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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Magnetic force between two point charges

I tried to derive the magnetic force between two point-charges for iterative computation. Starting out with Lorentz force and Biot–Savart law for a point charge. $$ \vec F = q_2( - \Delta \vec{v} ...
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27 views

Where can I learn about Motors and Generators?

` Where can I learn about the functionality of motors and generators, so I can answer questions such as these? I need a good textbook that starts from the basics (eg faradays) then moves up with ...
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33 views

What happens to the emf generated due to a change in magnetic flux in a coil?

When we move a magnet into a coil of wire (open circuit) and then out of it, we create a emf across the ends of the coil and another emf in the opposite direction. My question is what would happen to ...
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54 views

Aether/Ether in Electrodynamics?

From reading Maxwell's original papers on the formulation on the dynamics of electromagnetism, I saw that Maxwell kept mentioning aether in his paper. I know today in modern physics the Michelson ...
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36 views

Faraday's law in free space explaining away the constant vector?

Let's say that I have a plane electromagnetic wave travailing in free space, and I know the electric field part to be $\vec E$. If I am using Faraday's law to get the magnetic field part I will get ...
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28 views

Electromagnetic field to shield from EMP?

Could an electromagnetic field be use to protect against an EMP? As I understand, an EMP is an Electro Magnetic Pulse, so a sufficiently powerful field should be able to deflect one, right?
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36 views

Mie's scattering Theory Problem

Is Mie's theory which describes the scattering of EM wave off sphere , possible to extend to spheroidal ? object or arbitrary shape with finite series expression ? I tried to replace the radial ...
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58 views

Why do we define the magnetic field around a conducting rod as concentric instead of radial?

Why is it that we define the magnetic field around a conducting rod as concentric instead of being radially outwards? Ok, we know from the Lorentz force law, that the magnetic force is the cross ...
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170 views

Ed Leedskalnin's “Perpetual Motion Holder” (PMH)

Edward Leedskalnin (Coral Castle) describes a perpetual motion holder in his writings. I've built one and pretty much know how it works (I think). It is NOT a perpetual motion device by any means, ...
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52 views

Why is no work done by magnetic forces in a uniform B and E field (perpendicular to one another)?

Say $B$ points in the $x$ direction, and $E$ points in the $z$ direction. Assuming a charged particle begins at rest at the origin, its motion will be a cycloid that progresses indefinitely in the ...
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23 views

Earth's magnetic effect on my magnet

My magnet seems to work independently of, and unaffected by, the Earth's magnetic field, yet the magnetic field of my magnet changes as I introduce some other similar magnets of varied sizes into its ...
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35 views

Can a charge moving in an open trajectory qualify as current?

It is sometimes said that a point charge is equivalent to an electric current. If it were a steady current, I should be able to find it from Ampere’s law or Biot-Savart’s law. Even if the current is ...
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56 views

Noether current scale transform of EM

I'm trying to solve a question about scale tranform of free EM. I got the next trnaform rules (these two line where EDITed later) $\delta x = -bx$ $\delta A = bA$ the current I got $D^\mu = ...
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38 views

Fresnel equations of S and T waves and Isofrequecy Curves: Feeling confused

First of all sorry for my (probably) bad english. I've been studying propagation of light in anisotropic media from the Born and Wolf and from Landau "electrodynamics in continuous media" and I'm ...
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26 views

Frame dependence

I was reading an article about magnetospheres, and came across this quote: This supersonic ionized gas, or plasma, called the solar wind carries with it a magnetic field and a frame dependent ...
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60 views

Can photons travel through space independent of time?

I read an article about advanced photons and they stated that photons traveled back in time to hit an electron. Can photons really travel back in time and if so, how?
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46 views

Concrete example of Earnshaw's Theorem

I'm struggling to understand Earnshaw's Theorem. I've tried reading the original paper, and the wikipedia article. I know enough math to be able to understand the mathematics of the theorem, but I ...
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72 views

How can I calculate the Teslas and resistance of an electromagnet?

