# All Questions

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### Where would the dark matter particle fit inside a picture of the standard model?

While I am particularly fond of the Sterile Neutrino, I have not been able to find any example of a picture of the standard model arrangement of particles, with Dark Matter (and the higgs), inside a ...
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### General Relativity - Four Velocity Derivative Question

I am trying to get my head around a small point used in a book I am reading about General Relativity. The book states that because $u_au^a = c^2$ it follows that $u_a \nabla_b u^a = 0$ The first ...
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### Help with inclined slope motion? [on hold]

I have this question (5ii) and I was wondering why this wouldn't work, why can't I solve for acceleration using $v^{2}-u^{2}/2s$=$a$ then solve for $t$? I obviously have to resolve and use $p=fv$ but ...
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### Is Twin Paradox solved in Special Relativity or General Relativity? [duplicate]

I'm getting pretty frustrated about finding the true solution to the Twin Paradox. If I open 10 relativity books, they all tell that they have the correct solution and the other books are wrong. So I ...
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### Does the Advanced Photon Source use electrons or positrons?

Synchrotron light sources like the Advanced Photon Source (APS) (as well as SPring-8 and the ESRF) are typically mentioned as accelerating electrons up to the GeV range to produce extremely high ...
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### How to derive path difference ($\Delta l=d\sin \theta$) for double-slit interference?

The Wikipedia page for the double-slit wave interference experiment states that the path difference between waves diffracting from the two slits is equal to: $$\Delta l=d\sin \theta$$ where $d$ is ...
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### What is the meaning of “ Ψ is not a measurable quantity in itself”?

I want to know that why the wavefunction Ψ as a complex quantity (i.e $A+iB$ form) in quantum mechanics and somewhere I have studied that Ψ is not a measurable quantity in itself that's why we ...
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### How to determine which object in a special relativity physics problem has proper time?

I'm having some difficulty determining which object/location should have proper time applied to it in relativity physics problems. Example: If an electron travels at 40% the speed of light then ...
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### Can a brane have infinite volume?

I'm asking this within the framework of brane theory. My intuition is that branes are objects with finite volume, but then how can they accomodate an Universe that is infinite in extent?
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### Electric field due to a finite line charge [on hold]

I was wondering what would happen if we were to calculate electric field due to a finite line charge. Most books have this for an infinite line charge. In the given figure if I remove the portion of ...
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### Polarization of light for a fast moving observer

For a fast moving observer the frequency of light becomes shifted due to the (relativistic) Doppler effect. But what about the polarization of the light? Could it be, that e.g. circular polarized ...
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### When will the pringles can fall?

When I'm pushing a tall, cylindrical object stood on its end (like a Pringles can) I can push it near its bottom, and it will slide forwards, or push it near the top, and it will topple over. So, ...
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### Why is energy in a system typically able to be described using quadratic expressions?

This might be more of an applied math question. Why is the energy of a system typically able to be described using quadratic expressions. Is there an underlying mechanic that drives this?
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### Current carrying conductor with a loop at a distance [on hold]

In Fig, there are an infinitely long conductive wire and a circle conductive loop C with the radius r and the number of turns n. The distance L between the wire and the loop is much larger than r, ...
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### Can you ever exert more downwards force than your weight?

So, because I'm a hardcore person, I risked all this afternoon by going out in the wind, the rain and the cold to construct a willow den. Yes, it seems a menial task, but it was actually quite ...
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### Does the Meissner effect only effect magnetic fields?

I find this effect very interesting and was wondering what tests have been performed to check its effects on other fields? Also a side question related to this effect, can it trap a magnetic field. ...
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### For a light of given frequency, what does the amount of refraction in a variable medium depends upon?

I want to know whether the amount of refraction of a given monochromatic light depends solely upon the density of the of the medium ( increase the density to increase the angle of refraction), or ...
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### water pressure relationship to volume [on hold]

I have a one inch pipe 120 feet long and caped. I have a 60 pound input of pressure. I put a half inch pipe at the end and open it. What happens to the pressure in the one inch pipe? If I add another ...
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### Is there serious research on superluminal travel? [on hold]

I was wondering if there are any serious attempts, or any ideas for loopholes in the current theories, that would enable us humans to travel with a speed greater than the speed of light?
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### Is there a time dilation between my left and right arms?

Is there a time dilation between my left and right arms when walking? due to special relativity I guess Thanks
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### where is the logical hole in this reasoning? (special relativity)

I cannot see the problem in the following reasoning, so I'd be glad if you could help me out. The problem is defining a notion of "length" that is consistent with the constancy of the speed of light ...
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### Second law of thermodynamics (in terms of entropy)

Is the second law of thermodynamics (in terms of entropy) for closed systems or isolated systems? I thought it must be valid for isolated systems, such as the Universe. But the book Fundamentals of ...
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### Does the definition of compressibility depend on the frame of reference?

According to many authors, a fluid is defined to be incompressible if the material derivative of the density $\frac{D\rho}{Dt}$ is zero, that is to say, that in an frame of reference following the ...
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### Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [duplicate]

I want to know the configuration where the system would be most stable.I only know basic Physics & Maths and cannot start solving the problem.I can understand it for 4 charges and 6 charges as a ...
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### Charged particle inside a hole in a charged layer

The layer $-a\le x \le a$ is homogeneously charged with a electric charge density $\rho \gt 0$ and on the x-axis a thin hole is made. A particle with mass $m$ and charge $q \gt 0$ move on the ...
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### When I put 2 electrodes into a electrical conductive solution, does the volume of the solution around the electrodes have biological effect?

Media these days give me a common sense that it is able to hurt someone if they step on a wet floor with a electric cord dipped in, several movies have this scene.However, I wonder if I set up an ...
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### Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [on hold]

I want to know the configuration where the system would be most stable. But I cannot think of a way to start solving the problem. I've solved it for 4 charges and 6 charges and they have a symmetric ...
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### Field states, particles, QFT

I'm trying to self-study QFT and write a presentation paper on neutrinos. Regarding the $\left\{ \nu_L, \nu_R, \bar{\nu}_L, \bar{\nu}_R \right\}$ set of neutrino states, what is the correct word to ...
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### Working out length of taut rope orbiting the earth remaining straight and radially directed [on hold]

A taut rope is orbiting the earth with angular velocity $a$. It remains straight and radially directed. If the midpoint is located at radius $r$, find the length of the rope. I can't even imagine ...
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### How to calculate the potential energy of a magnetic dipole (with zero torque)

In the following problem, I would like to know how they arrived at their solution for finding the potential energy of a magnetic dipole (boxed in red). I understand I probably have to use the ...
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### Electric field calculation and its graph vs x [on hold]

Electric field along the line passing through two point charges, A point charge $Q_1= +3 \mu C$ is placed at the origin and a point charge $Q_2= -7\mu C$is placed at $x=0.4 m$ on the $x$-axis of a ...
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### What is the exact definition of Magneto-optical Polar Kerr angle?

As stated in the title. I would like to know the exact definition of the Magneto-optical Polar Kerr angle. Whether it is just the rotation angle of the polarized light or it is something else?
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### How can we define a frame of reference in general relativity?

I have started reading general relativity. (A First Course in General Relativity, Bernard Schutz). I am finding very hard to understand a frame of reference. When I was reading special relativity ...
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### Entanglement and the boundaries of fiction

If entanglement is just a correlation from when the particles were in proximity, and there is no causality between the two, can the state of one particle be changed after being measured, and that ...

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