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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Eigenstates of 2D harmonic oscillator in a constant magnetic field

I want to find the eigenstates of the 2D harmonic oscillator in a constant magnetic field $\vec B = \vec B(x,y)$. My Hamiltonian reads $H_0 = H_{xy} + H_z$ where $H_{xy}$, is the hamiltonian of the ...
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0answers
56 views

Could a photon also be a fermion? [duplicate]

Some phycisits have found photons that has a spin of 1,5. Now fermions has always a half spin and bosons like photons always with a whole spin. But if those photons really exists are they than ...
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1answer
37 views

Can a flow of current be produced in a wire if its is bombarded with Electromagnetic waves?

If you have a conducting wire and you bombarded it with EM waves, is there a frequency (lower then the threshold frequency to liberate the electrons) that would induce a current within the wire. I ...
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1answer
33 views

What causes a charged particle to follow circular motion in a magnetic field? [duplicate]

I would like to know why particles follow a circular path in a magnetic field, what path they trace and how this path is measured and controlled?
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0answers
22 views

The effects of multi-stranded wire on magnetic field strength

If I were to make a solenoid (with an air core) out of stranded copper wire- say for instance 8 strands- would this effect the magnetic field strength compared to, say, a solenoid with a single stand ...
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1answer
33 views

What happens when an electromagnetic wave passes through a magnet or charged capacitor?

What are the effects or interactions between propagating electromagnetic wave that passes through static magnetic field (big neodymium magnet) or static electric field (charged plates of HV capacitor)?...
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0answers
35 views

Determine potential function given initial conditions?

Assuming a radially symmetric circular disk (let's say r=1). Given two simple initial conditions: Potential at the centre is 4 V Potential at the edges is 0 V How would I determine the potential ...
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1answer
89 views

Electrons motion

Some days ago, I was reading a very simple text about photoelectric phenomenon (at high school level) that this question came to mind. How do electrons move (for example during their translation from ...
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1answer
50 views

Relativistic transformation of electrical current [closed]

If, in frame $S$, we have an electrically neutral wire with some current $I$, modelled as positive charges moving in $x$ direction and negative charges moving in $-x$ direction, then how would one ...
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0answers
31 views

Dynamic energy of capacitors in circuit

If I have 3 capacitors and 1 battery in a circuit how should I connect them in order to have maximum dynamic energy, when I connect them with the battery? Parallel or in series?
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0answers
32 views

Feynman's paradox : “conservation of angular momentum or Lenz's law ?” [duplicate]

When I was in high school, out of my interest I read electro-magnetism topic from Feynman's lecture on physics. There was a Paradox question in that topic, answer of which i am seeking here... Below ...
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1answer
124 views

What does a voltmeter actually measure?

For time varying fields (even quasistatic ones) the electric field is given by $${\bf E} = - \nabla \Phi - \frac{\partial {\bf A}}{\partial t}$$ So what does a voltmeter measure? Does it measure a ...
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2answers
54 views

Why does an oscillating electric field couple more strongly to electrons than to ions?

As stated in Principles of Plasma Discharges and Materials Processing, by M. A. Lieberman and A. J. Lichtenberg, about capacitively coupled plasmas: (...) the light and heavy charged particles in ...
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1answer
37 views

Electric field inside an insulator's cavity [closed]

I'm trying to find the electric field inside insulating sphere's cavity, and I don't know how. However, if there was an conductor I'd know that $E=0$ from Gauss's Law.
5
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1answer
113 views

What is relationship between electromagnetic mass and rest mass?

Is there a direct equation which compares rest mass $m_°$ and electromagnetic mass $m_{em}$? Nothing on web I found. $m_{em} = \frac{4 E_{em}}{3c^2}$ 4/3 problem The final solution of the ...
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1answer
25 views

is it possible to isolate and pair electromagnetic interaction? [closed]

is it possible for two electromagnets to interact each other, ie. repulsive or attractive forces to be exerted to each other, without being exerted to other metallic items or other electromagnetic ...
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1answer
28 views

What would happen if a magnet was pushed towards a copper tube in space?

