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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4
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2answers
128 views

Do physical entities with one dimension equal to 0 exist?

Within mathematics, a lot of entities with one or more size equal to zero exist and are fluently manipulated. For example, within $\mathbb R^4$, the entity defined as $z=0, t=2$ is a plan, the one ...
0
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1answer
83 views

Why does magnetic field and not electric field invert in a reflection? (related to another question)

When you are talking about an elctromagnetic wave that reflects on a surface (for example here), why do you say that the reflected magnetic field inverts and not the electric field? \begin{align} E_+ ...
1
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0answers
80 views

Relationship between the g-factor and the gyromagnetic ratio?

From what I have read the g-factor and the gyromagnetic ratio are two different quantities. It appears to me that the gyromagnetic ratio is the ratio between (any) angular momentum and the magnetic ...
0
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0answers
20 views

Electric field produced by polarized medium at the surface of a conductor

Suppose we have some conducting sphere of radius $R$ and charge $Q$ submerged half way into a medium with permittivity $\epsilon_1$. I have deduced that the electric field produced by the sphere will ...
18
votes
1answer
555 views

Do light waves precisely follow null geodesic paths in General Relativity?

In special relativity one may show that a plane wave solution of Maxwell's equations (in a vacuum), of the form $A^a=C^a\mathrm{e}^{\mathrm{i}\psi}$ has the following properties: The normal $k:=\...
1
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1answer
201 views

Relationship between the material properties of an edge and the fringes behind this edge

The double-slit experiment shows fringes on a screen. Closing one of the slits there is still an interference pattern on the screen behind the slit. Making the slit wider we still see fringes between ...
0
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0answers
21 views

What could be the cause of a phase shift between the torque and the angular speed in DC generator?

Introducing some variations in the form of sinusoids in the electromagnetic flux of a DC generator connected to a hydraulic turbine runner I obtained some strange results for the phase shift between ...
8
votes
1answer
258 views

Why is a stellarator-type nuclear fusion reactor so oddly-shaped?

My first impression: It's a mess. Why is it shaped like that? I can't find any info about its shape other than it's a special arrangement of magnetic coils. (link) Here's some more images of it on ...
1
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0answers
66 views

Self dual electromagnetic fields [closed]

Has anyone developed (or is working on) a self-dual EM field in toroidal coordinates? If so, please reference. Self dual refers basically to the EM field tensor but the practical meaning is that the ...
2
votes
2answers
271 views

Is light moving because of self induction? [duplicate]

Light is made by an electric field wave and a magnetic field wave. Induction laws state that a variation in the electric field creates a magnetic field and vice versa. Therefore can it be said that ...
0
votes
1answer
67 views

Ferromagnets - Permanent?

When researching about the Curie-Temperature and magnets in general, something got me confused. What is the difference between a ferromagnet and a permanent magnet? In a ferromagnet the spins are ...
0
votes
1answer
32 views

How do I show for an ideal transformer $M^2=L_1L_2$?

I've been stuck on this problem for about an hour. In an ideal transformer, the same flux passes through all turns of the primary and of the secondary . Show that in this case $M^2=L_1L_2$, where $...
0
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1answer
54 views

Why can't electrons leave negatively charged objects in a vaccum?

If an object is negatively charged, and electrons repel each other since they have like charges, why doesn't that negatively charged object "kick away" electrons? Why doesn't diffusion occur? Why ...
1
vote
1answer
71 views

How does electrical energy gets converted to sound energy?

I have seen that inside headphones there is a magnet with a coil of thin wire around it. There must be longitudinal waves coming out of it that is why we can listen to audio. There must be pressure ...
1
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0answers
39 views

What does this coordinate transformation in the Wave equation mean?

