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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168 views

Hidden momentum

I'm trying to learn about hidden momentum. After reading what I could find with a google search, I understand that it is equal to the momentum carried by radiation, calculated with the Poynting ...
1
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1answer
186 views

Can the physical properties of the EM field be described directly from the 4-gauge potential?

I'm trying to make an argument that classically, the EM field is considered a more 'real' physical quantity than the potentials, and am tempted to say that the fact that the field carries energy & ...
3
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1answer
33 views

Gauss law and electrostatic induction. Concentric spheres

Imagine you have hollow concentric spheres A and B with radius a and b (b>a), respectively. If A is a conductor and B has a certain density charge, I´ve been taught that B will induce some net charge ...
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1answer
29 views

How does sunlight undergo interference as shown in the video?

As far as I know, for interference to happen in a double-slit experiment, the light source should be coherent and monochromatic. If that is the case then how come sunlight undergo interference and ...
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1answer
23 views

Motion of an electric charge within an electric field with two electric charges

Assume that air resistance and gravity are negligible and the only significant force acting in the scenario is the electric force. There are two electric charges, both with an equal and positive ...
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2answers
35 views

Find the radius of the path of an electron in a magnetic field [closed]

In a question I am asked to find the radius of the circular path that an electron follows in a magnetic field. The field strength is $B=10^{-5}T$ along the positive y axis, the velocity of the ...
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1answer
41 views

Why do electric motors stop working when physically stopped (burned up)? [on hold]

I found a rock lodged between the fan and the radiator on my motorcycle. Now the fan does not work when the computer prompts it to. I tried directly attaching the 12 volt battery to it as well. No ...
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1answer
20 views

How, if at all, does the behavior of a parallel plate capacitor change in the presence of a magnetic field?

I'm an AP physics student curious about magnetism and my teacher couldn't answer this question. We already learned about velocity selectors, so I know that, when the plates of the capacitor are in the ...
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3answers
70 views

Why don't E&M fields change orientation after hitting a surface?

In essentially every derivation of the Fresnel equations, the general problem of radiation hitting a surface at a certain angle is broken into two parts (out of which we hope the solution any general ...
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1answer
49 views

Questions about Magnetic field [duplicate]

I have two questions about Magnetic Field. Given a particle with mass m, charge q and uniform B field. B is going into the page, and particle is moving to the right Like this. The textbook says ...
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2answers
163 views

How can the thrust due to radiation pressure be amplified in photonic laser thruster?

The thrust is amplified due to repeated bouncing of photons between two mirrors as shown in the diagram in this: Why does repeated bouncing of photons produce amplified thrust when the answer in ...
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0answers
40 views

Question about the fields in a solenoid

I am very familiar with using Ampere's Law to find the B field inside a solenoid ($\mu_0nI(t)$). Then I can use Faradays to find the E field inside ($\propto\dot I$). I want to get this result ...
3
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1answer
203 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 ...
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2answers
51 views

Is magnetic field of a uniformly moving charge constant everywhere?

As far as I understand, for the field of a uniformly moving charge, curl of $\mathbf E$ is zero everywhere. Since $\nabla \times \mathbf E = -\dfrac{\partial\mathbf B}{\partial t}$, magnetic field ...
3
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3answers
132 views

At an instant, does a system of gravitational charges exhibit equivalent behavior to a time-reversed system of like electric charges?

Question: In principle, does a system of gravitational charges exhibit equivalent behavior to a time-reversed system of like electric charges? (At a single instance in time?) Additional Notes: I am ...
2
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1answer
64 views

Why doesn't the changing field of a moving charge create EM waves? [duplicate]

EM wave phenomenon is usually described as "changing electric field creates changing magnetic field which creates a changing electric field etc." But fields of a uniformly moving (not accelerating) ...
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0answers
12 views

Easiest way to levitate a ferromagnetic material that is not a permanent magnet?

I want to levitate an iron cube that is not a polarized permanent magnet. What is the easiest way to do this?
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1answer
30 views

Is it possible to levitate large objects through diamagnetic levitation?

I am currently building a diamagnetic levitator with a strong neodymium magnet, two slabs of bismuth (a diamagnetic material), and a small neodymium cube to levitate. However, I was wondering if it ...
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0answers
13 views

Can a diamagnetic levitator levitate non-permanent ferromagnetic materials?

I am building a diamagnetic levitator that will eventually levitate a small neodymium cube. However, is it also possible for an iron cube to be levitated as well? I know that diamagnetic materials ...
0
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1answer
159 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 ...
2
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1answer
29 views

Wave Velocity vs. Phase Velocity

I am trying to understand the difference between 'wave velocity' and 'phase velocity'. I know that generally they are equal, but when is that not the case? I, of course, tried to google it, and ...
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2answers
51 views

how do we actually count the number of magnetic field lines and what does the gap between those lines describe?

on the internet,(http://nuclearpowertraining.tpub.com/h1011v1/css/h1011v1_53.htm), there is a statment which says that 1 Wb is $1\times 10^{8}$ magnetic field lines. My question is, How do we count ...
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2answers
960 views

Why do ferromagnetic materials channel magnetic field lines?

