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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5answers
491 views

Can one deduce absolute motion through magnetism? [closed]

I am trying to understand forces in relativity: Suppose there are two electrons A , B travelling side by side at 1 cm distance at .99 c (in space or at lHC, ignoring all other factors). I know that ...
1
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0answers
27 views

How does cavity resonance produce EM waves? [closed]

My understanding is it acts like a capacitor and inductor in a loop. The capacitor releases stored energy which is absorbed by the inductor through a magnetic field which then returns it to the ...
0
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1answer
61 views

Force on a charged particle in a field of an EM wave [closed]

For example if there is a charge q with mass m travelling with a velocity v "in the field" of a plane electromagnetic wave that is travelling in the z direction (in free space). My question is what ...
1
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1answer
43 views

Show the Berry phase is invariant under $U(1)$ unitary transform [closed]

Recall that $$\gamma_n = \oint A_n(R) \cdot dR = \oint \langle\psi_n(R)|i\nabla_R|\psi_n(R) \rangle \cdot dR.$$ Under the $U(1)$ transform, $$\psi_n \to \psi'_n \equiv e^{i\xi_n(R)}\psi_n,$$ where ...
2
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1answer
81 views

What is really sought when we purpose Einstein's postulates in Special Relativity?

Special Relativity can be motivated by looking at Maxwell's Electrodynamics and noticing that there is some kind of inconsistency between it and Newtonian Mechanics. Indeed, as Einstein pointed out on ...
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0answers
9 views

Lorentzian nature of reflected microwave power in Electron Spin Resonance

Reflected microwave power has Lorentzian shape when plotted against frequency in ESR. How to mathematically prove this?
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1answer
45 views

Derivation of Biot Savart law for a curve

I'm ok with the following expression for Biot-Savart: $$ {\mathbf B}({\mathbf r}) = \frac{{\mu _0}}{{4\pi }}\int\frac{{{\mathbf J}({\mathbf r'}) \times {(\mathbf{r-r'})}}}{{|\mathbf{r-r'}|^3 }}dV'. $$ ...
0
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0answers
33 views

Why do metal filings line up in parallel (non-curved) lines on a knife blade?

My girlfriend works at a knife factory and was grinding a new knife model today made of a very hard, magnetic steel. She noticed that the metal filings were lining up on the knife blade in ...
2
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1answer
36 views

What's the difference between electromagnets and induced magnetism?

I am studying over the basic introductory concepts of magnetism, and I cannot comprehend definition of the following words below: Electromagnets- objects that are magnetic only when electric current ...
2
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1answer
51 views

Confusion over plant's “magnetic field” being used to reduce wastage of pesticide

As far as I am aware, a plant does not have a magnetic field of any significant magnitude. What I wonder is, is there any electromagnetic related basis for the crop spraying technique outlined in ...
0
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0answers
37 views

What is the difference between length and velocity gauge when it comes to a dipole approximation?

Lets say we have plane wave with $\vec E$ perpendicular to $\vec k$. The dipole term will come from $\vec A\cdot \vec p$. Is the electric field longitudinal in the length gauge for the dipole ...
0
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1answer
56 views

Coulomb law and photons

When we consider process like $e^- e^- \to e^- e^-$ in QED, we see that from exchanges of one photon (tree-level diagrams) one can obtain Coulomb's law, while loop-diagrams give quantum corrections ...
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2answers
29 views

gradient strength units in MRI

This may not be the appropriate forum for this but seemed to be the closest. I am trying to understand some concepts around MRI physics and it is common to use external magnetic fields created using ...
0
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1answer
19 views

Energy (voltage) correction on energy level between metallic electrodes with dielectric and accounting for work function difference

My goal is to understand how to correct for the field drop and the work function difference when performing electrical measurements on a certain energy level of a sandwiched system. The situation is ...
0
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2answers
64 views

Can a grounded spherical shell have a charge?

Can a grounded spherical shell lying inside another bigger non-grounded shell have charge on it? If yes then why? Won't the charge on the grounded conductor flow to the ground?
0
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1answer
22 views

What would be the suggested material for blocking EM waves of a 600V 160kW 5kHz coil?

I am building up a reactor for heating material inside, but I need its EM waves not to interfere with the rest of my near circuitry. Its working conditions are: 600 VAC 300 A 160kW 5kHz What ...
0
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2answers
109 views

What is the inconsistency between Maxwell's electrodynamics and newtonian mechanics?

