0
votes
2answers
25 views

What is the problem if we use air as clad in fiber communication?

The refractive index of air is approximately 1 and that of core possibly be 1.5. The refractive index of clad could be 1.48 or 1.45. The refractive index of clad and refractive index of air both ...
0
votes
1answer
156 views

Negative Sign in Compression Modulus

I noticed that the bulk modulus often has a negative sign appended to it in order to cancel with a negative change in an object's volume; this allows the bulk modulus to be positive. However, I ...
-7
votes
0answers
36 views

What is the content for 4th dimensional space? [on hold]

For 1 dimension content is length For 2nd dimension it is area For 3rd dimension it is volume similarly what is the term for 4th and higher dimensions? is there a specific term?
5
votes
3answers
117 views

What are the original papers on the hydrogen spectral lines?

I am trying to find original sources for experiments that had observed spectral lines from hydrogen or other gases. I am looking into experiments that motivated Niels Bohr to write his ideas on the ...
1
vote
0answers
16 views
+50

Plasmon quenching vs plasmon decay. What is the difference?

I'm reading an article "Quenching, Plasmonic, and Radiative Decays in Nanogap Emitting Devices" (pubs.acs.org/journal/apchd5). I don't understand the following: Counterintuitively, we evidence ...
2
votes
1answer
88 views

does a rotating moving body in “flat” space curve its path because of frame dragging?

I am not a physicist. let's say we have a space with an object in it, where all other gravitational bodies are so far away that their affect on the shape of the space is negligible. let's say the ...
4
votes
1answer
227 views

Do the position-momentum uncertainty and time-energy uncertainty really exist in QFT?

It is well known from the Quantum Mechanics(QM) that for a particle, there is a position-momentum uncertainty relation: $$\Delta x\cdot \Delta p\geq \frac{1}{2}\hbar,$$ which bascically can be derived ...
3
votes
1answer
425 views

Do we need virtual particles?

I understand the $\Delta t \cdot \Delta E \geq \hbar / 2$ relationship and the idea behind them. However, I don't understand why do we need them at all. I'm a physics undergraduate. As far as I know, ...
2
votes
2answers
556 views

Quantum entanglement definition [on hold]

How can we define Quantum entanglement (in QFT)? What are the known mathematical settings and special physical (or logical) conditions of QE applied to Quantum computing?
5
votes
1answer
50 views

Particle on $S^1$ and $U(1)$-principal bundle

I have a question arisen from a simple QM problem: let consider a boson on $S^1$ minimally coupled with a constant gauge field $A$. Taking the stationary Schrödinger (S) or Klein-Gordon (KG) equation ...
0
votes
1answer
477 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 ...
-3
votes
1answer
44 views

Are black holes really just neutron stars? [on hold]

I was curious if it would be possible for blackholes to actually just be neutron starts that are so large that they trap light and gain mass from nearby objects. If this were true that would mean that ...
1
vote
3answers
27 views

Phases and sinusoidal waves

When we're talking about a wave, just a singular sinusoidal wave, what exactly is a 'phase'? I came across a question that gave values of frequency ($550$Hz), and speed ($330$m/s). The question then ...
0
votes
1answer
246 views

Where do the electrons go?

In our house most of the plug-points have 2 holes. I know that one hole is neutral and other one supplies electricity. I can say that when i plug any device and turn the switch on electricity starts ...
1
vote
3answers
156 views

Derviation of group velocity

I am working thru a derivation of the group velocity formula and I get to this stage: $$y=2A\cos(x\frac{\Delta K}{2} -t\frac{\Delta \omega}{2})\sin( \bar k x-\bar \omega t)$$ Then all the derivations ...
2
votes
1answer
22 views

Why Doppler shift is applicable to spectral lines alone?

