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 (5)

1
vote
0answers
50 views

Freely Falling Bar in a Magnetic Field

I have a horizontal bar on vertical rails and we can consider that does not exist any friction. Perpendicular to the plane of the rails it exists a magnetic field $B$. I am asked to find the ...
1
vote
0answers
64 views

Magnetic flux density a small distance off axis from a current loop

I'm currently studying physics at University and struggling with the problem mentioned, it's on a past paper I'm trying to do. I have calculated the B field on axis as (sorry don't know how to format ...
1
vote
0answers
41 views

Electromagnetic energy with P and M

In many books, for a linear dielectric medium in which we have Maxwell's equations and the relationships $${\mathbf D}=\varepsilon({\mathbf x}){\mathbf E}$$ and $${\mathbf B}=\mu({\mathbf ...
1
vote
0answers
74 views

Is it possible to increase the electromagnetic repulsion between two particles?

Given the fact that the force stopping me falling through the ground is the electromagnetic repulsion between the electrons in my feet and the ground, would it be possible to increase this repulsive ...
1
vote
0answers
32 views

Energy stored in a battery?

I want to calculate the energy lost from a battery to heat, and the energy stored in a battery. Are these formula's correct? $ E_b$ = $I$$V$ x $t$ $ E_H$ = $I$$R$$^2$ x $t$ $E_b$ = energy stored in ...
1
vote
0answers
62 views

Calculating Joule heating in magnetic field

I have problem with calculating Joule heating in alternating magnetic field perpendicular through circulate plate with radios a and height h. Lets say that alternating magnetic field is in form of ...
1
vote
0answers
80 views

Voltage in a lossless transmission line

I have a question where I'm deriving expressions for different variables within a lossless transmission line. Here's the question as posed: Consider a lossless transmission line of characteristic ...
1
vote
0answers
33 views

Do plasmons depend on the ambient EM field?

Imagine a situation: There's an illuminated metal slab in vacuum. Normally, there are some plasmons created running all over the slab. What would happen if we had turned a giant magnet near the slab? ...
1
vote
0answers
45 views

Electric field due to charge in one direction

I am supposed to calculate the electric field due to the charge density $\rho(x) = Ax e^{-\lambda |x|},$ where the density is supposed to be homogenous in $y,z$ direction. The problem is, that the ...
1
vote
0answers
67 views

Deriving the relativistic Larmor equation

I have derived the Larmor equation as $$P = \frac{q^2}{6\pi \epsilon_0 c^3} |\ddot{r}|^2.$$ How do I make this relativistic? Apparently, I have to consider the acceleration parallel and ...
1
vote
0answers
20 views

How might inducted current/ voltage in multiple coil layers connected in parallel behave?

This is a branch from this question. In the event that two or more layers are connected in parallel - would the energy created across each layer likely be significantly less? In the event of (say) ...
1
vote
0answers
212 views

Hysteresis Curve and how to implement it using Preisach model or other models

As a homework I need to draw a hysteresis curve (preferably an interactive one) using Matlab or any other programming language. The problem is I have trouble finding a good algorithm to do so. I need ...
1
vote
0answers
27 views

Could a strong AC electric field adversely affect the capacity of a lithium battery?

I run some battery powered test equipment in close proximity (~10cm) to a conductor carrying 25kV (50Hz AC). I find the battery life is much shorter than expected, having checked the current ...
1
vote
0answers
97 views

Cubic Gaussian Surface For Evaluating Electric Flux

i'm working through some problem sets about Gauss' law and all the examples I have come across so far require the use of a spherical gaussian surface for a point charge, so that it is possible to say ...
1
vote
0answers
91 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 ...
1
vote
0answers
213 views

Sommerfeld radiation conditions for an electromagnetic field

There is some confusion in the definition of Sommerfeld radiation conditions for an electromagnetic field, which are related to the asymptotic behaviour of the field for a distance $r \to \infty$ ...
1
vote
0answers
201 views

Electromagnetism - Proof of the Uniqueness theorem for an external problem

In the electromagnetic Uniqueness theorem, we consider a volume $V$ enclosed by a surface $S$. It is initially assumed that two different fields are valid solutions for the Maxwell's equations with ...
1
vote
0answers
49 views

