# Tagged Questions

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### Has magnetism been experimentally demonstrated at the quantum level?

I've learned that magnetic fields are generated by electric currents, and that electric current is the motion of electrons and stuff like that. Many textbooks also talk about "point charges" and have ...
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### Quantized modes of EM field in a cubic cavity

I am trying to solve for Electric field modes in a cubic cavity with perfectly reflecting walls. I know that for the modes, I have the standard Helmholtz Equation $$(\nabla^2+k^2)E_i=0$$ And I want ...
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### Stern-Gerlach experiment theory question [closed]

I have an assignment problem which I've been having some difficulty with. i know the answer but I want to know how to arrive at it correctly, and want to know where I've gone wrong. Determine the ...
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### Why can't electrons fall into the nucleus?

I read a book on pop sci book on quantum mechanics and the author said that electrons do not fall into the nucleus due to quantum mechanics- which principles suggest this (I think it was Heisenberg's ...
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### Question about electromagnetic Spectrum [closed]

I have question related to electromagnetic Spectrum. If energy of photon is $E=m_e c^2$, to which part of the electromagnetic spectrum does it belong ?
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### Momentum operator of a particle in an electromagnetic field

In quantum mechanics, to all observables correspond some self-adjoint operators. In the absence of an electromagnetic field the momentum operator is clearly $\vec{P}:=\frac{\hbar}{i}\vec{\nabla}$. ...
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### Why is optical orbital angular momentum (OAM) called “topological charge”?

The terminology "topological charge" is frequent in lots of research papers related to optical vortex or optical OAM, it is used to represent the optical OAM. Why? How to comprehend it?
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### Splitting of degenerate energy levels with a perturbed particle in a box

Suppose you have a particle in a square box $[0,L]\times[0,L]$. As the box is a square, the (2,1) and (1,2) eigenfunctions will have the same energy. If you were to apply an oscillating electric field ...
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### Energy in an electromagnetic wave

A radio antenna creates EM waves through switching the polarization in the antenna at a certain frequency. I assume the the energy of the photons produced in this process amount to E=hf for each ...
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### The gauge covariant derivative and it's substitution

I was wondering wether it would make a difference (in general) if I were to were introduce the gauge covariant derivative $$D_\mu=\partial_\mu+ieA_\mu$$ In the Lagrangian density and then derive the ...
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In "introductory Quantum Optics", by Gerry and Knight, the Jeynes model is considered. In this model of electron-EM field interaction the electron is approximated by a two state system ($\lvert ... 1answer 36 views ### Conduction and propagation [duplicate] What is the difference between conduction of electric wave in conductor and propagation of electromagnetic wave in dielectric? Why propagation term is used for dielectric and conduction for ... 0answers 11 views ### multiple frequency trapped power signal is there any possibility to generate a waveform that consists of multiple power signals with different frequencies such that these signals travel together like they constitute [to form a ... 2answers 95 views ### Suppose a light wave with wavelength 3m. What happens if one tries to contain that wave within a 1m container? Suppose a light wave with wavelength 3m. What happens if one tries to contain that wave within a 1m container? If I'm going about this entirely the wrong way or have wrong conceptions about light ... 2answers 107 views ### Why does a magnetic field raise the ground state energy of an electrical particle? I heard a statement that the ground state energy of a electrical particle in a magnetic field is larger than its ground state energy without the magnetic field. I just heard this statement. This ... 1answer 74 views ### What is the significance of the difference in the eigenvalue equations of Bloch functions for electrons vs photons? any text on photonic crystals will highlight the almost perfect analogy between electrons in a periodic potential and photons in a periodic dielectric. The analogies are: $$V(\vec r + \vec R) = ... 2answers 140 views ### How to derive the Aharanov-Bohm effect result? In the derivations of the Aharonov-Bohm phase, it is directly mentioned that due to the introduction of the vector potential A, an extra phase is introduced into the wavefunction for case A\neq0 ... 1answer 207 views ### Magnetic field due to electron in Hydrogen? We can calculate the current density \mathbf{j} of the electron in Hydrogen, and it is given by:$$ j_\phi=-e\frac{\hbar m}{\mu r\sin\theta}\left|\psi_{nlm}\left(r,\theta,\phi\right)\right|^2 $$... 1answer 319 views ### What is the conclusion from Aharonov-Bohm Effect? What is the conclusion that we can draw from the Aharonov-Bohm effect? Does it simply suggest that the vector potential has measurable effects? Does it mean that it is a real observable in quantum ... 1answer 123 views ### Phase Shift of Tunneling Wave What is the phase shift of a wave that tunnels through a barrier, meaning the difference in phase between the incoming (in front of the barrier) and the outgoing (behind the barrier) waves? For ... 0answers 160 views ### Explanation for the physics behind magnetic monopoles? Ok so I am looking for a simple explanation of how the process is done from the information I could access and the knowledge I was allowed I have the idea that it is a matter of quantum physics and ... 2answers 781 views ### Gauge Invariance of the Hamiltonian of the electromagnetic field The Hamiltonian for an electron of mass m and charge e in an exterior electromagnetic field is$$H=\frac{1}{2m}(p-(e/c)A)^2+e\varphi.$$The corresponding (via canonical quantization) quantum ... 0answers 30 views ### Opposite field's acting on a soft ferromagnetic material To external fields(H, - H) not equal to each other are acting on that material. Based on the hysteresis loop what would be the result? The hysteresis area of that materials is very narrow(i.e easy to ... 0answers 47 views ### Help in understand Magnetostatic Energy$$E_{\mathrm{ms}} = \frac{1}{2}\mu_0 \int_V \mathbf{M} \cdot \mathbf{H}_{\mathrm{ms}} d^3 r$$I can't understand this formula, what is the magnetostatic stored potential energy?! What does it show? ... 0answers 43 views ### Which is more energy efficient: optical demagnetization or heating beyond$T_c\$,

What is considered more energy efficient? Current research show that the amount of energy used for powering a laser to demagnetize a material is quite small. However, the demagnetization is very ...
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### Lasers can demagnetize ferromagnets?

How is it possible to demagnetize a magnet with a laser? Source: http://www.helmholtz-berlin.de/pubbin/news_seite?nid=13657&sprache=en&typoid And the paper: ...