Questions tagged [electromagnetism]

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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26 views

Magnetic Detection of Magnetite

I have a tool with a very thin and faded coating of what seems to be magnetite black oxide ($\mathrm{Fe_3O_4}$), I’m trying to see if this coating is magnetite, while a chemical test is possible, a ...
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What is the derivation of Rayleigh's Equation? How do i get to Rayleigh's equation? [closed]

im looking for an answer of the derivation of rayleigh's equation, ie; how to get to the equation through derivaiton, thanks
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If a constant current can create constant magnetic field , why do we need changing magnetic field to induce current?

The electrons only going from negative to positive are able to create a magnetic field, why does the magnetic field have to keep changing to induce a current? If I pass the same magnetic field through ...
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High efficiency motor design with lasers [closed]

I'm testing theories of lasers to push/repel another object in a motor like fashion, pulses of light to push said material into rotation at high speed. Solar sail like object in a smaller format to ...
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24 views

Orientation and sign convention in 2D electrodynamics using differential forms

I've been following this paper for a treatment of electrodynamics using differential forms. In particular, they demonstrate that Maxwell's equations expressed using differential forms are form-...
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1answer
52 views

An electrodinamic identity: starting point [on hold]

With this request, I would like to ask you kindly how you can prove this identity. I thank you for those who can help me. \begin{equation} \overline{\nabla} \times (\overline{\nabla} \times \...
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Naive question - Is Magnetic generator (like this) not a 'perpetual motion machine'? [duplicate]

Perhaps a question that is too naive to be on Physics.SE but I let the experts here decide (and downvote at will), but there seem to a certain company that claims to have created what it calls a "...
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19 views

Torque on a current carrying semicircular coil placed perpendicular to a magnetic field [closed]

I found out that the force on differential elements will be radially outwards so the net torque about C will be zero but I am confused on how to find the net torque about P. I understand that the ...
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2answers
103 views

H field Vs B Field inside a magnet

I was studying electromagnetism and was going the basic definition and trying to understand their importance. I could not figure the difference between The H- Field and B- Field at first. So I ...
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how to use electricity into weight [duplicate]

I have a doubt, it is possible that electromagnetic force can be used instead of weight bars. An electromagnet is simulated as weight in real-time? if I pull 5 kg weight in the electromagnetic field ...
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28 views

Direction of EMF and Induced current through the circuit

When the circuit shown above is moved with a constant velocity to the left I know that B is going to have the higher potential. And I believe that the current flows clockwise that is in the sense of ...
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15 views

Magnetic Field Lines Vs Magnetic Vector field

I am studying electromagnetic theory and when I started researching the history of conventions used in magnetic interactions I could not get them. The basics of how they modelled the magnetic ...
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2answers
51 views

Permanent magnet attraction from Maxwell's equations / Lorentz force [duplicate]

Edit: My question is different because I am not asking how permanent magnets come about. Rather, I am asking why (taking permanent magnets as a given) they attract or repel each other. I.e. What ...
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160 views

Compact expression of Maxwell's equations: missed minus sign

With much courtesy I ask a simple explanation to be able to obtain a minus sign missing from the compact form of Maxwell's equations: $$\boxed{\square \overleftrightarrow F=\mu_0 \boldsymbol{\mathcal{...
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Best books for Electromagnetism? [duplicate]

I would like to know some titles of the best books in Electromagnetism. Some poeple recommended me to read Griffiths. My big deal is to become a theoretical physicist in Particles/Fields and ...
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1answer
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Understanding of Gauss law using vector fields

I was going through the conventions and terminologies followed to describe the magnetic interactions. I understood that the field lines are just a simpler representation of the magnetic interaction ...
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1answer
44 views

Does protons moving parallel to each other exert magnetics force

If two protons are moving parallel to each other in same direction with equal velocities then do they exert magnetic force on each other.? As protons are moving they should produce magnetic field and ...
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69 views

