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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17 views

Are neutrinos affected by electromagnetic forces?

I know they don't interact with matter nor any electromagnetic forces, but I know they have mass, very little mass but they have. When something has mass it must be attracted by gravity and other ...
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2answers
18 views

Why does electromagnetic induction creates both voltage and current but static electricity only creates voltage and no current?

Why is it that electrons do not move the same way in triboelectric as in magnetic induction when both creates voltage? Triboelectricity can even create tens of thousands of volts like Van De Graf ...
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0answers
38 views

Sum rule and dense limit

Is the finite size of lattice constant important for derivation of sum rules, for example, the sum rule for diagonal conductivity $\sigma_{xx}$: $$ \int \limits_{-\infty}^{\infty} ...
1
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0answers
57 views

World's Largest Radio Telesope : How accurately does it need to be figured?

In Guizhou Province, China, the worlds largest radio telescope is almost complete, measuring 500 metres across. I am aware that todays largest optical telescope require very accurate figuring and ...
-3
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0answers
33 views

Is the magnetic field caused by the lenght contraction, as seen by us, in the frame of a fast moving charged particle?

If for example an electron moves very fast relative to us, then the length contraction as seen by us, causes the electric field lines to compress themselves in the direction of motion. Is this the ...
3
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1answer
51 views

Schrödinger-Pauli Equation Solutions

The Schrödinger-Pauli equation is the non-relativistic limit of the Dirac equation, and therefore describes spin-1/2 particles in an external electromagnetic field. It is given by: ...
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0answers
28 views

Confusion with calculating electric potential [on hold]

V = kQ/r I understand that this equation is a product of electric field and the distance through which the electric force acts, to calculate electric potential. Is not electric field non constant ...
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0answers
18 views

Magnetism and straight conductors [on hold]

Through two long, parallel straight conductors gårströmmarna 3.0 A and 2.0 A, as illustrated below. The distance between the wires is 4.0 m. Is there a point where the flux density is zero? Where? ...
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0answers
16 views

How to derive torque from a velocity dependent potential? [on hold]

In Jackson's Classical Electrodynamics, the rate of change of the angular momentum of the electron in its rest frame in constant external electric field $\textbf{E}$ and magnetic field $\textbf{B}$ is ...
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0answers
13 views

Variation of spin in the rest frame of an electron in an external magnetic field

In Jackson's Classical Electrodynamics, the equation of motion for the angular momentum $\textbf{s}$ of an electron in an external magnetic field is given by (eq. 11.101) ...
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1answer
23 views

If $T_{kl}=\epsilon_{kil}m_i$, how to show $m_i=0.5\epsilon_{ilk}T_{lk}$? [on hold]

In a book I am reading (about magnetic dipole), it is given that $T_{kl}=\epsilon_{kil}m_i$. Then, it says since $T_{kl}=-T_{lk}$, it can be shown that $m_i=0.5\epsilon_{ilk}T_{lk}$. I understand that ...
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1answer
20 views

Calculating the B flux density of a flat spiral coil with N turns

Consider the following topology for a flat spiral coil (with an air gap in the middle). It's been a very long time since I have used Maxwell's Equations and now I find myself trying to figure out the ...
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0answers
18 views

Magnetic field between 4 wires with the same current

if I have 4 long wires with a current I and all of them have the same distance from each other (looked at from the front you'd have a square) shouldn't the magnetic field vanish in the middle of all 4 ...
1
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1answer
35 views

Rewriting Maxwell's equation in tensor form [on hold]

Suppose $F_{ij}=\epsilon_{ijk}B_k $, how to prove the following: $\partial_iB_i=0$ becomes $\partial_iF_{jk}+\partial_jF_{ki}+\partial_kF_{ij}=0$ $B_iB_i$ becomes $F_{ij}F_{ij}/2$ I can see that ...
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1answer
30 views

Is it possible that propagation of acustic waves leads to emission of radiation?

