0
votes
4answers
26 views

Are elements of statistical ensemble fixed or dynamic?

I will use the simplest example I can think of to explain what I am trying to understand. Consider a system with ~$10^{23}$ particles in an equilibrium with fixed values of pressure, volume and ...
0
votes
0answers
21 views

Time resulting of a thermodynamics effect?

I heard in a documentary that : Irreversibility of time is linked to Heat Dissipation in thermodynamics. The theorist says "passage of time" is only a macro sensation, the underlying effect ...
1
vote
1answer
58 views

Why is the magnetic unit twice the electric one in CGS?

In CGS system the electric unit is the esu or statcoulomb equal to $2.08*10^9$ charges and two such units repel with a force of $1$ dyne. Magnetic force ratio is $v^2/c^2$, therefore the magnetic ...
1
vote
1answer
42 views

How do you get quantum Hamilton-Jacobi equation from Schrödinger equation? [on hold]

I am reading "The undivided universe: an ontological interpretation of quantum theory" and cannot understand this derivation. Schrödinger equation: $$ i\hbar \frac{\partial\psi}{\partial t} = -\frac{\...
0
votes
1answer
39 views

Why do quantum gates have to be reversible?

One possible reason I have come up with is that we are modeling quantum gates by unitary matrices. And since unitary operations are reversible we have to be able reverse the operation in the physical ...
0
votes
2answers
200 views

Coriolis force in free fall: Directions?

Inspired by this Phys.SE question, Coriolis force in free fall, I have to ask: Why does the Coriolis force act in the east-direction? I would say, if I jump from a high distance and look at the ...
1
vote
1answer
28 views

Does charge of capacitor at constant voltage change after dielectric material is inserted?

I have a planar geometry capacitor, connected to a battery that supplies V volts. Initially there is vacuum/air in between both plates. Afterwards, some dielectric material is inserted in between both ...
0
votes
0answers
11 views

Using bold face letters to label representations [duplicate]

In some papers I see the authors labeling representations of groups and algebras using bold face letters. As an example, from here, "There is a global $SU(4)\cong SO(6)$ symmetry, called an R-...
33
votes
7answers
2k views

In quantum mechanics, given certain energy spectrum can one generate the corresponding potential?

A typical problem in quantum mechanics is to calculate the spectrum that corresponds to a given potential. Is there a one to one correspondence between the potential and its spectrum? If the ...
0
votes
1answer
33 views

Reduced electric field strength in dielectric

Under what conditions does the field due to free charge is simply reduced by factor of 1/k where k is dielectric constant? I.e my book says if dielectric is entirely ...
0
votes
0answers
23 views

Is there scattering event if two wave functions overlap in momentum space?

Let's consider two particles, moving, for simplicity, in a 2D plane, represented by their wavefunctions in the form of (when being modulus squared) very very very narrow Gaussians (let's say close to ...
1
vote
3answers
107 views

What is the difference when we measure torque/angular momentum about a point and about an axis?

When do we measure torque about an axis and when do we measure torque about a point?Whats the difference? I tried searching this on google but did not get satisfactory answer.
8
votes
3answers
119 views
+150

Fluids with critical point at ordinary temperature and pressure

Are there any fluids with critical point near STP or that are supercritical at STP? If not would it be feasible to design a molecule for a substance with critical point near STP using theoretical/...
-5
votes
0answers
51 views

Why is $(4.9v*t^2)/4$ equivalent to $1.225v*t^2$? [on hold]

In this khan academy video: https://www.khanacademy.org/science/physics/one-dimensional-motion/kinematic-formulas/v/deriving-max-projectile-displacement-given-time At 6:58 he derives the second ...
0
votes
0answers
126 views

What is the mass and density distribution of a Schwarzchild black hole in the viewpoint of distant observer?

According to Schwarzschild metric the density element $$ \frac{\mathrm dm}{\mathrm dV} $$ becomes infinite on the event horizon if there is mass $$ \mathrm dm > 0 $$very near at the outside of ...
3
votes
1answer
33 views

Could heat detected from Jupiter's red spot explain the temperature of the Sun's corona?

This is an excerpt from BBC Infrared Telescope, published 27th July 2016 Jupiter's Great Red Spot - a hurricane three times bigger than Earth - is blasting the planet's upper atmosphere with heat, ...
-1
votes
1answer
47 views

Should any matter form a singularity before crossing the event horizon?