My tutor derived the following of which I do not understand the transformations (2.1) and (2.2): $$\Delta\vec{E} - \frac{1}{c^{2}} \frac{\partial^{2}\vec{E}}{\partial t^{2}} = \frac{4\pi}{c^{2}} \...
-6
votes
1answer
38 views

I need proof for dW=eIdt [closed]

I need help to understand from where this equation is formed inorder to continue to study energy stored in an inductor.
1
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0answers
63 views

Landau levels in uniform magnetic field

Intro Landau levels are obtained by gauging the vector potential to be $$ \vec{A}=\left(-By,0,0\right) $$ By which the Hamiltonian: $$ H={1\over 2m}\left(\vec{p}-q\vec{A}\right)^2 $$ can be ...
2
votes
2answers
347 views

Should the electric potential of a positively charged sphere be negative?

Because the indefinite integral of the electric field results in a negative value? (As the function is proportional to $r^{-2}$? I've got to be missing something... Help please!! Thanks! Also, I ...
0
votes
1answer
5k views

Potential energy of the dipole-dipole interaction for two parallel dipole moments

I am looking for an equation that gives me the potential energy of the interaction between two parallel dipoles.
1
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0answers
63 views

Radius of solenoid on the magnitude of magnetic field

I'm working on a project and have made a solenoid. I want to know the effective parameters on the magnitude of the magnetic field. $$B=μNi$$ In this equation, the radius of the solenoid don't have any ...
5
votes
2answers
685 views

How does a flywheel generate electricity at a constant voltage?

I believe I am missing something simple here. My question concerns flywheel energy storage. Say we have stored some amount of energy in a spinning flywheel. The flywheel is attached to a generator. ...
1
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0answers
31 views

Charged rotating sphere in Maxwell-ChernSimons theory

Does anybody know what the electromagnetic field of a charged rotating sphere in five dimensional Maxwell-Chern-Simons theory is? This theory has action \begin{equation*} S = - \frac{1}{4} \int d^5 ...
1
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0answers
35 views

Magnetic field of one electron

I want to reproduce a calculation of the magnetic field at the atomic nuclei produced by one electron in hydrogen: Maxwell gives us: $\vec \nabla \times \vec B = \mu_0 \vec j$ Doing the surface ...
4
votes
2answers
104 views

Stored energy and momentum in a magnetic field?

How is it possible for a magnetic field to store energy and momentum? And can deliver it to another object(charge/dipole) or field? I can't depict it. I know it occurs but how? For example, the ...
1
vote
1answer
77 views

Physical meaning of multipole moment

Is there a physical interpretation for multipole moments? For a quantity governed by the Laplace equation ($\nabla^2 \omega = 0$), I understand that the general solution is given by the multipole ...
1
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0answers
33 views

Surface bound charge density in dielectric displacement

In Griffiths, it derived that the electric potential caused by Polarization $\bf {P}$ is written $$V({\bf r}) = \frac{1}{4\pi \epsilon_0} \int_{\mathcal{V}} \frac{\hat{\gamma} \cdot {\bf P}{({\bf r'})...
0
votes
1answer
119 views

Motion of Particle due to Lorentz Force

So my professor gave us the following question: A particle with electric charge $Q$ and mass $M$ is initially traveling with velocity $v_0$ in the $x$ direction at time $t= 0$. There is a constant ...
0
votes
2answers
97 views

How to attract liquid metal with magnets

I would like to know if there is any way that I could make mercury or another liquid metal be attracted or repelled by magnets. Absolutely any solution would be okay with me. For example... can I ...
0
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0answers
49 views

Data analysis for a magnetic hysteresis loop

I'm a physics undergrad and I have MOKE data for a magnetic material (thin permalloy film on a silicon substrate). Here is one of the hysteresis loops I obtained, plotted using python: The form of ...
1
vote
1answer
32 views

What causes the magnetic field around a wire with current to be circular and perpendicular to the flow of current?

