Are the both process same?,if not how do they differ in their mechanism,selection rules.
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Quantifying electrical energy stored in a plasma

The energy stored in the electric field in a medium is given by $U = \frac{1}{2} \epsilon E^2$, where $\epsilon$ is the permittivity in the medium and $E$ is the electric field. When considering a ...
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Why a moving charge + wire with current in a stationary reference has no electric force?

I've saw the Current in Wire special relativity magnetism question, but the answer did not convince me at all. My doubt is crystal clear. I know the electrons move in a very high velocity in all ...
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1answer
34 views

Force on a ferromagnetic material attracted by a magnet

From the Lorentz force equation we know that the magnitude of the force between a current carrying wire and a magnet field is defined as $F = ILB$. This implies that there must be a current across the ...
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What is the theory behind the infrared-phonon scattering? [closed]

I want to know about the complete theory behind the infrared-phonon scattering like the mechanism of the process, selection rules for the process.
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3answers
34 views

Can a lightning which doesnt make light be made?

I was wondering if there is a way to make a lightning (lab lightning, nothing as chaotic as the real thing) that doesnt eject any electromagnetic waves? For example: How would a strong negative magnet ...
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1answer
36 views

Equation of an electric field of a Gaussian pulse

I am trying to write the equation of electric field of a Gaussian pulse of light to do some MATLAB analysis and other analysis. What I want is an electric field $E(y,t)$ of a Gaussian pulse traveling ...
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17 views

What are the differences between magnetometers, teslameters and gaussmeters?

What are the differences between magnetometers, teslameters and gaussmeters? I think that teslameter and gaussmeter are the same thing, but I am not sure about that either.
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Right-Hand Rule and Reactance

In this paper by Guo et al., it is claimed on p. 4 that for a coil in a magnetic field, the induced current in the coil can follow either a right-hand or a left-hand rule, depending on the reactance. ...
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1answer
35 views

How is Meissner effect consistent with the frozen field lines inside the superconductor?

From Meissner effect we know that the magnetic field $\vec{B}$ is zero inside the superconductor. Since $\vec{B}=0$ inside the superconductor (ignoring the tiny penetration effect for the moment), ...
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1answer
25 views

Does applying an electric field inherently mean applying a voltage i.e potential difference?

We generally see in physics that we apply an electric field,does that actually mean applying a voltage across?
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68 views

Lorentz invariance of charge in classical electrodynamics - What volumes to look at?

There is an (plausible claim) that the charge is a lorentz invariant quantity (best example would be that the electron as a point charge has the same charge in every frame of reference). I'm trying ...
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1answer
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I'm confused about electric flux?

In a previous physics class, I learned that the electric flux was $\vec{E}\cdot\vec{A}$ (dot product), and hence the unit is $Nm^2/C$. But in my electromagnetics book, it says the unit is Coulomb, and ...