Newton's third law in magnetic in magnetic fields

Say I have a charged particle moving through a magnetic field perpendicular to it. It will experience a force, but according to Newton third law Every force has an equal and opposite reaction. So ...
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20 views

Time derivative of dipole moment

While deriving the relation, $$\int_V \bar{J}d \tau = \frac{d\bar{p}}{dt} $$ in this question. We have, $$\frac{d\bar{p}}{dt} = \frac{d}{dt}\int_V\rho \bar{r} d\tau \\ \implies \int _V \frac{\...
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Doubt Related To Working Of A Cyclotron [on hold]

The condition good resonance in case of revolution of +ve charged particles in Dees is , Frequency Of Semi-Circular Motion Of +ve Charged Particle = Frequency Of H.F. Oscillator OR Frequency Of ...
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Poynting vector flux in a tube (geometrical optics)

Let's consider the following tube (defined as the solid described by two arbitrary surfaces dA1 and dA2, and by all the rays which connect their boundaries): I read in a textbook that, because of ...
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1answer
20 views

How to recover the potential field from Green's function and Poisson's equation for a point charge

I first find the Green's function for the following PDE in $n=3$ dimensions, where $k:=|k|^2$. $$\nabla^2G(x,x')=\delta^3(x-x')$$ Upon Fourier transforming both sides, and inverting, I find that $$G(x,...
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2answers
31 views

What do you see when you are inside a transparent conducting material?

Lets say that there exists a transparent conducting material. Lets carve a cavity in the meat of the conductor big enough for a person to stay in. There exists an external electric field. But, We ...
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2answers
109 views

Why doesn't a magnetic field accelerate moving charges?

As a magnetic field of intensity, $\mathbf{B}$ applies a force of $\mathbf{F}= q\mathbf{v} \times \mathbf{B}$ on a charge $q$ moving with velocity $\mathbf{v}$, this force $\mathbf{F}$ should be ...
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4answers
110 views

Electromagnetic waves according to Maxwell

If a variable Electric field creates a variable magnetic field and VICE VERSA (according to Maxwell's equations), then why don't we enter a loop where E vector and B vector keep creating one another ...
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33 views

Electromagnetism on 3 torus

We all know Maxwell equations in 3+1 spacetime, where the "space" is $\mathbb{R}^3$ and time is $\mathbb{R}$. Moreover, it is easy to construct (using differential forms) the corresponding theory in a,...
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Electric field from the intersection of two spheres with different charges

This question is repeated a lot, but I for two spheres with different charge densities, sphere one with radius a centered at the origin and charge density $\rho_1$, and sphere two with radius centered ...
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1answer
58 views

How can changing magnetic field produce instantaneously the electric field and vice versa? [duplicate]

Maxwell's curl equation for electric field says that time varying magnetic field produces electric field instantaneously but nothing can happen instantaneously according to special relativity. What is ...
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1answer
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Maxwell Laws Summary Diagram - Suggestions that I am missing? [closed]

I have been going through a summary book of Maxwell's equations and hope I have organised this correctly but I think perhaps I am missing things important prompts that I could add? Image below Thanks ...
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Guided propagation in transmission lines

Can you help me on understanding why we may say this transmission line the propagation is guided and there is not any radiation? It is a 2-conductors transmission line, in which the conductors are ...
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1answer
48 views

Do magnetic field lines actually cancel?

Typically when explaining why parallel conducting wires attract, it is said that their magnetic fields cancel out (in the case of same direction current) and hence produces an attraction force due to ...
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47 views

How does $H^2$ effect on the probability of photon detection?

Lets consider an electromagnetic wave, between two ideal conductive plates. Maxwell's theory predicts appearance of a standing waves(of $\textbf{H}$ and $\textbf{E}$), at that nodes($\textbf{E} = 0$)...
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65 views

Electrons expelled from the wave [closed]

The intensity of the electric field of an electromagnetic wave varies according to the law:$$E\left(t\right)=E_{0}\left(1+\cos\varOmega t\right)\cdotp \cos\omega t,\varOmega=2\cdotp10^{15}s^{-1},\...
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43 views

Can I think Transverse Modes in optical waveguides as an contructive interference phenomenon?