I understand that a moving charge will produce a magnetic field, but what causes them to appear circular and perpendicular to the flow of current, as they are?
0
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0answers
22 views

magnetic friction

If you take attracting magnetic fields, or opposing fields, and rotate them in opposite directions in close proximity, would this not generate an increase in temperature? This would also conclude that ...
0
votes
1answer
30 views

Resistance in A.C. circuits

Why do electromagnets offer maximum resistance in A.C. circuits?
0
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0answers
32 views

EMF produced by mutual induction

In the phenomenon of mutual induction, when primary coil is connected to an A.C. suppy, does the induced EMF in secondary coil also keeps changing with the changing magnetic flux?
0
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2answers
111 views

Induced Current in a wire

I am just surprised why EMF and Current are not induced in an unclosed wire. I know Maxwell's equation is only defines closed integral. But it doesn't means that it is not generated in a unclosed wire....
0
votes
1answer
63 views

induced Current I

I am working with the Problem which I've seen in a book. That Problem was : Direction of induced current I can't find any meaningful explanation for this problem in any source. So, I am working with ...
4
votes
2answers
144 views

How can one meaningfully say that one field generates the other in an EM-wave?

This is a follow up question to: Do the electric and magnetic components of an electromagnetic wave really generate each other? Clearly there are nuances of how one states the "mutual induction" ...
4
votes
2answers
89 views

Why is Kirchoff's Current Rule valid?

The fact that Kirchoff's Current Rule is valid means that whatever current flows in flows out. But this will only be valid for a steady current circuit, that is, when there is no accumulation of ...
0
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1answer
56 views

Advanced classical electrodynamics book [duplicate]

As I have already studied Griffiths, I want something with modern and advanced approach both towards theory and problem solving.
0
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3answers
62 views

relation between amplitude and frequency of a rotating electric field [closed]

I generated a rotating electric field produced by Ex=cos(wt) Ey=cos(wt-pi/2) in x and y directions. I ran a simulation and seems only in certain amplitudes and frequencies it makes a rotating field. ...
1
vote
0answers
31 views

Magnetic Field Flux Density Disambiguation

The Electric Field is defined as the electric force exerted on a positive test particle: $$\vec{E}=\frac{\vec{F}}{q}$$ The Electric Flux is defined as: $$\Phi=\iint \vec{E}\cdot \vec{dS}$$ The ...
1
vote
1answer
49 views

Electrical work and Coulomb's law

In some text books I've encountered the calculation of electrical work done on a point charge moving in an electric field (e.g. when demonstrating that electric force is conservative) is done by ...
1
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2answers
158 views

Energy stored in magnetic field [closed]

I have encountered the problem: Find the magnetic energy stored inside a 1m length of wire carrying 10 amp. The wire is 1 mm in radius, and the current density is uniform. I have found a solution ...
1
vote
2answers
215 views

Where does wave frequency come from

I am trying to wrap my head around where do oscillations in electromagnetic waves come from. As an example if I would take a string of guitar and ring it, it would produce a certain sound based on the ...
3
votes
0answers
84 views

Why must this boundary condition be met? (Electromagnetic wave at interface between two mediums)

My textbook says that The laws of Electromagnetic Theory (Section 3.1) lead to certain requirements that must be met by the fields, and they are referred to as the boundary conditions. ...
1
vote
0answers
48 views

Difficult induced current problem [closed]

consider the following setup shown below in the diagram. A circular conducting ring is placed in a increasing magnetic field into the page.Points $A$ and $B$ contain two bulbs. Initially both are ...
11
votes
2answers
5k views

How Special Relativity causes magnetism

So my physics teacher assigned us an article about how special relativity causes magnetism in a wire with a current, even with the low drift velocities of electrons in a current. It seemed that the ...
4
votes
0answers
81 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 ...
0
votes
0answers
28 views

What is the limit of the finite solenoid equation?

I'm trying to work out how long to make solenoid in order that the field is uniform over a certain length. I was wondering if there was a formula for this or any rule of thumb? I know the field inside ...
9
votes
5answers
7k views

What are electromagnetic fields made of?

I am trying to understand electromagnetic fields so I have two question related to them. What is a electromagnetic field made of? Is it made of photons / virtual photons? How about a static electric ...
0
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0answers
35 views

Effective medium approaches - Volume averaging vs homogenization?

In dealing with multiphase two phase systems as an effective medium there are two approaches that can be taken. Volume averaging and homogenization. Volume averaging is very intuitive, just take ...