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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194 views

Does Mansuripur's Paradox involve fictitious charges?

Mansuripur's Paradox involves a magnet moving at relativistic speeds in an external electric field. Additional: thanks to Retarded Potential, who found the original paper. If I understand correctly, ...
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43 views

Interaction of geomagnetism on free falling coil

Take the Earth, or a similarly large body with an Electromagnetic field. For now - expect atmosphere. Then take a much smaller object - say the size of bus, containing a coil with many windings. If ...
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115 views

Is there an equation for the magnetic field of a conductor attached to a magnet?

Let's say I have a hollow conductive rod, 10mm diameter (O.D.), and I place a magnet of known strength 50mm up the shaft. What is the microTesla (mT) or Gauss (G) of the magnetic field (or flux ...
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47 views

Why is low temperature required for optical lattice systems to enter magnetic regime?

"Optical lattice requires a very low temperature scale to enter magnetism regime." Why is that? What I know: optical lattice systems suppress kinetic energy (hopping parameter: $t$ small); ...
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45 views

Design and use of the RLC model for signal processing systems and spatial acoustics

Given a frequency response for a signal processing device, set of devices, or physical space it is possible to construct an equivalent (identical frequency response) series RLC circuit. 1) Does this ...
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37 views

Is it possible to create an electrified silicon gas vortex?

Is it possible to create, and sustain, an electrified silicon gas vortex? If it is possible: would it produce an electromagnetic field? And how would that field affect the vortex?
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96 views

What would the magnetic field look like for a rod like this?

Imagine I have a long rod of metal. Let's say it's 1m long, 1cm wide and 1mm high. Now suppose I pass DC through it. But instead of running the current through lengthwise, I want to run it sidewise. ...
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56 views

outward pressure in an confined electron gas

Suppose i have some electrons stored in a empty shell container with a negative ion layer in the inner surface so the electrons keep bouncing inside without being able to leave the inner cavity. I ...
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106 views

Can mu-metal reduce the negative effect of metal close to low frequency RFID antennas?

I have an 134.2 khz RFID antenna for sport events which is basically a 1x1 meter square sheet of rubber with 3 loops of antenna cable embedded. The problem is that the transponder recognition range is ...
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38 views

AWG chart for Tungsten

This is the American Wire Gauge (AWG) chart page for Copper that I found from Google: http://en.wikipedia.org/wiki/American_wire_gauge Is there a similar table for Tungsten/Wolfram available? Has ...
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59 views

Effects of EMP in superconductor-based devices/equipment?

What are possible effects of electromagnetic pulse / EMP on superconductor-based devices/equimpent/transportation? Are they resilient or more sensitive to EMP?
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50 views

Would ferromagnetic space debris have been magnetized by their orbit in the Earth's magnetosphere?

Given a nail, and a magnet it is possible to magnetize the nail by patiently rubbing the nail until it is magnetized; albeit the field strength may be less than that of the source. With several ...
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417 views

Calculating capacitance of integral PCB components

I posted this question originally with Electrical Engineering Stack Exchange but nobody seems to know the answer. So I thought a physicist might find the question more approachable. Formulas for ...
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72 views

How to apply Guass Law to Voltages

So, I know $\oint E\centerdot dA = 4\pi Q_{enc}$ I'm trying to solve for a TEM mode with two concentric (infinite) cylindrical wave guides of radius a and b, $a<b$. I know that for TEM modes, I ...
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285 views

Equations governing mutual inductance and transformers

What are equations for voltage ratio (primary/secondary) of... the action of a transformer with a turn ratio (turns primary/turns secondary) of X/Y and a toroidal core of cross-sectional radius R ...
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121 views

An electron is subjected to an electromagnetic field using the canonical equations solve

So I was given the following vector field: $\vec{A}(t)=\{A_{0x}cos(\omega t + \phi_x), A_{0y}cos(\omega t + \phi_y), A_{0z}cos(\omega t + \phi_z)\}$ Where the amplitudes $A_{0i}$ and phase shifts ...
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237 views

Electrical machines: electrical and mechanical properties of steels and cast iron

