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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(boundary conditions) Interface between two lossless media

I'm wondering why there's usually no free charges nor free currents in the interface between two lossless media? no free current "I guess" is due to the insulating nature of a lossless media but why ...
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23 views

Force Exerting on a magnetic train

A question is already asked ( How does this “simple” electric train work? ). But I've got a question about it. In order to calculate the force which is being exerted on the system including magnets ...
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1answer
36 views

Analogue of charge for magnetic fields?

Now, I understand how there are no magnetic monopoles, and hence no analogue of magnetic charge in terms of a scalar field, but is there a similar concept that instead uses a vector or spinor field to ...
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1answer
31 views

Does the electromagnetic force “split” at lower than normal energies?

Since we have working models for forces "combining" or being describable via a single framework at higher energies (such as the "electroweak" force and the aim of GUTs), does electromagnetism split ...
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64 views

How can one confirm creation of magnetic graphene?

Recently my high school physics teacher contacted me looking for an expert to ask about this situation. I am paraphrasing his correspondence below: I just had a a student accidentally create ...
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33 views

induced current in loop

I'm re-asking this question that was posted by @zhzh and subsequently closed. If you have a loop that is spun clockwise as a magnet is moved near it, is a current induced in that loop? If the ...
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20 views

Does the form of a hysteresis curve depend on the magnetic field change rate?

I have given some people access to a Monte Carlo program that I created to simulate ferrofluids. They adapted it in order to simulate hysteresis loops. I had warned that Metropolis algorithm can only ...
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62 views

Would a grid of $10^{57}$ hydrogen atoms collapse?

Assume we have a gridded cube of $10^{57}$ hydrogen atoms, with all atoms 1mm apart from other atoms. This 'cube cloud' is in an area of space that would otherwise be at zero g, were it not for the ...
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1answer
53 views

if there is no electric field then any charge exists or not? [closed]

If we assume a region of space in which there is no electric field, can we say that no electric charge exists? I think that there is no electric charge particles to create electric field for this ...
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1answer
52 views

Was decoupling actually detripling?

As I previously understood it, before recombination, high energy photons were bound up in interactions with excited electrons, meaning electrons couldn't settle into orbit with protons and other ...
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1answer
32 views

Cold Atom Hot Atom 2: Minerals Attracted to Heat

In electric hot water tanks why do calcium quickly form on the heating elements? I watched some one put in a new element. An hour later it stops working. Just to check he took the element and it had ...
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1answer
36 views

Why don't simple circuits cause the electrical breakdown of air surrounding them?

Electrical breakdown of air occurs when the electric field exerted by a charged object exceeds the electrical breakdown limit of air which is $3.10^6 V/m$. Since even 1 Coulomb of charge can exert an ...
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23 views

Magnetic Forces and Junkyard Magnets: What's Going On? [duplicate]

In my electromagnetic theory class, I learned that magnetic forces do no work. This is easy to see when observing a cyclotron; the speed never changes, so the kinetic energy never changes and ...
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60 views

Limitations on the use of Ampere's Law

I have tried to find a thread with an answer to my question but have not been able to do so. Suppose that you are asked to find the B-field due to a finite length of straight current carrying ...
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0answers
56 views

Simple Explanation of Kondo Effect

Does anyone have a simple explanation of the Kondo Effect? (i.e. a simple physical picture + maybe equations to think of?) My current understanding is this: If we consider an electron scattering ...
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0answers
15 views

EM Radiations, wavelength and Wein's Law of Displacement [duplicate]

Why can black bodies emit all wavelength radiations? Also, in Wein's law of displacement, how do we sat that wavelength corresponding to the max intensity of the radiation is inversely proportional ...
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0answers
29 views

Electric Field at a point some distance above a uniformly charged cylinder

In this problem I am trying to solve, I am trying to find the electric field at a point directly above a uniformly charged cylinder. The cylinder is oriented so that the two round face are parallel ...
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3answers
43 views

How does one apply Gauss's Law when dealing with two infinite planes?

