Tagged Questions
5
votes
1answer
90 views
Aharonov-Bohm Effect in Torus
I had a very brief introduction to the Aharonov-Bohm effect in class. The lecturer introduced the notion that $H(\Phi=\Phi_0)$ and $H(\Phi=0)$ gives identical energy spectrum and that the Hamiltonians ...
1
vote
0answers
62 views
The gauge-invariance of the probability current
It is simple to show that under the gauge transformation $$\begin{cases}\vec A\to\vec A+\nabla\chi\\
\phi\to\phi-\frac{\partial \chi}{\partial t}\\
\psi\to \psi ...
3
votes
1answer
41 views
Non reciprocal light propagation
In search for some explanation in why magneto-optical materials (like the one used in the Faraday rotator and, consequently, in the "optical diode") act in such a "strange" way, I saw that this kind ...
2
votes
1answer
100 views
Where is the amplitude of electromagnetic waves in the equation of energy of e/m waves? [duplicate]
Does the amplitude of the photon oscillations always stay constant and if it is not - what are the physical differences between the photon with higher amplitude in comparison to the one with the less ...
-1
votes
1answer
54 views
EM Waves Energy Loss
Where does the energy go when two photons interfere destructively at a point on a screen in Young's double slit experiment ?
2
votes
1answer
248 views
Bohr-van Leeuwen theorem and quantum mechanics
Preamble:
If one considers an ideal gas of non interacting charged particles of charge $q$ in a uniform magnetic field $\mathbf{B} = \mathbf{\nabla} \wedge \mathbf{A}$, then the classical partition ...
1
vote
1answer
89 views
Quantum Mechanics of Lenz's Law?
I've searched the internet and two famous QM books (Sakurai and Messiah) for Lenz's Law, but haven't found anything. So my question is what the quantum mechanical explanation to Lenz's law is? Can ...
4
votes
2answers
191 views
Do protons exchange photons with electrons?
I'm sorry for this question but, I just don't get it. According to the electromagnetic field theory, electrons repel each other by exchanging photons. How do protons attract electrons, by photon ...
5
votes
0answers
129 views
Local explanation of the Aharonov-Bohm effect in terms of force fields
Here is an interesting paper for the Physics SE community: On the role of potentials in the Aharonov-Bohm effect, Lev Vaidman, published in PHYSICAL REVIEW A 86, 040101(R) (2012).
You should check it ...
2
votes
1answer
116 views
Aharonov-Casher effect for charged particles
All the explanations of the Aharonov-Casher effect seem to imply it only "works" for neutral particles with a magnetic moment. This seems to stem from the duality of the A-C effect with the more known ...
3
votes
4answers
321 views
Collision of two photons
Could someone explain me how will be look like collision of two photons? Will they behave like:
Electromagnetic waves, they will interpher with each other and keep they wave nature
Particles and ...
4
votes
4answers
343 views
Can a photon get emitted without a receiver?
It is generally agreed upon that electromagnetic waves from an emitter does not have to connect to a receiver, but how can we be sure this is a fact? The problem is that we can never observe non ...
1
vote
0answers
67 views
NMR rotating frame
I'm reading about a linearly polarized field (in the context of NMR). The field is given by
$$ {\bf H_{lin}}=2H_1({\bf i}cos(\omega_zt)).$$
This can be created by having a pulse field plus its ...
6
votes
0answers
106 views
Nuclear Magnetic Resonance (NMR) Conceptual Questions
Let $M$ be the magnetic moment of a system. Below are the Bloch equations, including the relaxation terms.
$$\frac{\partial M_x}{\partial t}=({\bf M} \times \gamma {\bf H_0})_x-\frac{M_x}{T_2} $$
...
7
votes
2answers
287 views
Has The Aharonov-Bohm Effect Been Experimentally Proven?
I have encountered two contradicting papers on the Aharonov-Bohm Effect: One supporting,
The Aharonov-Bohm Effects: Variations on a Subtle Theme. H Batelaan and A Tonomura. Physics Today 62 pp. ...
1
vote
2answers
287 views
Vector Potential and Gauge Invariance in Quantum Mechanics
In classical electromagnetism, we are allowed to use gauge invariance through the argument that the only physical observable fields are the $E$-field and the $B$-field. So in that sense the scalar ...
2
votes
2answers
386 views
What is the difference between a photon and a phonon?
