question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Let's discuss about $SU(3)$. I understand that the most important representations (relevant to physics) are the defining and the adjoint. In the defining representation of $SU(3)$; namely $\mathbf{3}$, the Gell-Mann matrices are used to represent the generators
$$
\left[T^{A}\right]_{ij} = \dfrac{1}{2}\lambda^{A},... | 1,039 |
<p>So in the context of a set of notes I am reading about acoustics I get to equation (23) in this <a href="http://www3.nd.edu/~atassi/Teaching/ame%2060639/Notes/fundamentals_w.pdf" rel="nofollow">paper</a>. Basically it comes down to showing that (<strong>note the dots above the a's meaning time derivative!)</strong><... | 1,040 |
<p>I was wondering with a question for a quite long time, thought to ask here.</p>
<p>I need to know is there any material or element which can block magnetic field? I mean I am searching for such material or element that cannot allow magnetic field though itself?</p>
<p>The practical scenario is, there are two perma... | 0 |
<p>Why is the gravitation force always attractive? Is there a way to explain this other than the curvature of space time? </p>
<p>PS: If the simple answer to this question is that mass makes space-time curve in a concave fashion, I can rephrase the question as why does mass make space-time always curve with concavity?... | 81 |
<p>I am wondering what will be the physics to explain how two neutral, chemically nonreactive objects stick. I know that using van der Waals formalism, we can treat neutral body electrodynamic forces and arrive with attractive forces that pull the objects together. </p>
<p>Now, once the objects touch (say a mechanical... | 1,041 |
<p>I have a question about the relation:
$\exp(-i \vec{\sigma} \cdot \hat{n}\phi/2) = \cos(\phi/2) - i \vec{\sigma} \cdot \hat{n} \sin(\phi/2)$.</p>
<p>In my texts, I see $\phi\hat{n}$ always as c-numbers. My question is whether or not this relation can be generalized for $\hat{n}$ being an operator?</p>
<p>If so how... | 1,042 |
<p>The second postulate of <a href="http://en.wikipedia.org/wiki/Special_relativity" rel="nofollow">special relativity</a> deals with constancy of light in inertial reference frames. But, how did Einstein came to this conclusion? Did he knew about the <a href="http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_exper... | 1,043 |
<p>Does one need to invoke quantum mechanics to explain casimir force or vander waals force. I see that textbooks show derivation of vander waal force with no QM but casimir force is typically described with QM. </p>
<p>Is there a difference between vanderwaal and casimir forces ? Are there distinct examples of these ... | 1,044 |
<p>Einstein has suggested that light can behave as a waves as well as like a particle i.e, it has dual character. In 1924, Louis de Broglie suggested that just as light exhibits wave and particle properties, all microscopic material particles such as electrons, protons, atoms, molecules etc. have also dual character. T... | 1 |
<p>When studying the de Broglie relations, I have stumbled across the following problem:</p>
<blockquote>
<p>Consider an electron with known velocity $v$ and assume: $v \ll c$. Calculate the corresponding wavelength of the electron.</p>
</blockquote>
<p>Using the de Broglie relations from Wikipedia:
$$\begin{align}... | 2 |
<p>Are there any known uses of modeling with elastic fractals in current physical applications? (Especially uses concerning with self-similarity)</p> | 1,045 |
<p>When something falls down, potential energy is transformed into kinetic one. Furthermore, you can attach a pulley and extract some energy (like in an aljibe), for example with a dynamo... If the object fall in a deep well, we can extract more energy, till the object reach downhole..</p>
