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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Why ONLY Maxwell's equations are the basic equations of electromagnetism?

In electromagnetism we say that all the electromagnetic interactions are governed by the 4 golden rules of Maxwell. But I want to know: is this(to assume that there is no requirement of any other ...
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2answers
60 views

Can eddy currents be extremely reduced?

Is it possible to create a certain design of a conductor to reduce eddy currents greatly? So that the magnetic "breaking" can be reduced? Is it even possible for the force generated by the eddy ...
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3answers
646 views

Curl of an electromagnetic wave?

I can't understand the concept of the curl of an electromagnetic wave. $$ \nabla \times E = -\frac{\partial \textbf{B}}{\partial t} $$ All of the examples I find show a current through a conductor, ...
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3answers
690 views

Is an electron attracted to one of the magnetic poles in this scenario?

Do magnets attract electrons? I don't think so, but maybe in certain cases they can be? I guess it would depend on what direction the velocity and magnetic field is in so that the force acting on the ...
2
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2answers
171 views

Why is the Faraday Tensor derived from the Lorentz force?

If we start from the Lorentz force, $$\textbf{F}=q\textbf{E} +q\textbf{v}\times\textbf{B}$$ and use the four velocity u$^{\mu}$ and the four momentum p$^{\nu}$, then we get to ...
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2answers
195 views

Heating effects of microwaves

I understand the heating effect(dielectric heating) of microwaves. This heating is caused by using a frequency of 2.45 GHz and this is the same frequency at which Bluetooth works and the L and S ...
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4answers
137 views

Why change in Capacitance?

I do know it that the overall capacitance decreases if two or more capacitors are connected in series,but do not understand why? I do understand it mathematically but don't get the physics behind it.
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2answers
192 views

Energy of an inductor

I know that for an inductor having self inductance $L$ energy stored in its steady state when a current $I$ has been established is given by $U = \frac{LI^2}{2}$. But after this current has been ...
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1answer
1k views

Proving Lorentz invariance of Maxwell equations

I've read somewhere that one does not need to prove Lorentz invariance of the Maxwell equations $F_{\mu\nu,\sigma}+F_{\nu\sigma,\mu}+F_{\sigma\mu,\nu}=0$ because it is "manifestly Lorentz invariant" ...
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2answers
57 views

Is charge 'localization' implicit in the idea of current?

If it was possible for charge to assume arbitrary densities, like we often see electrostatic exercises, and one could spread charge density uniformly over a ring, then how one would, theoretically, ...
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2answers
2k views

1 Tesla electromagnet?

Is it possible to create a powerful electromagnet at home? With use of a ferromagnet it seems so... Using the following formula: $B(Tesla)= k\mu_0nI$. I understand some ferromagnet's like iron could ...
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2answers
155 views

How do waves meet at a single point?

In principle two objects can never meet,because of electromagnetic repulsions for example if I touch something, I am not actually touching it considering the fact that there is a small region left due ...
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2answers
1k views

Why do circuits work so fast?

Drift velocity (explained to me as how fast the electrons are moving) is really slow. My book says the electrons move at around 10 mm/ s. If electrons move so slowly how do circuits work so fast? If ...
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1answer
1k views

Why this perpetuum mobile can't be possible? [duplicate]

I know that this won't work but I'm asking Why? Becuase as far as the vehicle POV - there is a force which drags him to the right. Isnt $F=ma$ applies here? What is that im missing?
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2answers
353 views

Why do spherical waves diminish as 1/$r^2$?

Seeing the derivation of a plane wave in Giancoli, I can't understand why a spherical wave would diminish in amplitude. Shouldn't the peaks still be mutually induced, and therefore nondiminishing?
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1answer
403 views

Electromagnetic Tensor in Cylindrical Coordinates

I understand that the Electromagnetic Tensor is given by $$F^{\mu\nu}\mapsto\begin{pmatrix}0 & -E_{x} & -E_{y} & -E_{z}\\ E_{x} & 0 & -B_{z} & B_{y}\\ E_{y} & B_{z} & ...
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1answer
606 views

