1
vote
1answer
277 views

One way mirrored hollow sphere [closed]

Imagine a one way mirror, where from one side it appears to be glass, but from the other side, it appears to be a mirror. Now, fold that sheet into a hollow sphere, so the inside is mirror (and I'm ...
0
votes
0answers
767 views

How to calculate the centerline velocity inside a pipe?

Well, I was reading about fluid-solid/structure interaction models for make a simulation in COMSOL, and in few papers about it [1] I find an expression about the centerline velocity. I understand the ...
0
votes
0answers
25 views

Limit Of Temperature [duplicate]

The last couple of days i have been thinking about temperature and heat and i thought : What happens to temperature if i continually supply a particle with energy? Then i thought at sometime i ...
0
votes
2answers
228 views

Work done in adiabatic reversible process

I was solving a problem on turbine.the steam works on turbine adiabatic reversibly .Is change in enthalpy or is it change in internal energy which equal this work?
0
votes
1answer
35 views

With what speed must e.g. a car drive into a turn so it won't drift out? [closed]

I am trying to figure out the following question: with what speed must e.g. a car drive into a turn so it won't drift out (if a turn is a circumference of a semicircle)? e.g. $r= 5 m$ $a_r= w^2 \...
0
votes
1answer
159 views

How would the solar system change if the Earth were removed

I was reading a closed question with the same title and wondered if it would be on-topic with the following change: Could a large-mass object from interstellar space pass through the inner solar-...
0
votes
1answer
112 views

saturated water vapour pressure [closed]

A pressure steel tube has a volume of 215 cc and contains air at 207 bar. It also contains some water (put it is 0.5 cc) deriving from the condensation of air humidity during pumping air into the ...
2
votes
2answers
659 views

How much energy does a photon need to form a black hole?

I was wondering if it is possible for a single photon to form a black hole if it has a small enough wavelength.If so, what would this wavelength be? I came across this question because I am reading ...
1
vote
1answer
70 views

Ideas for improvised UV filter

I am doing a project where I would like to do some UV exposure to some concrete and stone samples. Therefore I have bought a couple of 400 watt UV bulbs, the product specification says it has an ...
5
votes
1answer
193 views

Can quantum mechanics be formulated without any reference to pictures?

NOTE: in the following with the word "picture" I refer to Schroedinger, Heisenberg, Interaction pictures, i.e. to the way the time-evolution is "distributed" between states and operators. We often ...
6
votes
1answer
240 views

Hydrogen energy levels and energy-time uncertainty principle

Some hydrogen atom exists in some excited quantum state, and after some time $\Delta t$ it's de-excited, emitting a photon carrying the energy difference. It is claimed that this photon will carry ...
3
votes
0answers
47 views

Boundary conditions for enthalpy waves inside a pipe

So I'm trying to solve a form of the wave equation for sound produced by a vortex distribution $\vec{\omega}$ convecting at velocity $\vec{v}$ . $$\left(\frac{1}{c_0^2} \frac{\partial^2}{\partial t^...
-1
votes
3answers
216 views

Does the Doppler effect disprove the constancy of $c$? [closed]

Why doesn't the Doppler effect disprove the relativity postulate that $c$ is constant relative to all sources or observers? It seems it does because of the following example: Suppose a ship of ...
4
votes
0answers
193 views

Are Lockheed Martin nuclear fusion claims realistic? [duplicate]

Lockheed Martin reported breakthroughs on nuclear fusion technology for energy. Are these claims scientifically realistic? The claims have been reported in the media: http://www.nbcnews.com/science/...
-3
votes
1answer
1k views

What could be the applications of Damped Oscillation? [closed]

I've been researching on Damped Oscillation for a few days for a research paper, however I couldn't find any of its applications on the web, though there are few examples of it, but they couldn't be ...
0
votes
0answers
59 views

Near field and Nuclear magnetic resonance (NMR)

Why does Nuclear Magnetic Resonance (NMR) physics not concern itself with near field physics? All resonance wavelengths in NMR are much larger than bough sample, pick-up coil and excitation coil. ...
2
votes
0answers
142 views

Detailed Balance for Quantum Master Equations from System Hamiltonians with Degenerate Spectrum

Kossakowski, Andrzej, et al. ("Quantum detailed balance and KMS condition." Communications in Mathematical Physics 57.2 (1977): 97-110) gave a proof that the stationary state of a quantum dynamical ...
2
votes
1answer
81 views

Is the $2\pi$ disclination topologically stable for a 2d nematic liquid crystal?