Question: Consider large cloud of gas. Assume it is electrically neutral (but as always, matter is composed of smaller things which are actually charged). Is it possible that propagation of sound ...
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1answer
22 views

Induced current in a rectangular loop [on hold]

The question is How much heat is generated in the resistor during the loop's entire path into and out of the magnetic field? Give your answer in J. I used Faraday's law and managed to get the ...
-1
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0answers
11 views

Type of motion when a long wire carrying current is inserted between two wires carrying current is moved normal to its length [on hold]

Two long rigid wires separated by a distance d and placed parallel, carry current I in the same direction. Determine the force developed . Now a third wire is placed in between the rigid wires keeping ...
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0answers
32 views

How do I determine the information needed to design a solenoid electromagnet that can ionize a gas? [on hold]

I have been trying to answer this question for a long time. I watched a video where a person used a solenoid to heat up aluminum till it became a liquid. I want to apply this, to a gas. I want take ...
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1answer
38 views

Correct Definition of Angular Momentum of a Charged Particle in an Electromagnetic Field? (Classical Mechanics) [duplicate]

What is the more correct definition of angular momentum $\vec{\mathbf{M}}$ in three dimensions? (I.e. classically/Lagrangian/Hamiltonian, not necessarily quantum or relativistic) ...
3
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1answer
63 views

Can the Biot-Savart law be derived from QED?

It's important that a new theory of physics contains the equations and results of previous related ones. Maxwell theory and QED both have explanations for electromagnetic phenomena so I'm wondering if ...
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1answer
30 views

A Formula for the Phase Difference Between the Electric and Magnetic Wave Oscillations?

A) Is there a formula for the phase difference between the electric and magnetic field oscillations, in vacuum, in an electromagnetic wave emitted from an antenna, as a function of the frequency the ...
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0answers
20 views

Does a cathode ray tube emits electromagnetic waves from a steady DC electron beam?

In cathode ray tube, heated cathode emits stream of electrons but when I wrap a coil around tube a current will be inducted in that coil? after all electron beam is a steady DC current? so no emf?
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0answers
39 views

Can someone explain me magnetic potential? [duplicate]

I don't understand why we can write the magnetic field as a potential vector A, and what exactly this potential is. Is it just a mathematical thing? And how can it help me calculate the magnetic ...
6
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1answer
115 views

Why is U(1) the gauge group in classical electromagnetism?

Can anyone give a physical reason that $U(1)$ is the gauge group for classical electromagnetism? I am familiar with the principal bundle formalism for Yang-Mills theory and see that since the Lie ...
2
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2answers
22 views

Should static electricity affect a Crookes radiometer?

I've been playing around with a Crookes radiometer for fun and I happened across something I can't figure out. I know the fundamentals of the radiometer (e.g. partial vacuum, thermodynamics, etc.), ...
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0answers
32 views

why was necessary the discovered of electromagnetism? [on hold]

Need to know much more for the necessity of electromagnetism. http://www.ck12.org/physical-science/Discovery-of-Electromagnetism-in-Physical-Science/lesson/Discovery-of-Electromagnetism-MS-PS/
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0answers
38 views

Eigenstates of 2D harmonic oscillator in a constant magnetic field

I want to find the eigenstates of the 2D harmonic oscillator in a constant magnetic field $\vec B = \vec B(x,y)$. My Hamiltonian reads $H_0 = H_{xy} + H_z$ where $H_{xy}$, is the hamiltonian of the ...
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0answers
22 views

A bar magnet is brought close to, but does not touch, a paper clip [on hold]

The paper clip moves toward the magnet. What does this observation show about the field associated with the bar magnet?
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0answers
32 views

What is r-r' in spherical polar coordinate and cylinderical coordinate? [on hold]

In solving Vector equations in Physics like Electric field and Magnetic field. $$E=\frac{1}{4\pi\varepsilon_0} \int\frac{\rho(r')\hat{\mathcal{R}}}{\mathcal{R}^2}d\tau'$$ $$B=\frac{\mu_0}{4\pi} ...
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0answers
17 views

what is the reaction force of electromagnetic force created on a conductor in a magnetic field? [on hold]

If a force is created on a conductor carrying a current in a magnetic field, what does the reaction of this force act on?
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0answers
49 views

Could a photon also be a fermion? [duplicate]

Some phycisits have found photons that has a spin of 1,5. Now fermions has always a half spin and bosons like photons always with a whole spin. But if those photons really exists are they than ...
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1answer
34 views

Can a flow of current be produced in a wire if its is bombarded with Electromagnetic waves?

