0
votes
1answer
44 views

If an atom emits a visible photon doesn't that mean it's visible?

A visible photon can be emitted and absorbed by an individual atom. Is this process sufficient for saying that we can see an individual atom with visible light? I realize the wavelength of visible ...
0
votes
1answer
20 views

How does entropy ensure that isolated thermal processes are 100% irreversible?

How can anyone prove that molecules in figure C will never return to their original positions in figure A? It will be more believable to say that the chance is very slim.
-2
votes
1answer
58 views

time distortion

Observer A is standing on a planet, and observer B is on a ship. At t=0 B is 1 light year away from A. Also at t=0 B will accelerate its ship to a 0,999999999...$c$ instantaneously (yes, its a very ...
1
vote
0answers
52 views

Holographic dual of pure-classical systems

There are classical systems (eg. see Sections VII and VIII of Kogut's review) that shares many of the properties of a pure-gauge SU(N) quantum theory including factorization and mass-gap, but with ...
1
vote
1answer
87 views

How to calculate the resistance (conductance) between two contacts embedded into a 3D object?

Pouillet's law, $R = \rho \frac{\ell}{A}$, is useful when dealing with a "column" (cylinder) of a conducting material, with cross section $A$ and height $\ell$. Using this equation has an underlying ...
0
votes
1answer
64 views

Is it true that all processes where entropy increases are permitted by the second law, if the system is isolated?

It is possible to deduce that in a thermodynamic process for an isolated system $\mathrm{d}S$ has to be greater than zero, from this it follows trivially that $ \Delta S > 0$. It is usually said ...
0
votes
0answers
44 views

How to measure resistance of gel electrolyte using multimeter

How can I measure the resistance of a gel electrolyte using a multimeter? I know the formula to measure the conductivity of a gel electrolyte is k = (1/R) * (d/a) where k is the conductivity (S/cm), ...
0
votes
0answers
140 views

What is the meaning of the point of inflection in this?

Consider the following flow velocity profiles near a boundary, and the boundary profile point of inflection,PI Regarding the effect of pressure gradient on boundary-layer profiles does the point of ...
2
votes
2answers
72 views

Is it possible that one of the quasars we see is an ancient Milky Way?

As I understand it, even though our current measurements of the Riemann curvature of the universe overlaps with flat spacetime, this doesn't restrict the shape of the universe to being infinite. It's ...
0
votes
2answers
147 views

Solenoid cannon (coil gun) possibility and recoil?

Similar to my other question If you are to pass a magnet through a solenoid a current is produced in the solenoid due to the magnetic flux. However, if you were to have a magnet sit inside a ...
0
votes
1answer
22 views

estimate air temperature changes from changes in sea surface temperature

Consider a body of water, where the change in temperature for a given time period can be estimated by: $$ \frac{dTw}{dt} = \frac{Q_{net} \times A}{\rho \times C_{pw} \times V}$$ where $dt$ is the ...
0
votes
1answer
398 views

Calculate pressure from partition function with separated volume geometric parameters?

How does one calculate the pressure from the partition function if it is specified in terms of three parameters defining the space of which the gas occupies, but all three parameters are not always ...
1
vote
3answers
201 views

How can flux be the number of electric field lines normal to a surface? [duplicate]

Shouldn't the number of field lines through any surface be infinite if there is a charge present. Or is there a finite number of field lines from a unit charge?
0
votes
2answers
886 views

Rate of flow of electrons in a simple circuit, given the current? [closed]

I have this question: The correct answer is C. I understand that the flow of electrons should be from Y to X because electrons flow opposite to "conventional current", which is from positive to ...
0
votes
1answer
47 views

Do I have some freedom when I define the quantum SHO ladder operators? [closed]

I tried to solve the quantum harmonic oscillator via the operator method. After doing it and looking up the solution I noticed that for some reason the ladder operators got an additional factor of (i) ...
2
votes
3answers
895 views

What is the relation between entropy and pressure in strict thermodynamic terms?

I read on the net that it is a general consensus that entropy in a system decreases as pressure increases and vice versa. How can one reach such conclusion using the characteristic equation in terms ...
5
votes
1answer
111 views

Non-hermiticity of Dirac Lagrangian: null momentum?