In astronomical spectroscopy, Doppler shift is an important parameter. But why is it applicable to spectral lines alone, and not to the continuous spectrum in the background? Shouldn't the motion of ...
-2
votes
0answers
29 views

Black Holes and dimensions

In a mental experiment, I was pondering the paradox of the event horizon of a black hole and the use of multiple dimensions. I have seen the question before. If gravity increases infinitely as you ...
0
votes
1answer
14 views

Which way is the magnetic field headed? [on hold]

Question Is the magnetic field directed into the page or out of the page? I am using this right hand rule --> RHR So anyhow, my index finger is pointing downwards, and since the magnetic force is ...
1
vote
0answers
22 views

Geometric Algebra formulation of EM in nonuniform dielectric media

Normally, there is a straightforward formulation of Maxwell's equations in free space under the GA framework, which reduces to (picking the right units): $$ \nabla F = \mu_0 J $$ with some ...
0
votes
3answers
923 views

Understanding magnetic force on charged particle

if we put any charged motionless or static particle in the constant magnetic field, then why does it don't feel a magnetic force? Mechanism by which electric and magnetic fields interrelate I have ...
2
votes
0answers
14 views

Boötes Void numbers, 2016

As a general science (hence Wikipedia!) reader, the latest information I have is that 60 galaxies have been found and counted inside the Boötes void, this of 1997. (1) What is the latest count of ...
0
votes
0answers
17 views

Momentum equation in a Lagrangian configuration

When writing the momentum equation in a lagrangian configuration is the the stress tensor used the first Piola-Kirchhoff stress tensor or the nominal stress tensor (which is the transpose of the 1st ...
4
votes
1answer
41 views

What causes the buzzing sound when the electricity changes into heat?

When I turn on any kind of electric heating (kettle, cooker, heater, ...), it keeps producing a constant buzzing sound. What is the exact cause of that sound? Do the electrons of the electric ...
-2
votes
2answers
40 views

Condition for a particle to move on a sphere

Is it possible for a particle of mass $m$ to complete a circular path on a sphere if it starts from the topmost point and no external force acts on it except gravity and frictional force between ...
1
vote
0answers
39 views

Can a lightning strike cause your car to not run? [migrated]

If lightning strikes a tree in your yard and your car is close by, can this cause your car to not work properly? I had an employee call in stating that lightning struck a tree beside their mobile ...
1
vote
0answers
24 views

Interaction of atoms of the same material

So I've been reading a section about energy levels and came across this statement: "As the atoms of a material are brought closer together to form the crystal lattice structure, there is an ...
1
vote
2answers
144 views

Motor Speed depends on voltage or number of turns

What limit the size of motor speed? Does the speed of motor depend on the voltage applied or magnetic field strenght or frequency or what?
1
vote
1answer
53 views

Could I pick up a human with a strong enough magnet? [duplicate]

Could I pick up a human with a strong enough magnet? Humans contain magnetic materials, such as iron.
0
votes
1answer
28 views

How image is formed within the eye?

So our eye has a layer of nerves. Our eye lens refracts and concentrates light rays of different amplitudes, and that concentrated impulse (of a mixed amplitude) induces a signal on some nerve; since ...
13
votes
6answers
9k views

What is canonical momentum?

What does the canonical momentum $\textbf{p}=m\textbf{v}+e\textbf{A}$ mean? Is it just momentum accounting for electromagnetic effects?
3
votes
2answers
65 views

Could 1 force cause a pure moment?

A friend of mine told me if there is only one force, it cannot cause only rotation. I wasn't convinced so I proposed a thought experiment, and now we are both confused. Suppose that we put a rod ( ...
-6
votes
0answers
25 views
2
votes
1answer
46 views

Why is the energy operator special?

Only the energy operator controls the time dependence of a quantum system, but not the others, why is that?
1
vote
3answers
261 views

Fringe Width and Spacing and Number of Slits in Diffraction Experiments

In a single slit experiment, the fringes are not equally spaced and aren’t of equal widths—the central maximum is the widest, the secondary maxima grow narrower and narrower outward, and the minima ...
0
votes
0answers
11 views

Rugged Energy Landcapes (Free Energy vs Potential Energy Questions)

A spin glass has what is called a "rugged energy landscape." That is, when you cool down below a certain temperature, the system divides into many wells, all corresponding to slightly different ...
-1
votes
0answers
12 views

How could you slow down or change direction with photonic propulsion?

