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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22 views

Reflection and absorbtion of EM-wave in dielectric plate (calculate through dipole)

The task: there is a plate with thickness $h$. Also $\sqrt{|\epsilon|}kh \ll 1, k = \omega/c$. Find reflection and absorbtion of EM-wave in this plate. EM-wave falling normally on plate. What I did ...
2
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4answers
549 views

Dipole in a spherical cavity in an infinite dielectric

In this example the assumption is made that inside a spherical cavity (with an infinite dielectric) with a dipole placed at its centre, the potential takes the following form: $$\phi_{in}= \frac{p ...
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0answers
11 views

Is electric field by a charge present where the net field is zero?

I have heard a lot of people say that, at all the points where electric field is zero, electric field by any of the charges never reaches there. It's quite commonly thrown around that electric field ...
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1answer
78 views

Rigorous justification of using symmetry in electromagnetism. (Calculating $\mathbf{E,D,H,B}$ fields)

This made a lot of sense to me before, but now that I think about it, I find it rather superficial. Suppose we are deriving the $\mathbf{B}$ field due to an infinite wire. One usual procedure is to ...
1
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1answer
34 views

Plane wave normal incidence on dielectric, direction of fields

I'm having an extremely hard time to figure out the direction of the $\vec E_R$ (reflected electric field) and $\vec H_R$ (reflected magnetic field) as well as the transmitted fields. I've been ...
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0answers
46 views

A 100 000 km wire in contact with a positively charged sphere

A long copper wire (see the picture), placed somewhere in the outer-space, having the length $L=100000 km$ and the cross section $S=1 cm^2$, comes in contact at one of its ends ($x = 0$) with a $+Q$ ...
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0answers
31 views

Lorentz force in Pauli's “Wave Mechanics”

I'm reading "Wave Mechanics" by Pauli and I can't understand the expressions he gives for the classical limit of Lorentz force. The Hamilitonian is in the form: $$ H=\sum_k \left\{p_k-\frac ec ...
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0answers
68 views

How is my guitar cable picking up clear radio-signals?

I've recently noticed radio-signals coming through my guitar amplifier. I'm on the top floor of a building in a densely populated city, with a clear visual path to many other buildings. My guitar ...
1
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0answers
20 views

Why do magnetic forces scale down so poorly?

Im told by experts in MEMS and nanotech that magnetic forces scale down very poorly. This is one reason we have many MEMS devices based on electric forces/electrostatics but not on magnetics. Can ...
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1answer
38 views

Would optical signal processing still suffer from slew rate?

In electronics, analog signal processing/computation suffers from parasitic capacitance which leads to slew rate—which is the maximum change of voltage allowed, so handling super-high frequency ...
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0answers
3 views

Parametrization of the medium change from solid to gas?

I am thinking the model where the parametrization of GEM (Gas Electron Multiplier) is open. I can reach a high sensitivity in similar systems where the medium is solid such as in solar cells (5 ...
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1answer
46 views

Do magnetism and light interact with each other?

If we bring along two types of energy magnetism and light. Do they in any environment react with each other and cause any of them to be manipulated.Apparently light has a part of magnetism in it.
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1answer
10 views

Sound range and depth it travells whe it hits sound

I know most people hear from 20hz to 20000hz and about the absorption spectrum of water absorption spectrum of water link but how deep does sound travel when it hits the skin and which range of ...
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1answer
33 views

Charge inducing electric field or electromagnetic fields?

I am thinking the therminology here which is about Gas Electron Multipliers (GEM). There is a continuous flow of the fill gas which is ionized so no particles created/destroyed: #1 By Gauss's ...
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0answers
35 views

What is the exact meaning (distribution) of unpolarized light?

Are there statistical properties to unpolarized light? For example, is the polarization of individual particles in an unpolarized beam has a normal distribution or a uniform distribution etc. of ...
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2answers
60 views

Does radar affect magnetism?

