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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Can asymmetrical Lorentz forces account for Relativistic affects near the speed of light?

The underlying thought here is that at low relativistic speeds all objects are subjected to emf radiation from all directions. This is basically the sum of all the radiation (light, infra-red, ...
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2answers
53 views

What is the link between observation wavelength and spatial resolution of an instrument? [closed]

It seems that when capturing and emitting EM waves matter proceeds differently depending on the wavelenght. According to an answer from another question, EM energy is captured following three modes: ...
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1answer
38 views

Introduction of the vector potential $A_{\mu}$ for the local gauge invariance of the complex scalar field lagrangian [duplicate]

In Ryder, when trying to restore the local $U(1)$ gauge symmetry of the complex scalar field $\phi=\phi_1+i\phi_2$, the final Lagrangian consists of the following four parts: ...
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2answers
90 views

Electric and Magnetic field's phase difference shift in linearly polarized electromagnetic waves

I am a high school student and we currently studying the electromagnetic theory. In my textbook i read that the oscillating electric the magnetic fields have phase difference equal to π/2 rad near the ...
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2answers
58 views

$ε_0$ affects electric field intensity, but $μ_0$ doesn't affect magnetic field intensity?

I'll be honest: this question is actually a homework problem. I've spent the past hour going through Google and several textbooks trying to answer the question "Why does $ϵ_0$ affect electric field ...
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1answer
21 views

What happens when a force is applied to a flux pinned superconductor?

When a force is applied to a superconductor to move it in a direction that it resists because it is flux pinned, where does the additional energy used to overcome the flux pinning resistance go? E.g. ...
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1answer
48 views

Thermal emission cathode electron velocity distribution

I can't find any experimental data (or theoretical expression) on what is the velocity (or energy) distribution of thermal emission cathode electrons emmited from the cathode at approximately 2000 K ...
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1answer
64 views

Current in an RC circuit inside in a magnetic field

Does my question make any sense? Context: The capacitor is charged with charge $Q_0$. There is a magnetic field $B=B_0 \hat{z}$ perpendicular to the monitor's screen. The length of the (AB) wire is ...
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1answer
57 views

Demagnetisation by throwing a magnet

I tried to answer this question in a book about electrodynamics: How to demagnetise a permanent magnet, ie. described by $ D_T$ change into described by (0,0) I figured out about heating it up ...
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2answers
63 views

Poynting vector plane wave

I'm calculating the poynting vector for a plain wave and I have some doubt. $$ \bar S = \frac 1 2 \bar E \times \bar H^* = ... = \frac {| \bar E|^2} {2 \zeta} \hat i_k $$ Now if I consider a ...
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2answers
38 views

Electric Field in Conductor Zero?

My textbook claims that the electric field in a conductor is zero in a static condition, as otherwise, a current would flow. But what if I go infinitely close to a proton; there will be an electric ...
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1answer
83 views

Is “scalar electromagnetics” real science?

This page claims that original Maxwell's equations, when formulated by Maxwell himself in quaternion form, had some special scalar part of electromagnetic field, which somehow appeared to describe ...
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142 views

Teflon and induction cookware

I remember once getting new Teflon (non-stick) cookware; however, when I tried this new cookware on my induction cooker the cookware did not heat up. My regular steel cookware worked just fine on the ...
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6answers
313 views

Do electrons flow only on the surface of a wire?

Since the $\vec{E}$ field inside a "perfect" conductor is zero, do the electrons(the current) flow only on the outer surface? This has bothered me since I studied electromagnetism. Thank you for ...
2
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1answer
51 views

Torque on wire summarized with magnetic moment

The magnetic moment of a current-carrying wire loop $L$ is $$ \boldsymbol\mu = \frac I2\oint_L\mathbf{r} \times \mathrm{d}\mathbf{r} $$ so the torque it experiences under a uniform magnetic field ...
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2answers
88 views

Can the magnetic fields of EM radiation be harnessed or measured?

We use the electric component of EM radiation to create the EM radiation and to detect it (antennas and Etc.), but does anyone know of a situation where the magnetic component of EM radiation is used? ...
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3answers
53 views

Magnetic moment - magnetic field relation without free currents

I'm trying to understand magnetostatics in the presense of ferromagnetic material. But I'm ending up in a contradiction: Lets take a piece of iron: Assuming that we don't care about the hysteresis ...
2
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1answer
43 views

Do magnets\ magnetic fields become weaker when exposed to para magnetic objects?

