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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Definition of self inductance of a coil

I saw a definition in a textbook for the term self-inductance of a coil as emf induced in a coil when rate of change of current is 1 ampere per second. But I think the following is correct: ratio of ...
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30 views

Wave propagation in micro strip waveguide

I am trying to understand wave propagation in micro-strip waveguide, the way i came to understand rectangular waveguide is this way (in brief): EM waves can be understood as reflecting from the ...
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32 views

Is there a Lagrangian that can lead to the Rayleigh-Jeans law?

Is there a way to derive the Rayleigh-Jean's law using classical statistical mechanics only? On the internet there is a common way to arrive at the equation by using concepts in electrodynamics. This ...
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1answer
50 views

Two Current Carrying Loops: Multiple Choice Question

I'm studying some simple multiple choice questions from an old test in electrostatics and I have some trouble intuitively grasping this question. I hope someone can explain the solution! Two current ...
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2answers
85 views

Electromagnetic wave and quantum mechanics [duplicate]

I'm very new to physics. I studied and read about quantum mechanics and what the assumptions are (wave particle duality, uncertainty principle, observation, wave function collapse, etc.), but I also ...
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3answers
77 views

doubts regarding the classical electron radius

When estimating the classical electron radius, people normally equate the energy needed to assemble a charged sphere to $mc^2$, due to the so-called mass-energy relation. However, personally I don't ...
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1answer
19 views

What is the magnetic property of an alloy?

If an alloy is made between a diamagnetic and a paramagnetic substance or paramagnetic and a ferromagnetic substance or a diamagnetic and a ferromagnetic substance, what will be the resulting magnetic ...
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1answer
38 views

Electric field a distance z above the midpoint of a straight line segment

In Griffiths there's an example to evaluate the Electric field a distance z above the midpoint of a straight line segment of length 2L. Which carries a uniform charge $\lambda$. In that calculation, ...
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1answer
37 views

Voltage of a quadrupole magnet

I have a simple question and it's my first one in this community. :) Does the voltage of a quadrupole magnet depend on the power of the electron beam in a synchrotron? Perhaps someone has a good ...
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1answer
37 views

Magnetic field inside parallel plate capacitor

Inside a parallel plate capacitor, we know that the electric field due to the static charge $E= \frac{\epsilon_0 A}{d} $ Now if we want to find the magnetic field inside the parallel plate capacitor, ...
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1answer
108 views

Why do I hear voices when I touch my turntable needle?

So I was trying to figure out the reason why my old (and probably sufficiently damaged) needle on my phonograph (turntable) was not working like it was a little while ago. With my headphones on, I ...
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0answers
49 views

Are photons just electric waves in an electron's frame of reference?

They say that electrons emit photons when they jump to a lower orbit. But the way electrons should see it, there's no any emission, really. There's just rapid change in electric field due to a rapid ...
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41 views

Boundary conditions for Maxwell's equations at the interface between two media

Consider the following simple Maxwell's equations: $$ \nabla\cdot\mathrm{D}=\rho $$ $$ \nabla\times\mathrm{E}+i\omega\mathrm{B}=0 $$ $$ \nabla\cdot\mathrm{B}=0 $$ $$ ...
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7 views

Enough high&configured field disabling electron avalanche?

The electron avalanche starts after sufficient high electric field through the hole where one electron is, often >300keV. However, I seem to be getting results, that at some energy instances of the ...
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1answer
84 views

Magnetic force paradox

Suppose a current carrying wire Is placed in vertical direction. A charged rod is placed is placed nearly horizontally.It is clear that magnetic field due to current carrying wire is inside the ...
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9 views

Net electric field of a nanowire in the vicinity of a quantumdot

I know how to find the electric field when both nanostructures are same and in the vicinity of each other. However, when it comes to nanostructures of different dimentionality (ie.nanowire and a ...
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1answer
17 views

In magnetostatics, is there any relation between flux and current?

