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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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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68 views

EMF induced in a dynamo is by photons of permanent magnets?

i know little about the quantum field theory and also that the permanent magnets have there fields because of exchange of virtual photons across or around the ends. so when we take a dynamo and the ...
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63 views

Any quadrupole approximation? Any example?

In atomic and molecular physics we quite often encounter with electric dipole approximation. The dipole approximation we do when the wave-length of the type of electromagnetic radiation which induces, ...
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33 views

How to derive the classical Hartree potential for a slab system?

I am now working on a slab system, but encountered some problems on the classical Hartree potential. This slab system is infinity along x-y plane, and has finite size along $z$ axis $z\in[0,L]$. I ...
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65 views

Can I transfer electricity through induction?

If I place a solenoid connected to a bulb inside a bigger solenoid which is connected to a power source, will the bulb glow?
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575 views

Magnetic field of solenoid in cone shape

I have done some drawings of the magnetic fields of cone shaped solenoid electromagnets. I based this on the work of Tesla and some explanations of Bashar, known as the Bashar Cones. I found very ...
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60 views

Maximise magnetic force at one point while minimizing at another

Is it possible to have a magnet that attracts one object strongly, but not another object behind that first object? Given an (electro-) magnet M above two thin parallel steel sheets P1 and P2 in the ...
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49 views

Conceptual way of understanding what material 'does' at critical angle

I would like a conceptual way of understanding how a material behaves at the critical angle. So why does it all reflect? I can see why it reflects in the maths, but conceptually, it doesn't make ...
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43 views

what are the main factors holding back magnetic energy storage systems?

Perhaps is it the magnet's own magnetic field that causes it to lose its superconductive state? It seems as though these systems could become incredible energy dense.
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38 views

I've been reading that it's possible to create a “mostly magnetic” wave, and I have a few questions

Would it be possible with the "mostly magnetic wave" to have it behave in such a way that it would be undetectable by radio triangulation? I read about the monument at the CIA headquarters that was ...
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69 views

Electric field screening for arbitrarily formed charge

if I have a not necessarily homogenous electric field of a charge distribution in an electrolyte and i want to find out what the electric field at some position in the electrolyte is. is there any ...
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301 views

Properties of electric field

I have the following vector field: $E=E_0(-sin(\phi),cos(\phi),0)^T$ and $E_0$ is some constant. Does anybody here have an idea what this electric field does to a metallic sphere that is in it? ...
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24 views

Two charges in a medium where different permittivity is adjacent

I was thinking about the following: Assuming that you have NON SPHERICALLY SYMMETRIC charges and they are both in medium 1. Does it make a difference(whereby I am referring to the total force) if ...
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816 views

Calculation of magnetic force magnitude from a parmenant magnet

I was wondering how strong a magnet should be in order to be able to horizontally attract 0.2 Kg of pure iron at a distance of 0.3 M. Since I know nothing about magnets, I started looking for ...
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80 views

How to size an electromagnet

How can I size an electromagnet? For example if I would to attract a mass of $x$ kg what are the calculations that I must do to size the ferromagnetic core and of course the solenoid? And thus, how ...
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42 views

Exchange operator and magnetism

in my atomic physics lecture notes it is said that depending on the values of the exchange operator $K_{ij}$ there can be different kinds of magnetism, say, ferromagnetism and antiferromagnetism, how ...
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102 views

How sharp is the direction of magnetic field of a cone magnet?

I heard recently that cone magnets can be used to focus and direct the field sharply at one particular point in a particular direction. I jus want to kno how accurate and sharp this field is? And if ...
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192 views

Easy question about magnetism?

I have to build a simple electric motor by attaching a magnet to a battery, extending the terminals of the battery (with stiff wires so they could act as supports), and placing a coil of wire on top ...
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35 views

Energy in the electric field of a translating charged sphere

The energy stored in the electric field of a uniformly charged non-conducting shell moving with a uniform velocity is more than the energy stored in the electric field of the same shell at rest. What ...
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407 views

How does a Fresnel rhomb work (half and quarter wave plate)?

How does a Fresnel rhomb work (half and quarter wave plate)? I am aware of birefringence, which creates a phase shift of $\Delta\phi=\dfrac{2\pi\Delta nL}{\lambda_0}$. But this doesn't explain how a ...
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114 views

Einstein +Maxwell 's tensor

Why is it true that we can deduce that Einstein's GR equations coupled with Maxwell's EM equations may be written in the form $$R_{ij}=C(F_{ik}F_j^{\,\,k}-{1\over 4}g_{ij}F_{mn}F^{mn})$$ without ...
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85 views

How to calculate how weak does a magnet get when you get an other magnet closer to it?

I heard that when you take two magnets and get them closer together so they reject each other (north pole to north pole or south pole to south pole) they weakens. Does anybody knows how to calculate ...
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178 views

Online magnetic field solver

Is there a site that allows you to give the approximate specs of a set of magnets and then it produces the graph of the magnetic field for you? Here is a situation I try to understand: I have a set ...
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75 views

NMR rotating frame

I'm reading about a linearly polarized field (in the context of NMR). The field is given by $$ {\bf H_{lin}}=2H_1({\bf i}cos(\omega_zt)).$$ This can be created by having a pulse field plus its ...
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197 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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128 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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52 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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103 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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57 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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113 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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66 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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51 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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73 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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292 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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123 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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262 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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302 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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158 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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83 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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137 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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431 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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351 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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12 views

Question on envelope-carrier description of traveling wave

I'm doing a research internship in attosecond physics right now, and one of the really important things in the field is the description of a propagating laser pulse as the combination of a slowly (or ...
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9 views

Does the skin effect and the proximity effect cancel each other out?

I'm interested in how the Skin Effect and the Proximity Effect interact with each other. From what I can understand: The Skin Effect is when AC current 'collects' on the skin of conductors due to ...
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14 views

Molecular field meaning in Liquid Crystal Theory

Given the Frank-De Gennes free energy $F = \int f(\boldsymbol{p},\nabla\boldsymbol{p}, ...)\ d\boldsymbol{x},$ for liquid crystals (see De Gennes-Prost, p. 107, formula 3.21), the vector ...