3
votes
1answer
85 views

Free energy variations

In a paper, I found this: $\mathbf{h}=\mathbf{h}(\mathbf{r})$ is called molecular field and is defined as the variation field of the Frank free energy functional $F_{d}$ with respect to the ...
2
votes
1answer
89 views

Any FLOSS Monte-Carlo package for reactor physics? [closed]

Any FLOSS Monte-Carlo package for reactor physics? Are there any Free and Open Source software packages for nuclear reactor processes simulation? Maybe, something similar to MCNP?
1
vote
1answer
132 views

Electrons of conductors Free? [duplicate]

Are electrons of any conductor really free ? I mean are they always already moving or do they move only when electrostatic field of some sort is applied across them. I suppose if they were always ...
2
votes
1answer
70 views

Purposes of QEC stabilizers

I am going through the idea of stabilizer formalism. Defined what is a Pauli group $P_n$ and its properties, we describe a stabilizer set $S$ as: $$S\subset P_n$$ The stabilizer set establishes ...
1
vote
2answers
88 views

Charged spheres - help with method to work these out? [closed]

Can anyone demonstrate how to get the answers to these questions? I'm just interested in the method I need to use in order to obtain the correct answer no matter what the values are. Three small ...
1
vote
3answers
133 views

Can a very thin sheet of any material float inside a liquid?

When a body is immersed in a liquid,buoyancy is the net force of all the forces acting on it. Now the forces are equivalent to those which will act on the same volume of liquid.Rightly so,but ...
2
votes
2answers
132 views

Why are all basic physical measurements ratios?

Why is it that "all basic physical measurements [...] are ratios"? This question comes from the book Mathematical Physics by Donald H. Menzel. Here is the explanation given: 1. The significance ...
2
votes
0answers
95 views

Ehrenfest's theorem on Gaussians

Considering the free evolution of a Gaussian wave packet, is it possible to use Ehrenfest's theorem to determine the average value of momentum given that of position? And I imply the simplified ...
1
vote
1answer
41 views

induction for massive objects

We know that when two charged bodies are kept near one another, they attract the charges and induce some charge near the surface. This happens even when only lne body is charged as the charges are ...
-1
votes
1answer
74 views

Statistics followed by Neutrinos [closed]

What does the neutrino particles follow- Dirac or Majorana Statistics?
5
votes
6answers
2k views

Intuitively, Why is Power Proportional to $I^2R$

As the resistance of a circuit goes down, the power increases because the current increases, assuming constant voltage. Why is this? I feel like resistance and current are inversely proportional, so ...
4
votes
1answer
1k views

What is the precise definition of Gravitational Sphere of Influence (SOI)?

I am trying to understand the gravitational sphere of influence (SOI), but all I get by searching is the formula that you can find on Wikipedia, that is $$ r_{SOI} = a \left( \frac{m}{M} ...
0
votes
1answer
128 views

How much the probability wave acts like a wave?

A superposition of two probability wave creates standing wave. Well, that is convincing. Dose waves described by schrodinger's equation have other properties of wave? like reflection, refraction, ...
0
votes
0answers
44 views

Calculate age of the Universe at 7 billion and 28 billion years old [duplicate]

If $1 / H_0 $ is about 14 billion years, then what happened when the universe was half its current age? Is the empirically determined $H_0$ supposed to have been twice its current value? And when ...
2
votes
1answer
168 views

Why is $0 \,\mathrm{K}$ so special?

I know that $0 \,\mathrm{K}$ cannot be reached, this is discussed here and here. But, why is it such an important statement? I mean, there are many properties which will never be zero, like: ...
2
votes
7answers
37k views

Power dissipated in series versus in parallel

Do two resistors in parallel dissipate more heat per unit time for an applied voltage when compared to two resistors in series?
3
votes
1answer
302 views

Vortices and chemical potential in topological superconductors

I am trying to read up some review articles about Majorana physics in topological material, but I am not really familiar with the condensed matter terminology (with condensed matter in general I ...
0
votes
4answers
492 views

Why do I get inconsistent answers with the kinematics equations?