So the question was inspired by one of curious comments on youtube. What exactly would happen if you pushed a strong neodymium magnet towards the copper tube (aiming for the opening in an effort to ...
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1answer
51 views

Fermi energy of electron gas with electrostatic interaction

I have been given the following exam question and am unsure how I would go about solving it: Consider the case of a one-dimensional metal, consisting of a chain of $N$ positive charges $+q$ ...
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7answers
3k views

Why are the electric force and magnetic force classified as electromagnetism?

I confuse the four kinds of fundamental interactions, so I think the electric force and magnetic force should not be classified as a big class called electromagnetism. Here is my evidence: The ...
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1answer
370 views

Confusion in Maxwell's derivation of Ampere's Force Law - Part II [closed]

I am reading Maxwell's "a treatise on electricity and magnetism, Volume 2, page 156" about "Ampere's Force Law". I have some confusion in the following pages: My question is of two parts: 1. ...
1
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0answers
58 views

advantages/disadvantages of a cylindrical microwave oven cavity in comparison to a rectangular cavity

Why are rectangular cavities preferred for standard microwave ovens with a frequency of 2.45 Ghz? What is the reason that you can hardly find a circular cavity? What are the disadvantages of ...
3
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0answers
49 views

Why is diproton unstable? [duplicate]

Diproton is an isotope of helium without any neutrons. It commonly forms in the Sun, where protons are fused constantly. However, it is extremely unstable, and will revert back to two protons almost ...
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0answers
24 views

What is the physical meaning of a magnetic conduction current?

In electrodynamics, it is possible to have an electric conduction current, whereby $J=\sigma_e E$, with $J$ being the current, $\sigma_e$ the electrical conductivity and $E$ the electric field (this ...
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2answers
66 views

Two Black Holes held stationary by EM forces

If two black holes with large enough mass (so that the tidal forces are minimal and the intersection is large) that are held apart by like charges (saddle point stability). Imagine the black holes in ...
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0answers
12 views

Magnetic field of a current loop on a boundary between materials

How can I find the magnetic field of a current loop on a flat boundary between two materials given their magnetic permeabilities $μ_1$ and $μ_2$ and a field $\overline{H_0}(\overline{r})$ which the ...
3
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1answer
31 views

Reaching equilibrium in a blackbody and light-matter interaction

Suppose we have a metallic cavity maintained at a fixed temperature. Suppose we start with any distribution of radiation that is not in equilibrium with the container. Gradually, when the equilibrium ...
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1answer
25 views

Mechanism by which a capacitor is charged, using surface charges

I want to gain a deeper understanding as to how a capacitor actually gets charged. Consider a situation in which an uncharged parallel plate capacitor is connected to a battery using two wires. I ...
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2answers
568 views

Why do we use gauges in Maxwell equation?

While solving the Maxwell's equation we often use the Lorenz or Coulomb gauge, but why is that? Are the equations unsolvable if the gauge is not fixed? Or is it just for the simplicity?
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3answers
162 views

Why geologist do not consider molten iron in the magma to be the source of Earth's magnetic field?

This was a question that came in a exam. How come is this possible? Actually, a question on the source of Earth's magnetic field was asked here on physics SE, which matches my opinion. The ...
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1answer
69 views

How I can prove refractive index in an environment is this? [closed]

in "Applied Quantum Mechanics" by A.F.J. Levi, is a problem that I couldn't solve it can any solve it: if electrical filed is: $$ \mathbf{E}\left(\mathbf{r}, \omega \right) =\mathbf{E}_{0}\left(\...
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3answers
927 views

What are the differences between the differential and integral forms of (e.g. Maxwell's) equations?

I would like to understand what has to be differential and integral form of the same function, for example the famous equations of James Clerk Maxwell: How to know where to apply each way? Excuse ...
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1answer
60 views

Tensor notation of Maxwell's equations

Tensor notation of Maxwell's equation read So when we explicitly try to find the Maxwell's equation from the above tensor equation we only get gauss law and curl of B. The div.B=0 and curl of E are ...
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1answer
36 views

surface charge on a resistive wire in dc circuit

I want to understand how does the energy transfered from battery to the resistor in a simple dc circuit . I readed that it is due to the surface charge the battery creats on the wire . So why this ...
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2answers
87 views

Is electromotive force really a force? [duplicate]

As far the definition goes emf of electromotive force is basically potential difference. It even has dimensions of potential. Then why is it called a force?
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2answers
45 views

Zero electric field in empty region of hollow conductor

A hollow conducting shell having a net charge of +Q has a point charge -Q placed at its centre. From the diagram, it looks like Suppose the radius of the inner shell from the origin is a and the ...
4
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1answer
61 views

Is diamagnetism a static or dynamic effect?

