# All Questions

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### Magnitude of magnetic field at the mid-points of the axis of current - carrying loop [on hold]

The diagram shows four arrangements of circular loops, centred at the vertical axis and carrying identical currents 10A in the directions indicated. The radius of smaller loop is 5 mm and larger ...
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### What is a projection method?

Quoting from Solenthaler et. al. Predictive-Corrective Incompressible SPH (ACM Transactions on Graphics, Vol. 28, No. 3, Article 40, Publication date: August 2009) (PDF link here) These ...
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### Do electromagnetic fields gravitate?

It's well known that electromagnetic fields contains energy but do they gravitate ? When we talk about the composition of the universe it's now accepted that the 74 % is dark energy , the 22 % is ...
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### Geometric structure of atomic nucleus? [duplicate]

The electrons in an atom have a certain configuration and we can predict in which space the electrons can be present of a certain energy level (s-orbitals have a sphere-shape,....). Recently I read ...
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### How to estimate the time spending along the fluid flow

I have a 2d flow field with a singular point $$\dot x=y-px^2\\\dot y=-x-qy^3$$ where $p,q$ are small parameters. How do I compute the cost time of a particle from $(x_0,y_0)$ to ambient of the ...
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### An analogy for resonance?

I learned that the phenomena of resonance occurs when the frequency of the applied force is equal to the natural frequency of an object. At this point, an object vibrates with maximum amplitude. How ...
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### How to be sure that a He-Ne laser light is monochromatic

How can I be sure that the emission of a He-Ne laser contains only one single mode of laser cavity? The only thing that I know is that if I use a diffraction grating and the light isn't ...
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### some questions regarding Doppler shifting versus absorption-emission

I just got in what I thought was a silly exchange where a self-identified physicist states that the difference between "red-shifting" (in the Doppler sense) and the re-emission of light at longer ...
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### What kind of energy does superfluidity use?

Liquid helium (and other similar fluids) can "climb up" the walls of their containers. Who does the work in this case, and what kind of energy does it use? I'm sure we can't make a perpetuum mobile ...
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### Why does total spin conservation law forbid the spin wave gap in Heisenberg magnets?

What is the explanation for total spin conservation forbidding the spin wave gap in Heisenberg magnets?
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### When is quasiparticle same as elementary excitation, and when is not?

Can anyone shed light on the comparison between these two concepts?
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For some reason, I feel like the concept of voltage is escaping my grasp. I've done much research on these forums and through texts, and come across answers that seem quite well thought out, but still ...
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### Do all massless particles (e.g. photon, graviton, gluon) necessarily have the same speed $c$?

I suppose there was a discussion already on speed-of-gravity-and-speed-of-light. But I silly wonder whether all the massless mediators of four fundamental forces, i.e. Graviton: $g_{\mu\nu}$ ...
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### What is the wave function outside the barrier region?

I've been trying to learn how to apply WKB for several days now. I asked a similar question already about trying to find the wave function inside the barrier region. Now I would like to understand how ...
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### Spin Glass Prince Rupert's Drop

Spin Glass is known to converge to its ground state under Simulated Annealing. The word choice is especially interesting since annealing is also the name of a process performed on actual glass. ...
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### Doubt about the momentum conservation [on hold]

A couple of days ago, I found this problem in a book, I found it interesting, I think I have the answer but I'm not completely sure, I don't know if I can consider only the two trucks as a single ...
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### Clarify formula in quantum perturbation theory

I'm studying perturbation theory in the context of quantum mechanics. My lecture notes say that in order to calculate the first-order correction of eigenfunction $\psi_n$, that is $\psi_n^{(1)}$, I ...
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### Streamlines in Boundary Layer

Suppose that a fluid is flowing parallel to and over a flat plate. Obviously, a boundary layer develops in which the velocity ranges from 0 to 99% of the upstream velocity U. Could somebody please ...
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### What's a vector?

The other day in class my teacher was explaining how to calculate the weight of an object ($f=mg$). I found it fascinating which is why I started to do some practice questions at home. My mom saw what ...
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### Applications of quarks or string theory? [on hold]

We wouldn't have computers if we didn't know about quantum physics. I understand understanding of general relativity is needed to make GPS work well. Has knowledge of quarks or string theory resulted ...
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### Do you need energy to exert a force?

Is force dependent or independent of energy?
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### How is it possible the universe expanded faster than the speed of light during inflation?

In a documentary written in collaboration with Stephen Hawking, the narrator (supposedly Stephen Hawkings) says that by the time the cosmos was 10 minutes old, it had already expanded thousands of ...
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### Does there exist electric field around all the substances?

A system of two equal and opposite charges separated by a certain distance is called an electric dipole. Electric dipole moment ($p$) is defined as the product of either charge ($q$) and the ...
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### QFT Literature recommendation [duplicate]

Before answering, please see our policy on resource recommendation questions. Please try to give substantial answers that detail the style, content, and prerequisites of the book or paper (or ...
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### Measuring spin direction by means of coherent light?