Does radar affect magnetism? Let's say I have two magnets, one is suspending the other. Would radar affect the magnetic field?
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0answers
24 views

Help with a problem in magnetism, kinetic energy

I couldn't fully understand how the author solved the problem c). Here's what was done: At first I thought he changed $v$ for $\sqrt{\frac{2K}{m}}$ in the equation $r=\frac{mv}{|q|B}$, but ...
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0answers
36 views

Magnetic field of a circular particle accelerator

Suppose there's a $500 \ GeV$ proton beam ($q=1.6 \times 10^{-19} C$) inside a circular particle accelerator, what would be the magnetic field intensity $B$ in Teslas required to keep it stable at a ...
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1answer
78 views

Finding the electric and magnetic fields from the vector potential $\vec A=\vec{E_0} e^{i(\vec k\cdot\vec r-\omega t)}$

I am trying to find the electric and magnetic fields from the vector potential $$\vec A=\vec{E_0} e^{i(\vec k\cdot\vec r-\omega t)},$$ I know $$\vec B=\vec \nabla\times \vec A$$ and $$\vec ...
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1answer
56 views

Combined function magnet

I am searching how a combined function magnet for accelerator physics works, but on the books that i have and on the web i can find only patents for this thing, that suppose to know already how this ...
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1answer
146 views

Why does an electromagnet attract iron according to Special Relativity?

I saw a video of Veritasium on "How Special Relativity Makes Magnets Work" and came up with a question. So please watch the video first before answering my question as it is related to the video. 1) ...
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0answers
11 views

How do i calculate the “attenuation effect” that of a perforated aluminum sheet?

I am conducting an experiment test different configuration of perforated aluminum sheets. I am working with radio waves but i am having am hard time finding any equations or properties for this ...
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2answers
177 views

Direction of H and B inside and outside a bar magnet

I seem to have encountered a contradiction when thinking about the directions of $\textbf{H}$ and $\textbf{B}$ inside and outside a bar magnet. Suppose that a bar magnet has a roughly constant ...
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2answers
133 views

George Green's derivation of Poisson's equation

I was reading George Green's An Essay on the Application of Mathematical Analysis to the Theories of Electricity and Magnetism, and I got confused on one step in his derivation of Poisson's Equation. ...
2
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0answers
45 views

Lorenz Gauge Dipole Potentials Formulation In SI Units? [closed]

After hunting in vain* for a documented closed form solution (ie: no integrals or differentiation in the formula) for $\phi$ in terms of A under the Lorenz condition, of an electrically short dipole ...
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1answer
46 views

High Power/Range Electromagnet [closed]

Pretty new to electromagnetism but my team and I are working on a project so have some questions before we spend more money doing R&D. We are looking to create a fairly small 10-20lb ...
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1answer
56 views

Induced dipole in a molecule with a permanent dipole moment?

How can there be an induced dipole in a substance with a permanent dipole moment? I thought an induced dipole can occur only in a non-polar substance. Yet, this is part of the proposed dipole-induced ...
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0answers
71 views

Unitary gauge transformation [closed]

I have the Hamiltonian of a charged particle without Spin in a time- independent magnetic field and an external Potential (no electric field). Also I have the standard Gauge-Transformation $A ...
1
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0answers
27 views

Kernel of Helmholtz Equation on a plane [closed]

On the $z=0$ plane I have the boundary conditions $V=\delta(x)\delta(y)e^{i wt}$ I want to solve for $z>0$. I though that spherical harmonics would be useful. The function should be independent of ...
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0answers
40 views

Hysteresis at low temperature [closed]

How will the hysteresis curve for a typical ferromagnetic substance change at low temperature(near 273K and near 0K) from its nature at room temperature ?
0
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1answer
18 views

Need to find module of magnetic field

I have a post-lab problem During the experiments I have a U magnet on a scale. Inside the U magnet there is a conductor with a steady current. The conductor is made so that the magnetic field is ...
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0answers
110 views

Designing Repelling Electromagnets [closed]

I need to design a pair of electromagnets to repel each other with maximum force while being less than a certain weight. Specifically, they must accelerate a a 1lb mass to 5 m/s vertically within 5cm ...
3
votes
1answer
148 views

Which is more fundamental: $H$ or $B$? [closed]

According to Wikipedia, $B$ is called the Magnetic flux density / Magnetic induction / Magnetic field, while $H$ is called the Magnetic field intensity / Magnetic field strength / Magnetic field ...
3
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3answers
89 views

If electric fields can't pass through a grounded shield, how can a magnetic force be generated on moving charges outside a wire? [duplicate]

Say an electron outside a wire is moving with the same velocity as the electrons inside, then due to Lorentz contraction, an electric field would be generated in the outside electron's frame of ...
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1answer
58 views

Solenoid and charged disk

If we put current on the solenoid, it makes change of B field. Then I think charged disk will rotate, but I don't know where the angular momentum came from.
5
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2answers
159 views

Transmitted Power and Poynting's theorem contradiction?