When we put a diamagnetic material in the presence of an external magnetic field $\vec B_0$, the magnetic field inside the material decreases to $$\vec B=(1+\chi_m)\vec B_0,$$ where the magnetic ...
2
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1answer
159 views

Confusion in Maxwell's derivation of Ampere's Force Law

I am reading Maxwell's "a treatise on electricity and magnetism, Volume 2, page 155" about "Ampere's Force Law". I have some confusion in the following pages: On the top of the page, Maxwell says:...
2
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1answer
91 views

Can light be a spinor?

A recent discovery suggests that photons can have half-integer spins. This seems to contradict the well understood notion that photons are vector (1-form) fields What does this mean for the ...
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0answers
25 views

The velocity of the charged particle in the magnetic field [duplicate]

Enrico Fermi considered that moving charged particle gains energy in the magnetic field, so its velocity increases. According to the Lorentz Law $\vec F=q\vec v\times\vec B$. Work is $A=\vec F\times\...
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1answer
41 views

Maximum electric field of a circular ring

How do you differentiate the equation for electric field of uniform ring $$ E_x = \frac{kxQ}{(x^2+r^2)^{3/2}} $$to get the maximum at a point? My book says $x = \frac{r}{\sqrt2}$. I tried ...
2
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1answer
74 views

Electric field due to a time and space varying current density?

Let us say I have a current density: $$\vec J\equiv\vec J(\vec r, t)$$ This will produce both a time varying magnetic field and a net charge density. Both these effects produce an electric field. If $...
0
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2answers
64 views

Does a rotating electric field vector (in circular light) moves slower than the speed of light?

We can imagine circular light as a combination of two rotating vectors moving through space: the electric field vector that´s rotating together in sync with the magnetic field vector. As the vector ...
0
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1answer
36 views

Can circular light be produced with more than one vector, tracing out multi stranded strand helixes in space? [closed]

Is it possible to construct circular light with more than one vector tracing out a one strand helix in space? For example, circular light with two vectors in opposite directions (on the same line), ...
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0answers
18 views

Magnetostatic field inside a wire and current density

Right now I'm studying magnetostatics an I ran across a problem when trying to understand a question in a book witch led me to thing that the steady-state current density inside a wire is not ...
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2answers
43 views

Why doesn't the group velocity of a plasma EM wave equal the phase velocity here?

For plasma EM waves we have the dispersion relation $$\omega^2=\omega_p^2+c^2k^2$$ where the plasma frequency $$\omega_p^2=\frac{n_e e^2}{\epsilon_0 m_e}$$ One can show that $v_p v_g=c^2$, i.e., the ...
3
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0answers
55 views

Does charge injection from electrodes increases the total charge in a (semi)conductive channel?

When a (semi)conductor is connected to a voltage bias, a charge is injected by the electrodes. When steady state is reached (constant current flow), does the total charge of the (semi)conductor differ ...
1
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1answer
59 views

B field of an EM pulse

I am trying to find the B field associated with the following E field (to eventually find the effect it has on a charged particle): $$E(\vec{x},t)= \Re[E_0(z-ct)]e^{ik_0(z-ct)}$$ Where $E_0$ is an ...
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1answer
42 views

Using 2 pair of like pole magnet side by side will increase magnetic field?

I would like to know if using two pairs of magnets with like poles side by side will strengthen the magnetic field? As I understand, placing 2 pair of magnetic with like poles side by side will dry ...
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1answer
20 views

Do we use rms values or peak value for calculating power of a transformer?

Do we use rms values or peak value for calculating power of a transformer? I have an A levels exam tomorrow and I wasn't able to find any kind of explanation in the book.
3
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1answer
124 views

Purcell's approach to Larmor's formula, assumption?

In 'Electricity and Magnetism' By E.M.Purcell, a derivation is given of Larmor formula (a version of which can be found here). I will give a brief overview here: A particle is considered at ...