# All Questions

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### Determinant of a propagator

Say I have a path integral $\int D \phi \exp(i S_0)$. $S_0$ is the usual free action $$S_0=\frac{1}{2}\int\phi (-\Box-m^2) \phi=\frac{1}{2}\int \phi G^{-1} \phi,$$ and at the moment I'm not ...
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### Machine readable database of gamma lines

Friends of mine did a lab experiment where they recorded $\gamma$-spectra in the range from 0 to 1500 keV with a soil sample. The data contains some background and a couple sharp peaks at different ...
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### Expectation to uncertainty

We know that in the case of $O$ being an operator, $\langle O^2\rangle-\langle O\rangle^2$ equals to uncertainty as long as $\langle\rangle$ means the mean value (expectation value). if we have $A$ ...
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### Does limiting to infinity violate laws of physics?

It is noteworthy that one cannot simply divide any length more than the Planck-length. If so, one cannot simply divide any volume more than the $(Planck-length)^3$. So if I want to find the limit of ...
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### $\rho g h$ and shape of container inconsistency?

The Scenario Suppose I have a cylindrical beaker and a conical flask (which cross-sectional area is bigger at the bottom), each located on an identical digital weight scale. Both of them have the ...
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### Help me select a motor! [on hold]

I am having trouble selecting a motor to power a crank-rocker system I am building. I honestly don't know much about DC motor selection so would you guys be able to help me out? I am looking for a 12 ...
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### How real is to get the charge about 1 millicoulomb with good isolation to avoid the discharge [on hold]

How I can get in practice the charge about 1 millicoulomb with good isolation to avoid the discharge.
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### What is crystal “supermodulation”?

I am researching the pair density wave in cuprates, and during my reading I came across a term "crystal supermodulation". I believe it relates to BSCCO. Can anyone give me a definition or give me a ...
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### Matter and Antimatter [on hold]

I'm a noob when it comes to physics and most of my knowledge of physics comes from popular science; it's more likely that I'm wrong than not about this. From what I've understood; Matter and ...
32 views

### Questions related to Lagrange points

For me, these two graphs are inherently different. The first graph portrays a "forbidden region" which is completely filled in, the other shows a collection of curves. Whats the difference here? ...
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### How does lightning make Ozone?

Oxygen is found as 2 molecules. How is O1 molecule taken from 02 and then combined to make 03 by lightning?
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### Twin and Detwin Crystals [on hold]

Hello i would like to ask , what are twin and detwin monocrystals? what has to do with their crystalographic symmetry? any consequences ? any image also would be really helpfull! Thank you
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### How does curved spacetime cause motion revisited

There was a previous question titled "Why would spacetime curvature cause gravity?" asked March 10, 2014. The answer given was essentially that since the time component of an object in curved space ...
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### Metric in complex manifold?

The Riemannian metric is expressed in complex coordinates as $$ds^2=g_{ab}dz^adz^b\hspace{3cm} (1)$$ My question is why do we seek a Riemannian metric? And is this a rule that we can write the ...
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### Measuring spin with Stern-Gerlach apparatus

I have a beam of electrons prepared in the state $|\Psi\rangle = cos(\theta/2)|+\rangle_z + sin(\theta/2)|-\rangle_z$ passing through a Stern-Gerlach apparatus which is free to rotate along the ...
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### Equations of above three variables cannot be solved with dimensional analysis. What does that mean?

I came across this statement while Googling about dimensional analysis. At first I thought that I understood what the statement meant, but now I realize that I really have no idea. What does the ...
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### Kinetic energy of fluid + collision

When a fluid is flowing, it has of course a kinetic energy and thus we can define kinetic power equal to ρAv v is the velocity and A is the surface of a solid for example. I have a question (maybe it ...
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### Normalisation of free particle wavefunction

The wavefunction $\Psi(x,t)$ for a free particle is given by $$\Psi(x,t) = A e^{i(kx-\frac{\hbar k}{2m}t)}$$ This wavefunction is non-normalisable. Does this mean that free particles do not exist in ...
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### End-point energy of the beta spectrum [on hold]

Calculate the End-point energy of the beta spectrum of the neutron (in Mev) from the neutron and the proton masses.
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### Water container insulation?

If I had a 2 gallon aluminum rectangular box (quarter inch wall) full of water and had it enclosed in a thin walled aluminum shell with a quarter inch spacing which would give the best insulation ...
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### Interpretation of QED gauge freedom

In quantum (or classical) electrodynamics we are free to make gauge transformations, which change the form of terms in the Feynmann diagrams (or the potentials) without affecting any physical ...
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### Definition of electric current

As I am taught in school that electric current is the flow of electrons, but in some places I faced another definitions like transfer of energy between electrons. I thought that it is the transfer of ...
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### Rotational motion yeeeeeeeeee [on hold]

interesting and good Question no. 1 & 2 on http://s29.postimg.org/kjcivjujr/20151128_002444.jpg
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### Additional quantum states of the infinite square well

The quantum states $\psi(x)$ of the infinite square well of width $a$ are given by $$\psi(x) = \sqrt{\frac{2}{a}}\sin\Big(\frac{n \pi x}{a}\Big),\ n= 1,2,3, \dots$$ Now, I understand $n \neq 0$, as ...
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### Gravitational mass defect

In nuclear physics we have a mass defect by the binding energy of the nuclides. A similar effect appears in the theory of gravitation induced by the gravitational binding energy, which reduces the ...
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### Physical meaning of $\left \langle \psi_{nml} | x | \psi_{n'm'l'} \right \rangle$ for hydrogen atom?

I know how to calculate the matrix element $\left\langle \psi_{nml} | x | \psi_{n'm'l'} \right\rangle$, but what is the physical meaning of it? In general, what does the following mean:  \left ...
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### Pulley Friction

Why is the frictional force of a rotating pulley 0? For example, consider two masses and a string that links those masses passing through a pulley. Why do we not account for the frictional force of ...
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### Matter and dark energy

So dark energy is the biggest thing in the universe, it keeps accelerating the expansion. But it's a constant so at some point there was a matter - dark energy equivalence. My question is how can you ...