I would like to know a good source of information for the common metals (steels and cast iron). Information that I need are basically the mass density and the electrical conductivity or resistivity. ...
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299 views

How to find the electric field at a point based on a uniformly charged surface

What is the general solution to finding the electric field at a point based on some (or multiple) charged surfaces. I know that we can perform a line/surface integral if a charge is close to a wire or ...
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153 views

Wave propagation in anisotropic media

I'm given a wave propagation in an anisotropic medium with the following properties: $\epsilon=\left[\begin{array}{ccc} \epsilon_{11} & 0 & 0 \\ \epsilon_{21} & \epsilon_{22} & ...
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82 views

How to set the electric potential on a certain boundary to a certain value experimentally?

In electrostatic boundary value problems, usually the potential is set to some function or a constant on a certain boundary. It is never taught or told in textbooks how such assignment might be ...
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136 views

Reflected electromagnetic wave relation

If incident electromagnetic wave is given as: $$\begin{align*}E_i&=A_e \cos(\omega t + bz)\\ H_i&=A_h \cos(\omega t + bz)\end{align*}$$ What would be relation for REFLECTED wave? Does it ...
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396 views

Can we increase the magnetic flux for a permanent magnet?

When we pass current to the permanent magnet does its magnetic flux, magnetic property of attraction and repulsion increases? if possible Is there any other way for increasing the magnetic flux?
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2k views

How can I find the potential difference of a plastic sphere in a capacitor?

A thin spherical shell made of plastic carries a uniformly distributed negative charge of -Q coulombs. Two large thin disks made of glass carry uniformly distributed positive and negative charges S ...
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329 views

Skin effect and currents

Here in this picture you can see I_W which is induced by H. But why I_W is not vice versa? Because of $$rot \, \vec B = \mu_0 \, \left( \varepsilon_0 \frac{\partial E}{\partial t} + \vec j ...
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6 views

Solving the Poisson-Boltzmann Equation for a charged plane with positive and negative ions in solution

I am trying to solve the Poisson-Boltzmann equation for a positively charged plane with charge density $\sigma$ at $z = 0$. $$ \phi''(z)=-\frac{e}{\epsilon \epsilon_0} \big(z_+n_{+} e^{-\beta z_+ ...
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21 views

Realtivistic explanation of forces between two conducting wires

The formula for the force between two infinite conducting wires per unit of length, $F_l = \frac{\mu_0}{2\pi} \frac{I_1 I_2}{r}$, is quite well known. It was used for definition of ampere and was ...
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7 views

Inductor's energy

I have some knowledge about LC circuits, like I know Maxwell's equations, the differential equations of circuit oscillator and so on. I am armed with equations to solve physical problems involving ...
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23 views

How to calculate force generated from a magnet coil to a magnet?

I go to a website http://easycalculation.com/engineering/electrical/solenoid-force.php They have the calculator for the force between a solenoid coil and another piece of ferromagnetic material. What ...
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8 views

Flux, intensity, etc in ferromagnetic core by integral

Cheng, Field and Wave Electromagnetics (newest ed.), ex 6-10, page 252 Some of the examples in this book are kind of sloppily described. Having trouble with this one. We have a toroidal core with ...
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38 views

“+” and “-” sign in Maxwell Stress tensor

I have trouble in determining the "+" and "-" sign of momentum per unit time, per unit area of the following question. Why in the second part, $d\vec{a}$ is pointing in the $ -\vec{z} $ direction? I ...
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12 views

Electrons Orbiting Sphere Magnet in Crooke's Tube

Were I to assemble a Crooke's Tube and insert a spherical magnet, with the poles of the magnet perpendicular to the electron stream, would the electrons begin to orbit the poles of the magnet as in ...
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22 views

Determining the path of a particle in a velocity selector

I am wondering how you can determine the path of a particle in a velocity selector provided its velocity doesn't equal $ \frac{E}{B} $. I understand that the equation is derived from this force ...
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19 views

Transformers rate equation

Going back to transformers after some years I realize they hide a possible missconception I'm not sure I really understand. It is not easy to find a full derivation of the well known relation ...
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30 views

