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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4
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1answer
509 views

Question about superconductivity

A long cylinder of radius $R$ is made from two different material. Its radius $r<r_0$ $(r_0<R)$ part is a material with superconducting transition temperature $T_1$, and its $r_0<r<R$ ...
26
votes
3answers
958 views

Do intergalactic magnetic fields imply an Open Universe?

According to a paper on the arXiv (now published in Phys Rev D), they do. How credible is this result? The abstract says: The detection of magnetic fields at high redshifts, and in empty ...
3
votes
1answer
41 views

A puzzler in induction and special relativity

Some reading I was doing jogged my memory about a puzzle in E&M that hit me back in my undergrad days, but I just let it go at the time and never found an answer. A pretty common undergrad E&...
0
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2answers
47 views

What is a magnetic line of force? [on hold]

Do magnetic limes of force 'flow'? If so, what is it that is flowing? What is the 'line of force' composed of?
0
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3answers
243 views

Dielectric boundary

I am trying to determine why electric field may be confined to a certain region if there is a large difference in the permitivity for example if electric field flows through water and then reaches a ...
1
vote
2answers
80 views

Why do we restrict to electric field when describing light?

Why do we restrict only to electric field when describing light as electromagnetic wave? I mean from Maxwell equations we can derive wave equation for electric field and also for magnetic field but ...
3
votes
0answers
43 views

Lagrangian of classical electromagnetism without $A_{\mu}$ field [duplicate]

Is there a Lagrangian reproducing Maxwell's equations without the use of the scalar and vector potential? Obviously $\mathcal{L} = -\frac14F_{\mu \nu}F^{\mu \nu}$ doesn't work since in terms of $E$ ...
7
votes
4answers
827 views

Least-action classical electrodynamics without potentials

Is it possible to formulate classical electrodynamics (in the sense of deriving Maxwell's equations) from a least-action principle, without the use of potentials? That is, is there a lagrangian which ...
7
votes
1answer
240 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 ...
0
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2answers
182 views

Does Faraday's law work both ways, and if so why don't we use d.c for a generator?

Faraday's law in the integral form can be stated as $V = -d\Phi/dt$, where the right-hand side represents the rate of change of the magnetic flux and the left the voltage difference. In other words, a ...
1
vote
1answer
76 views

What is capacitance, in general?

In circuit analysis software capacitance can be measured between any two nodes of a circuit or of a multiterminal device. In practical terms we take $C_{ij}$, the capacitance between $i$ and $j$ as ...
1
vote
2answers
756 views

How does the magnetic field get induced in car's tire?

I was amazed to see how my car's tire started attracting the nuts and bolts, how in the world did it induce the magnetic field? Never heard of such phenomena!!!
6
votes
3answers
195 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 ...
0
votes
0answers
51 views

Does gravitational radiation have a formalism similar to Wheeler-Feynman electrodynamics?

Binary systems radiate energy away in gravitational waves as the orbits of the two masses spiral in towards each other. My understanding of gravity is that we think of it as a mediator of particle-...
4
votes
1answer
243 views

What is problematic about the Moving magnet and conductor problem?

The problem is posed as follows: There is a conductor and a magnet in relative motion. This motion induces emf in the conductor. The value of the induced emf is independent of whether it's the ...
3
votes
2answers
123 views

Proton and electron joining

If I have a proton and an electron at rest at some distance apart. Will they form an hydrogen atom when released or they will join together? My intuition says it will form H atom. But I cannot ...
0
votes
1answer
32 views

How can a sinusoid be a steady current? [duplicate]

As far as I understand it, a steady/stationary/constant current is defined to have $dJ/dt=0$ (i.e., no explicit time dependence). So I would say that sinusoids cannot produce steady currents, yet ...
2
votes
1answer
407 views

Right hand solenoid example

I am just studying for my physics final exam. I came across this example and am not satisfied with the answer. My answer is that Z is South and the current would flow from Y to X because of the ...
1
vote
1answer
1k views

Electric field from conductive to dielectric media

I am interested in the main difference between transitions from electric fields from Conductive to Conductive/ Dielectric to Dielectric and Dielectric/Conductive media. What are the boundary ...
0
votes
0answers
42 views

What one would observe on extremely high voltages?

I am interested which physical processes generate the highest electrical voltage and what the highest measured voltage is. In everyday life, electrostatic charges e.g. while walking with socks on a ...
0
votes
0answers
26 views

Newton's third law, weak and strong law of action and reaction [duplicate]

In the case of a system of moving charges forces between charges is obtained by Biot-Savart law. But it violates both action and reaction law. How can we prove that?
0
votes
0answers
27 views

What difference does it make if the turns in a tesla coil overlap?

Would a tesla coil in which the primary coil is made by overlapping the turns of the wire work?
0
votes
1answer
41 views

Intuition differential ampere's law

Ampere's differential law states that - $$\nabla \times {\bf B} = \frac{4 \pi \, {\bf J}}{c}$$ I know to derive amperes integral form from special relativity, and to use stokes theorem in order to ...
5
votes
2answers
231 views

Path dependent phase in quantum mechanics

In elementary treatments of quantum mechanics, we are taught that the wavefunction of a single particle is complex valued ($\Psi : \mathbb{R}^3 \to \mathbb{C}$). In particular, the wavefunction has a ...
0
votes
1answer
35 views

Laser as an optical oscillator

How can Laser can be compared to a positive feedback amplifier? Does the two conditions for oscillator holds good for lasers too.
2
votes
1answer
130 views

What is the metric of a constant electromagnetic (pure electric or pure magnetic) field?