If you have two parallel planes with one density of 1 C/m^2 and the other with -1 C/m^2 density and you need to find the electric field at a point in the middle, how do you use Gauss's Law? I drew a ...
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1answer
69 views

What symmetry gives you charge conservation?

This is a popular question on this site but I haven't found the answer I'm looking for in other questions. It is often stated that charge conservation in electromagnetism is a consequence of local ...
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0answers
16 views

Time dependance of oscillating sheet of charge

I am working on a practice problem involving maxwells equations. We have an infinite sheet of charge density $\sigma$ in the x-y plane and it is oscillating as x= $\Re [x_0e^{-i\omega t}]$. I want to ...
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1answer
35 views

Difference between reflection mechanisms in dielectric, metals and plasma

How the reflection and transmissions mechanism are different in metals, dielectric and plasma? I know that the density of free electrons is playing the role. Can anyone give an insight what is ...
3
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0answers
38 views

Why is the susceptibility $\chi(t)$ real?

So my question is quite simple I suppose, and perhaps trivial. It is known that the frequency domain susceptbility $\chi(\omega)$ is complex, and that the two parts can be related with the ...
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1answer
32 views

Can a magnet pick up heated iron filings?

I heard that heat can destroy magnetism (somehow randomize the electrons orientation and reduce the magnetism), but I like to know if magnetism could affect heated iron filings? (Here heated means ...
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1answer
36 views

Understanding of dipole moment and its vector property

I have a trouble understanding the electric dipole moment. The electric dipole moment formula is $${\bf p}= \int {\bf r}' \rho({\bf r}')d\tau '$$ I'm interested in the coordinate, the origin of which ...
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2answers
57 views

Why bar magnet can produce magnetic field?

Say I wrapped a piece of wire around an iron bar in a closed circuit connected to a DC power supply, the electrons starts flowing and moving charge produce magnetic field. Yet a bar magnet can produce ...
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0answers
13 views

Boundary Value Problem in Plane-Wave Reflection by a Metal-Backed Dielectric Slab

Could somebody explain the Boundary Value Problem in Plane-Wave Reflection by a Metal-Backed Dielectric Slab using Finite Element Method? I tried looking up Finite Element Method in Electromagnetics ...
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19 views

influence of soft iron in magnetic lenses

I'm currently working as an intern in a research group which is specialized in transmission electron microscopes. I'm reading a book from David B. Williams and C. Barry Carter : Transmission electron ...
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2answers
154 views

Newtons third law with two charged particles

Imagine we have two charged particles, $q$ and $Q$. $q$ is at rest at a point and $Q$ is moving with a velocity. Now $q$ is exerting an electrostatic force on $Q$ and $Q$ makes a magnetic field but ...
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1answer
30 views

Electric Displacement Vector

How do I interpret what electric displacement vector is? I know that it exists and I know it's an equation but I'm not able to really understand or interpret what it is. $$\oint_A ...
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1answer
48 views

response function and Fourier transform

A response function defined as the kernel of the following integral: $\rho(t) = \int_{-\infty}^t \chi(t,t') E(t')dt'$ (1), where $\chi(t,t')$ is the response function. Physically, it relates ...
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2answers
32 views

Thomson scattering at high frequencies

When studying the scattering of a monochromatic plane E&M wave by a point charge and after finding the differential cross section of the process I read a sentence saying "This result is valid only ...
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29 views

For a straight circular wire, what is the relationship between the self inductance and frequency?

Due to the skin effect, the AC inductance of a straight wire will decrease as frequency increases. Is there any formula that can describe this relationship?
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2answers
59 views

Computational advantages of various notations for electromagnetism [closed]

Most undergraduate electromagnetism classes and textbooks use vector notation to describe Maxwell's equations. However, there are other notations like differential geometry and geometric calculus ...
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1answer
19 views

Larmor Frequency for Spin Transition

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/larmor.html Consider the process of Larmor precession of the magnetic moment associated with the spin angular momentum of an electron inside a ...
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39 views

Dipole moment of a system with net charge

I want to calculate the dipole moment of an object that is not neutral. I know for neutral charges the dipole moment has a rather simple form: $$d = \sum q \cdot z$$ But suppose I have a charge of ...
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1answer
92 views

Is magnetic field due to an electric current a relativistic effect?

