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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2
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2answers
55 views

Why is the introduction of a quantization volume necessary for quantization of the EM field

I have been working through the quantization of the electromagnetic field, and every source I find introduces a quantization volume with periodic boundary conditions in the process, in which we fit ...
0
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0answers
19 views

Ratio E/B and power in rectangular cavity

I would like to know if the relation $E=B*c$ still holds in a rectangular cavity Let's consider this rectangular cavity where the wave is travelling along the z direction ...
0
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0answers
31 views

Reactor for electrical energy design base assumption inefficient?

Im no physicist or engineer but as I observe our methods to obtain electrical energy I noticed a pattern where we cause a exothermic reaction, the resulting energy heats water, that turns into vapor, ...
0
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0answers
45 views

Regarding Ampere's Circuital Law

If I am to show that Ampere's Circuital law holds true for any arbitrary closed loop in a plane normal to the straight wire, with its validity already established for the closed loop being a circle of ...
1
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0answers
13 views

Coordinate Transformation across different media

I have an arrangement that is as follows : (1) inner cylinder(radius r1) filled with water (2) outer cylinder(concentric, radius r2>r1) made of glass I have a sensor S1 at radius r(r1) at angle beta. ...
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0answers
26 views

How is the electromagnetic tensor expanded?

The electromagnetic tensor is given by $F_{\mu \nu} = \partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu}$, and it appears in the Lagrangian as $L = -\frac{1}{4}F_{\mu\nu}^2 - A_{\mu}J_{\mu}$. The text I'm ...
0
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1answer
18 views

$H$ field from corresponding $E$ field (antenna)

The $E$ field at $kr >> 1$ due to a short dipole oriented in the $z$-direction and located at the origin is: $$E_0 = \frac{10^3e^{-jkr}}{r}\sin\theta\space\space(V/m)$$ Can I just solve for the ...
0
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1answer
30 views

what is the meaning of spatial function of Ex?

I came across this while i was studying Resonant cavities. Consider the component of $E_x $ of $ E $. Within the cavity $$ E_x = E_x(x,y,z) $$ Why should we take $E_x $ in all three directions?
2
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0answers
51 views

Spectroscopy from a classical light wave or photon only?

In chemistry we mostly regard light/electromagnetic radiation as a beam of particles or photons. This is a very useful model to explain molecular excitations and ionisations from quantum interactions. ...
0
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1answer
42 views

Apparent discrepancy between Lagrange field equation and Maxwell equation [closed]

I am deriving Maxwell's equations from a Lagrange field equation and have come across something I can not figure out no matter how hard I try. The problem is in the signs. If we take the Lagrange ...
0
votes
1answer
63 views

What is the recent most important discovery and study about magnets? [closed]

I believe that magnetism is a very powerful tool to do various things.It can make amazing machines.What is the recent most important piece of study that has been done of magnetism. The study that can ...
0
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0answers
8 views

EM wave - phase change - amplitude [duplicate]

A plane electromagnetic wave has the shape: $\vec{E}(\vec{r},t)=E_0\cdot cos(\vec{k}\vec{r}-\omega t)\cdot \vec{e}_y$ $\vec{B}(\vec{r},t)=(B_1\cdot cos(\vec{k}\vec{r}-\omega t)+B_2\cdot ...
0
votes
1answer
62 views

Phase on Aharonov-Bohm effect doubts

How I show that $$\Lambda(\textbf{x}')=\frac{q}{\hbar}\int \mathbf{A} \cdot d\mathbf{x'}$$ on $$ \tilde{\psi}(\textbf{x}',t)=e^{[\frac{iq\Lambda(\textbf{x}')}{\hbar c}]}\psi(\textbf{x}',t)$$ for ...
2
votes
2answers
107 views

Where do Maxwell's equations come from?

I recently started learning the basic forms (integrals) of the Maxwell's equations, and everything that is related to electromagnetism seems to be derived from these fundamental equations. Now my ...
0
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0answers
21 views

What is the equation to calculate the strength and radius of an electromagnetic pulse?

