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.

learn more… | top users | synonyms (6)

1
vote
0answers
118 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. ...
1
vote
0answers
60 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 ...
1
vote
0answers
129 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 ...
1
vote
0answers
50 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 ...
1
vote
0answers
82 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?
1
vote
0answers
55 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 ...
1
vote
0answers
75 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 ...
1
vote
0answers
299 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 ...
1
vote
0answers
132 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 ...
1
vote
0answers
328 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. ...
1
vote
0answers
307 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 ...
1
vote
0answers
161 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} & ...
1
vote
0answers
84 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 ...
1
vote
0answers
139 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 ...
1
vote
0answers
515 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?
1
vote
0answers
3k 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 ...
1
vote
0answers
397 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 ...
0
votes
0answers
15 views

What should the magnitude of the induced voltage on the 2nd loop of a transformer be?

so I'm trying to understand transformers and am reading this site: http://www.allaboutcircuits.com/vol_2/chpt_9/1.html I am a little confused about how to reason about the voltages involved in a ...
0
votes
0answers
16 views

How could the effective electric dipole interaction be derived

In some papers (e.g. Bernreuther equation (1.4) http://inspirehep.net/record/296679 ) you can find the electic dipole interaction defined as $$L_I=-\frac i2 d_f\bar\psi\sigma_{\mu\nu}\gamma_5\psi ...
0
votes
0answers
12 views

electron trajectory in Bfield with energy kick at midpoint

So I wanted to get some second opinions on this situation I have thinking about.Lets say an electron enters, normally, a section of bfield that is perpendicular to its motion such that the electron ...
0
votes
0answers
23 views

can we reuse the motion of a dc motor to power an ac generator

My question is ,when we make a simple dc motor, cant we connect another circuit to the rotating coil and make another circuit for an ac generator
0
votes
0answers
26 views

problem on electromagnetic induction and newtonian physics

Please imagine a solenoidal toroid (i.e. a donut shaped inductor) powered by an AC voltage source. It creates a changing magnetic field which is confined to the interior of the toroid (i.e. within the ...
0
votes
0answers
20 views

Earth's magnetic field and the equator

Suppose earth is like a bar magnet with the poles acting as N and S. If a charged particle from outer space heads towards the equator, why does it get travel around the field instead of the magnetic ...
0
votes
0answers
11 views

ratio between conduction current and displacement current

First, recall that Maxwell displacement current for a plane wave is $$ \vec j_D = \epsilon \partial_t \vec E = \epsilon \partial_t (\vec E_o cos(\vec k \cdot \vec r - \omega t)) = \epsilon \omega ...
0
votes
0answers
27 views

If we put diamagnetic material under strong electromagnet.Would the opposing magnetic fields strong enough to attract ferromagnetic materials?

Suppose we put a diamagnetic material (such as Bismuth or Pyrolytic Carbon) under a strong magnet (see image below). It would create opposing magnetic fields. Would the opposing magnetic field be ...
0
votes
0answers
13 views

Calculating the strength of an electromagnet with a closed magnetic circuit core

I am interested in calculating the magnetic field strength produced by an electromagnet with a core shaped like an O that forms a closed magnetic circuit, shown in the attached image that can also be ...
0
votes
0answers
14 views

Holding a photolithography mask (EUV litography) with magnets, to minimize deformation on the photomask?

Some background: what is this question about? On 20/11/2014, I visited the ASML Holding in the Netherlands, which is according to them, and according to Wikipedia: the largest supplier in the ...
0
votes
0answers
15 views

What is the charge distribution on inner walls of arbitrary cavity of a spherical metallic shell with charge present in it?

Consider a spherical metallic shell with a cavity and a charge $q$ present inside. The field at outside points will be as if charge was placed at the center of the shell.That means the field due to ...
0
votes
0answers
15 views

Are some sources of electromagnetic radiation theoretically (or perhaps technically!) more challenging to detect than others?

In a previous question, I learned that in order to detect an object in space, what matters is how much electromagnetic radiation it is giving off, and what sources of EM radiation the sensor can pick ...
0
votes
0answers
20 views

Anyone know of a flow chart or list of common/useful consequences of Maxwell's equations?

I just recently started to appreciate the Maxwell equations. I had never really take the time to study them but I feel like I'm finally more familiar with them. I've noticed that it seems like a lot ...
0
votes
0answers
19 views

Discernible “frequencies” of magnetic fields that do not affect each other

Two magnets secured to a surface close to each other in a fashion such that their constant attraction to one another is counteracted by the normal force of the securement of each. Is there a way to ...
0
votes
0answers
57 views

Divergence of the Poynting vector with static fields

The Poynting vector is an energy flux density, and applying the divergence theorem shows that: $$\int_V (\nabla \cdot \vec{S}) dV = \oint_{\partial V} \vec{S} \cdot d\vec{a} = -\frac{\partial ...
0
votes
0answers
9 views

Interaction between the induced field of a current carrying with an exterior field?

