Newest Questions
244,124 questions
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Is energy stored in pure thermal energy, or in temperature gradients? [closed]
I can think of two classes of thermal devices:
Class 1 devices convert usable energy (i.e. electricity) into pure thermal energy. They increase the total thermal energy in the universe. For example: ...
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Action invariant about Laplace-Runge-Lenz vector [closed]
The Kepler problem has Lagrangian
$$L = \frac{m}{2}\dot{x}^2_i + \frac{k}{r}$$
where $k>0$ and $\sqrt{x^2_i}$
Consider an infinitesimal transformation
$$x_i \to x'_i = x_i + \epsilon_j\delta_ix_j$$
...
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Fluid drag and fluctuation-dissipation relation
It is known that fluid drag and Brownian motion form an example of the fluctuation-dissipation theorem (FDT). But there are different types of drags. Are all of them dissipative or not? What is the ...
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What happens when generators act on wave functions?
Using the ground state $\phi_{0}$ and the first excited state $\phi_{1}$ of the harmonic oscillator, we define $\psi_{100}=\phi_{1}(x)\phi_{0}(y)\phi_{0}(z)$. Can we say that $L_{z}\psi_{100}=i\hbar\...
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Vectors | conservation of mass in 2D [closed]
Let's say I have a conservation cell as shown below defined by $A1$, $A2$, $B+$, and $B-$
so $S$ is the average of $B^{+}$ and $B^{-}$ vectors and $\hat{s}$ is the unit vector representing the ...
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Velocity distribution of thermally emitted electrons
In this text ELECTRON EMISSION AND CATHODE EMITTANCE the authors give a formula for the velocity distribution of thermally emitted electrons as
The velocity distribution for thermally emitted ...
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5
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Is white light a bunch of photons or a messy electromagnetic wave or both?
I'm a layperson so I hope you'll excuse my naivete. I have this notion that white light is made of many different frequencies. When I think about them being photons I can imagine them all bunched up ...
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How many microsieverts of radiation would a bolt of ionized plasma impart to organic tissue? [closed]
I'm a huge Star Wars fan and it just occurred to me, that the ion weapons used to disable droids, ships and other electronics would cause serious harm as well, to living beings, if they got ...
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393
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Interpreting Curved Spacetime
I understand that gravity is not a force, but instead that mass/energy curves space around them and hence, a object near some considerable mass, though always is travelling in a straight line in it's ...
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Does our universe have a "true" cosmological constant?
Few hours ago, I saw that the recent DESI survey claims that dark energy density of our universe is decreasing. This implies that the energy density is not constant and $w\neq-1$, obviously.
But on ...
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2
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358
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Drag caused by Unruh effect
I have recently learned about the Unruh effect, and I am wondering if the virtual particles can impart momentum to “real” matter. If so, would accelerating at sufficiently high levels result in a sort ...
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What processes leaves energy and surroundings same?
I was wondering about the case when the total energy of the system stays the same and the total energy of the surroundings stay the same but the system changes its energy mix so it has less exergy and ...
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Thought experiment:- Fuel usage related problem for a river boat problem [closed]
Help me answer this question:-
There's a river D meter wide with a constant flow of water at V m/s. A person with a motorboat having limited fuel wants to cross the river at a constant speed with the ...
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Gluon self-energy in cutoff regularization
I am consulting https://users.jyu.fi/~htpaukku/QFTII/Week12.pdf for the gluon self-energy. Eq. (3.200) contains the contribution of the gluon flower graph:
The contribution comes out to
$$
-g^2\...
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Wave Equation and EM Waves [closed]
No matter what the wave equation is, will the speed of EM wave remain constant (the constant being the speed of light)?
For example, Let the wave function be $$Ψ(x,t)= 10³sin π(3×10⁶x-9×10¹⁴t) $$then ...
