# Questions tagged [electromagnetism]

The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.

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### Why does a charge need to have a velocity to experience force in a magnetic field?

While studying magnetism, I learned that force on a charged particle inside a magnetic field is $$F=q (vxB)$$ where all symbols have their usual meaning, which implies that a charged particle must be ...
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### Why does the electric field only depend on the rod?

In the following exercise: We are asked to calculate the electric field at a certain distance from an exis where a rod is located. Previously, we are asked to calculate the charge density a ...
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### Electric charge conveyor trap

Normally one cannot trap both positive and negative charge within the same region by using electrostatic confinement as one charge would be attracted and the other repelled. I was wondering is it ...
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### Time evolution of scalar potential using Huygens principle

Huygens principle states that every point in space acts as a source of spherical waves. The amplitude for potential (scalar and vector) will be given by $V(r,t)=f(t-r/c)/r,$ where $f$ is a function ...
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### Conservative and non-conservative electric field due to to changing magnetic flux

Consider this situation in which a uniform cross section conducting neutral ring is placed in a changing magnetic field which is given by $B=kt(-\hat{k})$ ($k$ is a constant and $t$ is time). The ...
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### Capacitance coefficients of two enclosed spheres

I was reviewing G.B. Jeffery's work titled On a Form of the Solution of Laplace's Equation Suitable for Problems Relating to Two Spheres. To access the full text, you need to click "DOWNLOAD PDF&...
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### Why is the EMF zero in a conducting rod perpendicular to length

Consider a rod moving in uniform magnetic field with its length perpendicular to the field. My textbook says EMF induced is zero in this case, but why won’t there be a transverse electric field across ...
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### Is the Lorentz force proportional to $B$-field in the wire or immediately outside of it?

When considering the force on a current carrying wire in a magnetic field, is $B$ in the Lorentz force $F=IlB$ the field inside the wire where the current is flowing, or is it the field immediately ...
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### Understanding of flux [closed]

Q1. The question: to find flux through a “half sphere with top cut off” (closed surface) with point charge at sphere’s center For this question- flux as I understand it is the number of field lines ...
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### Why the dielectric permitivity matrix of lossless media is symmetric?

I am studying optics and I met a strange statement in the section 2.3.4 (page 34) of Fundamentals of Nonlinear Optics by Peter E. Powers and Joseph W. Haus. The relationship between $\vec{D},\ \vec{E}$...
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### Edited: longitudinal view of different modes of electromagnetic waves

We have a single, polarized $TEM_{00}$ and the same for a $TEM_{01}$/or any other. mode relative to the z-axe. Reformulated questions: In classical mechanics we have a standing wave. When we look from ...
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### How can auroras be visible at lower latitudes when a strong solar wind hits Earth?

Auroras are a product of electrically charged particles hitting Earth's atmosphere at the poles, where the geomagnetic field is weaker (where magnetic lines originate). How can a strong solar wind ...
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### Ambiguities in optical waveguide modes

While studying concept of slab waveguide mode, I got stuck on some problems. In textbook(Yariv chapter 3 pg 112), for guided TE modes it tells that the mode function is taken as which means that the ...
1 vote
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### What is the reletive permeability of structual steel?

Help, i need to know what the reletive permeability is of a few materials (listed below) but i can not find the data on the internet. Does annybody know the data or where i can find it? -s235jr -...
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### Can an oscillatory field produced by a time-dependent charge distribution fall off faster than $1/r$?

An electric charge has a field that decays at large distances like $1/r^2$. A charge distribution with total charge zero, but with a nonvanishing dipole moment, has a field that decays at large ...
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### Utilization of Hertz potentials in calculations

Electrodynamics textbooks, like Zangwill's Modern Electrodynamics, introduce the Hertz potentials $\boldsymbol{\Pi}_m$ and $\boldsymbol{\Pi}_e$(see Chapter 20 of the fore-mentioned book). While they ...
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### Laplace equation boundary condition

I'm reading a paper and seeing that the boundary condition for solving Laplace equation is set to $\frac{\partial V}{\partial y} = 0$ just because there is no charge at that boundary. Does this ...
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### Question about Fourier-coefficients in Griffith's Problem 3.15 (Electrodynamics) [closed]

I am having some trouble with problem 3.15 from Griffith's Electrodynamics. It states the following: A rectangular pipe, running parallel to the $z$-axis (from $-\infty$ to $+\infty$), has three ...
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### How do I calculate change in flux in an augmented rail accelerator without violating conservation of energy?

Suppose I have two rails and a wire connecting them I'd like to accelerate. Then $\frac{d\phi}{dt}=Bvl$, where $B$ is the magnetic field strength where the wire is, $v$ is the velocity, and $l$ is the ...