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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Does changing a closed surface in the manner outlined contradict Gauss' Law?

As I understand it, Gauss' Law states that the electric flux on any arbitrary closed surface is equivalent to the sum of all charges enclosed within the surface times a constant. Mathematically, this ...
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0answers
30 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
16 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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2answers
113 views

What is $\epsilon_\infty$ in this equation and why can it be neglected in the IR?

I'm reading this paper (warning, PDF) and they mention that the complex permittivity $\epsilon$ and complex conductivity $\sigma$ are related through the equation $$\epsilon - \epsilon_\infty = (4\pi ...
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2answers
60 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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1answer
21 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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2answers
335 views

How does back-emf oppose the input-current?

A circuit, has current $A$ flowing at a certain $V$. When there is a change in magnetic-flux, based on Faraday's law of induction & Lenz's law, we know that there is change in Potential ...
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1answer
47 views

Relativistic transformation of electrical current

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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1answer
174 views

Two concentric conducting shells connected by wire with modified Coulomb law?

This question is related to this one, but is a bit different. Consider two concentric and conducting spherical shells connected by a wire. Inner shell has radius $b$ and (unknown) charge $q_b$ while ...
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0answers
15 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
46 views

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

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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2answers
184 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 ...
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1answer
22 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
112 views

Motion of Thompson's jumping ring

Thompson's jumping ring experiment is set up as follows: There is a force acting on the ring $F(x)$ where $x$ is the vertical displacement. The force is due to the $90^\circ$ out of phase flux ...
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4answers
6k views

What is the difference between electromagnet and solenoid?

What is the difference between electromagnet and solenoid? Both these terms seem as the same thing to me. The only difference that I can find seems to be that an electromagnet contains a soft iron ...
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4answers
636 views

How would you define electrostatics and magnetostatics starting from Maxwell's equations?

I'm reading Griffith's text, and he starts by defining Electrostatics as requiring the source charges don't move. I've seen a few slightly different definitions of electrostatics and magnetostatics. ...
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0answers
29 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
36 views

What are Black holes exactly? [on hold]

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
76 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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0answers
207 views

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

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 ...
1
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1answer
124 views

Maxwell Stress Tensor at material boundaries

I am trying to grasp the meaning of the Maxwell Stress tensor $T_i^j$ at material boundaries. Concretely, I am trying to calculate the force between two waveguides. The results are given in an article ...
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1answer
37 views

Fermi energy of electron gas with electrostatic interaction

I have been given the following exam question and am unsure how I would go about solving it: Consider the case of a one-dimensional metal, consisting of a chain of $N$ positive charges $+q$ ...
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0answers
26 views

Does more electromagnetic mass means more electric field is given out?

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 ...
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0answers
21 views

Foce experienced by charge in a fluctuating magnetic field [on hold]

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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1answer
497 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 $r_0<r<R$ ...
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0answers
38 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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1answer
181 views

Is the uniqueness theorem correct in superconductivity?

There is an uniqueness theorem in electromagnetism. It says that the solution of Maxwell's Equations is determined uniquely by boundary conditions. We can treat superconductivity as a completely ...
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1answer
114 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 ...
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0answers
29 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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2answers
42 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 ...
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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 ...
3
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0answers
68 views

What is relationship between electromagnetic mass and rest mass?

Is there a direct equation which compares rest mass $m_°$ and electromagnetic mass $m_{em}$? Nothing on web I found. $m_{em} = \frac{4 E_{em}}{3c^2}$ 4/3 problem The final solution of the ...
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0answers
130 views
+50

Confusion in Maxwell's derivation of Ampere's Force Law - Part II

I am reading Maxwell's "a treatise on electricity and magnetism, Volume 2, page 156" about "Ampere's Force Law". I have some confusion in the following pages: My question is of two parts: 1. ...
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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 ...
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7answers
3k views

Why are the electric force and magnetic force classified as electromagnetism?

I confuse the four kinds of fundamental interactions, so I think the electric force and magnetic force should not be classified as a big class called electromagnetism. Here is my evidence: The ...
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1answer
261 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 ...
2
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1answer
116 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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1answer
26 views

Electric field inside an insulator's cavity [on hold]

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.
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0answers
31 views

advantages/disadvantages of a cylindrical microwave oven cavity in comparison to a rectangular cavity

Why are rectangular cavities preferred for standard microwave ovens with a frequency of 2.45 Ghz? What is the reason that you can hardly find a circular cavity? What are the disadvantages of ...
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1answer
234 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 ...
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1answer
25 views

is it possible to isolate and pair electromagnetic interaction? [on hold]

is it possible for two electromagnets to interact each other, ie. repulsive or attractive forces to be exerted to each other, without being exerted to other metallic items or other electromagnetic ...
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1answer
27 views

What would happen if a magnet was pushed towards a copper tube in space?

So the question was inspired by one of curious comments on youtube. What exactly would happen if you pushed a strong neodymium magnet towards the copper tube (aiming for the opening in an effort to ...
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5answers
6k views

Does a constantly accelerating charged particle emit EM radiation or not?

The Abraham-Lorentz force gives the recoil force, $\mathbf{F_{rad}}$, back on a charged particle $q$ when it emits electromagnetic radiation. It is given by: $$\mathbf{F_{rad}} = \frac{q^2}{6\pi ...
2
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1answer
231 views

How does EM radiation depend on the reference frame?

In special relativity, magnetism is electrostatics in a different reference frame. This is how we explain the magnetic field being produced by moving charges (aka currents). Charges that move produce ...
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1answer
64 views

How I can prove refractive index in an environment is this? [closed]

in "Applied Quantum Mechanics" by A.F.J. Levi, is a problem that I couldn't solve it can any solve it: if electrical filed is: $$ \mathbf{E}\left(\mathbf{r}, \omega \right) ...
3
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0answers
46 views

Why is diproton unstable? [duplicate]

Diproton is an isotope of helium without any neutrons. It commonly forms in the Sun, where protons are fused constantly. However, it is extremely unstable, and will revert back to two protons almost ...
2
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3answers
218 views

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

In a cavity of size $L$, 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 violate ...
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0answers
17 views

What is the physical meaning of a magnetic conduction current?

In electrodynamics, it is possible to have an electric conduction current, whereby $J=\sigma_e E$, with $J$ being the current, $\sigma_e$ the electrical conductivity and $E$ the electric field (this ...
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1answer
32 views

What is the interrelationship among PD, T1 and T2 in relation to MRI

Proton Density (PD), Spin - Lattice Relaxation Time (T1), Spin - Spin Relaxation Time (T2) are three major characteristics by which we can distinguish different types of tissues and all three are ...
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1answer
58 views

Is diamagnetism a static or dynamic effect?

When we put a diamagnetic material in the presence of an external magnetic field $\vec B_0$, the magnetic field inside the material decreases to $$\vec B=(1+\chi_m)\vec B_0,$$ where the magnetic ...