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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77 views

How can one produce a projected electric field? [closed]

Original question: How can one produce an electric field? I understand that there is a method involving metal sheets and running an electrical current through the parallel sheets. However, is there a ...
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0answers
24 views

Center of Lorentz Field

I am currently trying to write a particle physics library and I have implemented gravitational, spring, and Lorentz interactions between particles. These implementations can be seen here if desired. ...
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1answer
38 views

How to collimate the LASER light using an electric field? [closed]

The He-Ne laser beam is passed through electric field plates. What is the mechanism occururing there and the principle of LASER light interacting with electric field?
4
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1answer
3k views

Magnetic fields and friction

If I was to pass a metal object through a magnetic field would there be any friction?
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1answer
61 views

Retarded potentials and fields

Why can't we use retarded times to make an expression for retarded fields instead of potentials? As far as I know it doesn't work, since the solutions produced ("retarded fields") don't satisfy ...
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1answer
92 views

Magnetic field re-routing

Can a magnetic field be directed in a particular direction, that is re-route it, such that the magnetic field comes out in only one direction?
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0answers
84 views

Magnetic monopole using differential forms

I'm trying to understand the different variations of the Maxwell's equations using differential forms. The Maxwell's equations are $$dF=0\\ *d*F=J$$ where $F$ is the electromagnetic tensor ($F=dA$) ...
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1answer
41 views

How is an electron beam generated?

I am trying to get a better handle on how the EBPVD machine works in the lab I am working in. I understand that it produces an electron beam with a tungsten filament and that beam is then directed ...
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0answers
70 views

The Inertial theory of Sciama and an electromagnetic analogue

In 1952 D. W. Sciama introduced a paper On the origin of inertia. It presents a method in which inertia could arise from other mass in the universe. It goes along these lines: If you try to ...
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0answers
32 views

Magnetic field of a circular loop if r<R

Given a circular loop of radius R and is on the xy plane with the center at the origin. Let P=(λR,0,0) be a point on the x-axis such that λ<1. Find the vector potential A at P as a power series of ...
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2answers
4k views

Can sugar be affected by a magnetic field?

While I was making a morning coffee at work, some sugar from the spoon started to fly away, seemingly towards some foam cups. Can this be explained by magnetism?
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0answers
26 views

Does current understanding of EM theory provide any evidence of additional physical dimensions?

Some theories (such as variants of the String Theory) postulate the existence of additional dimensions beyond the 3 spatial dimensions. So I was thinking that if such dimensions exist, perhaps some ...
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3answers
84 views

Light interference with light and other EM waves [duplicate]

Lets assume a room with one or two sources of light (normal light bulbs or fluorescent lamps). So if we look at lamp from any direction we see it. We also see different objects in the room because of ...
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1answer
50 views

How to find the magnitude of electric and magnetic fields in an arbitary inertial frame?

In the context of special relativity, and using proper Lorentz transformations: If the electromagnetic fields have an uniform value [= constant in space and time] in an inertial frame, how will the ...
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1answer
47 views

Why are waveguide fields not infinite?

I was reading The Feynman Lectures on Physics, Volume II, when I got to the section on waveguides. Toward the end, Feynman uses the concept of an infinite number of alternating line sources to explain ...
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2answers
7k views
6
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1answer
772 views

Is there something like the Poynting vector for hydraulic circuits?

The Poynting vector is a representation of the energy flux in electromagnetics, showing the amount and direction of power flow at different points in space. In electric circuits, the energy is not ...
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1answer
31 views

Induced EMF in our body

I have learnt today that, Faraday And Henry independently found that In the changing magnetic flux, there will be Electric current in the conductor. Then why our body don't feel shock when we move ...
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0answers
11 views

Magnetization in a “fixed-ratio” (or “hard”) transformer

I've done a simple experiment related to 2 types of transformers: isolated transformer (regular transformer) and "fixed-ratio" (or "hard") transformer. For the former in which the primary and ...
3
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3answers
180 views

Interpretation of QED gauge freedom

In quantum (or classical) electrodynamics we are free to make gauge transformations, which change the form of terms in the Feynman diagrams (or the potentials) without affecting any physical ...
2
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0answers
108 views

How does lightning flip a car?

http://www.standard.co.uk/news/london/car-flips-into-air-after-being-struck-by-lightning-in-freak-electrical-storm-accident-10366208.html and a few others (http://news.google.com/news/i/story?ncl=...
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1answer
72 views

Dipole antenna $E$-field direction

I was looking up dipole antennas on Wikipedia, among other sites. I came across this animation: and was wondering why there wasn't any field lines in perfectly vertical direction. In the case of a ...
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4answers
240 views

Interesting problem involving pendulum, collisions, and electric charges

This problem was invented by the physics professor at the community college near me which he used on a past final exam: A pendulum consists of a massless rod of length L and a conducting ball of mass ...
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1answer
103 views

What form of energy is magnetism stored in?

