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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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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19 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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51 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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65 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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53 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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47 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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86 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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40 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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18 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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143 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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41 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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95 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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82 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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47 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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37 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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20 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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53 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?
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36 views

Magnetic flux and flow of electrons

What does change in magnetic flux mean? How can you change magnetic flux? How does a change in magnetic flux influence a current of electrons (electricity)?
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116 views

Splitting of degenerate energy levels with a perturbed particle in a box

Suppose you have a particle in a square box $[0,L]\times[0,L]$. As the box is a square, the (2,1) and (1,2) eigenfunctions will have the same energy. If you were to apply an oscillating electric field ...
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53 views

Physical reason for magnetic mirroring?

I understand the mathematical derivation of magnetic mirroring, which usually starts from the conservation of the magnetic dipole moment (e.g. in a plasma). But physically: a mirrored particle is ...
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83 views

Poynting Vector Volume Integral Inside a Cavity

Given an electromagnetic wave in resonance mode in a vacuum cavity inside a perfect conductor, on the boundary, the parallel component of $E$ field vanishes, and the perpendicular of component of $B$ ...
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56 views

Explain the infinitude of magnetic flux about a finite length of wire

Ok so it is clear the flux caused by an inductor is limited. If I integrate about a flat spiral inductor I will find that the flux lines going up are a fixed quantity. Since every flux line going up ...
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83 views

Penetration and skin depth in 'metallic' magnetic induction tomography (classical electromagnetism)

Does anyone know how AC magnetic fields behave in 'metallic' magnetic induction tomography (MIT). Do they form a magnetic circuit around a metallic specimen or penetrate through it, or both? This ...
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29 views

Magnetic needles in elastic media

I am studying a system with magnetic needles in a elastic media. The (two-dimensional) system is composed of $N$ magnetic needles distributed in an elastic matrix with Young's modulus is $E$. The ...
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66 views

Constructing conserved current given the lagrangian

Consider the following Lagrangian for a massive vector field $A_{\mu}$ in Euclidean space time: $$\mathcal L = \frac{1}{4} F^{\alpha \beta}F_{\alpha \beta} + \frac{1}{2}m^2 A^{\alpha}A_{\alpha}$$ ...
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71 views

Determining the attraction of a magnetic bob

I have a question concerning the calculation of the attraction to a ferromagnetic material in a coupled B-field, which of $N \geq3$ equally strong cylindrical permanent magnet is produced. ...
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40 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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257 views

Why does Coulomb's law not hold for fast moving charges?

We all remember calculating the electric force of interaction between a stationary nucleus and a revolving electron using Coulomb's law. The electron in this case is moving. Here's what I think about ...
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72 views

What is the necessary condition on EM field for vanishing Poynting vector?

It is well known fact that both static and dynamic EM fields can give $E\times B \not=0$. What can we say about EM field if $E\times B =0$ ? Can previous equation still hold in case of dynamic EM ...
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96 views

Numeric value of the electrons drift velocity in superconductors

Somebody knows the numeric value of electrons drift velocity in superconductors? How this value depends from the used superconductor material? What's about the current? Since the electrical resistance ...
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158 views

A question on an exercise from Gravitation by Misner, Thorne and Wheeler

My question is on problem 4.1 of Gravitation. In a generic case of electric field and magnetic field(i.e not $E=0$ or $B=0$ or $E$ and $B$ perpendicular), define the direction $\hat{n}$ unit vector , ...
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38 views

EM field from the electrons on the surface of a body and their influence to moving particles

Under this question quantum field theoretic models of decoherence @DanielSank gave a wonderful answer. Can I implement his answer to every material body? What about I'm thinking is that on the surface ...
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23 views

Explain polarization in RF in which the conductor is stationary

Consider a metal rod parallel to $x$-axis moving with velocity $\vec v =(0,v,0)$ perpendicular to magnetic field $\vec B=(0,0,B)$. Lorentz force will give rise to the electric field $\vec E = - ...
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29 views

Behavior of multiple flat coils in a cylinder

I am trying to wrap my head around how this would work. The setup is quite simple - there are multiple flat coils sealed in insulated disks, and an active coil with alternating current underneath. ...
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47 views

Physical, intuitive reason for divergence of dielectric constant at electronic percolation transition?

Several papers such as this (warning, PDF) and this (PDF again) talk about how, near the electronic percolation transition for a metallic 2D film, the real part of the dielectric constant diverges ...
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28 views

How to isolate and verify the source of optical absorption/effects?

This is similar to my other question, but not the same -- that one was about the energy ranges of various absorption mechanisms, and this one is more about experimental techniques to find them. Let's ...
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56 views

Is the dielectric constant of an insulator always positive?

I know there are many examples of metals with a negative dielectric constant at optical frequencies. But what about insulators?
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24 views

Sphere in homogenou magnetic field

I have to find out the magnetic dipole moment of sphere in homogenou magnetic field in the limit $\mu_r\rightarrow+\infty$. I don't know what does the condition $\mu_r\rightarrow+\infty$ mean. Does ...
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38 views

Difference between action-at-a-distance and a field according to Maxwell?

My question is more on a historical note that involves Maxwell’s equations. Besides the information that I have obtained from textbooks, I am mainly getting it from History of Maxwell's Equations and ...
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68 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 ...
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82 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 ...
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42 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 ...
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111 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 ...
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36 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 ...
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71 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 ...
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96 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 ...
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34 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? ...
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49 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 ...
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88 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 ...
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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) ...