Four-current, Induced Charge and Magnetic Flux

I'm studying Jackiw's "Fractional Charge and Zero Modes for Planar Systems in a Magnetic Field" DOI: 10.1103/PhysRevD.33.2500 but I have difficulties at some points. One of the problems is $$\langle ...
1
vote
0answers
65 views

Derivation of Boundary Conditions

Source: http://my.ece.ucsb.edu/York/Bobsclass/201C/Handouts/Chap1.pdf (page 6). I am trying to make sense of the derivation on the right side of these two integrals. The first one which says ...
1
vote
0answers
27 views

An EM problem of polarized sphere

Today, I'm doing an EM problem and my question is exactly the same as this site shows: http://www.physicsforums.com/showthread.php?t=133501 To reiterate my confusion, why we can't use that integral ...
1
vote
0answers
103 views

Currents and magnetic fields produce forces that affect things they're not touching?

I was doing this past paper and am a little confused by question 5) part c)ii) I correctly calculated that the force acting on the rod due to the magnetic field is 0.016N but I can't see how ...
1
vote
0answers
76 views

Debye Hückel Theory valid for ions?

I am wondering about the following: Is Debye Hückel Theory only used if you look at how an external "strong" field(like a potential by a sphere that has a charge that is 1000times higher than the ...
1
vote
0answers
36 views

EMF & Magnetic force at the same time?

A conductor is placed in a magnetic field, current starts to flow, and the wire experiences the Lorentz force of $x$ Newtons. However, what confuses me is that $x$ is a value that is calculated from ...
1
vote
0answers
73 views

What is $T_{\mu\nu}T_{\mu\nu}$ for the electromagnetic stress-energy tensor?

Given the electromagnetic stress-energy tensor components \begin{align} T_{\mu\nu} = \begin{pmatrix} u_{00} && s_{0 \nu} \\ s_{\mu 0} && \sigma_{\mu\nu} \end{pmatrix}_{\mu\nu} ...
1
vote
0answers
129 views

Drift velocity of electrons in a superconducting loop

Do electrons travel at the Fermi velocity in a superconducting loop? For metals the Fermi velocity seems to be around $10^6$ m/s. So would electrons (in a Cooper pair) travel around the loop at this ...
1
vote
0answers
65 views

Application of wavelets in computational electromagnetics

I am a first-year graduate student (electrical eng.); wavelets is one of the courses that I am taking presently. As part of the course, I plan to explore application of wavelets in computational ...
1
vote
0answers
93 views

Different phase in capacitively coupled RLC circuits

I was trying to work with some data for a lab report I'm writing about capacitively coupled RLC circuits. The setup is pretty simple and looks like that: Where $C^{'}$ is the coupling capacitance. ...
1
vote
0answers
103 views

Electric field produced by a charged ring

I have a question I couldn't find an answer for anywhere. There is a ring of radius $R$ which is charged uniformly with linear density $\lambda$, and I have to find the electric field on any point of ...
1
vote
0answers
87 views

Finding the induced EMF on a bar - Faraday's law

I have a couple of questions about the following problem: A conducting bar of length L moves with velocity v, in a rectangular region with a uniform and stationary magnetic field B_1. Near the bar, ...
1
vote
0answers
71 views

About Divergence in polar coordinates

I've got a conductor in a cylinder shape who is rotating with angular velocity $\omega$ around its axis, that correspond to the $z$ azis I want to calculate the electric field and the density of ...
1
vote
0answers
30 views

electron spin separation

I am having doubt whether the electron's up spin moment and down spin moment can be isolated from one another. If it got separated, will each moment acts as magnetic monopole (stable or unstable). ...
1
vote
0answers
401 views

Electric potential on a uniformly charged tube

A hollow cylinder, with no top or bottom, of radius $R$ and length $L$ is uniformly charged with density $\sigma>0$. I have to find the point on space where a point charge $q>0$ has to be drawn ...
1
vote
0answers
70 views

What are the implications of running a motor well above its rated frequency?