As far as I understand, when a modification of a theory is made it is because some observation required this modifcation. Quantum Mechanics is a nice example of that: observations of microscopic ...
0
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0answers
37 views

Amplitude of unpolarized EM wave after a polarizer

The amplitude of a linearly polarized wave after a polarizer is $$E_1 = E_0\cos(\theta)$$ and the intensity is $$I_1 = I_0\cos^2(\theta)$$ Now for unpolarized light, the time averaged amplitude is ...
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0answers
14 views

Derivation of Poynting theorem in matter

In most textbooks I have read they derive the Poynting theorem using the Maxwell's Equation in vacuum and the fact that the force density $f=\pmb{E} \cdot \pmb{J}$. Then they just generalize it ...
3
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1answer
92 views

How to solve “EM wave equation” for the field of uniformly moving charge?

Is it possible to show that the field of a uniformly moving charge, which is according to Biot-Savart law is given by... $${\bf E}({\bf r},t)=kq\left(\frac{1-v^2/c^2}{(1-v^2 \sin^2 ...
0
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2answers
41 views

An experiment related to Faraday's laws

This question is out of an Indian competition. I do not know calculus yet. I have some idea about how magnetic fields and electric fields work together but i don't know how to go about thinking ...
0
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1answer
22 views

Are deflection of compass and speed of electron relative to each other?

If one holds an electron in one hand and a compass in the other hand, and the starts running at the speed of light holding those, then will there be any deflection of the compass ?
2
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2answers
96 views

What does the Poynting flux represent?

I know that the Poynting flux is the cross product between $\vec E$ fields and $\vec B$ fields, but I'm wondering, are the field lines of the Poynting flux considered as electromagnetic energy? Let's ...
3
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1answer
44 views

Gauss law and electrostatic induction. Concentric spheres

Imagine you have hollow concentric spheres A and B with radius a and b (b>a), respectively. If A is a conductor and B has a certain density charge, I´ve been taught that B will induce some net charge ...
1
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1answer
39 views

How does sunlight undergo interference as shown in the video?

As far as I know, for interference to happen in a double-slit experiment, the light source should be coherent and monochromatic. If that is the case then how come sunlight undergo interference and ...
0
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1answer
50 views

Why do electric motors stop working when physically stopped (burned up)? [closed]

I found a rock lodged between the fan and the radiator on my motorcycle. Now the fan does not work when the computer prompts it to. I tried directly attaching the 12 volt battery to it as well. No ...
1
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3answers
73 views

Why don't E&M fields change orientation after hitting a surface?

In essentially every derivation of the Fresnel equations, the general problem of radiation hitting a surface at a certain angle is broken into two parts (out of which we hope the solution any general ...
3
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0answers
42 views

Question about the fields in a solenoid

I am very familiar with using Ampere's Law to find the B field inside a solenoid ($\mu_0nI(t)$). Then I can use Faradays to find the E field inside ($\propto\dot I$). I want to get this result ...
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2answers
52 views

Is magnetic field of a uniformly moving charge constant everywhere?

As far as I understand, for the field of a uniformly moving charge, curl of $\mathbf E$ is zero everywhere. Since $\nabla \times \mathbf E = -\dfrac{\partial\mathbf B}{\partial t}$, magnetic field ...
0
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2answers
41 views

Find the radius of the path of an electron in a magnetic field [closed]

In a question I am asked to find the radius of the circular path that an electron follows in a magnetic field. The field strength is $B=10^{-5}T$ along the positive y axis, the velocity of the ...
1
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0answers
24 views

What is the effect on measured values of potential differences if we assume that potential difference of earth is +100V instead of zero? [closed]

What is the effect on measured value of potential differences of earth is +100V instead of zero?
0
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0answers
15 views

Easiest way to levitate a ferromagnetic material that is not a permanent magnet?

I want to levitate an iron cube that is not a polarized permanent magnet. What is the easiest way to do this?
0
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0answers
15 views

Can a diamagnetic levitator levitate non-permanent ferromagnetic materials?

I am building a diamagnetic levitator that will eventually levitate a small neodymium cube. However, is it also possible for an iron cube to be levitated as well? I know that diamagnetic materials ...
0
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1answer
31 views

Is it possible to levitate large objects through diamagnetic levitation?