The usual Dirac Lagrangian is $L(\psi,\bar\psi)=\bar\psi(i\not\partial-m)\psi$. The canonical momenta are $$ \pi=\frac{\partial L}{\partial \psi_{,0}}=i\psi^\dagger \\ \bar \pi=\frac{\partial ...
0
votes
1answer
51 views

Is the car/wall comparison valid for speeds close to $c$? [duplicate]

At school, people commonly think about momentum and conservation of energy using the example of a car collision. A common phrase is "Do not try to think of two objects moving, think of one moving at ...
0
votes
1answer
112 views

What are the properties of center of curvature of a parabolic mirror?

What is so special about the center of curvature of a parabola (since a parabola can't actually have a center) ? I mean, it must be something unique for it to be defined. Why is it twice the focal ...
-2
votes
6answers
143 views

A contradiction statement to $F=ma$ [closed]

If I thrown an object of mass 1 kg up in the air it will always fall with an acceleration of 9.8m/s. If I throw it very high up in the sky, it falls with a greater force as compared to if i throw it ...
0
votes
2answers
39 views

Polarized light from any suface?

From a textbook I read something like this: "When sunlight is reflected from a horizontal surface, the plane of incidence is vertical, and the reflected light contains a preponderance of light that is ...
0
votes
1answer
44 views

Why is the resistivity $\rho_{xy}$ independent of scattering time in the Drude model for the Hall effect

I was reading about the Hall Effect, and how it can be explained through the Drude model of conductivity. I was looking at the 2D model, as I'm mainly interested in 2 dimensional electron gasses. You ...
0
votes
0answers
43 views

How to design a grating coupler to produce surface plasmon-polaritons (SPPs) at a desired frequency?

Following on from this question, which I found very useful on the topic, I was wondering how you would use the equation $\beta = k sin \theta \pm \nu g$ to fabricate a grating coupler to generate SPPs ...
3
votes
1answer
98 views

Is the Uncertainty Principle a logical consequence from the Wave-Particle duality?

I always thought of the Uncertainty Principle as a logical consequence that follows from the Wave-Particle duality, or more precise, from the fact that all particles behave as waves as long as they do ...
1
vote
1answer
99 views

From master equation to Fokker-Planck equation

For the continuous master equation in real space and time, we have for the distribution $f(x,t)$: $$\frac{\partial f(x,t)}{\partial ...
0
votes
2answers
51 views

Calculate Potential [closed]

$\vec{w} = \begin{pmatrix}w_r \\ w_{phi} \end{pmatrix} = \begin{pmatrix}\frac{Q_0}{2 \pi r} \\ 0 \end{pmatrix} $ 1) Show that the flow satisfys the continuity equation 2) Show that $\vec{w}$ ...
0
votes
0answers
28 views

Evaluation of a probability from Fermi Golden rule

In Marc Bee's book, he has described the principle of spectroscopy with reservoir (the material) and the probe as interacting systems with their own hamiltonians $H_R$ and $H_p$ respectively and $H_c$ ...
0
votes
1answer
50 views

Model of spherical wave fronts in relativity

In relativity, the 3-surface formed by light rays emanating from an event as they evolve in time has the shape of a hypercone wich is flat. I have difficulties seeing how can a spherical wave front, ...
0
votes
1answer
232 views

Direct vs. Compound reactions

I know there are different types of direct reactions like inelastic scattering and such. But is the main difference between direct and compound reactions that one excites (Or at least can) the whole ...
1
vote
0answers
179 views

Gravitational lensing on galaxy cluster with given potential

I am having a problem with gravitational lensing question where we are interested in deflection angle of light traveling in potential of galactic cluster, described with tensor ...
3
votes
1answer
67 views

How does a body accelerate that is put into a flow field with constant speed?

Imagine an infinitely long flow channel filled with water flowing at a constant speed everywhere parallel to the infinitely long dimension of this channel. Furthermore, imagine we place a body (say a ...
-1
votes
1answer
435 views

What is the freezing/melting point tap water?

Yes, I know purity is not a constant and depends on area etc. Does anyone have any experimental results on freezing/melting point of any tap water, as opposed to distilled, de-ionized, saline etc? I ...
1
vote
2answers
163 views

Why can't liquid nitrogen be sealed in gas cylinders?