<p>But what if we could have... | 1,046 |
<p>Say I have a linear motor [aka rail-gun] and use a x amount of electrical power. I fire the gun and the object exits at velocity v. I then reuse the same object as my projectile and fire the rail-gun a second time this time with 2x the electrical power. My lessons on momentum suggest it will go 2v. The Work-Ener... | 1,047 |
<p>Assume a spherical metallic shell over which a charge $Q$ is distributed uniformly. </p>
<p>Applying Gauss's law $\displaystyle\oint\textbf{E}\cdot d\textbf{a}=\frac{Q_{\text{enc.}}}{\epsilon_0}$ by considering a gaussian spherical surface concentric with the shell but with smaller radius, one can easily show that ... | 1,048 |
<p>Broadly speaking how do ideas of leading singularities and Grassmanian help in curing infrared divergences when calculating N=4 scattering amplitudes? My understanding is that one gets infra red divergences because the external gluon momenta becomes collinear with the the loop momenta. I am confused as to what Nima'... | 1,049 |
<p>In multipole expansion, we use monopole, dipole, quadrupole or octupole to describe an electromagnetic field. But I saw someone use <a href="http://www.google.com/search?as_q=sextupole" rel="nofollow">sextupole</a> to describe transition states. </p>
<p>If we expand an electromagnetic field by spherical harmonics, ... | 1,050 |
<p>I am writing this question here because I have a problem in understanding the Wigner Threshold law in Photodetachment and Photoionization.</p>
<p>The Wigner Threshold Law is given by:</p>
<p>$\sigma$=$E^{L+1/2}$.</p>
<p>where $\sigma$ is the photodetachment cross section, E is the kinetic energy of the detached e... | 1,051 |
<p>I have an intrinsic silicon layer sandwiched in between two aluminum contacts. I'm trying to figure out the band diagram of the entire device when a positive bias (much larger than the work function of the aluminium) is applied to one of the contacts. Intuitively, I would expect the i-layer part to be tilted (like i... | 1,052 |
<p>I had an argument about the most cost-effective way to keep the energy bill low in the winter (here, temperature usually have an average of -20°C (-4°F)).</p>
<p>He thinks that it's more effective to keep a temperature at a constant temperature at say 24°C (75.2°F), because It would cost as much or more to re-heat ... | 1,053 |
<p>I know that a hydraulic jump is formed when a zone of supercritical flow discharges into a zone of subcritical flow, but why exactly is a hydraulic jump formed?</p>
<p>From a mechanical point of view, are the only forces acting in the diagram weight and friction?
<img src="http://i.stack.imgur.com/3H1eU.gif" alt="e... | 1,054 |
<p>I want to know whether all solids are mono-atomic or not, and if there was diatomic solids or not,and if there was compounds of solids. </p> | 1,055 |
<p>I purchased a 90x refractor telescope with below configuration. </p>
<ul>
<li>Objective: 50mm diameter with 360mm focal length</li>
<li>2 Eye pieces: 6mm, 20mm (10-1/ 8" scope)</li>
<li>1.5x erecting eye piece</li>
</ul>
<p>It measures 13- 5/8” long x 2-1/2" diameter.</p>
<p>I was trying to see a building half Km... | 1,056 |
<p>I asked in this thread <a href="http://physics.stackexchange.com/questions/119923/time-dependent-schr%C3%B6dinger-equation-with-v-vx-t">Time-dependet Schrödinger equation</a> how to solve the Time-dependent Schrödinger equation. One of JamalS' recommendations was the Fourier transform, which is why I want to quote h... | 1,057 |
<p>I have two weights, weighing one ten times the other. I should figure out a way to make a pulley system that can lift the heavier mass with the smaller one. I would like to use the least number of pulleys possible because of the friction, but I think that anyway the rope would suffer from the same problem.