I guess the destiny of any object that falling into a black hole will depend on its size and the density of the black hole it falling in. And from distant observer it should looks different. A small,...
1
vote
0answers
54 views

Conformal group in 2D being a subgroup of Diff/Weyl - Polchinksi's 'String Theory' [on hold]

In the appendix on page 364 of 'String Theory', Polchinski defines the conformal group (Conf) in two dimensions to be the set of all holomorphic maps. On page 85 he explains how Conf is a subgroup of ...
0
votes
0answers
7 views

Material selecting of HV pannels [migrated]

I want to know that what would be the material selected for high voltage control panels outer body and what would be the breakers used as SF6 is used only in MV panels.
0
votes
1answer
19 views

Difference Group Written in Capital Letters and in Lower Case Letters

I sometimes see that people write group names in capital letters and sometimes in lowercase letters. Like the 3 dimensional special orthogonal group is sometimes written as $SO(3)$ and sometimes as $...
2
votes
1answer
115 views

Simplest Live Demonstration of Adiabatic Transport

I have to give a presentation on Berry phase. I would like to give the simplest live demonstration of adiabatic transport. If I move an object in a loop and return that object back into its original ...
0
votes
1answer
38 views

Does infalling matter ever cross the event horizon? [duplicate]

Assume you are immortal, then say if you fell towards a blackhole, to an observer far away you will appear to slow down as you approach event horizon and gradually come to stand still. However for ...
3
votes
1answer
53 views

What is the Difference between Lorentz Invariant and Lorentz Covariant? [duplicate]

Like my title, I sometimes see that my books says something is Lorentz invariant or Lorentz covariant. What's the difference between these two transformation properties? Or are they just the same ...
4
votes
1answer
44 views

What could be attractive in a desert? [on hold]

It is not the Sahara, but the possibility that there isn't any interesting until the GUT scale. On the Wikipedia, I've read: "The attraction of a desert is that, in such a scenario, measurements ...
3
votes
1answer
151 views

Sequential Stern-Gerlach devices - realizable experiment or teaching aid?

At least one textbook [1] uses sequential Stern-Gerlach devices to introduce to students that the components of angular momentum are incompatible observables. Viz., the $z$-up beam from a SG device ...
0
votes
0answers
46 views

Translatioal symmetry and generalized Heisenberg equation of motion in presence of force [closed]

Suppose, there are 2 plates; one at x=0 and another at x=L such that the area vector of the plate surface is parallel to the x axis and electromagnetic field is confined between this plates. I am ...
1
vote
1answer
344 views

Gas compressed and cooled

If a certain amount of a gas is compressed into a cylinder by the action of a piston that reduces its volume (lets say at a low speed), the kynetic energy of the gas molecules increases, what is ...
0
votes
0answers
40 views

How find/estimate Parasitic Area (CDA) in order to calculate V(L/D)max?

I am trying to calculate the speed which maximizes lift/drag for an aircraft. Using Carson's paper, it looks to me like the only unknown variable is "f", the parasitic area, which Carson describes as ...
1
vote
3answers
96 views

Length Contraction in Relativity

Let's suppose we have a one dimensional rod made of elementary point particles, in contact with each other placed along the x-axis.If the rod is moving along x-axis then we know (because of relativity)...
0
votes
1answer
29 views

Do III-V based photovoltaics “glow” (photo-luminesce) when illuminated but not loaded?

In this nice answer I started to learn about how the silicon photovoltaics cells on the International Space Station are managed. In that case, the cells are generally either delivering useful power to ...
-7
votes
0answers
39 views

Interesting question to figure it out [on hold]

A 50-cm-long iron rod is heated from 20 °C to 100 °C. The linear coefficient of expansion for iron is $1.2 × 10^{-5} K^{-1}$. How to determine the change in length of the rod. By which formula?
5
votes
1answer
304 views

Equations of motion of displacement field

We have an action: $$S[\boldsymbol{u}] = \frac{1}{2} \int dt \int d^3x \left\{ \mu (\frac{\partial u_{i}}{\partial t})^{2} - \nu (u_{ii})^{2} - \rho(u_{ij})^{2}\right\} $$ Where $u_{ij} = (\partial_{...
11
votes
2answers
528 views

Eigenstate of field operator in QFT

Why don't people discuss the eigenstate of the field operator? For example, the real scalar field the field operator is Hermitian, so its eigenstate is an observable quantity.
0
votes
1answer
34 views

Have conservation laws stayed constant since the Big Bang?