I have read that the total magnetic field of a ferromagnet, $\vec{B} = \mu_0\vec{H}+\mu_0\vec{M}$ where $\vec{H}$ is an external magnetic field and $\vec{M}$ is the magnetic field of the ferromagnet ...
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220 views

Magnet gyroscopic force spin

I was wondering whether a magnet exerts any measurable gyroscopic effects. I understand that magnetism is caused by alignment of spins of electrons which have angular momentum. (I realise that that ...
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0answers
20 views

Explanation of absorption from Bloch Equation

Suppose in a magnetic resonance experiment the microwave/rf field is applied in x-direction.How to say that the component of magnetization which is out of phase with the microwave magnetic field leads ...
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0answers
29 views

Electromagnetics B and H quadratic relationship! [closed]

So the ques is $B=\dfrac{H}{3} +(H^2\mu)$ and I have to find $\mu_{r}$ when H = 120 A/m. H:Magnetic field intensity $\mu$ is magnetic permeability $\mu_{r}$: relative magnetic permeability! Now ...
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1answer
148 views

From Liénard-Wiechert to Feynman potential expression

When studying the potential of an uniformly moving charge in vacuum, Feynman proposes to apply a Lorentz transformation on the Coulomb potential, which reads in the rest frame $ \phi'(\mathbf r',t') ...
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2answers
31 views

Water flow in salt solutions contemporary exposed to an electrical and constant magnetic field

When a permanent magnet is held motionless close to a salt solution which already has been exposed to an electrical field a flow in the water will be induced and can be detected by applying some ...
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1answer
53 views

Does the field of a unifirmly moving charge satisfy Maxwell's wave equation?

The so-called "electromagnetic wave equation" is so general that it should obviously hold for every point in space and for all field configurations (if there are no charges). Here it is: $$ \left(c^2 ...
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3answers
379 views

Currents induced by rotation of a coil about magnetic field lines

If the coil on the left is rotated about the magnetic field lines, will there be an induced current? I know that the flux concerns only the component of the magnetic field perpendicular to the ...
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3answers
868 views

What is / are the primary criticism(s) against Einstein-Cartan-Evans field theory?

What is / are the primary criticism(s) against Einstein-Cartan-Evans (ECE) field theory? On Wikipedia the references provided were: arXiv:physics/0607186, MR2372785 (2008j:83049b), MR2218579 ...
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2answers
35 views

is it possible to shape electromagnetic field?

Is it possible to produce a magnetic field of specific shape? For example a magnetic field that will be confined in a cylindrical shape of specific dimensions.
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43 views

Load matching in a transmission line [closed]

Can somebody explain me easily and clearly why when you want to transform a 50 ohm load impedance through a piece of transmission line in an arbitrary one let's say $Z$ (complex number); that it's the ...
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1answer
39 views

Can an electromagnetic potential be in two gauges at once?

I have a plane wave vector potential found using the free field form of Maxwell's equations and the Lorentz gauge: $\vec{A}(\vec{r},t) = \vec{A}_0 e^{i(\vec{k}\cdot\vec{r}-\omega t)}$ If I take the ...
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0answers
16 views

Load matching in a transmission line [duplicate]

Can somebody explain me easily and clearly why when you want to transform a 50 ohm load impedance through a piece of transmission line in an arbitrary one let's say Z (complex number); that is exactly ...
3
votes
1answer
90 views

High Level Understanding Q: What *is* a magnetic/electric field?

Note: I have seen this question -> (What is a magnetic field) and would still like some clarification. I have also seen https://www.youtube.com/watch?v=hFAOXdXZ5TM and ...
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0answers
40 views

How to compute the magnetic force between two electromagnets?

I wanna compute the magnetic forces between two solenoids with iron cores, is there any analytic formula for this? I guess that dipole-dipole interaction in the link ...
0
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1answer
148 views

What is wavelength of electric field generated in a wire? [closed]

I read link given below: http://en.wikipedia.org/wiki/Speed_of_electricity Above link says _The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic ...
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0answers
12 views

In electromagnetism are standing waves same as destructive waves [closed]

In electromagnetism are standing waves same as micro waves. also do standing waves decrease the actual intensity of wave.
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2answers
332 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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2answers
176 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 ...
2
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1answer
489 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 $r_0<r<R$ ...
4
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3answers
480 views

Poynting's theorem - energy conservation

Poynting's theorem: $$\int_V\left(\vec{E}\cdot\vec{J}\right)\,\mathrm dV = -\dfrac{\partial}{\partial t}\int_V\dfrac{1}{2}\left(\epsilon_0 E^2 + \dfrac{1}{\mu_0}B^2\right)\,\mathrm dV - ...
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39 views

Coulomb Gauge under Lorentz Boost

In the Coulomb gauge for the Maxwell potential we have $$ A^0 = 0 \\ \partial_i A^i = 0 $$ Under an infinitesimal Lorentz Transformation with parameter $\epsilon$, we have $$ A^\mu(x) \rightarrow ...
4
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3answers
4k views

Quantum levitation (locking) 3mm thick disk could carry 1000kg small car claim

I watched this TED presentation: http://www.ted.com/talks/boaz_almog_levitates_a_superconductor.html It is about superconductivity and quantum levitation. It tells that super-thin, three-inch disk ...
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1answer
458 views

What are the proposed theoretical explanations for the EmDrive?

The EmDrive is a proposed propulsion mechanism for spacecraft in which some form of microwave device provides the propulsion. The consensus from the physics community, including many voices on this ...
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2answers
70 views

Is the CHAMP missile capable of doing what they say it does? [closed]

CHAMP, A new counter-electronics directed energy USAF weapon was created by Boeing Phantom Works with the intention to damage and / or destroy electronic target equipment without causing structural ...
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2answers
42 views

Do Weyl fermions carry electric charge?

Do Weyl fermions carry ordinary electric charge? That is, do they interact with, for instance, electrons or photons?
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82 views

Can we use magnetic energy to produce electricity?

Magnets attract each other with a force (magnetic force), because they possess magnetic energy. My question is, is there any way, by which we can convert that magnetic energy into electrical energy? ...