# All Questions

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### The naive idea of the big bang

Many people think that according to big bang cosmology, first there was empty space, then there was an explosion in the middle of the emptiness, and now all the galaxies are flying away from that ...
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### Magnetic induction to generate EM waves

Let's say that I create a time varying magnetic field. This field then cuts a conducting circular loop normally. The loop has two protruding wires. Will the protruding wires emit EM waves? I ...
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### Quantum entanglement - problem with Bell's inequality

To ask the question, I will state the scenario first. Please let me know if the scenario is not described appropriately. The question is in the scenario itself. There are many questions marks in this ...
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### Coulombs Law on Quarks

As I know Quarks have fractional charge ,For this question lets take 2 Strange quarks(A and B) i.e charge of a quark is -1/3. As the Coulombs law states Force On A by B = Kq(A)q(B)/r^2 So F(ab) = ...
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So in my last question, @joshphysics showed me how to prove $K_\pm$ were ladder operators. Now I need to show that there is a lowest state, i.e $$\langle m_0|K_+=K_-|m_0\rangle=0$$ I am not ...
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### Motivation for integrals over scalar field

I'm looking for good examples of physical motivation for integrals over scalar field. Here is an example I've seen: If you want to know the final temperature of an object that travels through a ...
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### Why do some substances undergo sublimation while others do not?

This question is indeed lengthy...but please go through the question at least. From the study of kinetic theory I know that for intuitive answers we can associate the states (liquid, solid,gas) with ...
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### To which type of particles gauginos are supposed to couple?

I wonder about to which type of particles gauginos couple in general. I admit my knowledge in supersymmetry is very limited. Let's take an example: The photino. If it behaved similar to the photon, it ...
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### CFT and temperature

I have tried to think about this for some time but could not really go anywhere. Sorry for the sloppy question and thanks for any pointer. My question is about CFT at finite temperature and ...
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### Proof of Liouville's theorem: Relation between phase space volume and probability distribution function

I understand the proof of Liouville's theorem to the point where we conclude that Hamiltonian flow in phase-space is volume preserving as we flow in the phase space. Meaning the total derivative of ...
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### Mass, velocity and momentum

I am trying to figure out a Pinewood Derby Car and ways to make it better while remaining legal. I am a Den Leader, so am racing against other Den Leaders - so if I am DQ'd c'est la vie. Question: ...
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### Voltage of a battery in a circuit with an infinite resistance

I have a dilemma that I would like to share with you concerning batteries (without neglecting internal resistance), emf and resistance of a circuit. To better visualize my question you may need to ...
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### How to find the direction of an eddy current?

Suppose there is a magnetic field going from left to right. Suppose a thin sheet of metal conductor (e.g. a 1m*1m square) is dropped through the magnetic field such that the plane of the conductor is ...
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### Exponential Approximation of the Fermi Function

When $E-E_{F}>>kT$, the Fermi function $f(E)$ may be approximated by an exponential function. Similarly, when $E_{f}-E>>kT$, $1 - f(E)$ may be approximated by an exponential function. ...
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### Does ergodic hypothesis depend on the volume constraint of the macrostate or it only concerns with the energy constraint of the macrostate?

Ergodic hypothesis says that: [...] ergodic hypothesis says that, over long periods of time, the time spent by a system in some region of the phase space of microstates with the same energy is ...
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### Vectors finding direction include the difference between “north of east” and “east of north”

In what direction is your friend from the starting point after skiing 3 km east and then 1.5 km north? so far I know that angle= tan-1(opp/adj)=(1.5/3.0) angle= ...
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### Can we obtain interference pattern with single electron/photon in Young's double slit experiment? [duplicate]

Can we obtain interference pattern by using single electron/photon in Young's Double slit experiment? If yes, then how ...and if no, then why?
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### Inclined plane, circular motion and the friction

Suppose we have a cylinder on an inclined plane of mass $m$ and radius $R$ moving without sliding (so that $\varepsilon = a/R$). Why is the friction $F$ causing the circular motion sometimes lower ...
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### Why doesn't hydrostatic pressure glue objects to the seafloor?

Consider a cement block of the same density as sea-water resting on the (perfectly polished) seafloor. I also assume the side-faces of the cement block are highly polished, so that no vertical ...
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### Time Dilation and the direct opposite

// I just looked this up in google 30 kilometers per second Thus, the surface of the earth at the equator moves at a speed of 460 meters per second--or roughly 1,000 miles per hour. As ...
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### Could Dark Matter Exist Prior to the Big Bang? [on hold]

Recent discoveries that the universe is accelerating in its expansion has made me consider the possibility that dark matter might have existed prior to the time the universe sprang into existence, ...
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### Optical signals and the electromagnetic spectrum

Are Optical signals are not considered part of the E-M spectrum? Or are they?
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### Work and free body diagrams

I am a bit confused with how to find work when there is a free body diagram. I am trying to work out this problem, and in it a box is being pulled at a constant speed by a rope at a constant angle ...
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### Calculating the data rate for a baud signal

I have been working on these questions for the past few hours. I am working on calculating the data rate of baud signals, where each symbol can take on one of two levels. I wanted to know if I have ...
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### Work by Gravity using Tensors

Now I'm familiar with the various methods for deriving work done by gravity, but I noticed a few things about the situation, and wanted to see if I could properly apply a tensor treatment to the ...