The initial velocity is 14 m/s the final velocity is 0. The distance is 9.0 m and the time is 1.5 s. When solving for the acceleration, why do I get different values when using different kinematic ...
5
votes
1answer
287 views

Topological Mass Generation Mechanism

What is the topological mass generation mechanism? And what is its relation with the Higgs mechanism? Can we say that after the discovery of Higgs boson, the topological mass generation mechanism ...
2
votes
0answers
117 views

Seeking help simplifying this EOM equation

I am working on solving the equation of motion for a particular system. It has been a long time since I've worked with matrix equations and need help in simplifying the following: ...
1
vote
1answer
140 views

Objects falling on Slopes [closed]

An object falls on a slope and then rebounces....and it is known it hits the slope again...how do I calculate it's second point of contact with the slope....how can a projectory equation be used in ...
-1
votes
1answer
479 views

What is the difference between scale-free network and small-world network? [closed]

What is the difference between scale-free network and small-world network? I can't understand from the definitions around the web if they are both the same name for one thing. Do both follow a ...
1
vote
2answers
21k views

Perfect elastic collision and velocity transfer

So my teacher told me that when you have two identical balls in a perfectly elastic collision, the first ball A will collide with B and afterwards A will stop and B continue. Why is this? Doesn't ...
0
votes
2answers
427 views

Weighing a flying bird [duplicate]

Let thing of a bird standing still in a box on top of a weighing machine that shows a mass $m_0$. Now, imagine that the bird is flying, still in the same box and the same weighing machine shows a mass ...
1
vote
1answer
852 views

Refraction Vector (Ray tracing)

I am doing ray tracing and I do the refraction of the ray using the following relation (I got it from PDF called "Reflections and Refractions in Ray Tracing"): But I have seen it in another PDF as ...
2
votes
1answer
145 views

Question about complex emissivity and complex permeability

Consider a linear, isotropic material. We can then write: $$\textbf{D}(\textbf{r},\omega) = \epsilon(\textbf{r},\omega)\textbf{E}(\textbf{r},\omega)$$ In phasor notation. The complex emissivity ...
4
votes
1answer
216 views

Correct way to do a Thomas-Fermi approximation for cold gases

I have calculated the total Gross-Pitaevskii energy for a 2D Bose-Einstein condensate in an harmonical trap, using a variational gaussian wave function with a variational parameter b. Now I want to ...
2
votes
2answers
3k views

When can a surface charge density exist?

In my syllabus about electromagnetism, they state: "This surface charge density will not always be present, e.g. when considering two non-conducting dielectrics such surface charge density remains ...
1
vote
2answers
1k views

What is the significance of electron spin quantum number?

Somewhere I read that spin quantum number is a particularly interesting theory of quantum mechanics as what it really implies is that particles like electrons do not come back to the initial state of ...
3
votes
0answers
87 views

How many worlds does the world split into in the Many Worlds Interpretation? [duplicate]

I've been reading up on the Many Worlds Interpretation of Quantum Mechanics, and there is one thing (among many) that I really don't understand. How many worlds are 'created' by an 'observation' or ...
2
votes
1answer
1k views

Can two photons annihilate?

This is a question about definitions. When two photons interact to create an electron/positron pair, does this process 'count' as annihilation of the photons? I've struggled to find a good ...
5
votes
2answers
240 views

Dimensionless numbers or parameters that are $\ll 1$ or $\gg 1$

Many times, in various fields, authors use the notation: $$C\ll 1$$ or $$C\gg 1,$$ where $C$ is some parameter related to the system being studied. I know this is highly dependent on application, ...
0
votes
1answer
152 views

Analytic solution of particle in electric field [closed]

This is homework and I need some guidance. The question I struggle with is: Place a particle with $m=2$ , $q=3$ in a constant electric field $\vec{E}=(5,0,0)$ Choose $\vec{r}(0)=(0,0,0)$ and ...
3
votes
2answers
274 views

What happens from the point when we apply potential difference across an inductor?