More specifically, how does a wave-particle duality differ from a quasiparticle/collective excitation?
What makes a photon a gauge boson and a phonon a Nambu–Goldstone boson?
2
votes
2answers
148 views
Reference request for the Aharonov-Bohm effect
I am looking for a good reference to an online source or book, on the magnetic Aharonov-Bohm effect. I have read the appropriate sections from the book by Griffiths and Ballentine, and still haven't ...
4
votes
1answer
52 views
Order of magnetic phase transitions
Is there any phase transition occur in paramagnetism to diamagnetism transitions state. What should be the order and how will I calculate the order?
0
votes
1answer
213 views
Dipole moment of the electron
I've read that there are some restrictions on the value of a possible intrinsic electric dipole possessed by the electron, but isn't the dipole value dependent on the electron's wavefunction? Assuming ...
2
votes
1answer
176 views
Minimal coupling of an atom to the EM field
The Hamiltonian of an atom coupled to an EM field, both described quantum mechanically is:
$$H = \frac{1}{2m}(\hat{p}-q\hat{A})^2 = \frac{\hat{p}^2}{2m} ...
4
votes
2answers
173 views
Why possibility for X-ray to excite inner electrons higher than outer electrons?
It seems X-ray absorption spectroscopy is usually ascribed to the interation between photons and inner electrons. Does it mean inner electrons are much preferred by X-ray photons to outer electrons? ...
2
votes
1answer
61 views
Does a microwave resonantly excite the rotational levels when cooking?
Wikipedia states there is no resonance absorption, but says at the same time that the molecules are oscillating like dipoles, which is kind of the same if you are exciting the rotational levels ?
The ...
1
vote
2answers
586 views
Conservation of Energy in a magnet
When a permanent magnet attracts some object, lets say a steel ball, energy is converted into for instance kinetic energy and heat when attraction happens, and they eventually collide. Does this imply ...
3
votes
1answer
570 views
Darwin term and Zitterbewegung
I've noticed that in the discussion of the fine structure of Hydrogen atom standard QM texts claim that the Darwin term, which corrects energy of $\ell=0$ (or $s$-) states only, is related to the ...
4
votes
2answers
382 views
Aharonov-Bohm Effect and Flux Quantization in superconductors
Why is the magnetic flux not quantized in a standard Aharonov-Bohm (infinite) solenoid setup, whereas in a superconductor setting, flux is quantized?
2
votes
2answers
249 views
On Aharonov–Bohm effect
Aharonov–Bohm effect in brief is due to some singularities in space. In books it's infinite solenoid most of the time, which makes some regions of space not simply connected.
What intrigues me is the ...
3
votes
2answers
716 views
Quantum levitation (locking) 3mm thick disk could carry 1000kg small car claim
I watched this TED presentation: http://www.ted.com/talks/boaz_almog_levitates_a_superconductor.html
It is about superconductivity and quantum levitation. It tells that super-thin, three-inch disk ...
1
vote
2answers
292 views
Frequency and wavelength of photons
I try to better understand how electromagnetic radiation works. So I have some questions.
If an antenna emits at 100MHz (the charges on the antenna oscillate at 100MHz) what frequency will have the ...
2
votes
1answer
408 views
Work done on charged particle by magnetic field in quantum mechanics
Classically, we know from $\mathbf{F}=q\mathbf{v}\times \mathbf{B}$ that magnetic field does no work on a charged particle. In quantum mechanics, the Hamiltonian of a charged particle in a magnetic ...
1
vote
1answer
125 views
Impervious nature of solid matter due to quantum degeneracy pressure
On Wikipedia the following statement is made without reference:
Freeman Dyson showed that the imperviousness of solid matter is due to
quantum degeneracy pressure rather than electrostatic ...
2
votes
1answer
341 views
is space infinitely divisible?
As a child I remember hearing the popular paradox presented by Zeno proposing that Achilles could never catch a tortoise in a race since he would have to traverse the infinite space between himself ...
6
votes
1answer
372 views
Degeneracy Pressure, What is it?
There has been numerous question, some violent even in physics@SE regarding PEP and EM forces.
But what baffles me is what is degeneracy pressure? I know there are 4 fundamental forces- EM, gravity, ...
2
votes
2answers
259 views
Why does optical pumping of Rubidium require presence of magnetic field?