I'm trying to build a small electromagnet to use in a generator. Right now, I have a coil of insulated 16 AWG copper wire wrapped around a large iron nail with a diameter of 1.5cm. The length of the ...
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75 views

Why did Heaviside eliminate the magnetic potential from Maxwell's Equations?

Maxwell's original equations had magnetic potential, but Heaviside eliminated this variable. What was the reason for Heaviside's removal of the magnetic potential?
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36 views

Can electromagnetic fields be measured from a distance?

I know that direct measurements of electromagnetic fields can only tell information about the field near the probes, but I am curious if there is a way to measure the electromagnetic field in a not ...
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136 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 ...
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42 views

Electromagnetic Waves Speed

What is the relationship between the speed on the electromagnetic wave and the density of the medium in which the electromagnetic wave travel through?
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42 views

Is it possible to create arbitrary shapes of magnetic fields?

I've been reading about Transcranial Magnetic Stimulation (TMS) which can activate neurons using a magnetic field, which got me thinking... what if we can pick and choose exactly which neurons to ...
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34 views

Near Infrared for distance determination

Would near-infrared be an efficient frequency to use in determining the distance from the source of the infrared signal to an object, maybe in the range of 5 to 20 meters away? I need a formula for ...
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67 views

Mutual inductance theoretically decreasing while EMF is increasing in 2 square coil system

I have a quick question regarding electricity and magnetism. I am measuring the induced emf in a square coil of wire with an inductance of 439uH (the other coil is also 439uH and is the same shape). I ...
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27 views

Fresnel equations of reflection applied to microparticles

I wanted to know if the Fresnel equations of reflection, as described here, can be used to calculate the reflectance on the interface of particles which have a diameter near the size of the wavelength ...
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50 views

Question about calculating the torque of a magnet in an additive field

I did an experiment in the lab today where I placed a magnet in between two coiled magnets, with one coiled magnet having its south side up and north side down and the other coiled magnet with the ...
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103 views

Electric field due to rotating charged sphere

Consider a spherically symmetric charged object (charge $Q$) rotating about its axis. From Gauss's law we know that all that matters for the electric field $\mathbf{E}$ is the charge $Q$ enclosed ...
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64 views

Find magnetic field in a solenoid for different regions?

A steady current I flows along an infinitely long hollow cylindrical conductor of radius R. This cylinder is placed coaxially inside an infinite solenoid of radius 2R. The solenoid has n turns per ...
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54 views

$G_{\mu\nu}$'s field equations in electromagnetic duality

Given $$G^{\mu\nu} = -2 \frac{\partial L}{\partial F_{\mu\nu}}$$ it is written in http://arxiv.org/abs/hep-th/9506035 that the field equations are (eq 1.8) $$\partial_{[\alpha} \star G_{\beta ...
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46 views

Does the total energy in an electromagnetic field depend on the acceleration of the sources?

If I accelerate a charge from rest to some velocity $\vec v$, does the total final electromagnetic energy contained in the field depend upon the acceleration of the charge?
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44 views

Larmor Precession of a macroscopic number of electrons

I know that there are some similiar questions out there, but I'm still quite puzzled by the following problem. Say i have a box full of interacting electrons ( I'm not sure if it would change anything ...
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19 views

Mixing liquids when applying a voltage

I'm thinking in the following experiment: A) Two (non mixable (like water and oil)) liquids are going to lie in a container, in the extremes of the container there are two electrodes, those ...
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19 views

If there is a violation in magnetic interaction b/w two non parellel current carrying wires

when two current carrying wires are put near, there is a magnetic interaction b/w the wires. if they are kept parellel, they'll follow newton's 3rd law. i want to ask that if they are not kept ...
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20 views

Assumption of Positive Dielectric Value in Derivation of Dipole Field Around a Spherical Dielectric? Implications for Plasmonics

I am going through the solutions to Laplace's equation in spherical coordinates. In particular the boundary value problem of a dielectric sphere of radius $a$ and permittivity $\epsilon$ which has a ...
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56 views

Magnetic field derived from a scalar function

Question: Show that $\mathbf B = \hat r \times \nabla g(\mathbf r)$, where $g$ is an arbitrary scalar function, is a plausible magnetic field. What current density $\mathbf J $ can produce ...
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67 views

Analytic (or just qualitative) solution to *any* nontrivial electrodynamic dynamic problem?