I am in a serious doubt about it. Consider a battery of emf E and we connect it to an inductor. Initially the switch is open, now we close the switch. My question is: What mechanism happens just ...
1
vote
2answers
227 views

How to work out the acceleration of an object

I got given this question and im just lost. An object that weighs 25 kg experiences two perpendicular forces of 80N and 50N respectively. What's the acceleration that object gets? What i ...
3
votes
2answers
102 views

Identity in quantum operator tutorial

I'm reading this tutorial by Ben Simons entitled Operator methods in quantum mechanics in connection with his course in advanced QM, and I'm a bit puzzled by an identity in page 25, a bit above ...
3
votes
1answer
839 views

How to Calculate temperature, given speed of sound and relative humidity?

I know the solution in reverse direction, but I find it very complex to go the other way around and calculate the temperature when given the speed of sound and relative humidity, any ideas?
6
votes
2answers
364 views

How does the full string theory potential look?

Is the full stringy potenetial (for which it is claimed to be 10^500 vacua) written down explicitly somewhere? Any references? Thanks, Dave
2
votes
1answer
3k views

What's the relationship between concentration and refraction rate in a solution?

I am supposed to determine the concentration of a solution of ethyl alcohol and cyclohexane by measuring its refraction rate. Now I have some standard sample of the solution at concentrations 10%, ...
3
votes
1answer
595 views

How Does Cosmology Constrain the Number of Neutrino Species?

I know that based upon theories of structure formation cosmologists can constrain the sum of the masses of neutrinos - if neutrinos were too light or too heavy it would simply change the power ...
3
votes
3answers
5k views

Would a Cup of Tea Be Hotter If you Add the Milk Before or After Boiling Water?

This is a bit of dispute between work colleagues. An answer would be greatly appreciated. My argument is as follows: If you add X amount of milk at a temperature of M to a mug at room temperature R ...
2
votes
1answer
189 views

If Electricity and magnetism are the same viewed from a different reference frame then is electricity medium dependant?

If Electricity and magnetism are the same viewed from a different reference frame (they are the same force as unified by maxwell) then is electricity medium dependant? I came to this question when ...
0
votes
0answers
53 views

Should particles in Smoothed Particle Hydrodynamics (SPH) always move during a simulation?

Or can they just be used as an interpolation points and use some other "transported property" which are just evolved and propagated from boundary conditions like for eg. heat conduction through a ...
6
votes
1answer
409 views

What is the Moduli Space, and why do we care about it?

What is the moduli space of a QFT? What does it mean exactly that there are different inequivalent vacua? Can someone give a precise definition of the moduli space, and some easy examples? And why ...
4
votes
1answer
202 views

Does a diatomic molecule falling into a black hole dissociate?

I've just answered Dipping a Dyson Ring below the event horizon, and while I'm confident my answer is correct I'm less certain about the exact consequences. To simplify the situation consider a ...
4
votes
1answer
273 views

Percolation and number of phases in the 2D Ising model

Update. As my previous figure had conceptual mistakes I decided to change the picture to another, more instructive. After a long time I came back to try to understand an article on the Ising model. ...
1
vote
2answers
2k views

Getting Energies and Probabilities from the Hamiltonian

So I need to find the possible energies and the probabilities of these using the eigenvalues of a Hamiltonian. Once I obtain the eigenvalues, are those the energies E_n in and of themselves? Or do ...
2
votes
2answers
439 views

Dipping a Dyson Ring below the event horizon

The basic assumption about inescapability beyond the Event Horizon is that the necessary escape speed (orbital speed) would exceed speed of light, therefore no object can achieve it. Now, would it be ...
22
votes
3answers
909 views

Intuitive understanding of the entropy equation

In thermodynamics, entropy is defined as $ d S = \dfrac{\delta q_{\rm }}{T}$. This definition guarantees that heat will transfer from hot to cold, which is the second law of thermodynamics. But, why ...
2
votes
5answers
2k views

2 dimensional Coulomb's law equation

We can notice that in the Coulomb's law equation, $$\begin{equation}\tag{1}F=\frac{1}{4\pi\epsilon}\cdot\frac{q_1q_2}{r^2}\end{equation} $$ $4\pi r^2$ factor in the denominator expresses directly ...

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