Plenty of material on the web will tell you what to expect when you run a 50/60Hz 3-phase induction motor at 60-80Hz, but what if you would like to run it at 140Hz? or 250Hz? Or at any frequency? ...
1
vote
0answers
705 views

Calculating the electro magnetic field strength needed to repel a permanent magnet

I have a design where a permanent magnet is placed on top of an electromagnet. When the electromagnet is powered off, the permanent magnet is attracted to the iron core of the electromagnet. When the ...
1
vote
0answers
183 views

Explanation for the physics behind magnetic monopoles?

Ok so I am looking for a simple explanation of how the process is done from the information I could access and the knowledge I was allowed I have the idea that it is a matter of quantum physics and ...
1
vote
0answers
207 views

Complex polarizability of a dielectric sphere in a homohenious electric field

It is well known that complex polarizability of uniform dielectric sphere with radius $r$ and complex permittivity $\hat\epsilon_{in}(\omega)$ placed in a medium with complex permittivity ...
1
vote
0answers
85 views

Exotic coupling

I have encountered the minimal coupling between a field and charges before $$H = \frac{1}{2m}(p-qA)^2,$$ whereby I am considering the classical case. The description minimal leads me to ask if ...
1
vote
0answers
54 views

Electron-electron interaction in solids

We always consider a Coulomb interactions between electrons in the Hamiltonian to modelize a solid. Why not to take into account retardation effects of the electromagnetic interaction which go beyond ...
1
vote
0answers
49 views

Do these steps demonstrate that acceleration of charged particle is proportional to current?

One formulation of Maxwell's Gauss Law for electric field is: $$\bigtriangledown E = 4 \pi k \rho $$ This can be worked into the Divergence Theorem as follows: $$\int\int_{A} F_\perp \:dA= 4\pi k ...
1
vote
0answers
82 views

Lenz's Law and Eddy Currents

You can determine the direction of eddy currents according to Lenz's law. E.g. If a metal sheet is losing flux into the page, it will experience induced eddy currents in a clockwise direction to ...
1
vote
0answers
94 views

$E$ and $B$ fields in Axial Gauge

I am trying to compute the $\vec{E}$ and $\vec{B}$ fields in the Axial gauge ($n \cdot \vec{A}=0$) where $n^2=1$, but I'm having trouble seeing the usefulness/how it simplifies the equations.
1
vote
0answers
57 views

Boundary Condition for Generating Evanescent Waves

I'm reading through Novotny and Hecht's book on Nano-Optics (Principles of Nano-Optics), and I've come across a subtlety in the boundary conditions for evanescent wave generation (via total internal ...
1
vote
0answers
59 views

Transitions in a magnetic refrigeration

The graph below (see attached) shows the measured magnetization against temperature at room pressure for the material Gd and for another material for use in a magnetic refrigerator at room ...
1
vote
0answers
59 views

how does graphene affect the refractive index of an optical waveguide?

Could someone help me find data on the electro conductivity of graphene and its effect on the refractive index of an optical waveguide
1
vote
0answers
81 views

Hertzian dipole in time varying electric field

Suppose we place a Hertzian dipole (short, ends loaded with capacitance) in a time varying electric field $\vec{E}\left(t\right)$, with magniture $E\left(t\right)$ and direction as shown in this ...
1
vote
0answers
67 views

Demagnetization of a permanent magnet and lenz's law

This video ( http://www.youtube.com/watch?v=Vs3afgStVy4 ) demonstrates lenz's law, if the current produced by the magnet fall induces an opposing magnetic field , after many tries , can this field ...
1
vote
0answers
55 views

Long range repulsion in anomalous solids

As far as I know things like rocks, walls, rubber balls, polished tables etc. exert a short range repulsive force on other everyday objects that is responsible for hardness, softness, collisions, ...
1
vote
0answers
145 views

Non-zero charge density due to Lorentz contraction in current carrying wires

In trying to answer this question I came across the following problem. The original question relates to the idea that what looks like a magnetic field in one reference frame, ends up as an ...
1
vote
0answers
49 views

Benefits of the sign convention for electrons?

Benjamin Franklin considered electrons to be positive, but J.J. Thompson considered them negative. We obviously went with J.J. Thompson's convention. Why? What were the benefits of moving to J.J. ...
1
vote
0answers
76 views

The curl is not zero?

In Maxwell's equations, the curl of the electric field for a steady state processes (ie. No changing electric or magnetic field) zero. However, if we take a curl along the wire for some distance and ...