Do magnets (permanent) become weaker as they are exposed to para-magnetic objects? I was thinking about this after seeing this. I am buying a magnet and wish to know if a magnet (permanent) loses its ...
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1answer
119 views

If light is an electric and (magnetic field), how can it be absorbed?

I was wondering how light or any electromagnetic radiation can be "absorbed" if it consists of electric and magnetic fields. For example if there is a charge at point A, and the light reaches point ...
2
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1answer
81 views

Why is the perfect obstructor the perfect conductor as Heaviside 'believed'?

How might one consider a conductor to be an 'obstructor'? Might the strength of the 'skin effect' of a conductor be in direct relation to conductance? And how does this relate to insulators, as ...
2
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1answer
318 views

What is equation to find force of magnetic attraction

I was wondering as a student, when I was playing with magnets I thought like Gravitational force equation of Newton's Gravitation Theory, can we also calculate force of an magnetic attraction on an ...
2
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1answer
184 views

Value of weak force coupling constant

I'm trying to get my head around the weak force coupling constant $\alpha_w$ but getting confused by different resources. Hyperphysics suggests it is tiny compared with the strong force coupling, ...
2
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1answer
79 views

Why is a Electron negative not both?

I was pondering on the question of magnetic dipoles but then I had an thought that electron and other particles are either positive or negative or have no magnetic charge but then I thought of ...
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2answers
72 views

Force on a magnet in a magnetic field

I was wondering what happens when i put a wire in which current flows parallel to a magnet, something like this: where the straight line is the wire, the circle is a cylindrical magnet(with outgoing ...
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1answer
212 views

How to transform material permittivity tensor from Cartesian coordinates to another orthogonal coordinate system?

I have a material specified by a permittivity tensor written in Cartesian coordiantes: $$\begin{pmatrix} \epsilon_{xx} & \epsilon_{xy} & \epsilon_{xz}\\ \epsilon_{yx} &\epsilon_{yy} ...
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3answers
233 views

How do electrons actually move in a circuit?

Last year, we were taught about electricity, about how electrons in a closed circuit. But as our teacher had not taught us about electric fields yet, she gave us a simplified model of motion of ...
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1answer
81 views

What does it mean for an electromagnetic structure to be resonant?

There are many electromagnetic structures used in microwave engineering and EM devices. For example, patch antennas, metamaterials made from unit cells, etc. When they design structures like patch ...
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31 views

Electric & Magnetic fields - clarification

If (changing electric field)=(magnetic field) and (changing magnet field)=(electric field), then why is there a constant magnetic field around a current carrying wire when the electric field does not ...
2
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1answer
79 views

What exactly is three phase power? [closed]

What is three phase power? How does it differ from normal AC current?
2
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1answer
73 views

Can a single photon induce current in a very small coil?

As I know from Lenz's law, I can induce current in a coil just by changing the magnetic field flux inside the coil. As I know from physics course, photons are electromagnetic waves (so they are the ...
2
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1answer
98 views

Jackson, Classical Electrodynamics - page 97: how to deal with the indexes of a series to obtain Legendre polynomials

We want to solve Legendre's equation: $$ \frac{d}{dx}[(1-x^2)\frac{d}{dx}P(x)]+l(l+1)P(x)=0,\quad (1) $$ Jackson writes $P(x)=x^\alpha\sum_{j=0}^\infty a_j x^j$, puts this in eqn. 1 and then ...
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3answers
480 views

Why doesn't Lenz's law predict the behavior of a rod on springs in a magnetic field?

This comes from one of the free response questions from the AP Physics B 2014 exam. 5. (15 points) A conducting rod of mass $m$ and length $L$ hangs at rest from two identical conducting ...
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2answers
2k views

What is the difference between Biot-Savart law and Ampere's law?

What is the difference between these laws? Which law is more useful? When to use Ampere's law and when to use Biot-Savart law?
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3answers
91 views

Faraday's Law - recursive?