Let us assume that we have the ferromagnetic surface where all atoms have the same direction of spins. And we can interact with the single atom in such lattice. Is it possible to measure the ...
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### What is a Nyquist edge?

I've come to this sentence and I don't understand the term Nyquist edge. Because observing in the FM band is not feasible, a sampling frequency of 200 MHz has been chosen for most of the receiver ...
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### What is “kinematic inversion” (from geophysics) in mathematical terms?

I am a mathematician working on a seismic imaging problem, and am currently (attempting to) read some geophysics papers (this one (Ruiz, Madariaga 2011) and this one (Di Carli, Francois-Holden, ...
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### Is negative 20 psi / 1.5 bar possible?

If I understand correctly, negative pressure usually means relative pressure: the difference between inside and outside. If outside is normal (1 bar, 15 psi, 100 kPa etc), how low can the (relative) ...
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### Two particles state of a 1D massive scalar field

Perfectly localized states are not normalized so do not belong to the Fock space (they belong to the rigged version). Suppose we approximate localized states with gaussians, what is the mathematical ...
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### What is the optimal burn direction to lower periapsis of hyperbolic orbit?

I am an engineering student who is interested in orbital mechanics. I am doing some self study before taking some orbital mechanics courses next year. I was learning about various orbit types ...
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### Why Landau Level quantization is observed only in low temperature and strong magnetic field in real experiment?

I know that Quantum Hall Effect and Fractional Quantum Hall Effect origin from Landau Level quantization. In magnetic field, the energy of in-plane(plane perpendicular to magnetic field) degree of ...
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### Gravitational Time Dilation with big masses

From Wikipedia I read that the formula for calculating the time dilation caused by a mass is $t_0 = t_f{\sqrt{1-\frac{2GM}{rc^2}}}$ where: $t_0$ is the proper time between events A and B for a ...
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### How axiomatic is the symmetrization requirement (i.e. the Pauli principle)? (in QM)

I've so far always been told, that the symmetrization requirement is an axiom on the level of the Schrödinger equation and the statistical interpretation of the wave function (or it's absolute value). ...
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### 2D Elastic Collision of two objects [on hold]

I am looking for a straight-forward equation that can give me the velocity of two objects in the $x$- and $y$-directions after they collide; I have velocity of the two objects (in both directions) ...
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### What is the commutator? [on hold]

$e$ and $f$ are unit vectors, $L_e$ is defined by $L_e=eL$, where $L$ is of course the angular momentum operator. A similar definition for $L_f=fL$ The commutator that I can't solve: ...
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### mechanical strength [on hold]

Question asks Each of the two aluminum bars is subjected to a torque of magnitude $T = 150$ Nm. Knowing that$G = 26$ GPa, determine for the bar: The maximum shearing stress and its ...
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### Are images of three-dimensional objects also three-dimensional?

Suppose that I produce an image of a dog using a converging lens. I can draw ray diagrams for the nose of the dog as well as the back leg. These are definitely longitudinal points, not transverse. ...
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### Are composite bosons always bosonic (e.g. the pion-cloud surrounding the nuclei)?

The $\pi$-meson is a boson, but consists of quark-antiquark (fermions). It seems to me that at some energy level (equivalently distance) the inner structure (fermionic nature of the quarks) of the ...
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### Can a glass window protect from heat radiation?

I have been reading in this and found a statement saying : " Glass will not transmit heat radiation.". So now I am confused. If glass won't transmit heat radiation, then why do we feel hot when we sit ...
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### Thermal physics problem (slow expansion in a evacuated bottle) [on hold]

An evacuated bottle with non conducting walls is connected to a gas holder of essentially infinite volume, and which contains helium at a pressure of $P_o$ and temperature $T_o$. Helium bleeds ...
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### Why Inox Steel doesn't interact with magnets?

My dad has a HUGE magnet on his workshop. I love magnets, and when I saw it, I asked him what it was for. His reply was: "I don't know why, but inox steel bolts don't get attracted to it, so I use ...
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### Experimental evidence for non-abelian anyons?

Since non-abelian anyons have become quite fashionable from the point of view of theory, I would like to know, whether there has actually been experimental confirmation of such objects. If you could ...
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### reduced charge for attracting electrons?

The reduced mass in the two body problem is $\mu= \cfrac{m_1 m_2}{m_1 + m_2}$. Is there any analog to this with interacting charged particles (or at least that is of use somewhere in physics)? I have ...
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### Temperatures at extreme densities

Cosmology (and astrophysics) talk about the "initial singularity" (IS, became the big bang) and "black hole singularities" (BS, inside black holes), and these appear to be quite different: The IS is ...
Suppose we have a particle with mass $m$ and energy $E$ in a gravitational field $V(z)=-mgz$. How can I find the wave function $\psi(z)$? It should have an integral form on $dp$. Any help would ...