With this interesting answer on the blast force of a uniformly charged electron sphere, came another interesting question. What would be the strength and blast radius of an EMP launched from such a ...
0
votes
1answer
30 views

Field emission vs. electrical breakdown

In vacuum a tungsten needle sits in front of a copper plate at some separation $d$. How does the ratio of the voltage at a fix field emission current (e.g. 1 pA) $V_{fe}(1 \ \text{pA})$ and the ...
2
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2answers
76 views

Calculating the resistance of a 3D shape between two points

If I have an arbitrarily shaped object made of a uniform material of some specified resistivity, how would I go about calculating the resistance between two measurement points with known contact ...
1
vote
1answer
72 views

Can lightning actually weld fillings in your teeth?

So, I remember sometime in my childhood, someone was teaching me about lightning safety, and they explained that it was important to crouch low but keep as little contact with the ground as possible, ...
1
vote
1answer
52 views

Predicting the correct graph for the E.M.F induced

To be honest, this is a homework question. A screenshot of this question is given below. NOTE: The correct word for the one that I encircle with blue colour should be "rotates" My argument towards ...
1
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0answers
76 views

A classically charged point particle interacting with electromagnetism and gravity

Consider a classically charged point particle interacting with electromagnetism and gravity. The relevant dynamical variables are $\chi^\mu (\tau)$ of the particle, the electromangetic potential ...
0
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0answers
16 views

Why Stress Relieving Makes M2 Alloy Magnetic?

After alignment of M2 steel (removing all inside stresses) the alloy becomes magnetic, while before it was not (as accurate as I could measure). For certain, it became much more magnetic. What can ...
0
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0answers
30 views

What is the form of the skin effect in exponentially decreasing (or exponentially increasing) voltages?

I tried to replicate the standard derivation of the skin effect for exponentially shrinking or growing voltages (idealize the surface of the wire as a half-infinite volume of conductor) but I'm not ...
0
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1answer
119 views

Ηow does a current density becomes a charge density?

The transformations in special relativity of current and charge density fields are given as follows: $\bar J' = \begin{matrix} \gamma(J_x - Vρ) \\ J_y \\ J_z \end{matrix}$ $ρ' =\gamma (ρ - {V J_x ...
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0answers
22 views

Combining wave plates?

In the context of classical electromagnetism, is it always possible to reproduce the action of a large number of half-wave plates and quarter wave-plates with that of a single half-wave plate and a ...
0
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0answers
28 views

Three phase permanent magnet generator question

For my three phase permanent magnet generator, my coil plate is going to remain stationary to avoid having to use a commutator. Instead my magnetic plate will rotate. If instead of having just one ...
0
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2answers
26 views

Complex charge of a Hertzian Dipole

Im breaking my head over the solution of an old exam problem: Given is the following hertzian dipole: Given are also the equations: $I(t) = \Re\left(I_0 e^{j\omega t}\right)$, $Q(t) = ...
2
votes
1answer
73 views

Why are photons bosonic?

I am studying the quantization of the electromagnetic field. My text quantizes by changing amplitudes to ladder operators, by putting in an action and by imposing bosonic commutation relations upon ...
0
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0answers
46 views

Adding Magnetic Fields?

Ok, so we all know that the strength of a magnetic field can be increased if a wire with current flowing through it is surrounding the magnet. Because the current flowing through the wire is making a ...
7
votes
4answers
458 views

Does radiation force depend on group velocity or on phase velocity?

What is the radiation force $F$ due to a beam of photons of power $P$ undergoing perfect reflection? Is it $$a) F = 2 P / c$$ or $$b) F = 2 P / v_g$$ where $v_g$ is the group velocity ? Note that ...
0
votes
2answers
78 views

Magnet dimensions for 3-phase permanent generator

I'm making a 3-phase permenant generator. According to Faraday's law, the emf produced is negative number of turns times the change in magnetic flux over the change in time. If it is only the CHANGE ...
0
votes
1answer
38 views

Determining the Lorenz gauge condition

I'm having a bit of trouble understanding how the gauge condition is found. Consider the potentials $V$ and $\vec A$ and $V'$ and $\vec A'$ so that $$\vec E = -\vec\nabla V -\frac{\partial\vec ...
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0answers
22 views

Does light follow magnetic flux lines? [duplicate]

Will light naturally tend to align itself to magnetic flux lines?
0
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1answer
55 views

Books on Faraday, Maxwell

Can you recommend a/some good book(s) on Faraday for the lay person? In particular, in relation to his 'Experimental Researches in Electricity'. Also, any books explaining how Maxwell explained ...
0
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2answers
66 views

Particle beam in infinite magnetic field

In a physics exam at university I had the following problem: A proton-deuteron beam is accelerated by a $\Delta V = 10^7\,\mathrm{V}$ difference of potential. At some point, the particles enter ...
1
vote
1answer
49 views

If Coulomb and Esu have different dimensions, why can we convert simply by 1C= 3*10e9 esu?