Retrieving Maxwell's equations from the minimum action principle

I'm currently working at the start of Alexei Tsvelik's book Quantum Field Theory in Condensed Matter Physics. I'm kinda stumped on a few essential steps. Starting with the action: $$S = \int dt \int ...
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3answers
741 views

continuity of the electric potential due to a surface charge

The Electric potential due to a charge distribution on a surface is : $\Phi \left ( x \right )=\int \frac{\sigma \left ( {x^{}}' \right )dx{}'}{\left \| x-x{}' \right \|}da$ I want to show that it's ...
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3answers
486 views

Surface integral of Poynting vector around static sources

Consider fields $\rho \left( \vec{r} \right)$, $\vec{J} \left( \vec{r} \right)$, $\vec{E} \left( \vec{r} \right)$ and $\vec{B} \left( \vec{r} \right)$ in $\mathbb{R}^3$, with their usual meaning as ...
2
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2answers
243 views

locality vs non-locality

Suppose we have a circular loop of wire, and we put a long perfect solenoid inside it which is connected to an AC voltage source so that the magnetic field inside it starts to vary by time, does this ...
2
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1answer
771 views

How EM waves are produced by accelerating charged particles?

How the electro-magnetic waves are produced by the accelerating charged particle? Graphical explanations are most welcomed. Is the explanation given by the below mentioned article correct regarding ...
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2answers
2k views

Artificial planetary magnetic field

I wonder how difficult it is to create an artificial planetary magnetic field with generators? What power they would need? The question is inspired by thinking about possible colonization of ...
2
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1answer
651 views

Minimal coupling of an atom to the EM field

The Hamiltonian of an atom coupled to an EM field, both described quantum mechanically is: $$H = \frac{1}{2m}(\hat{p}-q\hat{A})^2 = \frac{\hat{p}^2}{2m} ...
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2answers
436 views

Invariance of Maxwell's Equations under inverting variables - Reference and use

Some months ago, an ArXiv paper mentioned in passing that Maxwell's Equations were invariant under reciprocating the variables, or at least this results in a dual set of Maxwell Equations. (Actually I ...
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1answer
3k views

Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why?

I need a full explantation for this concept. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid.
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3answers
4k views

Does the 'mAh' rating of a battery have something to do with its power?

I'm curious about the 'mAh' of a battery: how can this impact the power of the battery? I've done some research on the internet, and most of the articles I found explain about the 'amount of charge ...
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3answers
362 views

What makes Poynting's theorem consistent for a charge moving in a static electric field?

Poynting's theorem is given by $$\frac{\partial}{\partial t}\int_{v}Udv + \oint_{A}\vec S\cdot \vec {dA} +\int_{v}\vec E\cdot\vec J dv =0 $$ Where, the total electromagnetic energy inside the ...
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2answers
363 views

Origin of Electromagnetic Interactions between Molecules

What is the origin of electromagnetic interaction between molecules? Anyway, it should have some relation with atoms. Also, These electromagnetic interactions are playing a major role in different ...
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3answers
324 views

Electrial Conductivity of Thin Metal Films

What is the best way to find specific/electric conductivity which is dependent of very thin film thickness?
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1answer
295 views

light absorbing diodes characteristics

Recently, there was a publication regarding some new materials that would let thru light in one direction and either absorb it or reflect it in the other direction; the publication does not clarify on ...
2
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1answer
684 views

Analogy between magnetic bottle and Van Allen's radiation belt

A magnetic bottle is an arrangement that permits to confine charged particles. Here you can find a review for charged particle rotating in a magnetic field and at the bottom of the page a description ...
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1answer
253 views

Hairy ball theorem: references to applications

I'm looking for references to applications of the Hairy ball theorem. This is a result of mathematics (topology), but I am interested in applications. I already visited wikipedia and cited ...
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3answers
11k views

How can I theoretically describe the potential between two capacitors in series?

Suppose to have two capacitors in series: The voltage in the middle point will be: $$ V_X = V_1 \frac{C_1}{C_1+C_2} $$ How can this be explained? It's been asked in electronics, and explained in ...
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1answer
2k views

Which are other anomalies like Divergence of 1/r^2?

