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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31 views

Compensating Parallax problem of a washing machine's drum [on hold]

We would know how it is possible inside a washing machine, when the drum is full with garments, so it is very heavy, to compensate, when the drum is rotating at high speed for the parallax of rotation,...
2
votes
1answer
147 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 ...
1
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1answer
59 views

Reflectivity and transmissivity greater than 1

In plasmonics, it is often seen that reflection coefficient and transmission coefficient are greater than 1. How is energy conservation valid in such cases?
16
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6answers
7k views

Is it possible to project a magnetic field at a location in space?

A magnetic field strength drops-off quickly as the distance from a magnet increases. Is there any way to use electromagnetic fields to create a magnetic field at a location. For example, if there are ...
5
votes
2answers
594 views

Does a Faraday cage block outgoing signals?

I see lots of discussions about how a Faraday cage can block EM signals, but almost no one addresses the possible difference between incoming signals versus outgoing signals. It seems to me that those ...
4
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3answers
76 views

Why do magnetic coils consist of many thin wires?

Magnetic coils are usually made of thin wire turned into spring shape: Magnetic field which is generated by this solenoid is proportional to the number of turns N...
16
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8answers
10k views

Why no longitudinal electromagnetic waves?

According to wikipedia and other sources, there are no longitudinal electromagnetic waves in free space. I'm wondering why not. Consider an oscillating charged particle as a source of EM waves. Say ...
1
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2answers
773 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!!!
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0answers
46 views

High School Physics-Electromagnetism [on hold]

An insulated smooth square frame ABCD of side $a$ is able to rotate about one of its side taken as positive axis. The plane is initially located at x-z plane. A magnetic field present in the region ...
6
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4answers
9k views

Does a magnetic field arise from a moving charge or from its spin, or both?

I learned that a moving charge creates a magnetic field perpendicular to its direction of motion. I also learned that charged particles like electrons have spin and they also create a magnetic field ...
-5
votes
1answer
57 views

Why can't rotating magnets in space or zero gravity be used to create infinite energy? [on hold]

I would like to know if a system like the one below will possibly work. I understand that the laws of physics forbid the "creation" of energy but despite my efforts I haven't been able to figure out ...
0
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2answers
3k views

Landau Levels and Magnetic length

I am looking into Landau Levels and keep coming across a magnetic length defined as follows for a 2D system: $l_B=\sqrt{\frac{\hbar c}{e B}}$ I have seen numerous sources say this is: $l_B\approx ...
1
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2answers
36 views

Could a strongly enough charged black hole allow for a strongly charged particle to escape the event horizon?

If there is a strongly charged black hole, and a particle with a strong charge of the same sign goes inside of the black hole's event horizon while moving quickly, is there a reason why it would not ...
0
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1answer
45 views

Photons inside laser cavity

In a laser, the pumping mechanism excites an electron to a metastable state. This electron remains in the metastable state for a longer time and is de-excited to the ground state by emitting photons (...
5
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2answers
2k views

What role does electrical charge play in black holes?

Not having studied General Relativity, I have sometimes been puzzled by references to the behaviour for "classic" black holes — as they are popularly portrayed — as being true for black ...
6
votes
3answers
717 views

How to find the direction of an eddy current?

Suppose there is a magnetic field going from left to right. Suppose a thin sheet of metal conductor (e.g. a 1m*1m square) is dropped through the magnetic field such that the plane of the conductor is ...
1
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2answers
66 views

Can neutrinos interact by the EM interaction and gravity?

A definition of a lepton is: A particle that does not interact by the strong force but does by the 3 other forces.$^1$ Neutrinos are leptons, so from the above definition one would expect it to ...
1
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0answers
21 views

Spikes and valleys of ferrofluid

I can understand that the spikes are formed because of the elongation of the ferrofluid due to the difference in forces experienced by the two ends of the particle. But I can't understand why there is ...
1
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0answers
24 views

Is there theoretical description of such plasmonic nanostructure?