I found t... | 1,058 |
<p>Imagine you are a common man and want to prove that the Earth is Round, how would you prove it without any mathematical derivation or without the theory of the ships.</p> | 1,059 |
<p>Why is the earth shaped like a sphere and not any other shape: cube, prism?</p> | 3 |
<p>We know that in an LC circuit the voltage across the capacitor is the same as the voltage across the inductor (the emf induced in it). This is a direct conclusion of KVL (Kirchoff's Loop Rule) applied to the circuit. But can we use KVL in such circuits, where we have things like capacitors and inductors which affect... | 1,060 |
<p>Is it true that in Lattice Boltzmann method particles have only one degree of freedom even in 3D case? Can someone explain that fact or provide a link?</p>
<p>Thanks!</p> | 1,061 |
<p>In Green's superstring theory, Chapter 3, from equation 3.3.13 to 3.3.18, the author says that the singularity behavior of the ghost field $c^+$ must be no faster than $z^2$ as $z$ goes to infinity. And $b_{++}$ is required to approach $0$ as $z$ goes to infinity.</p>
<p>May I ask what is the reason for such constr... | 1,062 |
<p>Using a simple lattice model of conduction, where electrons are accelerated by an electric field, and are slowed down by bumping into the lattice, you get the following equation for current density:</p>
<p>$\vec{J}_n=nqμ_n\vec{E}$</p>
<p>Let's imagine an ideal DC voltage source connected with perfectly conducting ... | 1,063 |
<p>Has anyone ever heard of integrating out fields from classical Lagrangians if they are quadratic?</p> | 1,064 |
<p>I understand that the strings in string theory are posited to be many, many orders of size smaller than say, a quark, electron or any other particle. But if this is so, how does the string "expand" to produce the gargantuan, by comparison, particle? Is this expansion caused by its vibrational pattern or is there ano... | 1,065 |
<p>Given an atomic transition with associated E-field $E(t) = E_{0}\cos(\omega_{0}t)e^{-t/\tau}$ where $\omega_{0}$ is the natural line frequency and $\tau$ is the decay constant of the simple harmonic oscillator. Find an expression for the line flux, that is $I(\omega)/I(\omega_{0})$.</p>
<p>I'm trying to do the foll... | 1,066 |
<p>Basically, are the atoms that make up my body right now something that has existed since the big bang? </p> | 1,067 |
<p>I was hoping that someone could give me the more fundamental reason that we take as the temporal part of a quantum wavefunction the function $e^{-i\omega t}$ and not $e^{+i\omega t}$? Clearly $e^{-i\omega t}$ solves the time dependent Schrödinger equation whereas $e^{+i\omega t}$ does not. </p>
<p>However, the Sc... | 1,068 |
<p>Even though the thermal velocity of electron in a conductor is comparatively high, the thermal velocity is not responsible for current flow? Why is this the case?</p> | 1,069 |
<p>In time-dependent perturbation theory where $H=H_0+V$ and $V$ is considered small and has <em>no explicit time dependence</em>, the standard text-book treatment of the leading order probability amplitude for the system to make a transition from $|i\rangle$ to $|f\rangle$ is</p>
<p>$$
P_{f\leftarrow i}(\Delta t)=\bi... | 1,070 |
<p>This question is relevant to Euler's angles and Euler's equations for a rigid body.
Why aren't $\omega_1$, $\omega_2$ and $\omega_3 = 0$ in the body frame? How can we measure $\vec\omega$?</p> | 1,071 |
<p>I have a hard time understanding whether or not a wing placed in a potential flow, assuming there is no viscosity and no friction with the wing, will produce a lift. I've seen several contradictory (to me) versions of what happens in this case, in particular:</p>
<ul>
<li>In Landau - Lifshitz, Vol 6, §11 it is show... | 1,072 |
<p>How much lift does the average helium filled party balloon produce? (not including any extras like ribbon string)</p> | 1,073 |
<p>I am stuck on how to connect the ideas that two spin half particles must form a anti-symmetric wavefunction. Is there a proof on how to show that two spin one half particles must form a anti-symmetric wavefunction? </p>
<p>\begin{align}
\Psi(x_1,x_2)
=
\Psi_1(x_2)
\Psi_2(x_1)
-
\Psi_2(x_1)
\Psi_1(x_2)
\end{align}</... | 1,074 |
<p>The <a href="http://www.straightdope.com/columns/read/1886/does-black-clothing-keep-you-cooler">Straight Dope</a> ran an explanation of why nomads often wear black clothing - it absorbs heat better from the body. On the other hand, white clothing reflects sunlight better. Is it possible to get the best of both world... | 1,075 |
<p>One topic which was covered in university, but which I never understood, is how a spinning top "magically" resists the force of gravity. The conservation of energy explanations make sense, but I don't believe that they provide as much insight as a mechanical explanation would.</p>