I was reading a paper of the same name by Oleg D. Jefimenko; here is the concerned text: [...] relativistic force transformation equations demand the presence of an electric field when the ...
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2answers
48 views

Question about using Gauss' Law with a surface at infinity

While doing homework, I came across a situation where I tried to make this argument: For a finite distribution of charges, I know that the electric field drops off to zero at infinity. So therefore, ...
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1answer
57 views

How is the divergence of electric field related to the electric flux? [closed]

From the explanation of Maxwell's equations, I found, the flux of an electric field is mathematically represented by the by the divergence of the electric field.Then, how is the divergence of electric ...
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0answers
12 views

magnetic field due to current carrying coils

In the Helmholtz configuration, why is the magnetic field between the two coils uniform (I know the mathematical expression)? Can anyone please explain this physically? When the distance between the ...
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0answers
9 views

Behaviour of bubbles on the surface of a liquid [duplicate]

When you observe a group of very small bubbles on the surface of say, a cup of coffee, you can see that when the bubbles get close enough to the edge of the glass, the get attracted to it and ...
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1answer
23 views

Confusion about the total bound charge of a sphere placed in dielectric

There is a solved exercise in which a charged sphere of radium $r=a$ is inside a dielectric material. The surface bound charge and the volume bound charge are respectively: $$p_{sp}=\vec{P}\cdot ...
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1answer
37 views

electric field's area [closed]

How much area an electric field surrounds? since we're just able to draw the electric lines of force we sometimes think that the field is though 3d but surrounds a finite area.But is it measurable or ...
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3answers
79 views

What changes in the electrons before and after a voltage drop?

It is easy to visualize gravitational potential energy as a function of the position of height, and a change in this potential is manifested in a change in height. Further, by the work-energy theorem ...
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1answer
50 views

Does Gauss's law not hold when there are charges outside of the Gaussian surface?

For example, if I have a gaussian surface and a negative charge somewhere outside that gaussian surface, there's going to be a non-zero electric flux. However, According to gauss's law, electric ...
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0answers
31 views

Basic Vector field question about notation [closed]

I am taking my first class in electrodynamics and the problem I am working on has a notation I have never seen before Consider a vector field of the form $V= f(x)y + g(y)x$ Is this essentially the ...
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27 views

Can I emit light from an inductor? [duplicate]

As I understand it, inductors create a magnetic field when current flows through them, and light is an electromagnetic radiation. So, is it possible for an inductor to generate magnetic waves of the ...
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2answers
41 views

Why can't a neutral object attract another neutral object because of electrostatic induction?

So a positive/negative charge can attract a neutral object by causing the negative/positive charges to move closer to the source. However, if you have a neutral object and another neutral object ...
3
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1answer
34 views

Conservation of Angular Momentum in Einstein - de Haas effect

I am not really sure why the law of conservation of angular momentum should hold true in the Einstein - de Haas effect. Consider the following excerpt about the phenomenon (taken from Magnetism in ...
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0answers
34 views

Low kenitic Energy and High Kinetic Energy Atoms Attract

Will atoms of 2 difrent energy levels electron and/or Kinetic attract more than 2 Atoms at he same energy level? Do 2 high energy level atoms attract more than 2 low energy atoms?
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1answer
39 views

What's wrong with using the 4-current to find the potential of a moving particle?

According to Feynman (Lectures on Physics, Vol. II, 21–6), the potential of a moving point charge is: $$\phi = \gamma \cdot \frac q {4\pi\epsilon_0} \cdot \frac 1 {\sqrt{ \gamma^2 \left( x-vt ...