I just realized that, after a basic course in electrodynamics, I have no idea whatsoever how to solve the most trivial non-static example in an "exact" way. By this, I mean the following: I know (at ...
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60 views

How to solve the following set of equations (magnetohydrodynamics with anomaly term)?

Let's have system of equations: $$ \tag 1 [\nabla \times \mathbf E^{(1)}(\mathbf r , t) ] = -\frac{\partial \mathbf B^{(1)}(\mathbf r , t)}{\partial t} , $$ $$ \tag 2 [\nabla \times \mathbf ...
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56 views

Conductivity Matrix (Symmetry Information)

I'm trying to understand the symmetry content of the conductivity matrix: one information is, presence of time-reversal symmetry causes the off-diagonal terms to vanish. When this is broken (e.g. in ...
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95 views

The classical hydrogen atom

Suppose we want to analyze a hydrogen atom using purely classical mechanics. This obviously is not exactly how things work - quantum mechanics plays a huge role and probability distributions are ...
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46 views

What is DX technology and what are the effects on digital cameras?

I am photographing in a high power voltage field in Industry producing aluminium, called DX technology. How do I know if my digital camera will not be affected? At 350kA current my film cameras were ...
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21 views

Two conductor's in a magnetic field, canceling each other's EMF?

If two conductor's are in a $\Delta$B, oriented the same in the field, and they induce equal $\epsilon$, can their wiring be oriented in a way that they can cancel each other's induced $\epsilon$? So ...
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165 views

Hamiltonian for Electron in Magnetic Field with Symmetric Gauge in Polar Coordinates

I am new on the board and have a question about how to write the Hamiltonian for an electron in a magnetic field rotating at a fixed radius. I would like to write the hamiltonian using the symmetric ...
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50 views

Electrodynamics boundary conditions with complex $\epsilon$ and $\mu$

I wonder if the usual derivation for boundary conditions at an interface given in EMT textbooks hold for complex permittivity and/or permeability? Do the fields carry phase information themselves(i.e. ...
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117 views

Velocities of waves (such as visible light, and radio)

The speed of light in a vacuum is a constant 299,792,458 m/s. In water, it is much slower. Does this happen to such waves as radio, or X-ray? (Would say, a 3 meter wavelength travel slower in air than ...
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102 views

Conceptual question on helmholtz equation

Given the homogeneous Helmholtz Equation $[\triangledown ^2 + \kappa^2] E= 0$, I understand $\kappa$ represents the wavenumber $\omega_0 / c$. In light of this, what physical meaning can be taken from ...
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51 views

diamagnetism in constant magnetic field

"The diamagnetic materials repel the materials which produces magnetic field, so putting these materials in the proximity of the magnetic field generating materials produces the effect of the ...
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45 views

Deriving Ampère's Circuital Law from Ampère's Force Law?

Ampère's force $d^2\vec{F_{21}}$ of current element $i_2d\vec{\ell_2}$ on $i_1d\vec{\ell_1}$ is$$d^2\vec{F_{21}}=-\frac{\mu_0}{4\pi}i_1i_2\frac{\hat{r}}{r^2}\left[2(d\vec{\ell_1}\cdot ...
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21 views

Can various wavelengths participate in C/D Interference?

My question is can multiple wavelengths or at least two different wavelengths interfere with one another? I know that they usually have to be the 'same' wavelength, but you'd think they can vary a bit ...
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57 views

What is the physical meaning of the norm of the electromagnetic four-potential?

In SI units this would be $\frac{1}{c^2}\phi^2 - A_x^2 - A_y^2 - A_z^2$. Is this just not a physically meaningful quantity at all because it's not gauge invariant?