For a three dimensional liquid crystal, a $2\pi$ or charge $1$ disclination is topologically unstable. The is generally explained as the disclination can lose its core singularity by "escaping from ...
2
votes
1answer
239 views

Intuitive explanation of Huygens construction?

I am having problems thinking about Huygens construction when a wave front hits a surface and am looking for an intuitive / easy to understand answers of the following points consider the diagram ...
5
votes
2answers
920 views

Is a black body sphere inside a black body shell hotter than the shell?

I am missing something very basic here. Let us assume the shell is at a fixed temperature T by a power generator. The sphere inside will radiate the same power it absorbs. The power radiated by the ...
2
votes
2answers
110 views

How stable are Benard Cells when the thermal gradient begins decreasing?

I've found lots of information on the formation of Benard Cells and convection currents but very little information about what happens to the self-organized structures when the energy gradient being ...
2
votes
1answer
460 views

What prevents a star from collapsing after stellar death?

When the star stops burning because heavier elements like Iron are formed in its core. Then the gas pressure stops and as you know the gas pressure helps keep a star in equilibrium because it provides ...
0
votes
1answer
106 views

Newton's Third Law Opposite Angles

I am asking a related question here : Newton's Third Law Angular Bouncing Why, given newton's third law would a ball bounce at an opposite angle to it's original, if an equal and opposite force ...
0
votes
1answer
195 views

Newton's Third Law Angular Bouncing [duplicate]

I am asking a related question here: Newton's Third Law Opposite Angles If a ball is accelerating at a surface at a non-straight angle, it will bounce off with the opposite trajectory, like if ...
5
votes
1answer
113 views

Baryon in terms of quark fields – spinor index structure

What is the most general way to write down a current describing a baryon made from quarks $\psi_i^\alpha$? Let's say we suppress flavour indices but want to write colour $(i,j)$ as well as spinor $(\...
6
votes
0answers
104 views

Is there a null incomplete spacetime which is spacelike and timelike complete?

Geodesic completeness, the fact we can make the domain of the geodesic parametrized with respect an affine parameter the whole real line, is an important concept in GR. Especially, because the lack of ...
3
votes
3answers
2k views

What is the physical meaning of electric potential, potential difference, and voltage?

When resembling the electricity flow through a wire to people walking through a street: electrons are people, current is the number of people, resistance is the barriers on the way. But what is the ...
1
vote
0answers
93 views

How to construct singlet and other multiplets from two triplets

Let an $SU(2)$ isotriplet operator is given by\begin{equation}\bar{l^c}i\tau_2\vec \tau l=l^T Ci\tau_2\vec \tau l\sim 3\end{equation} and an isotriplet Higgs field \begin{equation}\vec \Delta\sim 3\...
1
vote
1answer
49 views

Why does an external laser drive only couples certain levels?

I was always wondering how is it that all the quantum optics levels schemes are depicted as if the laser couples only two certain levels with some frequency. For exmaple the standard lambda system ...
4
votes
2answers
2k views

Linear vs. quadratic dispersion relation

In wave mechanics the dispersion relation between frequency $\omega$ and wave number $k$ is linear: $$\omega_n=c k_n$$ But in quantum mechanics, based on Schrödinger's equation, one can show that we ...
0
votes
1answer
54 views

Flip of polarisation of light

Consider an optical experiment with photons or light pulses. Is there an optical element that acts in the polarisation degree of freedom like the unitary $$ U = \frac 1 {\sqrt 2} \begin{pmatrix} 1 &...
2
votes
1answer
67 views

Does velocity determine a geodesic?

If the gravity effect we witness is due to objects travelling along geodesics, why is the geodesic different for objects with different velocities if there is no gravitational force as such? For ...
2
votes
0answers
110 views

A driven quantum harmonic oscillator (DQHO) [closed]

I'm trying to find the dispersion relation for the DQHO with Lagrangian $$ L(q,\dot q,t)=\frac{1}{2}\dot{q}^2-\frac{1}{2}\omega q^2+F(t)q $$ with $F(t)$ being non-zero for $0<t<T$. The ...
2
votes
0answers
246 views

Feynman propagator with general $\xi$ parameter

Hey from my notes in my PS book it seems I have solved this some time in the past, but I cannot seem to get the indices straight this time around. So in deriving the Feynman photon-propagator which ...
1
vote
1answer
3k views

