# Tagged Questions

0answers
29 views

### 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 ...
0answers
26 views

2answers
136 views

### 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 ...
1answer
48 views

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 ... 0answers 22 views ### Conduction and propagation 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 78 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 ... 1answer 51 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 37 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: $$V(\vec r + \vec R) = ... 2answers 104 views ### How to derive the Aharanov-Bohm effect result? In the derivations of the Aharonov-Bohm phase, it is directly mentioned that due to the introduction of the vector potential A, an extra phase is introduced into the wavefunction for case A\neq0 ... 1answer 191 views ### Magnetic field due to electron in Hydrogen? We can calculate the current density \mathbf{j} of the electron in Hydrogen, and it is given by:$$ j_\phi=-e\frac{\hbar m}{\mu r\sin\theta}\left|\psi_{nlm}\left(r,\theta,\phi\right)\right|^2 $$... 1answer 183 views ### What is the conclusion from Aharonov-Bohm Effect? What is the conclusion that we can draw from the Aharonov-Bohm effect? Does it simply suggest that the vector potential has measurable effects? Does it mean that it is a real observable in quantum ... 1answer 78 views ### Phase Shift of Tunneling Wave What is the phase shift of a wave that tunnels through a barrier, meaning the difference in phase between the incoming (in front of the barrier) and the outgoing (behind the barrier) waves? For ... 0answers 132 views ### Explanation for the physics behind magnetic monopoles? Ok so I am looking for a simple explanation of how the process is done from the information I could access and the knowledge I was allowed I have the idea that it is a matter of quantum physics and ... 2answers 417 views ### Gauge Invariance of the Hamiltonian of the electromagnetic field The Hamiltonian for an electron of mass m and charge e in an exterior electromagnetic field is$$H=\frac{1}{2m}(p-(e/c)A)^2+e\varphi.$$The corresponding (via canonical quantization) quantum ... 0answers 19 views ### Opposite field's acting on a soft ferromagnetic material To external fields(H, - H) not equal to each other are acting on that material. Based on the hysteresis loop what would be the result? The hysteresis area of that materials is very narrow(i.e easy to ... 0answers 44 views ### Help in understand Magnetostatic Energy$$E_{\mathrm{ms}} = \frac{1}{2}\mu_0 \int_V \mathbf{M} \cdot \mathbf{H}_{\mathrm{ms}} d^3 rI can't understand this formula, what is the magnetostatic stored potential energy?! What does it show? ... 0answers 39 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 ... 0answers 63 views ### 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: ... 1answer 68 views ### In a strong field, how long would it take for domains to align? How fast is the rate of "switch" for the domains to align with an exterior field? Possibly in milliseconds? I assume it won't take much time since domains are very small, and they only turn from a ... 0answers 18 views ### Calculating torque applied on domain? How is it possible to calculate torque that is applied on a domain due to the magnetization force[H]? 1answer 53 views ### Magnetization force on domains after alignment? When a domain is aligned to an exterior uniform magnetic field. There are no forces acting on it? Magnetization force = 0, and all other force? 1answer 314 views ### What prevents an atom's electrons from “collapsing” onto its protons? [duplicate] Forgive me if the answer to this is obvious. I have no formal physics training, and I remember that when I asked my physics teacher this, she just frowned and said "Good question." An electron is ... 1answer 127 views ### How can Superconductivity materials levitate permanent magnet? I have thought that by eddy current. But how eddy current in superconductivity materials can be generated by using permanent magnet? 1answer 120 views ### electric potential energy symbol in Schrodinger equation In my introductory physics class, V is the symbol for electric potential (joules per coulomb) and U is the symbol for electric potential energy (joules). Since the Schrodinger equation is the ... 1answer 210 views ### Coercivity of a ferromagnetic material? I understand that coercivity is the field/force required to demagnetize/magnetize a ferromagnetic material. What if we had two opposite magnetic fields of different strengths values H acting on the ... 2answers 193 views ### The meaning of potential in Bohm-Aharonov experiment The Bohm-Aharonov experiment involves a magnetic field inside a cylinder which is zero outside that cylinder. Nonetheless it affects the electrons moving outside the cylinder. The explanation for this ... 1answer 110 views ### Particle Spacing in a Vacuum Four questions: (To start off, I know very little about physics it isn't even funny (I probably use a ton of wrong terms here and leave out vital information, if so I will try to edit it in as you ... 3answers 103 views ### Curie temperature and magnetization? If an ferromagnetic object is heated and reaches Tc the magnetization gradually drops as we get closer to Tc or it's a instant drop? Can I assume as I heat the object, the magnetization is weakening ... 