# 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 to calculate the electric field and potential inside a dielectric surface placed into a homogenous field

In an experiment we placed a long dielectric cylindrical shell (cylindrical tube)(with inner and outer radii r1 and r2, respectively) in a homogenous field such that its axis was orthogonal to the ...
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### Degenerated Anderson Model Simulation

I'm trying to simulate the degenerative Anderson model. So depending on an energy difference first orbital and afterwards spin magnetism occurs. First i try to solve an easier ansatz with a limitation ...
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### Field of Solenoid

I was reading this, where in the very beginning I stumbled on the "particle in a solenoid field theme". What's written in there is: The potentianl $\textbf{A}$ is chosen to be that of a solenoid ...
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### Experimental tests of electric and magnetic fields in a gravity field

Has anyone experimentally verified that the measured values of the electric and magnetic fields do not change due to gravity, that there is no post-Newtonian effect on the strength of either $E$ or $B$...
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### Spikes and valleys of ferrofluid

I can understand that the spikes are formed because of the elongation of the ferrofluid due to the difference in forces experienced by the two ends of the particle. But I can't understand why there is ...
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### Can Lenz's rule really be used to determine the direction of induced current?

Faraday's Law states that the induced emf in a closed circuit is the negative of the rate of change of magnetic flux through the surface enclosed by the loop. To obtain the direction of the induced ...
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### Hamiltonian formulation of the semiclassical Model of electrons

I'm currently reading the book Solid State Physics by Neil W. Ashcroft and N. David Mermin. In Chapter 12 they introduce the "Semiclassical Model of Electron Dynamics". In short: After having solved ...
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### Clarify example of Faraday's law

Im wondering if it is possible to induce a high voltage current (above 1k Volts), simply using a falling magnet and a copper wire - it probably is, but then what does it take to do so. I've done ...
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### How is there not an infinite regress in the emf of a motor?

Say we have a coil connected to a battery in a uniform magnetic field, perpendicular to the magnetic moment of the coil. This is a simple motor. There is a torque on the coil that varies with the ...
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### Charged pendulum oscillations

Recently, a question was asked in our school, regarding the calculation of the time period of a charged pendulum bob suspended in an electric field with the help of an insulating thread(gravity also ...
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### optical properties of metal-dielectric-metal microcavities

I would like to figure out the optical properties of metal-dielectric-metal microcavities, used in the fabrication of micro patch antenna. The paper that I'm reading is this one. Now the specific ...
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### Mass term in Maxwell's Lagragian for Electromagnetism

In the scalar field Lagrangian the mass term is given by $$m^2 \phi^2.$$ But the equivalent term in Maxwell's Lagrangian for electromagnetism is $$m^2A_{\mu}A^{\mu}.$$ But I don't know why the ...
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### Charge that moves inside a conducting sphere

I have a conducting sphere of charge Q and inside it we set a charge -q from the centre with initial velocity uo and i would like to know with what speed it reaches the surface of the sphere and what ...
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### Self propagating EM waves mechanism of propagation

Electric fields generate magnetic fields and visa/versa,and this is attributed to be how a light ray self propagates. Can anyone further clarify how exactly light rays self propagate? If the mechanism ...
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### Effect of shielding on a miniature Helmholtz coil

So a bit of background... I'm a university graduate student with primarily digital signal processing and embedded experience. However I've managed to get myself involved with a project that requires ...
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### Amplifying an electromagnet's generated field

Given an electromagnet like this: which is essentially an iron casing with coils inside: Is it right that the centre disc would have one polarity whilst the outer housing another? To boost the ...
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### World's Largest Radio Telesope : How accurately does it need to be figured?

In Guizhou Province, China, the worlds largest radio telescope is almost complete, measuring 500 metres across. I am aware that todays largest optical telescope require very accurate figuring and ...
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### Can orbital angular momentum of an electron be changed?

In a lab at my university they are working on a project that deals with changing the "net magnetization" of a material by "flipping" the spins on some electrons. Is orbital angular momentum not ...
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### With the help of a given charge is it possible to obtain a charge many times greater in magnitude

Consider a spherically conducting sphere. If a charge(say positive) is placed near the sphere, then it will lead to separation of charges inside the sphere.My question is, can we create charges more ...
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### Attraction between electromagnet and a permanent magnet - at which point is the force the strongest?

You have an air-core inductor with current applied, so that the magnet in the picture will be attracted to it. At what position will the force between the two be the strongest and at which the weakest?...
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### Wigner-Eckart theorem and Van Vleck paramagnetism

Using the Wigner-Eckart theorem, we can express the matrix elements of Langevin's paramagnetic Hamiltonian $L_z + g_S S_z$ using only the quantum numbers of the total angular momentum, $J$ and $m_J$, ...
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### What is a simple model to find the jump height for the Thomson's Jumping Ring experiment?

I'm trying to devise a basic formula that could give a rough estimate for the jump height reached in the Thomson's Jumping Ring experiment, as detailed here. However, it's pretty difficult as most ...
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### Can a circuit produce a magnetic force on itself?

Well I think that it is kind of obvious, because the magnetic force does not specify if the fiel is produced or not by the circuit that feels it, but I had never heard about "autoinduced forces" or ...
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### Electromagnetic Tensor under Lorentz transformation, $F'(\Lambda x)= \Lambda F(x) \Lambda^T$?)

Suppose we have a configuration of electric and magnetic fields $E(x1,x2,x3,x4)$ and $B(x1,x2,x3,x4)$, they depend of position and time for a fixed coordinate system. And I want to know how someone in ...
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### Energy density inside anisotropic materials

I'm taking some college courses on electromagnetism and there was some talk of energy stored by electromagnetic field and its density. The expression that we use to calculate energy density stored by ...
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### Electro magnet strength to weight ratio

I was wondering. How would I work out how strong a magnet would have to be to support my weight.
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### Is frictional heat just electromagnetic interactions creating infrared radiation?

Example: Rub your index finger on a sheet of paper and you will feel that it will get noticeably hotter Is the reason you feel this increase in heat (technically an increase in kinetic energy of the ...
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### How do Hertzian dipoles relate to reflection of EM waves?

We recently performed an experiment where the intensity of microwave radiation reflected off different materials was measured. A comment in the script noted that the mechanism by which reflection of ...
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### Turning a k-space integral into an energy integral for a conductivity tensor

Looking over a derivation of the conductivity tensor for magneto-resistance, I got stuck trying to go from (1.133) to (1.134), transforming the k-space integral into one over energy. In this ...
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### Transformer core area

I want to ask you people that where does this formula ca = 1.152 ×√ (output voltage × output current) I am keen to know about 1.152 factor and amaze to see that how vs and is are reslonsible for max ...
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### multipole moments of dipole with finite spacing

Can a dipole with finite spacing between poles be represented by pure multipoles centered at the origin? Say for example that I have a dipole with finite spacing $2\epsilon$ between the poles. I ...