Relationship between polarization density and electric field

Imagine I have an electric field $E$ created due to some free charges. Then I introduce a dielectric material somewhere. What confuses me is the polarization field $P$, which is now proportional to ...
7
votes
3answers
786 views

Mathematical understanding of Quantum Mechanics

Assuming that $\phi(r) = F (\psi(r))$ for some operator $F$ in Quantum Mechanics. Then, in our lecture today, we said that $$\phi(r) = \langle r|F |\psi\rangle = \int_{\mathbb{R}} \langle r |F| r' \...
1
vote
0answers
80 views

Geometrised Units

I am curious as to how to express a area units in geometrised ones. I was reading on wikipedia and saw that when angular momentum is converted into geometrised units, it is expressed as a dimension of ...
2
votes
1answer
123 views

Mirror that flips polarisation?

Is it possible to build a mirror which not just reflects a photon but also flips its polarisation from horizontal tho vertical (or vice versa)? The reason why I ask is the following: If I put an ...
0
votes
1answer
75 views

Can a current source provide Voltage to a resistor?

We know that the tension between a perfect current source is 0 We have Va-Vb= 0 but we also have by ohm's law Va-Vb=RI=5V so 5 = 0?
0
votes
0answers
41 views

A confusion about the proof of $\hat{p}|x\rangle=i\hbar\frac{\partial}{\partial x}|x\rangle,$ using $[\hat{x},\hat{p}]=i\hbar~?$ [duplicate]

How to prove $$\hat{p}|x\rangle=i\hbar\frac{\partial}{\partial x}|x\rangle,$$ using $$[\hat{x},\hat{p}]=i\hbar~?$$ The question seems to be uncomplete because for any $f(x)$ $$[\hat{x},\hat{p}+f(x)]=i\...
1
vote
2answers
162 views

Is the temperature rise caused by reflection of sunlight linear?

I have saw a YouTube video showing large Fresnel lens can focus sunlight into a spot which can melt iron. I am very interesting of that, but large Fresnel lens are not that popular, so I was ...
1
vote
5answers
1k views

What is divergence?

What is divergence? I was learning about Maxwells equations and don't understand the divergence part of it. Can someone give an intuition of what divergence is in relation to maxwells equation. To ...
1
vote
0answers
104 views

What is DX technology and what are the effects on digital cameras?

I am photographing in a high power voltage field in Industry producing aluminium, called DX technology. How do I know if my digital camera will not be affected? At 350kA current my film cameras were ...
1
vote
0answers
28 views

Two conductor's in a magnetic field, canceling each other's EMF?

If two conductor's are in a $\Delta$B, oriented the same in the field, and they induce equal $\epsilon$, can their wiring be oriented in a way that they can cancel each other's induced $\epsilon$? So ...
54
votes
3answers
5k views

Why do the big nuts always remain at top? The Brazil-nut Effect

Most of the time when I mixed different nuts in a bowl, I observed that the big Brazil nuts were always on top while the small peanuts settled near the base. No matter how you take it, if the big nuts ...
1
vote
1answer
289 views

Constructing matrix for spin in Stern-Gerlach experiment for arbitrary angle

This is a conceptual question about a problem in Sakurai. I understand how to solve the problem, but there's something about it that irks me, and it feels like I'm missing something. In the problem, ...
6
votes
2answers
235 views

Classical logic in concern with QM Mathematics

In no way am I a physicist, so please excuse improperly used terms. It is in my understanding that Quantum Physics does not obey Classical Logic, hence the existence of Quantum Logic. My questions ...
1
vote
1answer
296 views

How to derive the critical temperature for Bose-Einstein condensation of photon?

I found in Nature magazine that photon can have Bose-Einstein condensation. But I have a question how to derive the critical temperature for photon? Because the chemical potential of photon is zero ...
4
votes
2answers
781 views

Diffraction by small holes

This is a follow-up to this question: What happens to waves when they hit smaller apertures than their wavelenghts? Hans Bethe wrote a paper in 1944, "Theory of Diffraction by Small Holes," Phys. Rev....
4
votes
6answers
1k views

What happens to waves when they hit smaller apertures than their wavelenghts?

I was wondering this for quite a long time now. Let's say you have a water wave (like ripples, not the ones you see during tsunamis) with wavelength 10 m. Imagine you put a boundary with an opening of ...

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