I am studying about Transverse Modes formations in optical waveguides. Q1. I got an impressions that this is a constuctive interference phenomenon. while waves that have phase difference 2pi*m; for ...
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Magnetomotive force in a specific case (the 2 in the nominator)

I am doing a research concerning some linear generators and therefore I am going trough a paper which describes magnetic circuits etc... We all know that the energy of a magnetic field per volume unit ...
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17 views

Capacitance of insulated conductor with charge on insulation surface

I have an insulated wire at high voltage (10s of kV) running above a conducting ground plane. In my case, I expect that corona discharge will occur briefly after the HV generator is turned on, but ...
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2answers
43 views

Do magnetic field lines indicate how a mangetic field will act on an “idealized” test magnetic north monopole?

We imagine an electric field and a magnetic field as vector fields. When we are introduced to a static electric field, we usually picture it as an infinite number of vectors (magnitude,direction) in ...
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1answer
51 views

Can we calculate the magnetic field of a permanent magnet?

We are always introduced to magnets by pictures illustrating a parallepiped magnet, a horseshoe magnet, etc... Anyway the first time we actually calculate a magnetic field is for eelectromagnets. ...
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1answer
36 views

In a circuit, do surface charges get influenced by external electric fields?

Hello ,This image represents surface charges in a circuit caused by the battery's electric field, if you were to place an other electric field source of the same magnitude (but not connecting it to ...
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1answer
63 views

Skin Effect Explanation

I do not understand some things about the Skin Effect. Its Wikipedia definition is: Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor ...
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1answer
33 views

Help me distinguish between an Amperian loop and a surface

This image is from the Resnick-Halliday-Krane textbook. These images have been used to see that a correction was needed in Ampere's circuital law. What I am confused about is, how are the two end ...
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23 views

On electric potential and corresponding formulae

Why is it that signed quantities of charge are used in determining electric potential but not electric force (by Coulomb’s law)?
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26 views

Electric field generated by disk and conductor

I'm trying to solve the following problem but I have some doubts. I have a disk of radius $R$ with charge $Q$ (positive) and, at distance $d$, an uncharged conductor (of radius $R$ as well). Both are ...
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2answers
37 views

Effect on radio waves from forcing two magnets together

Wrapping up a cellphone in aluminium foil or putting it inside a microwave will block out all signals. Somebody suggested to me that forcing two very powerful neodym magnets against each other and ...
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25 views

Force on a current carrying loop

I recently encountered a question which went like this, A current-carrying loop is placed in a plane perpendicular to a long current carrying wire at a distance from it. What is the force acting on ...
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30 views

Does Larmor precession of a magnetic spin produce a (time-averaged) electrostatic near-field?

I have been wondering whether or not applying a magnetic field to a material containing magnetic spins could produce an electrostatic-like field as a result of a Larmor precession of the embedded ...
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MHD pump liquid metal flow speed

a rather simple question, are there any studies or some information about the flow speed of liquid metal inside a tube? My setup is basically a 50cm diameter circular tube (could be another diameter) ...
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1answer
37 views

Electromagnetic field of a point charge seen from a rotating reference frame

Let us consider a point charge sitting in the origin of our coordinate system. If we change to a rotating system, will the field of the point charge still look the same? Intuitively I would say yes, ...
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1answer
36 views

Biot - Savart Law and time - variable current [duplicate]

Is the Biot Savart law valid also with currents which are functions of time (for instance a sine wave)?
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31 views

Helmholtz equation and sources

it is known that starting from the Maxwell equations it is possible to get the following Helmholtz equations: In time domain it corresponds to a sinusoidal EM field, according to the wave equation: ...