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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92 views

Consistency of equation with special relativity?

The following is the equation which, I want to know, if it is valid in relativistic domain. Consider two equal charges moving in same direction with velocity $v$ and charge $q$ at a separation of ...
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160 views

Doubts about the Aharonov-Bohm effect

In F. Schwabl, Quantum Mechanics p.148 it is explained that if we have a particle in an electromagnetic field given by potentials $\varphi$ and $\mathbf{A}$ with wave function $\psi$, then a gauge ...
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89 views

Mie Scattering for spheres with constant dipole moment

I was wondering whether there exists a theory that describes Mie Scattering for spheres that have a constant dipole moment. Since there are theories that describe Mie scattering in the case of a ...
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106 views

How the dielectric rigidity depends on the shape of material?

A research article says that, "The conical shape improves the dielectric rigidity", but how I am not able to understand.
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174 views

Charge above a conductor; effects due to Lorentz force law for moving charges

Currently working through a practice preliminary examination problem. I have your standard charge situated a distance d from a infinite conductor(lets say in the $\hat{z}$ direction and neglecting ...
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695 views

Transmission Line Theory: Coaxial Cable Per Unit Length Series Resistance Derivation

Brief Background A coaxial cable is an example of a transmission line. A transmission line can be analyzed by using a distributed element model in which there are a repeating set of per unit length ...
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225 views

Current to cancel Earth's magnetic field

I'm making a lab report where I've used a Helmholtz coil and a magnet to find Earth's magnetic field intensity in the area by relating the frequency of oscillation of the magnet when a certain current ...
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622 views

Relationship between current, voltage, magnetic field in a torus

I'm trying to find the relation between current density $\boldsymbol{j}$, voltage $v$, and magnetic field $\boldsymbol{B}$ for the time-harmonic approximation in a cylindrically-symmetric coil (a ...
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197 views

Solving the equation of relativistic motion

How does one solve the tensor differential equation for the relativistic motion of a partilcle of charge $e$ and mass $m$, with 4-momentum $p^a$ and electromagnetic field tensor $F_{ab}$ of a constant ...
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193 views

Fourier Transform of ribbon's beam Electric Field

I have a monochromatic ribbon beam with $E(x)e^{i(kz-\omega t)}$ being the electric field's amplitude. I want to show that the lowest order approximation in terms of plane waves is ...
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563 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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54 views

What name would you give to the method of approximating an arbitrary magnet with many smaller dipoles?

Let's say I had an arbitrarily shaped permanent magnet, with total magnetic moment $M_{0}$. Ways to calculate the magnetic field of this magnet include an analytic solution (if one exists), as well ...
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198 views

How can I determine the type of magnet used in a DC motor?

I repair electrical motors in a workshop and sometimes I must repair permanent magnet DC motors and other motors that use permanent magnets. I need to specify type of permanent magnet (Ferrite or ...
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206 views

Where can I find a complete list of metamaterials up to today?

Where might I find a list of all the metamaterials up-to-date?
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114 views

How much current would be generated by polarity reversal of Earth's magnetic field?

Continuing from my previous question Is reversal of magnetic polarity in a planet an instantaneous occurence? A change in magnetic flux is expected to generate an EMF. In the case where the ...
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612 views

Are there any non magnetic materials that attract to each other as if they were magnetic?

