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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2
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1answer
138 views

Ampère's law and superconductors

I have been reading about superconductors and emerge me a inquietude about the explanation of existence of currents inside the superconductor while their magnetic field (inside too) is zero. Based in ...
10
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4answers
1k views

Do electrostatic fields really obey “action at a distance”?

In an electromagnetic theory class, my professor introduced the concept of "action at a distance in physics". He said that: If two charges are at some very large distance, and if any one of the ...
-3
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2answers
88 views

“X-rays”, “gamma rays”, “sun rays”… But electromagnetic waves are NOT rays and DO NOT consist of rays?

In a separate question I'm struggling to figure out the nature of EM waves. But it's a vast topic and I'm trying to narrow it down to small specific questions. It turns out that all electromagnetic ...
3
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5answers
1k views

How do EM waves propagate?

I have read about this and what I surmise is that when charged particles such as electrons accelerate they produce time-varying electric fields. These E-fields produce H-fields and the process goes ...
0
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1answer
29 views

Field emission vs. electrical breakdown

In vacuum a tungsten needle sits in front of a copper plate at some separation $d$. How does the ratio of the voltage at a fix field emission current (e.g. 1 pA) $V_{fe}(1 \ \text{pA})$ and the ...
0
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1answer
206 views

Surely force on shell can't be balanced by field momentum?

Imagine a particle with charge $q$ at rest at the origin. It is surrounded by a concentric spherical insulating shell, also at rest, with charge $Q$ and radius $R$. At time $t=0$ I apply a constant ...
0
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1answer
56 views

How is light slowing down in a medium thought of in the photon picture? [duplicate]

The speed of light in any medium besides vacuum is smaller than $c$. In a classical way, I just look at that as a wave that propagates less fast, the change in EM-field is passed on slower. How should ...
-2
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1answer
62 views

Is gravity weak negative electric charge? [duplicate]

This could be true since the both have infinite range and other common properties. They both have fields.
3
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1answer
94 views

Physical distribution of salt anions and cations during electrophoresis

If I have a volume of $L$ liters of salt water at a concentration of $\approx N$ mM NaCl and I pour it into an electrophoretic apparatus (like this one: ). Once we turn the apparatus on, and set the ...
0
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1answer
117 views

Reflection coefficient as a function of frequency

I am trying to relate the equation for reflection coefficient in oblique mediums to the frequency but can't figure out how the frequency affects the reflection of light. $n_1$= intrinsic impedance of ...
0
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2answers
449 views

Torque per unit length on infinite rotating charged cylinder

For homework I have the following question, but I am stuck on finding the torque on the cylinder. An infinite cylinder of radius $R$ carries a uniform surface charge $\sigma$. We start rotating the ...
5
votes
3answers
7k views

2 ways to generate electromagnetic wave

According to Maxwell's equations, accelerating charges emit electromagnetic radiation. According to Quantum physics, heating causes electromagnetic radiation too. These 2 radiations, are they ...
2
votes
1answer
90 views

How can radiation be a transverse wave? Does light really resemble a rope? How can a 3D field be a medium for non-spatial 1D waves? Need mental model

I understand longitudinal waves. For example, I've got a clear mental modal of air waves: a slice of air becomes overcompressed, then the slice next to it becomes overcompressed and the first slice ...
0
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1answer
24 views

Is internal resistance relevant in motional EMF?

When a conductor passes a magnetic field and connected to a circuit, the induced voltage is calculated via the motional EMF($\epsilon$): $$\epsilon=-vBL$$ Is the conductor's resistance (or internal ...
3
votes
2answers
169 views

Current Electricity and E.M.F of a cell

The E.M.F of a cell is the work done in moving a unit positive charge in a loop or from the terminal to the same terminal. The force it experiences is a conservative force. Therefore, the work-done in ...
0
votes
1answer
220 views

Why do we always consider the area of inner solenoid while calculating the mutual inductance of two coaxial solenoids?

