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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11 views

Could a civilisation contact us by laser from 50 light years away?

The Kepler Space Mission has discovered over 1,000 planets. These discoveries may increase the confidence of some people that other civilisations exist. This however, is an opinion issue, and not ...
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0answers
22 views

Reason for strange magnetic ball movement

I was playing with a set of those neodymium magnet spheres and noticed a couple of strange behaviors (which I believe are related so I'm only positing a single question) and I was hoping to get an ...
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0answers
20 views

Verification of Lenz's law in magnetic induction

So the device is a Galvanometer. According to the Lenz's Law, when we take the magnet towards the coil, the pole at the right end, should be north pole and when we take it away, the pole should be ...
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5answers
676 views

Why does optical pumping of Rubidium require presence of magnetic field?

The optical pumping experiment of Rubidium requires the presence of magnetic field, but I don't understand why. The basic principle of pumping is that the selection rule forbids transition from ...
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0answers
42 views
+50

Two induced EMF's from separate magnetic fields opposing each other with an odd change in B?

A conductor in case 1 has two separate uniform magnetic fields $B_1$ & $B_2$: The magnetic fields(the blue rectangles are the field regions parallel to the conductor, while X's are the field ...
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3answers
968 views

Why don't photons split up into multiple lower energy versions of themselves?

A photon could spontaneously split up into two or more versions of itself and all the conservation laws I'm aware of would not be violated by this process. (I think.) I've given this some thought, and ...
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0answers
12 views

About to purchase a 3d-printed Keppe Motor Kit for art project - what should I test for?

I'm about to apply for art-grants in order to purchase a educational student toy called a 3d-printed Keppe Motor Kit. Says on their page "Designed with educators and students in mind".. So.. It is ...
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1answer
32 views

Fleming's right hand and left hand rule

Why are there two rules: Fleming's left hand and right hand rules? What is the difference between the two and why can't we use just one rule? Suppose the magnetic field is from right to left and ...
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1answer
188 views

Right hand rule confusion

I have a question that I am trying to figure out: Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions. The wire on your right ...
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5answers
963 views

Intuitive definition of electromagnetic field

I am curious about the following: Checking about what is an EM field in wiki it says: An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged ...
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3answers
53 views

Why is Kirchhoff's second law commonly used for circuits involving inductivity?

I have often seen in introductory literature, e.g. for the activation process of a circuit with a power source which delivers the voltage $U$, current $I$, resistance $R$ and an inductivity $L$, that ...
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2answers
191 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 ...
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8answers
6k views

Is gravity just electromagnetic attraction?

Recently, I was pondering over the thought that is most of the elementary particles have intrinsic magnetism, then can gravity be just a weaker form of electromagnetic attraction? But decided the ...
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1answer
194 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 ...
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2answers
58 views

Explanation for: A monopole antenna must contain a resistor (or equivalent) and therefore must have 2 terminals?

Could someone explain why this sentence makes sense: A monopole antenna transfers energy from electrical domain to the electromagnetic domain, hence must contain (equivalently) a resistor, hence ...
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0answers
16 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
77 views

Dyon condensation and generalized Meissner effect

In section 2.B of Metlitski and Vishwanath's paper: "Generally condensation of a dyon with charges $(q,m)$ gives rise to an analogue of a Meissner effect for the gauge field combination ...
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0answers
18 views

Books on Hall integrated circuit (IC)? [on hold]

Can anyone suggest a good reading on Hall integrated circuit that is used in practicals on magnetism?
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0answers
14 views

Magnetic field due to closed donut [on hold]

How to find magnetic field due to a torroid? Thanx in advance. Im studying for jee and our prof tried to teach it but i didnt understand.help please
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0answers
20 views

Unable to solve cable theory equation correctly [on hold]

First time posting, let me know if I'm in the wrong board. I tried this over on the math board and was redirected here. In my spare time I enjoy reading outside of my field (software development). ...
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2answers
489 views

What is the mechanism by which magnetic fields do work?

I've seen some conflicted answers to this question in texts and on the web, in the case of a dipole, for example. Do magnetic fields do work directly, or is it their induced electric fields that do ...
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2answers
678 views

How do magnets work?

I've read a classbook on the field theory (including EM): it perfectly describes quantitive patterns in EM-theory, but I have no luck understanding how and why it works. I mean, magnetic substances ...
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2answers
142 views

Does a magnetic field sustain a current in a loop?

A particular current produces a constant particular magnetic field. If the fact holds under scrutiny, why doesn't a magnet held within a loop sustain a particular current? Are the electron spins ...
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2answers
853 views

If you are carrying a magnet, can you tell when you cross the event horizon of a black hole?

By the no hair theorem, a black hole is completely characterized by it's mass, charge and angular momentum. Therefore dipole and higher pole magnetic fields are completely expelled when a black hole ...
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0answers
8 views

Experiment measuring vacuum permittivity and permeability in high speed

Suppose that we do NOT know anything of constancy of speed of light, to say nothing of special relativity. It is that we acquired a constant speed of light from Maxwell's Equations that we finally ...
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0answers
6 views

Magnetic field lines for perpendicular current carrying wires [on hold]

Given two straight current carrying conductors, carrying the same current I kept perpendicular to each other. What would the magnetic field lines look like?
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4answers
4k views

Is the Keppe Motor “real”?