So you have a laser shooting at a sort of solar sail to transfer momentum in the forward direction but could you have an onboard laser and turn the laser around to hit another sail? How could you turn ...
0
votes
0answers
10 views

Showing that the Yang operator creates an elementary excitation in the 1D Hubbard model using EOM approach

Hamiltonian of the 1D Hubbard model: $ H = -t \sum_{\langle i,j \rangle,\sigma}( c^{\dagger}_{i,\sigma} c_{j,\sigma}+ c^\dagger_{j,\sigma}c_{i,\sigma}) + U \sum_{i=1}^N n_{i\uparrow} n_{i\downarrow} ...
0
votes
2answers
57 views

Is time a coordinate or a parameter in Newtonian mechanics?

In classical (Newtonian) mechanics we only ever seem to consider 3-dimensional space, with physical quantities being represented by 3-vectors. My understanding for this is because in classical ...
-3
votes
0answers
19 views

Eigen energy for charged particle in a magnetic field [on hold]

How can I determine the eigen energy for charged particle in a magnetic field?
1
vote
1answer
15 views

Baryon Acoustic oscillations - simple confusion about length scales

I am confused about length scales and baryon acoustic oscillations. I am clearly missing something very simple. The length scale found in the $SDSS$ and $2dF$ data is quoted as being $150Mpc$. ...
2
votes
2answers
216 views

Timelike Boundary

I was reading in a paper (see 1st paragraph of introduction section in http://arxiv.org/pdf/1510.00709.pdf) that in AdS space, waves can reach the boundary in finite time and, since said boundary is ...
2
votes
0answers
24 views

Is there high ring-down frequencies in LIGO's recent discovery?

This question is from Physics overflow: question in physicsoverflow. I am reading LIGO's new discovery of gravitational waves by black hole merger. During the merger, two phases are not hard to ...
2
votes
5answers
1k views

If wavefunction is just a probability function, how does an electron interfere with itself

I have read lots of quantum mechanics books. The chapters that are talking about De Broglie, lots of them name the chapter as "Wave-particle duality" and says: "Electrons are both waves and ...
1
vote
1answer
2k views

4-momentum of photon

The 4-momentum is defined as $p=mU$ where m is the rest mass of the particle and $U$ is the 4-velocity. Now I am confused as to how this applies to a photon for which one can't define $U$ since there ...
-1
votes
0answers
15 views

Coupled spring mass-system

Below is an old exam question I am trying to solve (it's not homework or an assignment, just an interest of mine). I have a few gaps in my attempted solution that I would like help with. Specifically: ...
17
votes
4answers
3k views

Is the centrifugal force a real force?

Everyone calls the centrifugal force a pseudo force and claims that it is not really present, even though there are so many machines listed as taking advantage of it (e.g. centrifuge, washing machine, ...
0
votes
0answers
30 views

The $T\rightarrow \infty $ limit in quantum field theory

I am new to quantum field theory. Prior to this, I have been using quantum mechanics for a few years. I am reading the book by A. Zee, ''quantum field theory in a nutshell'', 2nd Ed.. On page 18, ...
3
votes
1answer
53 views

How to build tetra-quark mesons symmetry group?

I was thinking about the issue while reviewing my group theory notes. One can construct mesons with a nonet as an octet and a singlet, $SU(3)\otimes SU(3) = 8\oplus \bar{1}$. In a same way but for ...
3
votes
1answer
2k views

How much magnetic field will be required to levitate a human? [duplicate]

According to this video: http://www.youtube.com/watch?v=BqKeiiezqzc it should be possible to levitate humans because the water in our bodies is diamagnetic - but it is stated (at 1:14) "although ...
0
votes
2answers
1k views

Why 2s state is lower in energy that 2p state in atoms?

The s orbital have higher probability to be closer to the core and feels larger attraction than the p orbital and on average is further away and in addition p has repulsive potentilal l(l+1)h^2/2mr^2. ...

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