While we know that flux linked to an area is the dot product of the area vector of the loop(and not the actual area encountering the field lines) and the magnetic field linked to it, why then do we ...
1
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1answer
90 views

Separating aluminium sheets with magnetic field

all! I would like to know if it would be possible to induce a strong enough magnetic field in sheets of aluminium so they would be separated between each other, like when you use magnets to separate ...
0
votes
1answer
156 views

How is Magnetic force on a current carrying conductor $Blb$

I was reading an answer about torque acting on a rectangular current carrying loop kept in a uniform magnitude field B. Force acting on each sides is $F_1$, $F_2$, $F_3$, $F_4$. It's written here : ...
0
votes
1answer
75 views

Could electromagnetic charge curve something like spacetime in analogy with general relativity? [duplicate]

Newtonian gravity and electrostatics have the same form; this analogy is extended when we look at full dynamic electromagnetism, and correspondingly "gravitomagnetism". We are quite capable of ...
1
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1answer
113 views

Constant magnetic field attenuation by µ-metal (mu-metal)

I am interested in the magnetic field attenuation by µ-metal. Specifically shielding from earth's magnetic field $\boldsymbol{H}_E$ through closed cylindrical layers of such a metal, yielding an ...
1
vote
1answer
172 views

Force of a solenoid on a ferromagnetic material

As I was trying to find an answer to another problem, I was informed that the equation I was using would not work. The equation I was using was $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$ If this ...
2
votes
2answers
129 views

Far Field Diffraction of EM waves: what does the zero frequency signify?

If you have a system of independently radiating electrons/point-charges, the far field distribution of the EM waves can be approximated by the fraunhoffer diffraction integral, or simply by the ...
1
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0answers
47 views

Question about Elon Musk's Hyperloop Suspension [closed]

So one of the proposed suspension systems that will be used on the hyperloop include the externally pressurised air cushions. These cushions lift (or atleast help lift) the capsule and reduce drag ...
2
votes
0answers
2k views

How to calculate magnetic pole strength?

I have 2 magnets. I need to know the force between them. In a previous Phys.SE question, conclusion was: we need to use a dipole-dipole interaction equation, which included m, which the magnetic ...
2
votes
3answers
151 views

What is supposition of equilibrium? How do Rayleigh, Jean know the electromagnetic wave in equilibrium behave?

In a cavity of dimension L, the wave must give zero amplitude at the wall, means wave equation has zero amplitude. Why? Answer from hyperphysics "since a non-zero value would dissipate energy and ...
1
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2answers
111 views

electromagnetic induction and magnetic shielding

In the figure I have a circular conducting wire. Somehow, in the middle circular region I have a magnetic field (this means the magnetic field is shielded in this region and it is possible from what ...
2
votes
2answers
630 views

Neither Biot-savart nor Ampere Law can solve this problem?

I'm confused about the use of the Ampere's Law and the Biot-Savart Law due the inconvenience of each law. I want to calculate the magnetic field due to current carrying a circular loop over itself, ...
3
votes
1answer
158 views

Are magnetic hysteresis losses relevant to alternating currents flowing in a wire?

Say we have an AC in a magnetically lossy material, like iron. Because of iron's relatively high permeability, skin effect will be more pronounced than it is in say, copper, so this iron wire isn't so ...
2
votes
1answer
252 views

Symmetries of a Uniform Magnetic Field

Simple question. A system with a uniform electric field everywhere in space has translational invariance in the directions perpendicular to the electric field but no translational invariance parallel ...
1
vote
1answer
136 views

How is momentum conserved when a magnet attracts a metal?

Suppose your have any magnetic object and no external force acts upon it, and the object comes near a metal which causes an impulse (think that will happen). However, the magnetic force is internal to ...
1
vote
2answers
65 views

Physical meaning of wavelength of a EM Wave

The wavelength of a wave is defined as the spatial separation after which it repeats its shape. It is easy to visualize it for one dimension but if we consider a light wave/EM wave which is ...
1
vote
1answer
49 views

question about Gauss law

If I have an infinite plate with the surface charge of sigma. I know that my electric field is constant $2\pi\sigma$ (using Gauss's law). If I build the Gaussian surface above the plate the charge ...
1
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1answer
38 views

Force of electromagnet on a wire [closed]

I'm trying to produce an equation for the force produced by an electromagnet on a wire. I'm very aware I don't know any vector calculus but I think as it's the special case (Perpendicular) I can just ...
4
votes
2answers
350 views

What happens when you pass a current through a coil made of a ferromagnetic substance?

