# All Questions

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### Example for System Given Hilbert Space

What are some concrete examples of physical systems such that their corresponding Hilbert space is given by $\mathbb{C}$? Also, what is the physical difference between a system whose corresponding ...
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### Gauss's law and charge on surface

Consider a cone (not necessarily right cone), with a charge $q$ at its apex. Fix its base, and let the vertex be movable. Now suppose we intend to find the flux through the base. Since the flux ...
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### How does this youtube video demonstrate quantum entanglement? [on hold]

The following is an experiment that shows "spooky action at a distance" of quantum entanglement; that is, when we measure some properties of two entangled photons, we find that measuring property of ...
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### Dimension of vector resulting from tensorial product

I'm quoting what I found in a book about quantum computation: Individual state spaces of $n$ particles combine quantum mechanically through the tensor product. If $X$ and $Y$ are vectors, then ...
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### Find the equivalent capacitance

On the plane capacitor below, the surface of the boards is $A$ and the distance between the boards is $d$, the dieletrics constants are $k_1$ and $k_2$. Find the capacitance of the capacitor in ...
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### Why Does Moving a Cup of Coffee Up and Down whilst carrying it Make it less Likely to Spill?

Sometimes I have a Very Full Mug of Coffee and I am trying to carry it without it spilling. I noticed that if I moved the Mug up and down when carrying it, it seemed to settle the coffee and make it ...
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### Feynman paths of FTL velocity have imaginary momentum?

In this Phys.SE answer it is discussed that Feynman path integrals sums amplitudes for all possible paths, including those that are not time-like. If you take the momentum-space path integrals, I ...
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### Is it possible that gravity is created by the empty space in all matter? [on hold]

Everything is made up of atoms, which are made up of 99% empty space. Thus, everything is made up of 99% empty space; furthermore everything has gravity. Given this, is it a plausible theory to ...
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### Are magnetic hysteresis losses relevant to alternating currents flowing in a wire?

Say we have an AC in a magnetically lossy material, like iron. Because of iron's relatively high permeability, skin effect will be more pronounced than it is in say, copper, so this iron wire isn't so ...
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### Reduction of Nambu Goto action to true degrees of freedom

First consider the particle $$S=m\int\sqrt{-\dot{X}^2}d\tau$$ if you choose the static gauge $\tau=X^0$ and replace it in the action you get $$=m\int\sqrt{1-\dot{X}^j\dot{X}^j}d\tau$$ So now, you ...
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### Invariant mass not conserved in lab frame, yet conserved at center of momentum frame

In the following case it seems that the invariant mass is not conserved. A particle of mass $M$ and incoming velocity $w$ collides with a particle of mass $m$ and incoming velocity $u$. The velocities ...
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### Where does this relation between gamma, energy and mass come from?

I am doing a course that has used this relation a few times now: $$\gamma = \frac{E}{mc^2}$$ It makes sense physically, when $E = mc^2$ the particle is at rest and ...
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### Find the molar specific heat for each gas

A mixture of two ideal gases, the first one atomic and the second two atomic are put in normal conditions in a calorimeter with volume 1 liter hermetically closed. After it is given 10J thermal energy ...
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### How does humidity affect the path of a bullet?

Background Last night, I was reading the FM 23-10 (The U.S. army official field manual for sniper training), and I've noticed that they're potentially teaching snipers incorrect information. ...
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### Graphene and relativistic dynamics

Is it possible to rewrite the Lorentz-transformations (for quantum particles) in terms of effective mass m* known from condensed matter physics? "From pencil lead to relativistic quantum physics" "A ...
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### Specific heat at constant volume

Me and my friend came across this derivation is some lecture notes of our thermal physics module. We have been trying to calculate the partial differential of the internal energy but cannot get the ...
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### Travelling at a relative speed greater than the speed of light [duplicate]

I've wondered about this since I was a kid. I've been told the speed of light is a constant ($c$), which would mean that light always travels at the same velocity. Now, here's what interests me: if ...
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### What does this equation mean?

So I have just entered 11th grade and started limits on my own but my Physics textbook has an equation which I don't understand, I suspect it uses integration which I haven't learned yet. So can ...
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### Twin paradox, with a meeting at a halfway point

Suppose body A, at rest in its reference frame, is passed by body B which is travelling at a constant 0.6 c, heading toward Z, a point 6 light years away by A's reckoning, and as bodies will, they ...
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### Why can insulators be charged by friction but not by conduction?

When you charge an insulator by friction, the close contact of two electron clouds (each from a different medium) allows for electrons to be transferred between them. Yet why can the same not be ...