I have noted while trying to find analogy between electrostatics and magnetostatics, for the equation, flux = charge/epsilon, is there any corresponding equation in magnetostatics, relating magnetic ...
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18 views

Is the shear force required to separate two magnets different than the pull force?

i.e. given 2 magenets with some distance between them, what is the force required to separate them in a shear fashion? And how does it relate to the pull force required to separate them the typical ...
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1answer
42 views

Eddy Currents – Tubes with slits

When a magnet falls down a tube, eddy currents form and flow around the tube, perpendicular to the direction in which the magnet falls. However, when there is a vertical slit in the tube, are ...
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44 views

Reproducing electricity [closed]

We all know reproducing solar energy is possible. Same stands for mechanical energy (air, water, coals) - they are all reproducible. But what about other types of light ? A diode light for example ...
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2answers
32 views

Difference between steady and moving electrons

Recently I am reading about the elecctromagnetism. When the electrons are at rest, they produce electric field and when in motion they produce magnetic field. Why so? What happens to a electron when ...
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1answer
28 views

what is the meaning of “x dB of isolation” for Faraday cage box?

I need a Faraday-cage box that block the device from transmitting or receiving any signals when it is in it. When I search for such a box I always see the companies that are making describe it is ...
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1answer
30 views

Can colour be synthesized from frequency?

Given the frequency of a mechanical vibration in the audible range, one can synthesize the sound on a computer. For example, I ask "what does 440Hz sound like?" and I can listen to this frequency as ...
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24 views

Magnetic force between an infinite and a finite current carrying wire

My question is simple. What would be the magnetic force between an infinite and a finite but obliquely placed current carrying wire? One end of the finite wire is at a perpendicular distance $a$ ...
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2answers
48 views

Does Biot-Savart law apply in changing electric field or it needs a modification just like Ampere's law, to become as true as Maxwell's 4th equation?

Does Biot-Savart law apply in changing electric field or it needs a modification just like Ampere's law, to become as true as Maxwell's 4th equation? In the update to Ampere's circuital law, the ...
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2answers
44 views

How does infrared radiation increase temperature?

Temperature is proportional to the average kinetic energy of particles in a medium. When impinged by infrared radiation, what happens on the microscopic level that translates that EM wave into the ...
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5answers
667 views

What does it mean for a physical quantity if its mixed second partial derivatives are not equal?

This goes for every problem (either in electromagnetism or fluid dynamics) that has to do with vector fields. Say we have a fluid flowing in a closed circular pipe (or an electromagnetic field, the ...
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25 views

Dispersion relation in wave guides

I am reading Griffiths section 9.5. Assume that wave guides are surrounded by perfect conductors, and geometry is $z$-independent, as in the text. I understand he proved that in a hollow wave guide, ...
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23 views

Current flow direction, based off the equipotential line?

From the following diagram: Given the wires are only connected to a certain portion of the conductor, will current flow all around the conductor? Or only throughout the equipotential line(diagram ...
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1answer
72 views

Can photons accelerate? [duplicate]

I was just wondering if there's a (hypothetical) situation where a photon could accelerate and what the consequences of this might be?
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19 views

Using the Mirror Rule to determine the magnetic field of an infinite slab

Consider a slab infinite in the y and z direction but with finite width W in the x direction. Current flows in the (+y) direction. I'm supposed to use the "mirror rule" to show that at a point in the ...
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1answer
54 views

How did Einstein know that it was necessary to include “stimulated emission”?

How did Einstein know that it was necessary to include "stimulated emission" which was in the same direction as the incident photon and in phase with it?
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0answers
50 views

Would a super conductive insulation completely prevent the propagation of a magnetic field from a wire where it is wrapped around?

