# Tagged Questions

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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### 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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### 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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### 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?
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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### Why do bar magnets have least attraction in its center?

Why do bar magnets have the least attraction in its center?
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### 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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### 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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### 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 ...
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### 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 ...
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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...
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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### 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 ...
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### 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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### 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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### Precession of a charged rotating sphere

Can anyone explain to me the second part of this question?
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### What causes the blur when my fingers are almost touching? [duplicate]

I can see this with my bare eyes
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### 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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### 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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### 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 ...