Are there any non magnetic materials that attract to each other as if they were magnetic? This is an argument I am having with a friend. Thanks,
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500 views

Dielectric in Parallel Plate Capacitor

Given a parallel plate capacitor of width $w$, length $l$, with a dielectric moving along the length $l$. Let the dielectric be from $x$ onwards. The capacitance will be $\frac{w \epsilon_0}{d} ...
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178 views

Energy loss rate for periodic movement

How to prove that if a particle performs cyclical motion then its energy loss rate averaged over the period equals averaged radiation intensity? The energy loss rate is the quantity of energy that ...
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242 views

Solar wind and the Earth's magnetic field

I have again an old question from a comprehensive exam I took a couple of months ago. Lucky for me one could pick 5 out of 8 questions, because on some of the problems I didn't even know how to start. ...
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258 views

The effect of an EMP on circuits

Which of these is the current (also, what about voltage?) induced by an EMP pulse within a circuit most dependent on? The area of the region enclosed by the circuit The orientation of that area with ...
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315 views

Levitation rotation speed involving laser acceleration, pyrolytic graphite and a vacuum

The experment would involve a small NIB magnet levitating between or on the diamagnetic material pyrolytic graphite, unlike other forms of levitation this doesn't require power to run such as ...
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904 views

How to calculate the electric field and potential inside a dielectric surface placed into a homogenous field

In an experiment we placed a long dielectric cylindrical shell (cylindrical tube)(with inner and outer radii r1 and r2, respectively) in a homogenous field such that its axis was orthogonal to the ...
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64 views

Degenerated Anderson Model Simulation

I'm trying to simulate the degenerative Anderson model. So depending on an energy difference first orbital and afterwards spin magnetism occurs. First i try to solve an easier ansatz with a limitation ...
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27 views

What causes the Shubnikov-de Haas Oscillations?

If I have a 2DEG with a voltage in the $x$-direction and a $B$-Field in the $z$-direction (so I also get a hall-voltage in the $y$-direction (classicaly)). But if I do this stuff at low temperatures I ...
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64 views

What unit system puts a bunch of powers of ten in Maxwell's equations?

In what unit system can we get the Maxwell equation in the following form (section 1.2 from Lewin's book Advanced Theory of Waveguide) $$\nabla\times \vec E = -10^8\mu \frac{\partial \vec H} ...
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25 views

EMF and Distance

As a professional underground service locator, EMF and Inductance are at the very core of what we do. Very few of us truly understand the detailed physics behind what makes it possible for us to ...
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34 views

Why do Superconductors make Magnetic Fields Bend Away

When superconductors reach their "threshold temperature" their electrical resistance turns 0. This makes the magnetic field lines not pass through the superconductor but instead bend itself around it ...
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32 views

Transfer function of a space varying wave equation

$$\frac{\partial ^2 \psi}{\partial x^2}-\mu \epsilon \frac{\partial ^2 \psi}{\partial t^2}-\mu \sigma \frac{\partial \psi}{\partial t}=0$$ Is the wave electromagnetic wave equation in lossy, source ...
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22 views

Recommended books that describe emission and absorption of light and light/matter interactions

Hello I am a Chemical Engineer that has ventured into the field of optics and I was wondering if there is any recommended book/books to understand the maths and also some answered exercises or ...
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42 views

Lack of symmetry in Poynting vector

I've noticed that there's a lack of symmetry in the definition of the Poynting vector, being defined as: $$S=E\times H$$ meaning, using the electric field cross the magnetizing field instead of the ...
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13 views

Coordinate Transformation across different media

I have an arrangement that is as follows : (1) inner cylinder(radius r1) filled with water (2) outer cylinder(concentric, radius r2>r1) made of glass I have a sensor S1 at radius r(r1) at angle beta. ...
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76 views

A classically charged point particle interacting with electromagnetism and gravity

Consider a classically charged point particle interacting with electromagnetism and gravity. The relevant dynamical variables are $\chi^\mu (\tau)$ of the particle, the electromangetic potential ...
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22 views

Combining wave plates?

In the context of classical electromagnetism, is it always possible to reproduce the action of a large number of half-wave plates and quarter wave-plates with that of a single half-wave plate and a ...
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20 views

Is Magnetic field inside solenoid dependant on volume of its shape?

