# All Questions

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### Both Eigenvalues and Operators are “Observables”? [duplicate]

I am having a bit of difficulty wading through the what seems to be multiple usages for Observables in Quantum Mechanics. " Mathematically observables are postulated to be Hermitian operators.. " ...
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### Vacuum pressure equivalent in a siphon hose filled with water?

So, I was thinking about how siphons worked today, and no matter how high or low the tube goes, as long as the end is lower than the start, water will flow. So, if you took a hose, ran it up 50 ...
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### How can I interpret $P(t) = \frac{1}{Q(t)} \frac{dW(t)}{dt}$ physically?

Generally speaking, one can calculate the work, $W$ (energy) required to compress a volume, $V$ of gas by integrating the pressure-volume 'loop' in a phase-space as $$W=\oint PdV$$ where $P$ is the ...
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### The quickest way to reduce an isolated system's temperature

If you are in an isolated room, having an air conditioner and a ceiling fan. What is the quickest way to cool the room. Using only the air conditioner or both of them?
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### Why doesn't the moon crash into the Earth?

I was searching about 'why do not moon crash to earth due to its gravity?'Then by reading physics stake exchange existing questions I came to know that its the sideways motion of the moon that keeps ...
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### What's the difference between the Fermi level and the electrochemical potential?

I was asked in a Thermostatistics test to compute the electrochemical potential $\mu(T)$ and the Fermi level $\epsilon_F$ for a system of non-interacting fermions, with two possible energetic states ...
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### What should the brake force in this problem be? [closed]

Alright so I think I know how to do this but I require help in calculating what acceleration would be in terms of some sort of friction coefficient. So model a particle going down a hill. The slope ...
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### What is the analogous effect of cosmological redshift for particles with mass?

Due to the metric expansion of space, light emitted from earlier times in faraway parts of the universe and travels for a long time to reach us get progressively redshifted, decreasing the energy of ...
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### Total energy loss of a sphere as it falls through a distance $h$ [closed]

A block of mass $M$ is placed on a rough horizontal table. A string attached to the block runs horizontally to the edge of the table, passes round a smooth peg, and supports a sphere of mass $m$ ...
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### Adding fluctuations to a hydrodynamic simulation to trigger instabilities

I'm doing a 2D combustion hydrodynamic simulation and there's a hydrodynamic instability that should be triggered because of the particular physical properties of my system. The key to the instability ...
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### What is blocking the magnetic field of this neodymium magnet?

I opened up my hard drive and pulled out (among other things) the top and bottom braces for the reading arm. Each bracket contains a really powerful neodymium affixed to its underside. When the ...
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### How does uncertainty/error propagate with differentiation?

I have a noisy temperature (T) vs. time (t) measurement and I want to calculate dT/dt. If I approximate $dT/dt = \Delta T/\Delta t$ then the noise in the derivative gets too high and the derivative ...
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### Assumptions needed to derive Hawking radiation

To derive many singularity theorems in GR you need only assume that GR is correct and the weak energy condition or something similar. My question is what are the assumptions needed to derive Hawking ...
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### Do quantum fluctuation particles have any trend regarding their average velocity and direction? If so does that infer and inherent reference frame?

In a vacuum particles appear from no where due to quantum fluctuations. In various reference frames would the overall mass of all these particles be moving in a direction? Could I find a reference ...
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### Colour changing material/ink

i am not sure if this is the right place to ask but is it possible for me to make an ink or material that changes colour when electricity goes through it at home? (as much colours as possible and low ...
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### Tesla Coil stops sparking until restart [closed]

I have a tesla coil with NT-1530-OUT Transformer, 23 turns (max) primary, 1m secondary(~1600turns), with MMC and rotary sparkgap. Gets 50cm sparks but try to tune the tesla coil by shifting top ...
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### Difference in Light's speed in various mediums [duplicate]

Light, despite not needing a medium and traveling due to oscillations of the electric and magnetic fields, slows down in mediums such as glass. I used to think it intuitively made sense, as we ...
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### Feynman rule for current-current operators

I wanted to know what is the Feynman rules for current-current vertex like this one:  {\cal{ L}} = G^\prime_F \hspace{2mm} \bar{d} \gamma^\mu (1-\gamma^5) u\hspace{3mm} \bar{s}\gamma_\mu ...
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### Necessary requirements for current

So i was in a course yesterday and the "teacher" told us the following (which i had a hard time believing/understanding) There is a load connected to a transformer. Applied potential difference is ...
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### Probing beyond the black hole event horizon

Black holes are interpreted to have a "break down" of general relativity at their point of singularity. The region near the singularity is expected to be described by some theory of quantum gravity. ...
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### How does the Higgss field change with the expanding universe?

Does the expanding universe really have an effect on the Higgs field? Say, is it like the matter getting diluted with the expanding universe? Or does the expansion does not have any effect on the ...
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### Wavelength Of Light

How can we change different wavelengths/frequencys of Sunlight to produce single wavelength to achieve maximum efficiency of Solar Cells ?
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### Transperancy of Solids [duplicate]

Why are some solids opaque and others transparent? If electrons are omnipresent in matter then how does light pass through them without colliding?
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### Can we detect a photon's direction?

The question of if a photon even has a direction may be up for interpretation, but I wanted to know if it's possible for a device to absorb most light from every which direction and only detect light ...
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### Energy specific question [duplicate]

I am math undergrad, so I am sorry if my question is trivial here. Given a equation for the potential how do you determine if the specific system is conservative ? can you determine by adding K + V ...
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1.A turbine is rated at 650 hp when the flow of water through it is 0.85 m3/sec. Assuming an efficiency of 84%, what is the head acting on the turbine.
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### Faster-Than-Light Communication using Entangled Photons

Based on my understanding of the “Double-Slit Quantum Eraser Experiment”, documented here: http://grad.physics.sunysb.edu/~amarch/, it seems that Faster-Than-Light communication is possible. Of ...