Energy in an electromagnetic wave

A radio antenna creates EM waves through switching the polarization in the antenna at a certain frequency. I assume the the energy of the photons produced in this process amount to E=hf for each ...
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27 views

Proving two forms of atom-field interaction perturbation Hamiltonian are equivalent

In the presence of an electromagnetic field in the dipole-approximation (${\boldsymbol A} = {\boldsymbol A}(0,t)$) we have the two forms $$H_{{\boldsymbol d}\cdot {\boldsymbol E}} = - q {\boldsymbol ...
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38 views

Deduce magnetic field based on electric field

I'm learning Maxwell's electromagnetic equations and i can't wrap my head around this problem: Given the volume $x\in [0,1], y\in [0,1], z\in [0,1]$, electric field $\vec E(x,y,z,t)$ and material ...
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17 views

When a pole of magnet comes near another pole possessing the same charge does it generate electricity?

That's all there is to it. Well... I was daydreaming about making gloves that had the ability to shock people when you punched them. I thought how it would be better if they didn't need a battery and ...
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19 views

Question regarding 2 conducting spheres connected by a long fine line (electric potentional)

I'm having a bit of trouble understanding a pretty simple issue. Assuming I have 2 conducting spheres uniformly charged connected by a long fine line (as shows in the added photo) and im being asked ...
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28 views

Magnetic forces and generators

i'm really struggling to break this question down into manageable chunks and identify which quantities are relevant. I'm also unsure of some of the wording in the question. A bar of length ...
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27 views

Is this expression of electric field correct?

I know that the electric field component of electromagnetic wave should be written as the first equation shown, but some times it can be expressed in terms of complex amplitude of electric field as in ...
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5 views

why field cooling is necessary in Exchange bias?

Why is field cooling necessary for exchange bias? For instance, if we take an example of Ni/NiO, in this sample NiO is already anti-ferromagnetic in nature at room temperature. And as we know that ...
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18 views

Can energy be harnessed and collected safely from a magnetic/electric field within a tube with the following scenario?

Scenario: Is it possible to safely collect energy from the following: Friction of a metallic object moving around a circular tube that is filled with water Inside the tube, magnetic forces are at ...
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19 views

What equation should be used when this conductor passes a magnetic field?

A large thick copper wire(or bar if you like,) passes a magnetic field. What formula is best to calculate the $EMF$ here? $$\epsilon = \frac{\Delta \Phi \ }{\Delta t} $$ or, $$\epsilon = ...
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24 views

Does back emf occur in transformers?

Does back emf occur in transformers and if so does it reduce the efficiency of the transformer and can it be reduced?
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20 views

A conductor passing a magnetic field?

A large thick copper wire(or bar if you like,) passes a magnetic field. What formula is best to calculate the EMF here? $$EMF = BA / Delta(t)$$ or, $$EMF = vBL$$ When the conductor passes the ...
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15 views

How to compute radiated power from known instantaneous potential distribution

Friend of mine has a device that has an oscillating electric potential and he wants to know how much power it radiates. He can simulate the instantaneous electric potential using a software package, ...
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14 views

The Magnetic Field around the Proton Beams in the LHC

How would one most appropriately model the magnetic field around each bunch of protons in the LHC at maximum operating speed? Is the assumption of a wire of the same length of the beams (~30cm) with ...
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51 views

how do I calculate the B field (strength and direction) on a point charge due to a permanent magnet

I am trying to create a simple 2D Simulation of magnetic fields similar to this; showing the field lines or the effect of permanent magnets. I keep coming across equations like this: ...
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32 views

Field outside a solenoid?

Say you have a solenoid with diameter $d$ and length $L$. How can I show that as $d/L$ approaches 0, the field outside the solenoid is zero? I'm looking for a formal proof involving integration. ...
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36 views

Resistance of a cylinder contacted by two smaller circular faces

Suppose we have a solid homogeneous cylinder with radius $a$, heigth $h$ and conductivity $\sigma$. The top and the bottom face is contacted with a smaller circular face with radius $b$. How can I ...