# All Questions

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### Question on a variant of Atwood machine with strings unwinding in one side

The figure is standard Atwood machine except that for the right object string tension acts on the left side of the object, and strings unwind from the object. No slip condition on a rolling ...
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### Effective magnetic moment

How can one calculate effect moment from susceptibility (SI*10^6) versus temperature (K) graph? What is the typical range of effect moment for ferromagnets?
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### Should the liquid come out of the tank if a hole is drilled in the vertical wall?

This is a tank filled with water kept on ground. The points $A$ and $B$ are at 'same horizontal level', hence, as per an interpretation of pascal's law, pressure at $A$ must be equal to the pressure ...
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### About $U(1)_A$ symmetry,

I know a $U(1)_A$ symmetry is related with a global symmetry. (Is it axial or anomaly ) What is A stands for? In the context of supersymmertry, Fundamental and anti-fundamental chiral multiplet has ...
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### Wave-like description of Compton scattering and photoelectric effect

I have found in the wikipedia page for QFT the following statement: ... Although the photoelectric effect and Compton scattering strongly suggest the existence of the photon, it is now understood ...
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### Nonlinear constitutive state equation

Between the Tait equation, and the B/A type of equation, which one is better suited to approximate the isentropic equation of state? Why B/A type is mostly used in nonlinear acoustics?
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### Interesting (new to me) things in the exposition of Landau's book on QM

In section I.1 (The uncertainty principle), a principle I already know, the author suggests a "relaxing" picture (Unusual): "We have defined "apparatus" as a physical object which is governed, ...
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### Conical intersections - phase

Can anyone explain why at a conical intersection the wavefunction changes sign? My understanding is that it is a test to see if the crossing IS indeed a conical intersection or just a coincidence of ...
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### Bound states and extensive field configurations

What are extensive field configurations in QFT (instantons, monopoles etc.)? What is the difference in description of their contribution in path integral value or in $n$-point operator functions ...
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### Unbalancing a system of rotating masses - what happens?

Lets say you have a rod spinning on its long axis and this rod has a few smaller beams attached perpendicular to the rod at varying angles and with varying masses. Here's a picture from wikipedia to ...
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### Hamiltonian governing liquid to a solid transition

What is the Hamiltonian 'H' (at the atomic or molecular level) that governs the phase transition from a liquid to a solid state? Actually, I want to explicitly verify the Hamiltonian 'H' admits the ...
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### Hot wire anemometry and gas species

Hot wire anemometry is a technology that measures mass flow of a gas stream in the neighborhood of a heated wire. The sensitivity of a flow sensor using this technology is usually specified for a ...
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### Nyquist plots in electronics

Being purely biologist I'd like to obtain some general background in the application of any forms of Nyquist plots for study of signal transduction. For instance from one of the electronic lecture ...
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### Problem in Classical electrodynamics Jackson

There are two problems. On page 35, Jackson try to use scalar potential that satisfy the poisson's equation. But, i completely lost the step. 　　　...
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### What is the difference between photoelectric effect and Compton scattering?

What is the difference between photoelectric effect and Compton scattering? These two effects explains interaction of photon with electron. Why in photoelectric effect whole energy of photon is used ...
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### What does traveling close to speed of light mean?

This has been bugging me for a while. We all know in relativity that if you travel close to speed of light, all sorts of crazy things happen. But what does it mean to travel close to speed of light? ...
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### Quadrupole moment of a valence proton

The state of an unpaired nucleon in the nuclear shell model is given by the quantum numbers $l$, $s$, $j$ and $m_j$ resulting from coupling $l$ and $s$ when we add spin-orbit interaction. In chapter 5 ...
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### Thevenin's equivalent of Wheatstone bridge

I tried to calculate the Vos and Isc and both of them are zero..so the Thevenin's resistance is 0/0=undefined. How do I calculate the resistance when Vos/Isc fails,such like the Wheatstone ...
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### Standing waves on a compound string

I've been having some difficulties in understanding standing waves. The questions that I have are as follows: 1) Suppose I have a compound string, made up of two strings. What is the correct way to ...
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### Would a portable superconducting coil “battery” be impractical due to magnetism?

I'm working on a science fiction story idea, and trying to make sure I get all of the physics right. One of the concepts I'm using is superconducting coils as "batteries," because they can store huge ...
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### gibbs free energy and maximum work

I'm getting confused between two important results.... Gibbs free energy G = H-TS where h is the enthalpy and S is the entropy. This relation indicates only when the temperature and pressure are ...
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### Does Dowell's Method of determining losses include winding losses?

Dowell's Method of determining losses uses the DC resistance of the portion of wire in the equation, however does this give the total resistance of the wire? Or only the resistance due to the ...
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### What is the minimum volume in which, for a given temperature difference $\Delta T$, natural convection would occur?

I'm trying to figure out if convection will occur in a plastic bottle slice and what length of slice would be optimal to achieve high R value transparent insulation on the cheap. The bottle slice is ...
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### What are the “name” and “coname” of operators?