If you have a conducting wire and you bombarded it with EM waves, is there a frequency (lower then the threshold frequency to liberate the electrons) that would induce a current within the wire. I ...
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1answer
28 views

What causes a charged particle to follow circular motion in a magnetic field? [duplicate]

I would like to know why particles follow a circular path in a magnetic field, what path they trace and how this path is measured and controlled?
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4answers
95 views

How do light waves get their size?

An atom or (small) molecule has the size of about 100pm. Elektromagnetic waves range from about 0.1nm up to 1 km. The most common way waves (like light) are caused by 'jumping' electrons to another ...
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0answers
17 views

The effects of multi-stranded wire on magnetic field strength

If I were to make a solenoid (with an air core) out of stranded copper wire- say for instance 8 strands- would this effect the magnetic field strength compared to, say, a solenoid with a single stand ...
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1answer
29 views

What happens when an electromagnetic wave passes through a magnet or charged capacitor?

What are the effects or interactions between propagating electromagnetic wave that passes through static magnetic field (big neodymium magnet) or static electric field (charged plates of HV ...
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1answer
49 views

Why do some stars become end up as black holes? [closed]

The answer involves the gravity and the internal pressure within the star. These two things oppose each other -- the gravitational force of the star acting on a chunk of matter at the star's surface ...
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0answers
33 views

Determine potential function given initial conditions?

Assuming a radially symmetric circular disk (let's say r=1). Given two simple initial conditions: Potential at the centre is 4 V Potential at the edges is 0 V How would I determine the potential ...
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0answers
40 views

What are Black holes exactly? [closed]

A Black Hole is a very large rip in the atmosphere that opens after to many shuttles have traveled into space. It happens after about 5 million years of shuttles traveling in and out of spaces ...
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1answer
83 views

Electrons motion

Some days ago, I was reading a very simple text about photoelectric phenomenon (at high school level) that this question came to mind. How do electrons move (for example during their translation from ...
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1answer
50 views

Relativistic transformation of electrical current [on hold]

If, in frame $S$, we have an electrically neutral wire with some current $I$, modelled as positive charges moving in $x$ direction and negative charges moving in $-x$ direction, then how would one ...
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0answers
26 views

Does more electromagnetic mass means more electric field is given out? [closed]

Does a moving charge give more electric field since it has more electromagnetic mass ? Or Let I have a moving charge with speed 0.9c. kinetic energy hence gained is $m0.81 c^2$. Total energy of ...
-1
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0answers
27 views

Foce experienced by charge in a fluctuating magnetic field [closed]

A charge moving in a magnetic field experiences a force given by qv x B where q is the charge v is the velocity of the charge B is the magnetic field and x denotes the cross product. This is the ...
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0answers
42 views

Antimatter in the solar system, Charge of the sun, and Annihilation

Since the sun is creating a lot of helium at once, and one of the protons has to undergo beta plus decay, Shouldn't there be at least a little bit of antimatter orbiting the sun? I know most of the ...
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0answers
30 views

Dynamic energy of capacitors in circuit

If I have 3 capacitors and 1 battery in a circuit how should I connect them in order to have maximum dynamic energy, when I connect them with the battery? Parallel or in series?
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0answers
240 views

Galactic binary engine found in the center of the Milky Way? [closed]

It is accepted science that Sagittarius A* is the black hole in the middle of our galaxy, and motion measurements of Sag A* show that it is more or less stationary relative to our Sun, so why would ...
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0answers
32 views

Feynman's paradox : “conservation of angular momentum or Lenz's law ?” [duplicate]

When I was in high school, out of my interest I read electro-magnetism topic from Feynman's lecture on physics. There was a Paradox question in that topic, answer of which i am seeking here... Below ...
3
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1answer
121 views

What does a voltmeter actually measure?

For time varying fields (even quasistatic ones) the electric field is given by $${\bf E} = - \nabla \Phi - \frac{\partial {\bf A}}{\partial t}$$ So what does a voltmeter measure? Does it measure a ...
4
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2answers
45 views

Why does an oscillating electric field couple more strongly to electrons than to ions?

As stated in Principles of Plasma Discharges and Materials Processing, by M. A. Lieberman and A. J. Lichtenberg, about capacitively coupled plasmas: (...) the light and heavy charged particles in ...
0
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1answer
31 views

Electric field inside an insulator's cavity [closed]

I'm trying to find the electric field inside insulating sphere's cavity, and I don't know how. However, if there was an conductor I'd know that $E=0$ from Gauss's Law.