# 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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### Would a magnetic current cause a looping electric field?

An electric current, composed of electrons moving in a wire, creates a magnetic field looping around the wire. Would a current of magnetic monopoles moving through a wire create an electric field ...
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### Dipole moment in cylindrical symmetry

So I am trying to find the dipole moment for an uncharged sphere in an electric potential, and I am stuck in the following step: $\vec p = \int_V \rho_{density}(\vec r')\vec r' dV'$ Since we are ...
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Imagine a plate beeing irradiated from all sides with a specific wavelength. One side of the plate is smoth and reflects most of the incoming radiation, the other side is covered in grooves with the ...
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### Measure Position of Electron Directly

What is the most directly way to measure the position of free electron in an expirement? I don't asking about theoretical suggestion but rather on practical expirement which people have done.
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### Electromagnetic field around a conductor with current

According to this video https://www.youtube.com/watch?v=bHIhgxav9LY I have a question: If the glowing of a light bulb is the result of energy supplied from the electromagnetic field around a conductor,...
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### Examples of current densities

I am trying to imagine how do the continuous current density look like. When we speak about charge density, if it is discrete, one can picture multiple point charges in a region in space. If the ...
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### Electric field in the center of hemisphere shell without double/triple integrals

I'm trying to derive the electric field in the centre of a solid hemisphere of radius $R$ where the charge is distributed uniformly. I have seen different methods involving double/triple integrals ...
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### What is net dipole moment of a spherically symmetric charge distribution?

There is some unknown spherically symmetric charge distribution $\rho(r)$ with total charge zero. For this charge distribution how will be monopole and dipole moment? Will they be zero or non zero? ...
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### How can a plasma exhibit both quasineutrality and collective motion?

Since, over a Debye Length $\lambda$, very small compared to the characteristic length $L$ of a plasma, a potential due to a source charge is essentially screened, how can plasma particles communicate ...
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### How do I find the current density vector in an electromagnet that has a time-varying current?

I know that the current $I$ is a scalar quantity, and to calculate current density $J$ , the cross sectional area $A$ is needed, to give us $J = IA$ . $J$ also has other relations involving ...
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### How to determine the directional behaviour of the magnetic vector potential?

I was wondering if someone could please help explain the directional behaviour of the magnetic vector potential? I understand that the magnetic vector potential $A$ is perpendicular to $B=∇×A$ but ...
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### Maxwell’s first equation in conductor we take E=0. And I have read that’s true for practical time scales. But in 4th equation we use non zero E, why?

\begin{align} \nabla\cdot E&=0\\ \nabla\cdot B&=0\\ \nabla\times E&=-\frac{\partial B}{\partial t}\\ \nabla \times B&=\mu J+\varepsilon\mu\frac{\partial E}{\partial t}=\mu\sigma E+\mu\...
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I have encountered a "paradox" while studying electromagnetism and I can't seem to understand where I am messing up. Consider a uniform, time-dependent magnetic field B(t) = $t^4 \hat{i}$ in ...
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I've been told that the radiation pressure of light can be understood(?) by considering a charged particle as a damped driven harmonic oscillator where the forcing term is the electromagnetic field, ...
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### On what physical principles the measurement of intensity of light is based?

As far as I understand, theoretically intensity of light is defined using the Poynting vector of the corresponding EM field. How is the intensity of light measured in practice? On what physical ...
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### What good reason to hang long cable carrying electric current high above the ground? [closed]

Assume no flooding or other natural disasters to damage the cable if it is laid beneath the ground, then what good reason for them to be suspended high above the ground? The cables are insulated and ...
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### Is radiation pressure wavelength dependent (does a blue photon move the solar sail more then a red photon)?

I have read this question: Where John Rennie says: Does the wavelength of the light matter? No Now in the same question, another answer, by DavePhd says: Does the wavelength of the light matter? ...
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### Is it possible to make a magnetic box that will compensate Earth gravity allowing magnetic objects inside to fly on orbits like in space? [closed]

Is it possible to simulate solar system using magnetic spheres and some kind of box that will compensate the Earth gravity by magnetic force?
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### Given a magnet in each known phase of matter, does that magnet contain any lone pairs? [closed]

Given a monopole or dipole magnet in each known phases of matter ( solid, liquid, gas, plasma ), does that magnet contain any lone pairs?
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### What is the formula for inductance? [closed]

I am very new to Electromagnetic Induction. I had this question on a test recently. It went like - If both the number of turns and core length of an inductor is doubled keeping other factors constant, ...
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### What is the electric potential of a particle when it is initially released in a cyclotron?

Lets assume a positively charged particle in a cyclotron. When released it will move to a dee. Hence, does it move to an area of higher electric potential or lower electric potential? In my ...
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### What are the physical reasons for considering the Maxwell invariant ${\cal G}=E.B$ in the action?

As I know, the Maxwell invariant ${\cal G}=E.B$ is the fundamental invariant such as ${\cal F}=\frac{1}{2}\left( {{{\bf{B}}^2} - {{\bf{E}}^2}} \right)$ that can be used to construct all possible ...
I’m trying to calculate a Lorentz vector in $\mathbb{R}^3$ with those vectors but I keep getting an integer as an answer: There’s a velocity vector of $(3,-2,1)$ , a magnetic field vector of $(1,2,-2)$...