I know when you pass a current through a length of copper coil or a solenoid, there is the induction of a magnetic flux. But what of the coil made of the ferromagnetic material, the permanent type ...
3
votes
1answer
110 views

Resource for mass-charge interaction

My GR professor mentioned that trajectories of charged particles in GR are not the same as those of non-charged particles (i.e. charged particles don't move on geodesics). As I understood it, the ...
1
vote
3answers
364 views

More about the right hand rule?

We started learning about electromagnetism in physics class, and the Right Hand Rule comes in handy as seems easy to use, but I'm curious as to how it actually works. I guess it's more of a math ...
15
votes
8answers
6k views

What is the electric field generated by a spinning magnet?

Consider a cylinder of permanently magnetized material, with uniform magnetization pointing along the cylindrical symmetry axis (the $z$-direction). The magnet is rotating about its cylindrical ...
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0answers
43 views

How did Weyl's 1918 paper; Gravitation and Electricity, influence classical physics? [migrated]

The main-stream view seems to be that Weyl's 1918 paper Gravitation and Electricity was initially considered a failure for reasons first pointed out by Einstein. But these initial ideas were reapplied ...
1
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2answers
203 views

Use of Amperian loop to calculate the $B$-field inside a co-axial wire

The problem asks to calculate the magnetic field at point $a$ of a co-axial cable with a wire at the center surrounded by a rubber layer, and then another hollowed cylindrical wire followed by a ...
2
votes
1answer
3k views

Physical difference between Lorenz and Coulomb gauge-fixing conditions

Lorenz and Coulomb gauge-fixing conditions. What is physical difference between these two gauge-fixing conditions? Mathematical expression are clear but how to we choose one of these means what they ...
2
votes
4answers
318 views
1
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1answer
1k views

Force from solenoid

I'd like to approximate the force from a solenoid, or at the very least find a formula which is proportional to the force so that I can experimentally find the constant for my particular case. ...
0
votes
1answer
95 views

Explanation of force amplification inside a solenoid

For a system being actuated by a motor, the force can be amplified by gearing. The energy is being used for force instead of distance, so it produces more torque but moves slower. For a system being ...
1
vote
3answers
172 views

Induced EMF of a rectangular loop should be zero?

Considering the shape of a rectangular loop in a changing magnetic field: The induced $\epsilon$ would be zero? Since a rectangular loop is a combination of wires in series to create such a shape. ...
2
votes
1answer
78 views

Why do high voltage transmission line workers need a Faraday cage suit?

In this video the high voltage transmission line workers are wearing a Faraday cage suit. Why is this needed? Without the Faraday cage, the resistance of the human would be very high compared to the ...
0
votes
1answer
183 views

Boltzmann Distribution of Electrons in Confining Potential

I have a particle simulation wherein many non-interacting electrons are trapped in a electric potential well. I would expect, and therefore I initialize according to this, that the electrons would ...
1
vote
1answer
49 views

Why doesn't light vibrate in-situ?

Light always moves in a straight geodesic path (shortest distance between 2 points in flat space where gravity is homogeneous) across 3 dimensions of space and 1 dimension of time. It is consists of a ...
0
votes
1answer
68 views

Cylindrical capacitor in an electric circuit

I've come across a tricky question and would appreciate some hints or explanations as to why the given solution is the way it is. The question reads as follows: A coaxial cable consists of a wire ...
1
vote
3answers
134 views

What can change a photon's frequency?

I found this question: Is it possible to apply force to a light particle? As it states, gravity can change the frequency of light by changing its momentum. My question regards other phenomena that ...
1
vote
1answer
69 views

Electric Motors: why do they draw more current when stalled, and less when moving? [duplicate]

I'm familiar with how an electric motor works, and also familiar with what stall current and free current refers to in an electric motor. I'm also somehow familiar with the notions of energy being ...