I was reading Chapter 12.1 in Hayt & Buck "Engineering Electromagnetics" 8-th edition. Here they discuss the reflection of uniform plane waves at normal incidence. They derived the following ...
4
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1answer
264 views

Why can protons collide?

Electromagnetic repulsion is inversely related to the square of the distance between both objects. Shouldn't this mean that the integral of the force between two protons is infinite if the distance ...
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0answers
65 views

Spherical Conductors in Dielectric - Potential

I have computed the electric field of the following system between the two spheres, but my calculations for the potential do not make sense. The potential should be proportional to $\frac{1}{r}$ but I ...
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1answer
40 views

Moving magnetic fields?

I was reading through Feynman Lectures on physics vol II when I came across this paragraph which I don't quite seem to understand: Since electric and magnetic fields appear in different mixtures ...
0
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1answer
49 views

Why does the electric potential of a conducting surface becomes zero when it is connected with another surface with potential zero?

Suppose there a conductor at potential $\theta$, enclosed by a surface of potential $0$. Why, when the conductor is connected to the zero-potential surface, its potential becomes zero as well? ...
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0answers
18 views

Ampere's Law and frame

We have following situation. What will happen with frame if frame turns on 90 degrees? Let's assume that we have homogeneous magnetic field.
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0answers
23 views

Faraday's Law magnetic field rate of change from induced current

A rectangular wire loop has a magnetic field traveling perpendicularly through it with a field strength of $2T$. The resistance of the loop is $2\Omega$. A change in magnetic flux induces a constant ...
0
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0answers
61 views

Distance of the electric field generated by a Slayer Exciter ( Variation of tesla coil )

I'm currently trying to create a really basic simulation of a slayer exciter for a demonstration I have to give at my college. The thing is we want to know how far does the electric field produced by ...
1
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1answer
91 views

Interaction of magnetic fields with the magnetic field produced by current?

In this picture, the magnetic field from the permanent magnets exerts a force on this wire, and the direction and magnitude is described by $F = iL X B$ But doesn't the wire also generate a ...
0
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1answer
89 views

Maxwell's Equation

I was reading a book and I found the following equation. I'm not good at physics and I couldn't understand where does it come from, can anyone explain me why is it valid? $$ \mathbf E = -\nabla\phi - ...
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0answers
35 views

If I know how many atoms I have in a film, can I know the total magnetic moment?

Say I have a Co film and I know its volume so I know the total number of atoms in it. Using this plus the knowledge that each atom has a magnetic moment of 1.7 Bohr magnetons, would the total magnetic ...
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0answers
54 views

Index of refraction for travelling EM wave problem

Let $n_1$ be the index of refraction of the first medium and $n_2$ be the index of the second medium. When $n_2>n_1$, then for an incident angle of $90^{\circ}$ we get a refracted light at a ...
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1answer
47 views

Can we produce a wave by oscillating current? [closed]

If Radio waves can be generated by using oscillating current so if we changed the properties of current to produce less wavelengths or light waves - I'm not asking about the possibility of producing ...
0
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1answer
37 views

TM modes expression for a cylindrical cavity, Jackson's book

Consider a cylindrical cavity with circular cross section of radius R. The height of the cylinder is d; the walls are considered as being a perfect conductor. I'm facing a difficulty findind the TM ...
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0answers
34 views

Action functional of Born-Infeld model

I have a Born-Infeld action functional like this $$I[A,\phi]~=~\int b^2(\sqrt{1+(|\bigtriangledown\times A|^2)/b^2}-1)+|D_A\phi|^2 + b^2(1-\sqrt{(1-|\phi|^2)^2/b^2} ).$$ Have any books or notes talk ...