So we know that the EMF is induced by change of flux. The thing that was always confusing me is the following: we start changing the magnetic field which in turn induces electric field which makes ...
2
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1answer
123 views

Walter Lewin's lecture on Faraday's law

In Walter Lewin's lecture on Faraday's law, he does a demonstration with a solenoid where he shows that current is induced in a loop that surrounds the solenoid as the magnetic flux is changing. He ...
2
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1answer
111 views

Shielding RFID with aluminium foil

I've been playing around with some contactless bank cards and an RFID reader app on my phone. As expected, if I wrap the card in foil, the reader no longer detects it. But I was surprised to find that ...
2
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3answers
779 views

Force on a point charge q inside a cavity in an uncharged conductor

This is problem 2.40 from Introduction to Electrodynamics by D. J. Griffiths: A point charge $q$ is inside a cavity (not necessarily spherical or anything similarly regular) in an uncharged ...
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2answers
111 views

Does electric field cause changing magnetic field also?

According to Faraday's law, changing magnetic field causes eletric field (imprecise wording, but generally accurate). My question is, can Faraday's law be interpreted in opposite way - that is, ...
2
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1answer
102 views

Motional EMF and EMF?

What is the difference between motional EMF = $-vBL$ , and Faraday's law of induction $\displaystyle\mathcal{E} = \left|\frac{d\Phi_B}{dt}\right|$? Aren't they the same? What is the relation of ...
2
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2answers
156 views

Electromagnetism duality theorem

Concerning Electromagnetism, textbooks often refer to the Duality Theorem. Sometimes it is presented like this: «Consider the Maxwell's Equations (with phasors) and a known field $\mathbf{E}_1$, ...
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1answer
138 views

Biot-Savart Law from linear to volume current distribution

Biot-Savart law for a linear current distribution is: $\displaystyle \vec{B}=\frac{\mu I}{4\pi}\int\frac{\vec{dl}\times \vec{r}}{r^{3}}$. In the book that my professor uses says that if we have ...
2
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1answer
228 views

What does the electric field caused by a charged cylinder look like?

I am talking about a cylinder with a large enough radius:length ration that it cannot just be treated as a line. I would think that the electric field lines come out the curved and flat surfaces ...
2
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2answers
103 views

Suppose a light wave with wavelength 3m. What happens if one tries to contain that wave within a 1m container?

Suppose a light wave with wavelength 3m. What happens if one tries to contain that wave within a 1m container? If I'm going about this entirely the wrong way or have wrong conceptions about light ...
2
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2answers
107 views

Is a magnetic field affected by the presence of air?

Does air affect a magnetic field's ability to attract ferromagnets? If a magnetic field and a ferromagnet were placed in a vacuum would there be a better performance?
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5answers
346 views

Is the canonical momentum conserved when a particle moves in magnetic field?

Here is a question about the canonical momentum that I had asked some days ago, but I still have one point that I am not understand. Considering a particle moves in a magnetic field with charge $q$ ...
2
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2answers
239 views

What force creates ions out of neutral atoms?

Consider the reaction between Na and Cl to form NaCl. Na loses an electron and "gives" it to Cl because this makes both atoms more stable. But what forces "pulls" the electron from Na to Cl? Both ...
2
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2answers
506 views

Does AC current produce EM waves?

Does AC current in simple wires produce electromagnetic waves? AC current entails very rapid changes in polarity and therefore the electrons in the metal will feel rapidly changing forces which should ...
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1answer
66 views

Separating the convective and the inductive electric field

My question is basically this, if I am only able to measure the total electric field and the magnetic field at a few discrete points in space and time, is it possible to separate the convective and ...
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2answers
690 views

Work done by Lorentz Force in case of motional emf

In the classical example of the slidewire generator where the rod slides on a U-shaped conductor in a magnetic field, we get a charge separation due to the Lorentz force. The way the induced emf is ...
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1answer
91 views

$\hat{\imath}$ component of force exerted on an electron by a magnetic field?

The magnetic field over a certain range is given by $\vec{B} = B_x\hat{\imath} + B_y\hat{\jmath}$, where $B_x= 4\: \mathrm{T}$ and $B_y= 2\: \mathrm{T}$. An electron moves into the field with a ...