So, I've been reading articles about categorical quantum mechanics, and I keep coming across definitions of "name" and "coname" of an operator. Googling these basically only turn up the papers I've ...
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### Velocity in relativity

We just started learning about 4-vectors in my physics class, and I'm a little confused about the relationship between the 4-velocity $U=\gamma(c,\vec{v}),$ and the velocity transformations given by ...
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### pair correlation function for heterogeneous nuclei

I have a system with heterogeneous size of nuclei of two liquids within a mixed fluid phase of those two liquids. I was wondering what would be the interpretation of pair correlation function for a ...
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### allowable compressive stress in discretely laterally supported lateral buckling

The maximum allowable compressive stress corresponding to lateral buckling in a discretely laterally supported symmetrical I beam does not depend upon : the modulus of elasticity can anyone please ...
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### Calculating Velocity in motional EMF

To calulate motional $\epsilon$, we use the following formula: $\epsilon$ = $-vBL$ What is the proper formula from what is below to calulate the velocity of a conductor moving in a magnetic field? ...
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### Destructive and Constructive Interference Sign Problems in Sound Speakers

The problem statement, all variables and given/known data Problem b). Looking at the attached document of my teacher, the visual representation of the answer does make sense. Relevant equations ...
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### Complex dielectric constant in ultraviolet range

Dielectric constant of a material could be a complex number, which is dependent of the frequency of electromagnetic wave. From the Springer material website, I learn that both the real part and ...
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### Relation between the curvature of a manifold and the number of covariantly constant vector fields that it admits

Suppose that on a four dimensional manifold we are able to explicitly construct four linearly independent covariantly constant vector fields $K^a_{\mu}$: $$D_{\mu}K^a_{\nu}=0,$$ $a=1,2,3,4$ then it ...
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### Uncertainty of measurement with goniometer

I got a goniometer with scale -90 to 90 degree. I use only 0 to 90 degree. One section of the scale has 1 degree. I read a value of $62^\circ$. What is the uncertainty of this measurement? I thougt ...
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### Appropriate order of the sources in the phase difference formula (Waves)

Please look at b). My teacher defines delta(x) to be x1-x2 and then says that phi naught of 1 =0. However, because she defined the difference to be "1"-"2", the phi naught difference should also be ...
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### Determine flow rate of side outlet from known flow rate in river

What reading is recommended to determine the initial flow rate of water through an intake from a river, given known intake diameter, and angle of incidence. I am aware that Bernoulli's equation and ...
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### Sheer leg derrick tension in cable for equilibrium is not what it should be?

As you will note, the final solution of $5.79$ kN is not equal to that of $w$. Isn't this impossible? If there is no friction at point B and the cable is assumed to be massless, shouldn't the ...
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### How long did it take for the universe to become 1 one light year?

Given the density, pressure and other cosmological parameters. At this point we're not even thinking of time... But would this have occurred during or post Inflation? Could this be the Expansion ...
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### Magnesium Diboride - why was it missed?

In 2001 it was found to superconduct at 39K, which is about twice the record for materials up until the 1980s when the cuprate high temp superconductors were discovered/invented. My question is ...
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### When can you apply Ehrenfest's theorem?

I know when the initial state ($\Psi(x,0)$) is given, $\frac{d\langle x\rangle}{dt} \not=$ $\langle p\rangle$. I thought you can only apply Ehrenfest's theorem when $\Psi$ is a function of $x$ and ...
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### Free body diagram of mechanisms

The image below shows a mechanism with 2 pin joints. On one of the pin joints, there is a torsional spring that exerts a torque $M_s = \kappa \theta$ (rest state is at $\theta = 0$). A force $F$ is ...
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### Gauge invariance in arXiv:1406.1804

I am reading the paper arXiv:1406.1804. I don't show that the invariance of the connection under the gauge transformation (2.48), I have written an email to the authors about this question. However, ...
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### Dicke states, spin squeezing and quantum metrology

Dicke states are by definition simultaneous eigenstates of the $J_z$ and $J^2$ operator. What is the difference between these states and Dicke squeezed (DS) states? I know that these are "entangled" ...
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### What sort of things do condensed matter experimentalists measure and how?

What sort of things do condensed matter experimentalists measure and how? Do they do scattering experiments? If voltages are measured then how? I want to know what specific experiments are done. The ...
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### Does Gauss' Law apply to real physical solid conductors?

In a conductor there is no electric field because there is no charge. There is no charge inside because any charges present inside would repel each other and be driven to the surface of the conductor. ...
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### How to read this state in quantum physics?

I am having a little trouble understanding this state: $$\,^3D\left[3/2\right]_{1/2}$$ What does the $[3/2]$ indicate here?
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What is the true difference between radar and sonar? My understanding is that radar uses a reflected EM wave, while sonar uses a compression (shock wave) of the material it's in. (It compresses water, ...
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### Electrical Resistance of Spherical, Contacting Colloids

So, I work a lot with Magneto-Rheological (MR) fluids - which are essentially electrolyte solutions with suspended, paramagnetic colloids/particles. Once a magnetic field is applied to such a fluid, ...
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### Could an object higher than the stationary orbit be returned to the outgoing point on this orbit?

In the question Centrifuge speed of an object higher than a stationary orbit, I asked: Does an object higher than the stationary orbit move slower or faster around the world than the top of a tower ...
Currently I am having troubles calculating the pressure distribution $p(x,y)$ at the surface of a vibrating plate. I have a simply supported rectangular baffled plate which gets excited by a harmonic ...