1answer 54 views ### How many domains are there in a ferromagnetic material? How many are there? Also what is the size of those domains? Finally, when domains align with exterior magnetic fields do they move or are they all fixed? I assume they are all fixed because the atoms ... 0answers 44 views ### Energy required to demagnetize a soft iron? How much energy is required to demagnetize a soft iron ferromagnetic material, that has a very low coercive force And a small hysteresis area? Also, would it be possible to demagnetize that same ... 0answers 47 views ### Magnetization energy density and Magnetic field energy density. Are they the same? I mean the energy required to magnetize/demagnetize a ferromagnet is highly dependent on the hysteresis loop that is E= \int H dB. The energy density of the same field is equal ... 2answers 77 views ### Are there any known, non-spectroscopic effects of EM directly on Light? Photons have no charge. Light is a form of electromagnetic energy. All spectroscopic effects (to my knowledge) are due to changes in electron state, induced either through an interior or exterior EM ... 2answers 689 views ### Do electric and magnetic lines of force physically exist? As per my imagination any thing can't impose force on the other by not giving even a touch(i,e action at a distance). So I thought there must be some physical existence of lines of force. Although ... 1answer 141 views ### Classically, how can an electron orbiting a proton radiate given its relativistic energy In classical relativistic Electrodynamics, we are often told that any accelerating point charge inherently radiates (Bremstrallung). (This is the basis for the need for a QM conception of electrons.) ... 2answers 122 views ### Why don't charges move transverse to an EM wave? Image we have an ultra-high intensity, ultra low frequency laser, with wattage on the order of terawatts and a wavelength on the order of a lightsecond. We rotate it that the electric field component ... 2answers 193 views ### Rabi oscillation, electron in a box This page on Rabi oscillation says the Hamiltonian has an interaction term d \cdot E(t), where d = -er. (I'm sure what they mean is, that's what the off-diagonal terms of the Hamiltonian look ... 0answers 48 views ### The electron and classical dynamics Can I use Newtonian laws of dynamics and kinematics applied to electrons (like F = ma and s = s_0 + v_0 t + at^2/2)? If not, why not? I know that everything in principle behaves in a quantum ... 2answers 671 views ### What is the difference between the Balmer series of hydrogen and deuterium? In my quantum mechanics textbook, it claims that the Balmer series between hydrogen and deuterium is different. However, I was under the impression that the Balmer seriesH_\alpha, H_\beta, ... 1answer 348 views ### Covariance of the Dirac equation and Infinitesimal Lorentz transformation Okay, I've got really desperate now. I've spend 10 hours of work (for a few days) trying to prove 'trivial' equation in Quantum Electrodynamics. To anybody who want to write an answer for my questions ... 1answer 2k views ### What causes electron to orbit the nucleus in an atom? [closed] What causes the electron to orbit the nucleus? Which is the force that causes it to do so? Is it related to the Electro - Magnetic force? . 2answers 98 views ### What are correlated magnetic moments? My book has the following sentence and I don't understand what correlation or lack of correlation means: At high temperature the magnetic moments of adjacent atoms are uncorrelated (to maximize ... 0answers 37 views ### Spin angular momentum AND spin magnetic moment [duplicate] Since magnetic moment come from circulation of current or magnet. Because spin of electron is not classical spin of body so what is origination of spin magnetic moment and angular momentum? Is ... 0answers 101 views ### Doubts about the Aharonov-Bohm effect In F. Schwabl, Quantum Mechanics p.148 it is explained that if we have a particle in an electromagnetic field given by potentials\varphi$and$\mathbf{A}$with wave function$\psi$, then a gauge ... 1answer 60 views ### Radiation interactions: how is the transition from the “electric” regimen to “particle-like” regimen? When we study the interaction of the electromagnetic radiation with free electrons we can find two different approaches in the literature: for low frequency (RF, light...) a classical view is used and ... 1answer 190 views ### Can a force stop a Photon since Photons have momentum and What does momentum mean when talking about massless particles? Momentum measures how hard it is to stop an object. While Photons are massless they still have relativistic mass and energy. My question is can something stop photons other than being absorbed by ... 1answer 2k views ### Why does the refractive index depend on wavelength? [duplicate] Why do different wavelength get impeded more or less when in different materials? Moving with the same speed, but a longer physical distance would imply that the fields oscillate less times in the ... 1answer 174 views ### What do we mean when we say the QM wave function is a section of the$U(1)\$ bundle?

I have a couple questions here. To keep the discussion simple lets stick to the following case: what is the quantum mechanics of a single particle in the presence of a background EM field, such as ...