I'm preparing a research about plasmonic nanoparticles and I'm interested about their arrays placed above a metallic film (like on the picture). Until now i found following articles: pubs.acs.org/...
3
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1answer
5k views

Optical constants of noble metals: the Drude model for microwave modelling

I have a question regarding the optical constants of noble metals. According to Johnson and Christy's paper Optical Constants of Noble Metals (Phys. Rev. B 6, 4370–4379 (1972), doi:10.1103/PhysRevB.6....
0
votes
1answer
38 views

Any good electricity and magnetism books for highschool students? [duplicate]

I really want to learn about electricity and magnetism for a long time but never have gotten to it, are there are good books that are conceptual on the topic of electromagnetism? I do not know ...
0
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1answer
38 views

Split up electromagnet coil, put in parallel.Why doesn't anyone do that?

If the goal is to make a strong electromagnet, wouldn't it be wiser to cut the coil in different sections and then connect them to a power source in parallel? total of 2k turns: (+)--- <- 1k -----...
1
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1answer
28 views

Why is the electric field perpendicular to a circuit zero?

Griffith briefly addresses the uniformity of the electric field in a wire using Laplace's equation by assuming that the electric field is always parallel to the wire (i.e. $\mathbf{E}\cdot\hat{n}=0$). ...
5
votes
1answer
129 views

A “figure-8” EM field created by a dipole antenna

This question pertains to the EM field of a Pulse W5017 dipole antenna. The data sheet of this antenna can be found here (which contains information regarding the radiation patterns). There are TWO ...
3
votes
1answer
141 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 ...
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2answers
55 views

Possiblity for particle to be carried by a wave such as a photon or electromagnetic wave/waves in general for means of transportation/travel? [closed]

I am wondering whether it is possible for a photon/EM wave to carry a very small particle like an elementary particle or smaller on it like a highway carries a car traveling on the highway or an ocean ...
0
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0answers
22 views

Efficient weak form for numerically generating a static magnetic field from arbitrary current distribution (FEM)

This may stray into computational physics, but I'm curious to know if there is some more efficient way for what I am trying to do. Perhaps a better gauge formulation is needed. Consider two ...
0
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0answers
32 views

How to understand method of images in electrostatics without much maths

How do you explain Method of images for school students without much maths i.e without boundary condition or uniqueness theorem. If it's not possible what are the rules to be followed to solve ...
2
votes
3answers
469 views

What is the relationship between the magnetic units oersted and tesla?

How are the units oersted and tesla related? For example, how would you express $20\:\mathrm{Oe}$ in tesla?
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2answers
70 views

Why don't electrons moving around in a orbit produce electromagnetic waves in their natural state? [duplicate]

If moving electrons produce changing electric field, and if changing electric field produces magnetic field, every electron must produce an electromagnetic wave. This means an atom in its natural ...
1
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1answer
31 views

Can this physical quantity be simplified into a smaller form?

I have a quantity I call fake current. $$ I' = \frac{\mathrm{d} \oint \nabla \mathcal{E} \cdot \mathrm{d} \vec{A}}{\mathrm{d} t} $$ Current is: $$ I = \frac{\mathrm{d} q}{\mathrm{d} t} $$ Charge ...
3
votes
0answers
40 views

Why do we assume electromagnetic fields to be doubly differentiable? [duplicate]

It seems like the identities of curl of gradient, divergence of curl, and the simple derivations of electromagnetic waves from Maxwell equations all rely on the symmetry (interchangeability of their ...
2
votes
2answers
233 views

Scalar and Vector Potential

I am a physics undergraduate student currently studying electromagnetics. I have previously studied electrostatics and magnetostatics yet the concept of scalar potential, $V$ and the vector potential, ...
8
votes
4answers
278 views

A contradiction between Biot-Savart and Ampere-Maxwell Laws?

