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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15 views

If the magnetic force doesn't do work then what does it?

Let's assume I have a conductive rod with mass $m$ and with steady current $I$. I can make the current flow in such a direction and magnitude that the magnetic force will make it move up, thus ...
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Does the minimum slit width change with different photon frequencies?

Send white light through a vertical polarizer and then through a second horizontal gap that is just wide enough to let all the light through. Now slowly close the second gap until it becomes a slit. ...
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What exactly is the framework (or model) in which Electromotive Force is a meaningful quantity?

As far as I understand, there are two definitions of "Electromotive Force", one being the integral of a non-conservative (non-dissipative) force per unit charge acting on electrons along a path in a ...
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Conceptual question about special relativity in electrodynamics

I‘m currently taking Physics II and I have a conceptual question about SR in edyn. Suppose I have two electron beams with linear charge density $\lambda$ paralell two each other in a resting system $...
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What is the force on an iron object due to a magnetic field?

Say there is a solenoid that creates a constant magnetic field in the space around it. An iron ball bearing is placed at one end of the solenoid where the field lines spread out. What would be the ...
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Using Biot Savart law for magnetic field of a wire gives wrong results when integrating over angle

So, most of the documents on the internet use Biot Savart law and integrate over length of the wire (from minus infinity to infinity) for an infinite wire magnetic field, but I have tried to integrate ...
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1answer
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Is Bohr's postulate really necessary from classical perspective?

Quoting the first sentence of the first postulate on wiki: The electron is able to revolve in certain stable orbits around the nucleus without radiating any energy, contrary to what classical ...
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Equations with relevance to motion of a charged particle in attractive and repulsive field

I have three related questions on Rutherford scattering The first one is based on the derivation given here When momentum is conserved isn't angular velocity $\frac{d \theta}{dt}$ where $\theta$ is ...
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186 views

What determines if magnetic spins align parallel or anti parallel in a material?

As we all know, the magnetic field around a dipole looks like the following: Notice how, directly above and below the magnet, the magnetic fields likes are parallel to the north-south axis. However, ...
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Applying torque to a nonuniformly charged black hole

As matter reaches the event horizon of a black hole, it slows due to time dilation and effectively sticks to the surface of the event horizon. If a large quantity of electrons was added to a point on ...
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31 views

Electron's velocity speed and angle with time [closed]

An electron follows a helical path in a uniform magnetic field, does its velocity, speed and angle changing with time?
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Using Maxwell and electromagnetism to solve for $T$

$$\textbf{F} \cdot d\textbf{l}=q(\textbf{E}+\textbf{v} \times \textbf{B})\cdot \textbf{v} dt$$ If we denote $q=\rho d \tau$ and $\rho \textbf{v}=\textbf{J}$ $$\frac{dW}{dt}=\int_{V} (\textbf{E} \cdot ...
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Minimal coupling in Dirac equation

In the framework of relativistic quantum mechanics (not QFT) the Dirac equation in presence of external electromagnetic field is obtained by means of the minimal coupling, i.e. the substitution: $$p_{...
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Rutherford Model of Atom

When finding the closest distance of approach of helium nucleus to the gold atom, we apply TME conservation. But the alpha particle is accelerated and hence, emits radiations. Why don't we consider ...
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For this derivation of time dilation, what is the orientation of the electric and magnetic fields in each inertial frame?

I wanted to review special relativity having now completed my junior year at college and my Intro to Electrodynamics course this past semester. Since we covered Griffiths' Intro to Electrodynamics ...
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Rainbowish phenomenon outside my home [closed]

I took a photo of an amazing sight I had never seen outside my home ( southern india ) but I could not tell if it was a rainbow type thing or an aurora borealis. Can someone tell what this is and it’s ...
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How to falsify the postulated new electron mass to elementary charge relation? I couldn't find a way [closed]

Abstract: This manuscript postulates that electron rest mass $m_e$ and elementary charge $e_o$ are bound by formula $\frac{m_e}{e_o} = \frac{G}{2^9\pi \alpha}$, where $\alpha$ is fine structure ...
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How to use symmetry arguments in solving this electric flux problem? [closed]

I am trying to solve this problem using symmetry arguments. I had solved a few problems using symmetry arguments, one of them was this (Flux through side of a cube). I tried using a similar idea but ...
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57 views

Can Electric field line form a right angle?