There are two types of solenoids: one cylindrical, one spherical. Let's assume the dimensions of the cylindrical solenoid are set such that its base radius is that of spherical solenoid $a$, and the ...
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73 views

Lorentz force on superconductor vortices

I am reading a paper on superconductivity and in it it says that the vortices are subject to a Lorentz force given by $$\vec{F}_L=\frac{\Phi_0\vec{I} \times \vec{H}}{cH}$$ Here $\vec{F}_L$ is the ...
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29 views

Magnetic dipole near black hole

Usually it is said that black holes cannot have electric or magnetic dipole, only electric charge and angular momentum are allowed quantities besides mass So, it would seem that black holes behave as ...
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33 views

Question about Meissner Effect video

In this video, what material is on top of the superconductor disk that keeping it cold? Is it just a circular chunk of dry ice? http://www.youtube.com/watch?v=Ws6AAhTw7RA I'm planning on recreating ...
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40 views

Ampere's law and magnetic circuit

For magnetic circuit there is an equation NI=HL. This equation is obtained by applying Ampere's law. H is magnetic field intensity and L is the length of the circuit. In following picture the equation ...
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21 views

How can I have a voltage in hall effect with zero magnetic field?

How can we obtain a voltage with no magnetic field is applied to the semiconductor? They told me that if the points where I measure the potential difference are not at the same level I would obtain a ...
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29 views

Boundary conditions for vector wave equations

Assume the time-harmonic case of Maxwell's equations, one can obtain the following vector wave equations: $$ ...
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109 views

Confused on how to apply the volume integral form of the Biot-Savart law

In Viscous evolution of point vortex equilibria (Jing, 2011) the author explains that the velocity equation for the Lamb-Oseen vortex is found by applying the 2D Biot-Savart law to the vorticity ...
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27 views

Uniform field through a disc

Let us say that we have a magnetic field of the form $B_0 \sin(\omega t) \hat e_z$ in all space. Now let us say we put a conducting disc within this field. I want to find the electric field within ...
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22 views

Calculate characteristic frequency from atomic polarizability

With Lorentz model, the plasma frequency can be calculated from electron density $$\omega_p=\sqrt\frac{4\pi N e^2}{3m}$$ But I also found in this paper that it could also be calculated from atomic ...
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65 views

Why are cereals attracted by a magnet?

Many cereals (from the supermarket) are attracted by a magnet. This can be seen by crushing the cereals into a very fine powder and approaching a strong magnet. The usual explanation is that cereals ...
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51 views

Does Lorentz force affect the magnetic field?

When a charged particle moves thru magnetic field, it is affected by Lorentz force. But does the magnetic field surrounding the particle experience a force opposite to the particles Lorentz force ? ...
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47 views

Electromagnetism and magnetic fields

Would it be possible to fill hollow non-magnetic blocks of metal with ferromagnetic fluids and use magnetic fields to move the blocks in a certain way? I am only asking this because I think that if it ...
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0answers
27 views

What does it mean to perturb the electromagnetic energy with respect to a change in a Lorentz frame?

I am perturbing the energy of an electromagnetic field using \begin{align} \dfrac{\partial U}{\partial \zeta} = \dfrac{1}{\mu} \boldsymbol{H}\cdot \dfrac{\partial \boldsymbol{H}}{\partial \zeta} + ...
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94 views

Divergence Theorem, mathematical approach to Gauss's Law?

Let $D$ be a compact region in $\mathbb{R}^3$ with a smooth boundary $S$. Assume $0 \in \text{Int}(D)$. If an electric charge of magnitude $q$ is placed at $0$, the resulting force field is ...
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20 views

Halbach array possible shapes?

Looking at images on the web most hallbachs are either rings or blocks but I have seen a couple pictures of what look to be rectangles or pyramids. They are just illustrations though and maybe ...
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23 views

What's the shape of electric field line in a rectangular metal under varying magnetic field

We know that,the shape of electric field line in a cylinder under varying magnetic field is circle,and I wonder,what's the situation if it is a piece of metal with rectangular cross section? I think ...