I am currently building a diamagnetic levitator with a strong neodymium magnet, two slabs of bismuth (a diamagnetic material), and a small neodymium cube to levitate. However, I was wondering if it ...
2
votes
1answer
64 views

Why doesn't the changing field of a moving charge create EM waves? [duplicate]

EM wave phenomenon is usually described as "changing electric field creates changing magnetic field which creates a changing electric field etc." But fields of a uniformly moving (not accelerating) ...
1
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2answers
67 views

how do we actually count the number of magnetic field lines and what does the gap between those lines describe?

on the internet,(http://nuclearpowertraining.tpub.com/h1011v1/css/h1011v1_53.htm), there is a statment which says that 1 Wb is $1\times 10^{8}$ magnetic field lines. My question is, How do we count ...
2
votes
1answer
34 views

Wave Velocity vs. Phase Velocity

I am trying to understand the difference between 'wave velocity' and 'phase velocity'. I know that generally they are equal, but when is that not the case? I, of course, tried to google it, and ...
-1
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1answer
59 views

Questions about Magnetic field [duplicate]

I have two questions about Magnetic Field. Given a particle with mass m, charge q and uniform B field. B is going into the page, and particle is moving to the right Like this. The textbook says ...
1
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1answer
23 views

How, if at all, does the behavior of a parallel plate capacitor change in the presence of a magnetic field?

I'm an AP physics student curious about magnetism and my teacher couldn't answer this question. We already learned about velocity selectors, so I know that, when the plates of the capacitor are in the ...
2
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2answers
37 views

is it possible to shape electromagnetic field?

Is it possible to produce a magnetic field of specific shape? For example a magnetic field that will be confined in a cylindrical shape of specific dimensions.
1
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1answer
40 views

Can an electromagnetic potential be in two gauges at once?

I have a plane wave vector potential found using the free field form of Maxwell's equations and the Lorentz gauge: $\vec{A}(\vec{r},t) = \vec{A}_0 e^{i(\vec{k}\cdot\vec{r}-\omega t)}$ If I take the ...
-4
votes
0answers
16 views

Load matching in a transmission line [duplicate]

Can somebody explain me easily and clearly why when you want to transform a 50 ohm load impedance through a piece of transmission line in an arbitrary one let's say Z (complex number); that is exactly ...
3
votes
1answer
96 views

High Level Understanding Q: What *is* a magnetic/electric field?

Note: I have seen this question -> (What is a magnetic field) and would still like some clarification. I have also seen https://www.youtube.com/watch?v=hFAOXdXZ5TM and ...
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0answers
47 views

How to compute the magnetic force between two electromagnets?

I wanna compute the magnetic forces between two solenoids with iron cores, is there any analytic formula for this? I guess that dipole-dipole interaction in the link ...
1
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1answer
53 views

Does the field of a unifirmly moving charge satisfy Maxwell's wave equation?

The so-called "electromagnetic wave equation" is so general that it should obviously hold for every point in space and for all field configurations (if there are no charges). Here it is: $$ \left(c^2 ...
0
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1answer
29 views

Motion of an electric charge within an electric field with two electric charges

Assume that air resistance and gravity are negligible and the only significant force acting in the scenario is the electric force. There are two electric charges, both with an equal and positive ...
0
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0answers
21 views

Explanation of absorption from Bloch Equation

Suppose in a magnetic resonance experiment the microwave/rf field is applied in x-direction.How to say that the component of magnetization which is out of phase with the microwave magnetic field leads ...
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0answers
40 views

Coulomb Gauge under Lorentz Boost

In the Coulomb gauge for the Maxwell potential we have $$ A^0 = 0 \\ \partial_i A^i = 0 $$ Under an infinitesimal Lorentz Transformation with parameter $\epsilon$, we have $$ A^\mu(x) \rightarrow ...
0
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2answers
76 views

Is the CHAMP missile capable of doing what they say it does? [closed]

CHAMP, A new counter-electronics directed energy USAF weapon was created by Boeing Phantom Works with the intention to damage and / or destroy electronic target equipment without causing structural ...
0
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3answers
113 views

Can we use magnetic energy to produce electricity?

Magnets attract each other with a force (magnetic force), because they possess magnetic energy. My question is, is there any way, by which we can convert that magnetic energy into electrical energy? ...