I have limited understanding about super conductors and see them as expelling magnetic fields purely due to eddy currents produced without resistance opposite the magnetic field. I have read that ...
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1answer
42 views

Meaning of “electrostatic” and “nonresonant laser” fields

I just read the following sentence: The molecule is subjected to an electrostatic field $E$ combined with a nonresonant laser field of intensity $I$, whose linear polarization is collinear with ...
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1answer
25 views

Transmission of light, sub-wavelength apertures, and cut-off frequencies

I was hoping someone could please explain how the transmission of light through a sub-wavelength aperture in a metal film, at a particular wavelength, changes when the aperture is: i) above cut-off ...
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2answers
50 views

Why conductors don't scatter light?

Air molecules can be oscillated by E field and re-radiate EM waves in different directions. However, if light is shined to a conductor the E field oscillate the free charges but the effect is to ...
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1answer
67 views

Accelerate neutral particles

I know it is not possible to accelerate particles via the Lorentz force $F=q(E+v\times B)$, because $q=0$. However, the magnetic moment $\vec\mu$ for such a particle usually is $\neq 0$. Is there a ...
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1answer
32 views

Maxwell Stress Tensor at material boundaries

I am trying to grasp the meaning of the Maxwell Stress tensor $T_i^j$ at material boundaries. Concretely, I am trying to calculate the force between two waveguides. The results are given in an article ...
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1answer
143 views

What is the meaning of $\vec{E}\times\vec{B}$?

Consider that for a single $\mathbb{R}^3$ point-source emitter of RF, the $\mathbf{E}$ and $\mathbf{B}$ fields (when treated as transverse sinusoids and ignoring interference properties) are always ...
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2answers
52 views

Solenoid cannon (coil gun) possibility and recoil?

Similar to my other question If you are to pass a magnet through a solenoid a current is produced in the solenoid due to the magnetic flux. However, if you were to have a magnet sit inside a ...
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17 views

Polarized light from any suface?

From a textbook I read something like this: "When sunlight is reflected from a horizontal surface, the plane of incidence is vertical, and the reflected light contains a preponderance of light that is ...
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27 views

How to design a grating coupler to produce surface plasmon-polaritons (SPPs) at a desired frequency?

Following on from this question, which I found very useful on the topic, I was wondering how you would use the equation $\beta = k sin \theta \pm \nu g$ to fabricate a grating coupler to generate SPPs ...
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1answer
101 views

Difference in induced current, when magnetic field “span” is reduced?

A conductor of known volume $(V)$ passes a uniform magnetic field$(B)$with a constant velocity $(v)$ the conductor is a source of induced EMF, a power source to a circuit. The induced EMF can be ...
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59 views

Is it degeneracy pressure rather than electrostatic repulsion that stops us falling through the floor? [duplicate]

From Wikipedia: Degeneracy Pressure Freeman Dyson showed that the imperviousness of solid matter is due to quantum degeneracy pressure rather than electrostatic repulsion as had been previously ...
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3answers
374 views

Why do magnets silence anvils?

Today I've been to a forge. The blacksmith demonstrated that if he beats the anvil without a magnet attached, it make horrible noises. As soon as he reattached it, the sound of the anvil was way more ...
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1answer
41 views

Can someone please explain extraordinary optical transmission (EOT)?

Can someone please explain extraordinary optical transmission (EOT)? I'm hoping someone can describe the physical process by which light is transmitted through a periodic metal hole array which is ...
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0answers
21 views

Help understanding Diamagnetism in external field

Lorentz force can not do work. Therefore it can not change the velocity of electron. Then how do you explain diamagnetism in terms of speed of a pair of electrons in the orbit?
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1answer
155 views

What is the difference between the magnetic field of a permanent magnet, and that of an electromagnet?

What is the difference between the magnetic field of a permanent magnet, and that of an electromagnet? In the diagram below, you can see that the magnetic field of a wire which carries a DC ...
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2answers
83 views

Does voltage produce a physical field?

Does voltage produce an electric field, like how a current produces a magnetic field?
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1answer
111 views

Asymmetry of relativistically treated EM force between atoms

There are two neutral atoms set separated at a long distance $R$ and let's consider them phenomenologically through Bohr model. Let's also assume that the nuclei (charged $+q$) of the atoms are fixed ...