The optical pumping experiment of Rubidium requires the presence of magnetic field, but I don't understand why.
The basic principle of pumping is that the selection rule forbids transition from ...
4
votes
3answers
390 views
Is photon emission possible without electrons changing energy levels?
Does molecular vibrational transition and consequent emission of infrared radiation involve electrons changing energy level? In wikipedia, about vibronic transitions it says "Most processes leading to ...
9
votes
1answer
1k views
Can you magnetize iron with a hammer?
We know that a piece of ferromagnet, such as iron, can be magnetized by putting in a strong magnetic field to get domains parallel to the field grow.
I also remember from pop. culture and MacGyver ...
3
votes
1answer
305 views
Higgs Field compared to EM field
So, I've been reading about the Higgs because of all of this excitement lately with the LHC. I'm just a layman in physics but one thing I understood was that the Higgs field permeates all of space ...
0
votes
1answer
267 views
electric dipole momentum calculation
I'm studying the linear electric susceptibility, using Schroedinger equation and perturbation theory of the interaction potential
$$V=-\mu \cdot E$$
and the book arrive to an expression where
...
4
votes
2answers
483 views
Canonical momentum in different coordinate system
The canonical momentum is defined as
$p_{i} = \frac {\partial L}{\partial \dot{q_{i}}} $,
where $L$ is the Lagrangian.
So actually how does $p_{i}$ transform in one coordinate system $\textbf{q}$ to ...
6
votes
3answers
302 views
Lorentz force in Dirac theory and its classical limit
It is well known that in Dirac theory the time derivative of $P_i=p_i+A_i$ operator (where $p_i=∂/∂_i$, $A_i$ - EM field vector potential) is an analogue of the Lorentz force:
$\frac{dP_i}{dt} = ...
2
votes
0answers
268 views
Gauge invariance and Feynman path-integrals
Let me look at the Hamiltonian of a charged particle in a plane in a constant magnetic field ($\vec{B}$) pointing upwards - then in usual notation it is,
$$\hat{H} = \frac{1}{2m}\biggl(\hat{p} + ...
9
votes
2answers
356 views
Essential background for QFT study
The preface to Mark Srednicki's "Quantum Field Theory" says that to be prepared for the book, one must recognize and understand the following equations:
$$\frac{d\sigma}{d\Omega} = ...
2
votes
1answer
208 views
Using the Scalar Electrostatic Potential to Calculate Transition Probabilities
transition probabilites of atomic systems prone to some time-varying electromagnetic field are very often calculated using perturbation theory leading to expressions including the vector potential ...
8
votes
2answers
323 views
Quantizing EM field
Why when we quantize EM field, whe quantize the vector potential $A^\mu$ obtaining vectorial particles (photons) like the elastic field (phonons) and we can't quantize directly the EM-field tensor ...
3
votes
3answers
3k views
Does a magnetic field arise from a moving charge or from its spin, or both?
I learned that a moving charge creates a magnetic field perpendicular to its direction of motion. I also learned that charged particles like electrons have spin and they also create a magnetic field ...
13
votes
4answers
6k views
Why do electrons occupy the space around nuclei, and not collide with them?
We all learn in grade school that electrons are negatively-charged particles that inhabit the space around the nucleus of an atom, that protons are positively-charged and are embedded within the ...
0
votes
2answers
618 views
Can quantum communication really replace electromagnetic waves for telecommunication medium in future?
Currently I am planning to get masters degree. So I am thinking about a subject in which I have to get masters degree. Following are my questions to leading physicists..
Which technology is the ...
3
votes
3answers
325 views
What is the density of virtual photons around a unit charge?
It seems that virtual photons also exist in vacuum. So the precise question is:
What is the additional virtual photon density due to the electric field of a unit charge?
Or: How many virtual photons ...
7
votes
3answers
1k views
Are Classical Field Theory and Quantum Mechanics of a single particle (nonrelativistic or “classical”) limits of Quantum Field Theory?
Recently I talked about QFT with another physicist and mentioned that the Quantum Field Theory of a fermion is a quantisation of its one-particle quantum mechanical theory. He denied this and ...
3
votes
4answers
500 views
Radiation from a pair of charged objects orbiting each other
This question on binary black hole solutions, led to me think about the similar question from the perspective of what we know about the Hydrogen atom.
Prior to quantum mechanics, it was not ...