In physics class I was told that there are 9 forms of energy: -Electrical -Light -Thermal -Nuclear -Elastic Potential -Gravitational Potential -Sound -Kinetic -Chemical So, my question is, ...
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2answers
75 views

Magnetic field at the center and ends of a long solenoid [closed]

A long solenoid has current $I$ flowing through it, also denote $N$ as the turns per unit length. Take its axis to be the $z$-axis, by symmetry the only component of the magnetic field inside is $B_z$....
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1answer
245 views

Clarification on factors of $c$ in the Lorentz' force

I was told that Lorentz' force is given by $${\bf F}= q{\bf v} \times {\bf B}.$$ But I have read that it is given by $${\bf F}= \frac{q}{c}{\bf v} \times {\bf B}.$$ Why have these two relations ...
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1answer
64 views

Constant $c$ in Lorentz force [duplicate]

I met some of examples of force in studying classical dynamics, and Lorentz force was represented as $$ \mathbf{F}=\frac{q}{c} \mathbf{\dot{r}} \times \mathbf{B} $$ I've searched for meaning of $c$, ...
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2answers
289 views

why don't large magents repel themselves

This question may have been asked before so I apologize in advance if it has. I've been playing with some magnetic buckyballs I got recently (highly recommend getting some if you dont have any) and ...
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1answer
306 views

Huggins Displacement Theory and Retrocausality

I was looking at the Wikipedia entries on Time Travel and the Grandfather paradox and noticed a paragraph on the so-called Huggins Displacement Theory. I haven't been able to find the source although ...
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0answers
24 views

Vector potential $ \vec A$ of two parallel conductors

Let's say we have two parallel conductors of length $l$ parallel to the x-axis at $y=y_0$ and $y=-y_0$. Let's say the upper conductor has the current density $j$ and the lower one $-j$. Now I want ...
3
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2answers
109 views

Any quadrupole approximation? Any example?

In atomic and molecular physics we quite often encounter with electric dipole approximation. The dipole approximation we do when the wave-length of the type of electromagnetic radiation which induces, ...
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2answers
76 views

Can an electric field be there without a charged partical?

How does a photon have an electric field around itself without any charge particle inside it.
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0answers
20 views
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2answers
57 views

Do a receiving antenna interfers with an emitting antenna?

As I understand: Accelerating electrons generate electromagnetic waves. An emitting antenna have an alternating current (electrons are moving) which generates an electromagnetic waves. The ...
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1answer
42 views

How does current increase in an LR circuit in order to reach a steady-state?

The equation of voltage of an LR circuit is given by: $$\boldsymbol{\varepsilon_0} - L\frac{dI}{dt}= RI\;.$$ Now, before the circuit is closed, $i= 0\;$ As is written in books, the current then ...
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0answers
35 views

Given magnetic field, calculate electric field

The B field depends on z and t so that $B = j B_{0}cos(kz-\omega t)$ where k is the wavenumber, $\omega$ is angular frequency and $B_{0}$ is constant. The electric field is $E = E_{x}i + E_{y}j +E_{z}...
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0answers
30 views

magnetic field and permeability

Doubt on magnetism. The the problem with Magnetic Flux Density($B$) and Magnetic field intensity($H$). I can Imagine magnetic flux($\Phi$) lines and flux density($B$) Physically. But magnetic field ...
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1answer
67 views

Self induction in a circular coil

There's a formula for self inductance : $$ L=\frac{n\Phi}{i}$$ where n is the number of loops. But the book also says self inductance is directly proportional to $ n^2 $ I totally agree with the ...
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0answers
21 views

Does inductors oppose the same change in current that it itself produces in case of DC Current?

We know that the inductor is a solenoid. In that solenoid, due to self induction it produces its own emf. That causes a change in the initial current. To counter this change the inductor produces ...
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2answers
143 views

George Green's derivation of Poisson's equation

I was reading George Green's An Essay on the Application of Mathematical Analysis to the Theories of Electricity and Magnetism, and I got confused on one step in his derivation of Poisson's Equation. ...
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0answers
20 views

Are magnets attracted to mu-metal?

Are magnets attracted to mu-metal? Be aware that when watching videos of mu-metal they may have metals that are attached to the mu-metal and are attacted to magnets. Please don't get them confused.
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1answer
49 views

Time dependent electric field: Mathematical expansion for local electric field

In many articles and books I see that local electric field is expanded as $$\vec E_0(\vec r(t)) = \vec E_0(\vec R_0) − (\vec a(t) \cdot \nabla) \vec E_0(\vec R_0) \cos(\Omega t) + \ldots $$ For ...
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1answer
1k views

Interacting magnetic fields

Is there a reason why two magnetic fields perpendicular to each other do not interact? If they are parallel or at a non-90 degree angle they interact. Is it because magnetic field lines can be viwed ...
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1answer
61 views

Wightman function for massless vector fields in Coulomb gauge

I've been looking for quite some time an expression for the Wightman functions for a massless vector field in the Coulomb gauge $\nabla\cdot\mathbf{A}=0$ (I think it is equivalent to the Feynman gauge ...
0
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1answer
25 views

Why does emf of a cell equal to $\frac{F_b d}{q}\;?$

In Concepts of Physics by H.C.Verma, it is written: Some internal mechanism exerts forces on the charges of the battery material. ... We show the force on a positive charge $q$ as $\vec F_b\; .$ ...
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1answer
63 views

Is there a way to write the Lorentz force in terms of one field, $L$, and one charge, $X$?

I have heard that physicists like to write electromagnetism as one force (the Lorentz force) and define it as $\vec{F_L}\left(q, \vec{v}, \vec{E}, \vec{B}\right) = q\left(\vec{E} + \vec{v} \times \vec{...
2
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0answers
27 views

Why are only some materials ferromagnetic? [duplicate]

I've been told in my solid state class, that ferromagnetism occurs when electron spins are alligned. This happens, as I understand it, when it is "energitically favorable" and when the wavefunction is ...
0
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4answers
173 views

Why does the frequency of a Transformer not change?

I was reading about the transformer, when I came across a note by the author that stated that the Frequency is not changed as the flux linked to the secondary coil in a transformer changes. Is there ...
0
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1answer
62 views

Does the alternating current “move” such that there can be Lorentz force present on the wire?

As in question, does the alternating current "move" such that there can be Lorentz force present the wire? Becuase the current alternates on a fixed place there can be no Lorentz force?