For example, imagine a magnetic field $B_x$ directing in $\hat{x}$ direction filling all the space. What is its associated metric field? I can construct the electromagnetic stress-energy tensor for ...
0
votes
1answer
426 views

What are the boundary conditions for EM waves normally incident on the interface between two dielectric media?

An EM wave, amplitude $E_0$, frequency $\omega_0$, is incident upon a material with relative permittivity (dielectric function) $$\varepsilon \left( z \right) = \left\{ \begin{gathered}{\varepsilon ...
2
votes
1answer
127 views

How force get transmitted when a magnet attracts iron?

According to particle physics , every fundamental force has its force carrier particle. Photon is a force carrier particle of electromagnetic force but how does force gets transmitted when a iron is ...
2
votes
1answer
211 views

Opacity/transparency of conductive meshes to charged particles (electrons/ions)

When using a conductive (metal) mesh, effectively a metallic woven fabric, in vacuum applications as a "grid" for charged particle optics, how does one calculate (or at least estimate) the opacity or ...
0
votes
1answer
74 views

How to find the magnetic field due to a revolving electron of hydrogen atom in first orbit

So, I was thinking about the Bohr model of atom and I started to wonder how we could find the magnetic field due to a revolving electron (produced at the location of proton) of hydrogen atom in first ...
0
votes
0answers
21 views

Circuit with capacitor and battery- why same voltage?

If we connect a capacitor and a battery in the same circuit, what makes the charge move until the voltage on the capacitor is the same as voltage on battery?
1
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2answers
141 views

How to find the parts across which emf is induced?

Is there a general rule that will allow one to find the parts where the emf is induced? Consider for example the following two cases: Case 1: A rod is made to move normally to the magnetic field at ...
4
votes
1answer
96 views

Is it possible to push together two charged particles of the same charge hard enough so it becomes a black hole?

My chain of thought is the following: To push together two charges of the same sign you need to do work. The energy spent will be turned into electrostatic potential energy. Can we pump so much ...
8
votes
2answers
88 views

Two charged black holes in equilibrium

Consider a pair of (possibly rotating) charged black holes with masses m1, m2 and like charges q1, q2. It seems that under certain conditions gravitational attraction should exactly cancel ...
1
vote
2answers
112 views

Pumping charged particles (of same charge) into a blackhole

Would would happen if you started pumping charged particles of same charge into a black hole? Let's assume that you have an infinite number of those charged particles. What will happen to the event ...
2
votes
0answers
38 views

Consistency of atomic magnetic dipole spatial orientation with Stern-Gerlach picture of electrons

I've been recently trying to understand the concept of paramagnetism, but I feel like I'm running into 2 conflicting models. Stern–Gerlach seems to suggest that electron spins always point up ...
0
votes
1answer
40 views

What happens when a magnet is dropped through a solenoid with a current running through it?

I know when a magnet is dropped through a copper tube or a copper solenoid it induces a current in the copper and the magnet actually slows down as it falls through the tube, but if I did this with a ...
12
votes
3answers
5k views

Is it possible to kill a human with a powerful magnet?

I'm asking in terms of physics. Can powerful magnetic induction rearrange spins of my body in such way I will die? How? Or maybe it can rip all iron from me, which would make my blood cells useless? ...
2
votes
1answer
34 views

How to properly apply Ampere's Law in this case?(Square Loop)

Suppose ABCD is square loop (conducting). There is a wire carrying a current $I$ into the plane of paper within the region of loop. So how to properly apply Ampere's Law in this case? The closed ...
2
votes
1answer
139 views

What is the difference between emu and esu?

Ok...so this is the statement given in my book: a) In C.G.S System the unit of charge is electrostatic unit of charge (E.S.U). It is also called Stat Coulomb (StatC). b) In C.G.S system, the unit ...
1
vote
1answer
55 views

Electricial impedance - why does it work?

I learn electricity from Purcell's book. Analyzing AC circuits is easier with complex numbers. I understand you have to replace the regular representations with those containing complex numbers ...
-2
votes
0answers
31 views

Plane wave propagation [closed]

Can anyone help me please understand how this is done? and whats epsilon ? many thanks
-5
votes
0answers
29 views

research and development guidance [closed]

Ramaswami writes about a powerful electromagnet that he has made. He mentions that the copper wire needs to be thick. I have questions regarding the electromagnet he has made. How thick is the copper ...
0
votes
1answer
32 views

main cause of self charging of unshorted capacitors?

In the lab, we keep all of the high voltage capacitors shorted when not in use, and rightfully so. They tend to spontaneously charge when left for some time and become extremely dangerous. while the ...
0
votes
2answers
35 views

Electric field of uniformly charged plane

Which are the null components (in a Cartesian coordinate system) of the Electric field of uniformly charged plane in $x=0$? I consider the coordinates : $(x,y,z)$ I think that $E_x = 0$, $E_y \ne 0$, ...
2
votes
2answers
3k views

The electric field of a conductive sphere containing a charge - grounded vs not grounded

Let's suppose we have a sphere but unlike theoretical ones it'll have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge $q$ ...
0
votes
2answers
35 views

Need for pulsed laser [closed]

Pulsed laser emit light in non continuous mode.How this makes it superior to cw laser? Why there is need in reducing the time-lag between the pluses of pulsed laser.
0
votes
1answer
38 views

Possible reasons of electrocution in a good earthed appliance during sudden power off [closed]

I was working in a industry. When I was using a machine, I felt slight electrical shock at the exact moment when the power supply went off. The machine is properly earthed. In spite of that I got ...
1
vote
1answer
927 views

Forces on a wire moving in a magnetic field?

When a wire is placed inside a magnetic field and current starts to flow in that wire, that wire experiences the Lorentz force = $IL \times B$ and beings to move. Aside from induced motional - $\...