As one might have learned in the basic science (ex. Electrodynamic theory), when we apply the divergence theorem to the vector function like 1/r^2 with it pointing in the radial direction (like ...
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1answer
715 views

Work done on charged particle by magnetic field in quantum mechanics

Classically, we know from $\mathbf{F}=q\mathbf{v}\times \mathbf{B}$ that magnetic field does no work on a charged particle. In quantum mechanics, the Hamiltonian of a charged particle in a magnetic ...
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3answers
570 views

Gauge invariance and form of the vacuum polarization tensor

In quantum field theory or condensed matter physics, the fermionic one-loop diagram gives rise to the polarization tensor $$ Π^{µν} = Tr[ γ^µ G γ^ν G ] $$ If we couple the electrons to an ...
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4answers
4k views

What is magnetic conductivity?

I searched google for the meaning of magnetic conductivity but couldn't figure out what is it? electric conductivity is usually means that there is the electric field parallel to the interface is ...
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2answers
254 views

What are the specific electronic properties that make an atom ferromagnetic versus simply paramagnetic?

As I understand it, paramagnetism is similar in its short-term effect to ferromagnetism (spins of the electrons line up with the magnetic field, etc.), though apparently the effect is weaker. What is ...
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3answers
499 views

What does physics study? [closed]

Wikipedia definition: Physics (from Ancient Greek: φύσις physis "nature") is a natural science that involves the study of matter[1] and its motion through spacetime, along with related concepts such ...
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4answers
2k views

Some questions about car radio and cellphone antennas

1-Why the antenna of the radio of cars is located outside the car and not inside? 2-If the answer to 1 is because that cars are like Faraday cages then how come my cell phone can receive signal ...
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3answers
3k views

Physical meaning of the energy density of an electrostatic field

I understand the physical meaning of electrostatic energy of a system of charges (or a distribution with given density) as the energy stored in the system while working to carry the charges from ...
2
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1answer
1k views

infinite parallel conducting planes

two infinite parallel conducting planes grounded and are separated by a distance d. place a point charge "q" between the two planes, using the "green teoerma reciprocity" how I show that the total ...
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1answer
2k views

Relativistic charged particles in a constant uniform magnetic field

How can i derive the dynamic of a relativistic charged particle in a uniform magnetic field $B=(0,0,B)$?
2
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1answer
497 views

Magnetic moment of relativistic rotating ring

Let's consider rotating charged ring. Theoretically mass of this ring has no limit as rotation speed increases. So what about magnetic moment of the ring? Is it limited by the value of speed of ...
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3answers
3k views

Visualizing Electromagnetic Waves in 3D Space [closed]

I did one module of physics for my GCSE one year ago which taught me about transverse EM waves & the EM spectrum, but since then, I do not understand how a wave would move in 3D space. Can someone ...
2
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3answers
955 views

Does the energy of a magnetic field decrease when it moves a conductor carrying a current?

When a charged particle moves in an electric field, the field performs work on the particle. Thus, the energy of the field decreases, turning into kinetic energy of the particle. Does the magnetic ...
2
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2answers
152 views

Utility of displacements potentials in geophysics

In the elasticity theory, you can derive a wave equation from the fundamental equation of motion for an elastic linear homogeneous isotropic medium: $\rho \partial^2_t \overline{u} = \mu \nabla^2 ...
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3answers
120 views

Is it possible to create a beam of light with frequency of 0?

Is it possible to create a beam of light with frequency of 0? So this would involve photon(s) that move forward without fluctuating with any frequency. If yes, how could this be done? Also, ...
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2answers
47 views

Magnetic Field and Flow of Vector Potential

I am sorry, when my question is not really concrete, but here we go. Consider the Hamiltonian function $$H(x, \xi) = \frac{1}{2m}\bigl|\xi - eA(x)\bigr|^2$$ corresponding to a charged particle in a ...
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2answers
85 views

Could synchrotron radiation be produced by a gravitational field instead of a magnetic field?

I know that synchrotron radiation is produced when a charged particle is accelerated radially by a magnetic field, but I was wondering if synchrotron radiation could also be produced by an uncharged ...