Can Electric field line form a right angle ? something that look like the letter L.. please be as rigorous as possible. Thanks in advance.
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39 views

Force exerted by a charged ball on another one [closed]

Consider two charged balls in space with radii $R_A$ and $R_B$, and total charge $Q_A$ and $Q_B=\rho_B\space V_B$. They are separated by a distance $D = \|\overrightarrow{AB}\|\geq R_A + R_B$. I was ...
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Magnetic field of infinite cylinder with angular motion of charge [closed]

I have an infinite cylinder of radius $a$. inside there is a charge with uniform volume charge density $\rho$. the charge is moving inside the cylinder with speed of $\omega(r)=\omega_0\frac{a}{r}$. I ...
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2answers
65 views

Charge distribution related to electric field $E=A\frac{e^{-br}}{r}\hat{r}$ [closed]

I'm going over some problems with a solution manual in order to brush up for a coming exam and one of the problems I came across was this: What is the charge density related to the field $E=A\frac{...
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1answer
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Converting units, for the magnetic moment

I found, that magnetic moment is measured by $\rm J/T$, and equals magnetization times volume: $$\vec{m}=\vec{M}V$$ Magnetization, also equals magnetic susceptibility times external magnetic field: $...
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Does an electromagnet have a magnetism limit? [duplicate]

I came across a question asking whether there is a limit to the magnetism of an electromagnet.
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Converting $\frac{dB\mu A}{m}$ to $\frac{dB\mu V}{m}$?

I am trying to convert $\frac{dB\mu A}{m}$ to $\frac{dB\mu V}{m}$ So, I know that; $\frac{dB\mu V}{m}$ = $\frac{dB\mu A}{m} + 51.5$ However, I cannot find a source explains where 51.5 comes from. ...
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If mag.field and Ele.field are same,what is the need of studying both?

We learnt magnetic field is electric field but viewed from a different frame of reference. Then why do we need to worry about B. We could very well take a frame where it is E?
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Magnetic levitation: completely zero friction or just very low and if the latter, what is the source of the friction?

I am thinking of the now easy-to-obtain speakers where a spherical speaker is suspended above a platform. If this was in a vacuum and the sphere was spinning, why would it ever slow down? What is the ...
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1answer
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Electric Flux through an infinite sheet [closed]

This Question pertains to Gauss' Law In finding Flux through a sheet of width a which is infinitely long, kept so that a charge ($+Q$) is kept at $\frac{\sqrt{3}a}{2}$ length away from the plane of ...
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1answer
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Dipole oscillators question from Feynman lectures 1.28-29

I am confused by the Feynman lectures Vol1Ch28-29. In all the pictures, there is an electric dipole oscillating vertically. We're assuming the intensity is $E^2$ and that in the far r limit $E$ ...
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31 views

Magnetic field equals 0 [closed]

If I have a coaxial cable of infinite longitude and the magnetic field equals 0. Is it possible electric current exist?
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25 views

What was Faraday's experiment's of induction?

I'm searching about the experiments, which Faraday has done in order to discover the electromagnetic induction phenomenon. I didn't find what I need on google scholar nor google books. Can you ...
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1answer
36 views

Magnetic force on the proton due to the current [closed]

Figure shows a snapshot of a proton moving at velocity v = (-200 m/s)j toward a long straight wire with current i=350mA so mA At the instant shown the proton's distance from the wire is D 2.89cm In ...
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If all the multipole expansions apart from the monopole is zero, then is the charge density spherically symmetric?