If a current carrying wire is placed inside a magnetic field(B), and the wire creates it's own magnetic field($B_w$), will $B_w$ be in opposition to the applied external magnetic field(B)? Will there ...
0
votes
0answers
37 views

Electric Flux through cube from point charge

"A point charge is located at the origin. Calculate the flux of E through a cube centered on the origin and aligned with the Cartesian axes. Evaluate the surface integral directly and verify that the ...
0
votes
0answers
9 views

Magnetic field generated by wires with magnetic cores

Describe the magnetic field generated by alternating current as it passes through a wire's special core of tiny, metal-coated, cylindrical rare earth magnets? Examples of real-world consequences of ...
0
votes
0answers
15 views

Phased non linear array antenna - First Sidelobe

I have a problem I cannot seem to solve and I REALLY need some help. It's about phased-array antennas whose dipoles are not equally spaced, not equally phased, not equally fed (amplitude). Let's ...
0
votes
0answers
29 views

What do you call this “asymmetric polarization”?

I am considering this unusual polarization of EM waves: which travels in the x-direction and has magnetic and electric fields as shown. This can be produced by non-oscillatory currents. What name ...
0
votes
0answers
9 views

Field strength of a discrete solenoid

First, I want to clarify that I mean a solenoid made by coiling a fine wire, and not the type made from a continuous piece of conductive material. That said, I know I can find the magnetic field ...
0
votes
0answers
33 views

If gravitational field has negative energy density, how does gravitational radiation carry positive energy?

The following question uses the analogy between EM (electromagnetism) and GM (gravitomagnetism). In order to force two like electric charges nearby, some work has to be done. This implies that the ...
0
votes
0answers
36 views

Derivable Concepts in Mechanics and Electromagnetism

In Classical Mechanics, one of the possible foundations is based on three concepts aka mass(equivalent to energy), length and time. This is a foundation because we can model everything ( pressure, ...
0
votes
0answers
16 views

Mosotti-Clausius formula from the first principles

I would like to understand how to get the Mosotti-Clausius formula for the dielectric susceptibility of a dielectric material with spherically symmetric molecules from the first principles, where by ...
0
votes
0answers
28 views

Separating Aluminium sheets with magnetic field

all! I would like to know if it would be possible to induce a strong enough magnetic field in sheets of aluminium so they would be separated between each other, like when you use magnets to separate ...
0
votes
0answers
23 views

Discrepancy between Sidebottom and Kittel's Solid State Textbooks

There seems to be some discrepancy between Sidebottom and Kittel in the value of the diamagnetic susceptibility of the hydrogen gas. Sidebottom states that it is $-2.2\times 10^{-9}$, while Kittel ...
0
votes
0answers
30 views

Why does charge build up at the boundary surface of two media?

On a homework problem, we are asked to to use the first two Maxwell equations, $$\nabla\cdot \mathbf{B} = 0$$ $$\nabla \cdot \mathbf{D} = \rho$$ to show that along the boundary surface of two ...
0
votes
0answers
10 views

The movement of magnetic rings along a current carrying wire

The creation of circular magnetic rings around a direct current is easily illustrated by sprinkling iron filings onto a horizontal sheet, which has the conducting wire passing vertically through its ...
0
votes
0answers
25 views

Deriving Lorentz force on a point charge moving perpendicular to external magnetic field using Maxwell stress tensor?

I heard that when we use Maxwell stress tensor to derive Lorentz force on a point charge moving perpendicular to external magnetic field, the result is not $qvB$ but $\frac{2}{3}qvB$. This should be ...
0
votes
0answers
19 views

a quandry into electromagnetic fields and generating usable power

I have a question, regarding generated electricity via earth's magnetic field. What if you put a coil of flat high conductive wire with short intervals between the loops on a maglev train? Would that ...
0
votes
0answers
14 views

Why breakdown voltage decreases with increasing FWHM of an asperity?

I am running a simulation for a dielectric breakdown. I am getting breakdown voltage decreases with FWHM, which does not make sense as field enhancement is higher for a small width. Simulations solve ...
0
votes
0answers
14 views

How to conserve power at the reflection boundary of perfect conductor?

How to conserve energy during the reflection ? I am taking the abs value of $\sum E_{field}$ along spacial direction and plotting at each time step. Then it is normalized to the input E filed. ...
0
votes
0answers
15 views

How can two Electromotive forces exist at the same time?

This thought is derived from counter-induced $\epsilon$ in a motor, there is an applied voltage source that creates an $\epsilon$ to allow current flow from the power supply to the motor's windings to ...