By observing the phase diagram of nitrogen, hydrogen and carbon dioxide, I discovered the supercritical region. I can easily buy a gas tank of carbon dioxide at 250 Bars. However I never saw any ...
1
vote
1answer
60 views

Ground state of 113Sn from shell model

The shell model predicts that the ground state of 113Sn with 63 neutrons would have J=5/2+. But the ground state is taken to be 1/2+. What is the reason behind that? Has it got something to do with ...
3
votes
2answers
155 views

Why is the Reynolds number “the way it is?” Why is its order the way it is?

Why is the Reynolds number “the way it is?” Why is its order the way it is? I'm not sure if this is an appropriate question for this context, but I would like more intuition on this matter and so ...
0
votes
1answer
32 views

Help reading power spectrum graphs?

How would I go about figuring out how long a source was measured when given a graph of the power spectrum? From notes I'm following, they just state the total observation time as being roughly ...
8
votes
1answer
141 views

Why does Landau theory not fail when dealing with a first order phase transition?

Here is a problem where I can do the calculation, but I am not understanding the philosophy behind it. It is about Landau theory: The Landau theory of phase transitions is based on the idea that the ...
2
votes
3answers
316 views

How do I know what variable to use for the chain rule?

In my textbook the tangential acceleration is given like this: $$a_t=\frac{dv}{dt}=r\frac{dw}{dt}$$ $$a_t=rα$$ I understand that the chain rule is applied here like this: ...
0
votes
0answers
40 views

Does an iron rich substance stay magnetised?

I am doing research (i.e. playing around) with a dry magnet and a material that has about 10% contained iron. The balance of the material is non-magnetic (i.e. silica and non-magnetic metals). It is ...
-1
votes
2answers
75 views

How is electric dipole moment analogous to mechanical moment?

Diplole moment is q*2l. I don't understand the similarity between dipole moment and ordinary mecanical moment.
0
votes
1answer
122 views

Difference in induced current, when magnetic field “span” is reduced?

A conductor of known volume $(V)$ passes a uniform magnetic field$(B)$with a constant velocity $(v)$ the conductor is a source of induced EMF, a power source to a circuit. The induced EMF can be ...
0
votes
1answer
37 views

particles from waves?

If you slide a styrofoam cup containing milky coffee accross a formica tabletop, the friction of the styrofoam on the formica, will produce a wave interference pattern on the surface of the coffee. ...
0
votes
2answers
174 views

How did people discover the conservation of mechanical energy?

I want to write about the history of energy, and am focusing on mechanical energy at the moment. My question is: Can I attribute the conservation of mechanical energy to the power of maths, ...
0
votes
1answer
47 views

Why can only asymptotically flat and AdS black hole have the thermodynamics? What's about asymptoticaly dS black hole?

Almost all advanced GR textbooks will have the content of black hole thermodynamics for asymptotically flat black hole. And this paper solve the asymptotically AdS (Anti-de Sitter) black hole ...
3
votes
0answers
116 views

How to determine the collapse operator for a Lindblad equation

Given a Hamiltonian $H$, how can I relate the collapse operator for the Lindblad equation to a given environmental effect? Also, how can I relate the constant $\gamma$ in front of the sum of the ...
0
votes
0answers
84 views

Will objects heat up and become hidden at relativistic speed?

Let us assume there is a mirror travelling at extremely relativistic speeds, perhaps few picometers away from speed of light, and let us assume we have a very thin detector which is very small perhaps ...
1
vote
0answers
45 views

Has there been any research done in fluid dynamics within a mobius strip?

I was wondering if there has been any research done with the flow of fluid within a mobius strip? The reason I am interested is, assuming the fluid would flow around a center axis point, at certain ...
4
votes
0answers
64 views

Is it degeneracy pressure rather than electrostatic repulsion that stops us falling through the floor? [duplicate]

From Wikipedia: Degeneracy Pressure Freeman Dyson showed that the imperviousness of solid matter is due to quantum degeneracy pressure rather than electrostatic repulsion as had been previously ...
0
votes
0answers
50 views

How to apply contrast sensitivity function to an image?

I would like to apply contrast sensitivity function (CSF) to an image. My idea is to do the Fourier tranform of the image and then do the filtering in the frequency domain by applying the CSF. However ...
1
vote
1answer
57 views

What is the range of degeneracy pressure?

In what way is degeneracy pressure related to the separation of fermions? Is there any influence at ranges like a meter and beyond. I expect the influence at those ranges to be immeasurably small. I ...

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