By conservation laws I mean quantum number conservation, such as baryon and lepton numbers. As far as I know, we have a reasonable confidence that experimental data confirms a lot of features of our ...
4
votes
1answer
257 views

Closed timelike curves in the spin-2 gravity formalism

Let's say we take some topologically trivial CTC spacetime, like the Gödel metric: $$ds^2 = -dt^2 - 2e^{\sqrt{2}\Omega y} dt dx - \frac{1}{2}e^{\sqrt{2}\Omega y} dx^2 + dy^2 + dz^2$$ And then I ...
14
votes
1answer
295 views

Do Franck-Condon oscillations have natural lineshapes?

I recently found a paper (for the curious, this one) that talks about observing the motion of a nuclear wavepacket in H2O, as initiated by tunnel ionization. This wavepacket should be thought of as a ...
0
votes
1answer
42 views

What metal (or any other material) is a good thermal coductor but a bad conductor of electricity?

Also, this material needs to be easily manageable and accessible. So, I am trying to make a DIY soldering iron and I need to insulate the part that makes the heat and the part that transfers the ...
2
votes
2answers
97 views

What does it mean for an integral's differential to be raised to a power, like e.g. $d^3r$ or $d^3u$?

I was reading Zwelfel's book on reactor physics and saw the following notation: Notice that the differential of the integral is raised to the third power. What is the meaning of this notation? ...
0
votes
0answers
12 views

Non-singlet and singlet flavor combination [duplicate]

In the perturbative QCD, specific partonic distribution functions (pdf) linear combination is called "flavor singlet" or "flavor nonsinglet" combination. What is the combination, and why are they ...
0
votes
0answers
27 views

Non-singlet and singlet flavor combination [duplicate]

In the perturbative QCD, specific partonic distribution functions (pdf) linear combination is called "flavor singlet" or "flavor nonsinglet" combination. What is the combination, and why are they ...
5
votes
4answers
112 views

What causes more damage, a head-on car crash at 30km/h or one car at 60km/h crashing into a stationary one?

Which will cause a greater impact? Two identical cars colliding head on (in opposite directions), each going at $30\;\mathrm{km/h}$ OR One car travelling at $60\;\mathrm{km/h}$ colliding into a ...
0
votes
1answer
105 views

Motional emf and ohm's law

Suppose a thin, closed loop of wire is in motion in a static magnetic field. Let's define a few things $$\vec{F_B} = \vec{w}\times\vec{B}$$ $$\Phi = \int_S \vec{B}.\vec{dS}$$ $$\mathcal{E}_m=\oint_{...
1
vote
1answer
38 views

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 ...
0
votes
1answer
23 views

Heat transfer direction in fins

I'm unsure of what exactly is changing the heat transfer direction in the triangular fin. $$q_{x} = -kA(x)\frac{dT(x)}{dx} (1)$$ $$q_{x+dx} = -kA(x)\frac{dT(x)}{dx} - k\frac{d}{dx}[A(x)\frac{dT(x)}{...
2
votes
1answer
44 views

Optimal axis of rotation of a baseball for lateral movement

Suppose a baseball travels at $90\;\mathrm{mph}$; what is the ideal axis of rotation for lateral movement of the ball? (two-seamer or cutter). So far I think that the following factors play a ...
2
votes
3answers
85 views

Does electron absorb energy? [on hold]

According to my teacher, an electron is point sized and it does not absorb or release energy. Moreover, my teacher says their orbital absorbs energy rather than the electron. If that is the case, then ...
1
vote
1answer
49 views

I cannot verify if given transformation is canonical (CT) [on hold]

I'm going on a list of exercises and there's 6 days that I can't figure to this. Prove that given transformation is canonical: $\Large Q=\frac{p}{mw}\sin(\frac{mwq}{P})$; $\Large P=p\cos(\frac{...
8
votes
2answers
753 views

Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is an hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic materials,...
5
votes
3answers
3k views

What will happen to a permanent magnet if we keep the same magnetic poles of two magnets close together for a long time?

What will happen to permanent magnet's magnetic field or magnetic ability if we keep same magnetic poles of two permanent magnet for long time? Will any magnetic loss happen over the long period of ...
17
votes
3answers
544 views
+100

trouble reconciling doppler shift for energy and momentum of light

[See late addition at bottom for what currently remains unresolved in this question.] I have seen the assertion in a couple of places that if you trap light in a reflective resonator, or any other ...

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