I came across a problem that I cannot get my head around. Consider two very small spherical metallic balls given charges +Q and -Q. Assume that they can be approximated as point charges. Now, they ...
0
votes
1answer
16 views

What is conductive half space in the context of electromagnetics?

What is conductive half space in the context of electromagnetism? I was looking into skin effect, where the author has used half space of a cylindrical conductor. But I am lost on what it means.
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0answers
35 views

Question about electric flux [on hold]

Question: Suppose a point charge is located at the center of a spherical surface. The electric field at the surface and the total flux through the sphere are determined. If the radius of the sphere ...
2
votes
2answers
143 views

Reference frequency

In my experiment, I have to obtain a relation between magnetic field of a solenoid and the applied Vp-p. The setup is as follows. http://www.teachspin.com/instruments/faraday/ Does my choice of ...
4
votes
3answers
148 views

Minimum frequency of an electromagnetic wave

Is it possible to create an electromagnetic wave of near zero frequency? An electromagnetic wave carries energy. If we can make the frequency of an EM wave vanishingly small and make it practicality ...
0
votes
1answer
337 views

Magnetic field inside of a long rotating cylinder

I have a simple question. I need to find out what is the magnetic field inside a rotating long cylinder with a charged density $\sigma$. The cylinder rotates around its axis with angular speed $\...
6
votes
1answer
135 views

What force causes the induced EMF of a loop? And, the difference between a loop EMF to motional EMF?

If a loop of wire is placed perpendicular to a changing magnetic field, there is an induced EMF such that the induced current is flowing in a direction to create an opposing magnetic field like this ...
0
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0answers
20 views

Can Fluctuation-Dissipation Theorem Apply to Magnetic Forces in Multi-Spin Systems

Let's say I have multiple spin systems (atoms in a protein) in a solution of water and the spin systems are all producing a magnetic field $\mathrm{B_{loc}}$ that affects nearby spin systems. Will the ...
1
vote
1answer
81 views

Fusion plasma compression with liquid metal

General Fusion plans to use an imploding shockwave of molten lead to compress a magnetized plasma "spheromak" target in order to make it burn more efficiently. How come the lead does not quench the ...
62
votes
6answers
7k views

If like charges repel, why doesn't a charge break itself apart?

How can it be that, if like charges repel, they don't repel themselves? In other words, why don't charges break apart? About the possible duplicate: I want to know about charges in general, not ...
0
votes
1answer
260 views

Can the intensity distribution behind edges and slits be explaint by the interaction with the surface electrons of the edges?

Reading about diffraction of EM radiation on edges, slits and multi slits as well as about electron diffraction behind a wire I came to the conclusion that the intensity distributions on an observers ...
2
votes
2answers
253 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 ...
0
votes
2answers
387 views

Magnet dimensions for 3-phase permanent generator

I'm making a 3-phase permenant generator. According to Faraday's law, the emf produced is negative number of turns times the change in magnetic flux over the change in time. If it is only the CHANGE ...
-2
votes
1answer
67 views

Why a homogeneous magnetic field will not deflect neutrons? [on hold]

According to the comments below the answer of the question about Experiments with Alpha particles in a homogeneous magnetic field an inhomogeneous magnetic field will deflect neutrons. Why a ...
1
vote
1answer
104 views

Modeling magnetic field shielding

I am wondering what is the best way to model magnetic and electric field shielding from a magnetic dipole in the near field? For example, let's say you have a coil of current carrying wire in the x-y ...
-1
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0answers
28 views

I live close to high tension wires and also the rail lines over stevens pass wa. i constantly hear a pulsing hum and feel a vibration [duplicate]

I live very near high tension wires and the railway over Stevens Pass WA. I constantly hear a pulsing hum and feel a vibration could one of theses thing be the cause?
2
votes
3answers
200 views

What symmetry gives you charge conservation?

This is a popular question on this site but I haven't found the answer I'm looking for in other questions. It is often stated that charge conservation in electromagnetism is a consequence of local ...