Say I have a charge density $\rho(\vec{x})$ in some finite volume $V$, such that all of the multipole expansions apart from the monopole moment (meaning dipole, quadrupole and so forth) are zero. Does ...
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Spin-flip of electrons in non-neutral hydrogen atoms in water and fat molecules

What is the Spin-flip of electrons in non-neutral hydrogen atoms in water and fat molecules? I know there is known spin-flip RF of electrons in neutral hydrogen atoms (hydrogen line). Thanks, Cheers
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Density of States (DOS) to energy graph

I am trying to find the amount of electrons in a conduction band in Si (Silicon), all I've got is a graph similar to this one: I've tried to integrate like this: $$ N = \int_{1}^{\infty} \frac{1}{1+\...
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Torque on a ring with some charge on its rim rolling on a rough horizontal ground in a constant vertical magnetic field [closed]

What is the magnetic moment of a ring of radius R with some charge uniformly distributed over its rim and rolling on a rough ground with a constant angular velocity? My textbook assumed the magnetic ...
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1answer
23 views

Dimensions of EM potential/field tensor components in curvilinear coordinates

According to this resource on Maxwell theory in curved spacetime, the form of the field strength tensor is independent of the choice of coordinates: $$F_{\mu \nu} = \partial_\mu A_\nu - \partial_\nu ...
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How does relative permittivity and conductivity of a surface affects the propagating wave?

INTRODUCTION I am working on project related to atmospheric ducting, the natural phenomenon that traps the propagating radio waves, thus allowing it to travel far beyond the radio horizon with less ...
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2answers
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Why do my lights become brighter during a thunderstorm?

Today, during a thunderstorm, the lamps in the room suddenly flickered and then gradually became brighter in less than a second. The lamps remained brighter than normal for a few seconds before ...
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1answer
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Light in a Medium Question

For the medium let’s use water. When light passes through water its wavelength decreases. It’s frequency stays constant. It changes its direction upon entering the water unless it enters the water ...
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1answer
28 views

Magnetic monopoles and magnetic field lines

in all my physics courses I have been told that magnetic field lines are absolutely closed lines. It is well explained in this wikipedia page, which states: A magnetic field has no sources or sinks ...
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6answers
82 views

How is it physically possible that the electric field of some charge distributions does not attenuate with the distance?

Let's consider for instance an infinite plane sheet of charge: you know that its E-field is vertical and its Absolute value is $\sigma / 2 \epsilon _0$, which is not dependent on the observer position....
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1answer
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The Aharonov-Bohm effect for arbitrary $B$-field

The Aharonov-Bohm effect is discussed for the case of particles moving along a closed loop through a region with zero magnetic field, however I was wondering whether it still holds for arbitrary ...
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Electroweak field-strength tensors

The Lagrangian density for the interaction term of the bosons $W_1,W_2,W_3,B$ in the electroweak theory is $$ \mathcal{L}_g=-\frac{1}{4}\operatorname{Tr}(W^{uv}_aW_{uv}^a)-\frac{1}{4}B^{uv}B_{uv} $$ ...
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Power Absorption of Radio Waves on Metal Dishes

Im looking to figure out how much power is absorbed by a radio dish in reflecting radio waves of a certain wavelength assuming a thickness larger than the skin depth. I would prefer highly accurate ...
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Why would a ring magnet's flux decrease once distance starts getting small?

I went ahead and use python magpylib to simulate a ring magnet joystick, and then graph flux over distance of the ring magnet. Here's the code: ...
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$U(1)$ gauge invariance

I am looking at some exercises in an online course in QFT and there is a question about the $U(1)$ gauge invariance of this operator: $$i\bar{\psi}\sigma^{\mu\nu}\gamma_5(\partial_{\mu}A_{\nu})\psi$$ ...
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Proximity effects at high frequencies

I was trying to understand Skin and Proximity Effects in conductors when I stumbled onto this. I'm using QuickField 6.4 for reference. According to theory, when I place a permeable material, such as ...
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Wiley Encyclopedia of Electrical and Electronics Engineering [closed]

I was wondering if someone had an ebook version of this encyclopedia by Webster Actually this collection is very expansive (around 14k$ for the complete set) and not very easy to get in libraries I ...
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Computing magnetic field from eddy currents

Suppose a body with arbitrary shape, uniformly magnetized (with a magnetization $\textbf{M}(t)$) and submitted to an external magnetic field $\textbf{H}(t)$. The variable $t$ is the time. Based only ...

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