Its makers say that it's a highly efficient motor because it resonates with (what they call) "Essential Energy", which is free energy that is everywhere in space. (I think that’s just a different name ...
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2answers
450 views

Electric field from current without Maxwell's law of induction

A long, straight wire carries a current that decreases linearly with time. What is the direction of the induced electric field outside the wire? I would interpret this as follows: a current ...
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1answer
28 views

Do you know any graphing software for graphing equipotential lines? [on hold]

well, do you know any software for graphing equipotential lines? I only know how to graph straight lines :( Thanks for any information.
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1answer
146 views

Why do electron and hole mobilities decrease with temperature?

From page 35 of "Microelectronics" by Millman Grabel Mobility $\mu$ decreases with temperature because more carriers are present and these carriers are more energetic at higher temperatures. ...
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2answers
86 views

What are diamagnets and paramagnets?

A paragraph in my text reads: An atom or ion with all electrons paired is not attracted by strong magnets and is termed 'diamagnetic'. In contrast, spins do not cancel when unpaired electrons are ...
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1answer
166 views
+100

What are the characteristics of light entering a disk spinning at near $c$?

If I were to spin a translucent disk so that the edge is spinning at .9c and shoot a laser beam at it perpendicular to the edge, what would happen to the light as it travels in one end of the disc and ...
0
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1answer
43 views

What makes B-field not be arbitrarily large very close to an electric conductor?

Assume an inifinitely long, straight thin electrical conductor with current I. It follows from Ampere's law that the B-field intensity is proportional to 1/r, where r is the distance from the ...
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0answers
20 views

$\vec{E}$-and $\vec{B}$-fields in RCL circuit from Maxwell equations

Consider a basic RCL-Circuit consisting of an ideal resistor, an ideal capacitor and an ideal inductor in series. How do the $\vec{E}$- and $\vec{B}$-fields look like in dependence of the time? I ...
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1answer
2k 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. ...
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1answer
61 views

Why are GPS transmitting signals made so weak?

Twice this year, my car's GPS receiver got totally lost. It seemed the cause of this was heavy cloud, (because I can't think of any other reason), and the GPS stayed in "Recalculating" mode, until ...
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0answers
19 views

how much voltage and current require to pull 5 kg load by electromagnet? [on hold]

I made 600 coil turn electro magnet area of electro magnet 2.235 m square. I want pull nearly 5 kg load distance between load and electromagnet is 40 mm. So how much current and voltage required??? I ...
13
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5answers
654 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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2answers
41 views

Motion of electron and proton in semi infinite magnetic field?

An electron and a proton are moving on straight parallel path with same velocity. They enter a region of semi infinite magnetic field perpendicular to velocity. What will happen there? Will both of ...
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0answers
24 views

effect of earth's magnetic field on period of pendulum [duplicate]

I want to know will earth's magnetic field change period of pendulum if pendulum is made up of- 1. ferromagnetic material 2. paramagnetic material.
3
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1answer
240 views

Could the Faraday's rotating wire experiment be explained without using Lorentz force?

I read Faraday's rotating wire experiment which resulted in the invention of the homopolar motor. He was clever enough to think it that way and make the wire rotate around one of the poles of the ...
2
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0answers
26 views

What is the pressure of a charged gas?

I have $N$ ${\rm H}^+$ gas molecules in a sealed, electrically insulated container. What equation can I use to accurately calculate the pressure of the gas? It seems to me that $PV = nRT$ will not ...
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3answers
231 views

Can you stop an electron in vacuum?

If we shoot an electron in vacuum tube, then stop it with electromagnetic field, and switch off the field, what will happen with electron? Will it continue its movement? If there is a gravitational ...
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2answers
49 views

Is the electrostatic field really static? Does thermal vibrations not affect it?

We know that if a conductor has any net charge, the charges reside on the surface. The electric field immediately outside the surface is perpendicular to the surface. But the charged particles, say ...
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1answer
25 views

Why is there longitudinal conductance in a partially-filled Landau level?

Suppose I consider an infinite, non-interacting (so no FQHE should happen) 2DEG in the magnetic field $\vec B=B\hat z$ with a non-integer filling factor, say 0.13 or whatever. Suppose I apply an ...
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2answers
47 views

How to determine the angular velocity of a particle with mass $m$ and charge $q$ in a constant B field? [on hold]

$\textbf{PROBLEM:}$ A particle with mass $m$ and charge $q$ moves in a constant magnetic field $B$. Show that, if the initial velocity is perpendicular to $B$, the path is circular and the angular ...
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1answer
47 views

Why in electrostatics is dV=-E.dr but in electromagnetic induction, EMF=+E.dS?

In electrostatics we learned that dV=-E.dr. I understood the derivation which was used to derive this. Now when I have come to Electromagnetic Induction,I see that when there is a time varying ...
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0answers
16 views

The induced electric field of an infinite current carrying wire

I am given, without motivation, that the induced electric field from an infinite, straight, current carrying wire is parallel to the wire itself. $$ \vec{I} \times \vec{E}_{\text{induced}} = ...
3
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1answer
131 views

How can Drift Velocity of an electron causes change?

Assume we have a conductor that has current flowing and its placed in a magnetic field so that it experiences the Lorentz force, and it gains Kinetic energy due to that force. Would drift velocity ...