I was always told in school we cannot convert an apple into a potato, so we have to have the same dimensions on both sides. When converting coulomb to esu, we do not seem to bother with dimensions. ...
3
votes
2answers
121 views

Spin zero photons

As I understand it, the reason why there is no Spin 0 Photon is because the polarisation of an EM field lives in two dimension. Hence we only have two basis vectors, yielding two pairs of ladder ...
3
votes
3answers
177 views

Why the induced field is ignored in Faraday's law?

Suppose we have a conducting ring in a constant magnetic field $\vec{B}$. Suppose that the ring is being deformed. We know from Faraday's law that such an action will induce a current in the loop. ...
2
votes
1answer
97 views

Why is the electromagnetic four-potential $A_{\mu}$ not an observable?

Why within classical field-theory the electromagnetic four-potential (usually $A_{\mu}$) not an observable? In classical mechanics we don't have problems with energy measurements and in quantum ...
1
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2answers
74 views

Larmor Precession - What does precession actually means?

Larmor Precession - What does precession actually means? Is it change in the orientation of the axis with which electron revolves around the orbit or what. But, shouldn't the radius of the orbit ...
1
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0answers
20 views

Is Magnetic field inside solenoid dependant on volume of its shape?

There are two types of solenoids: one cylindrical, one spherical. Let's assume the dimensions of the cylindrical solenoid are set such that its base radius is that of spherical solenoid $a$, and the ...
0
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1answer
31 views

Geometry confusion with incident E field

My geometry is very rusty and I'm having trouble understanding why for the incident E field the X component is multiplied by cos and the -Z component is multiplied by sin instead of the other way ...
0
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0answers
18 views

magnetic effects of electric current

If a magnet cant have one pole then in electric motor working we two magnet symbolized with names N and S. Are the single poled or bipolar? and what is the effect of magnets in working of DC motor.
0
votes
1answer
39 views

Boundary condition for E field

My book says that the boundary condition for the E field is: $$\hat{n} \times (\textbf{E}_1 - \textbf{E}_2) = 0 $$ and then concludes that the above condition can be summarized by the statement, "The ...
1
vote
1answer
60 views

What is the metric of a constant electromagnetic (pure electric or pure magnetic) field?

For example, imagine a magnetic field $B_x$ directing in $\hat{x}$ direction filling all the space. What is its associated metric field? I can construct the electromagnetic stress-energy tensor for ...
0
votes
0answers
50 views

How to solve Laplace equation in a domain with one boundary along a curve?

Is there a way to solve the 2D Laplace equation $\frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2} =0$ on $0 <x<\infty$ and $0 < y < \infty$, such that the domain is ...
1
vote
0answers
47 views

Tesla's Egg of Columbus [closed]

trying to make Tesla's egg of Columbus for a science project (https://www.youtube.com/watch?v=pG6KPtpEl7M). I have managed to cast a small rod of solid aluminium into a solid egg shaped piece of ...
-3
votes
1answer
59 views

Weight of magnetic objects and polarization [closed]

I am an Iranian engineer and have a question which no one has answered me yet. In weighing a strong magnet, there is a difference between the weights from different polarization directions, why is ...
0
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0answers
28 views

Force between magnets with different sizes

I would like to know how to calculate pulling or pushing force between two the same shaped magnet but with different sizes. Specifically, I'm looking for cylindrical and bar magnets. I tried solve ...
1
vote
1answer
54 views

Finding the magnetic field given the electric field [closed]

I'm reading a book on Electricity and Magnetism. I was solving some problems and found this very interesting one: WARNING: The next problems don't have to be solved applying Maxwell's equations; ...
0
votes
1answer
56 views

Is the Biot Savart Law applicable only for continuous currents?

There is a widely known formula for the magnetic field due to a moving charged particle. $$\frac{\mu_0}{4\pi} q \frac{\vec{v}\times\vec{r}}{r^3} $$ The usual derivation is as follows. $$ dB = ...