<p>The <a href="http://hyperphysic... | 920 |
<p>I think that relativity and quantum mechanics would provide some good examples.</p> | 1,076 |
<p>Does the scientific community consider the <a href="http://en.wikipedia.org/wiki/Loschmidt%27s_paradox" rel="nofollow">Loschmidt paradox</a> resolved? If so what is the resolution?</p>
<p>I have never seen dissipation explained, although what I have seen a lot is descriptions of dissipation (i.e. more detailed path... | 344 |
<p>I just took a rare earth magnet out of an old hard drive. Lacking an appropriate screwdriver, force was used, and the magnet broke into two pieces; one about a quarter of the original size and one about 3/4 the original size.</p>
<p>Let's say this is the magnet:</p>
<pre><code>>>>>>>>>
</co... | 715 |
<p>What would theoretically happen to an observed object's length (let it be a 5 meter line) moving at some speed greater than that of light in a straight path?</p> | 1,077 |
<p>While writing these answers: <a href="http://physics.stackexchange.com/questions/16354/hypercharge-for-u1-in-su2xu1-model/16685#16685">Hypercharge for U(1) in SU(2)xU(1) model</a> and <a href="http://physics.stackexchange.com/questions/16340/is-there-a-concise-but-thorough-statement-of-the-standard-model/16684#16684... | 1,078 |
<p>Sorry to go on about this scenario again but I think something is going on here.</p>
<p>Imagine a stationary charge $q$, with mass $m$, at the center of a stationary hollow spherical dielectric shell with radius $R$, mass $M$ and total charge $-Q$.</p>
<p>I apply a force $\mathbf{F}$ to charge $q$ so that it accel... | 1,079 |
<p>I am looking for examples of physical indeterminacy impacting the macroscopic world. By physical indeterminacy, I mean physical sources of randomness such as quantum indeterminacy or brownian motion.</p>
<p>One example is of particular interest here: whether such randomness influences which sperm cell fertilizes a ... | 1,080 |
<p>Is the curvature of space caused by the local density of the energy in that area?Could gravity be a separate phenomenon only arising from the curvature of space? For instance if the density of energy in a particular area cause that area of space to ”curve” but the effect that we understand as gravity, (causing any... | 1,081 |
<p>Title says it all really.. Why is the XX spin chain a free fermion (non-interacting) model, and the XXZ chain not? </p>
<p>Is it right that $\sum_l a_l^\dagger a_{l+1}$ isn't an interaction between fermions because it's creating a fermion on one site and destroying it on another? But why is $\sum_l a_l^\dagger a_l ... | 1,082 |
<p>Proof of gravitational potential energy. </p>
<p>Work done by gravity in bringing mass from infinity to a distance of $r$ between masses. </p>
<p>When we use the integration formula and arrive at the answer we get $-GMm/r$ taking lower limit as infinity and upper as $r$.</p>
<p>But this work should be positive as... | 1,083 |
<p>I have a question about this motto used by Sean Carroll in his <a href="http://www.preposterousuniverse.com/blog/" rel="nofollow">blog</a>: </p>
<blockquote>
<p><em>In truth, only atoms and the void.</em> </p>
</blockquote>
<p>Can you explain what this sentence means? My interpretation is that the sentence does ... | 1,084 |
<p>I'm trying to get my head around a problem (I should have checked whether I had the answer in class, the exams are coming up now and I don't know if I'll get a lecturer response over the holidays)</p>
<p>I can't get figure out the relationship between $\theta$ and $2\theta$ in the diagrams supposedly making clear h... | 1,085 |
<p>Imagine that a pebble is placed on a uniformly rotating, frictionless disk. What will happen to this pebble? Will the disk slide under it and the pebble stay as is? Or will there be a centrifugal force on the pebble and it'll be thrown off the disk?</p> | 680 |
<p>I'm making a scratched hologram and I'm interested in we have to make curved lines to get a 3D image.</p> | 1,086 |
<p>If we have an array of telescopes attached one after another, would the resultant magnification be multiplied?Also would such a contraption be feasible to make telescopes with amazing magnification?</p> | 1,087 |
<p>I'm trying to understand Newton's Shell Theorem (Third)</p>
<p><a href="http://en.wikipedia.org/wiki/Shell_theorem" rel="nofollow">http://en.wikipedia.org/wiki/Shell_theorem</a></p>
<p>However this applies to a sphere of <em>constant density</em>. How is this formulated for sphere of <em>varying density</em>, e.g.... | 1,088 |
<p>As always the caveat is that I am a mathematician with very little knowledge of physics. I've started my quest for knowledge in this field, but am very very far from having a good grasp.</p>
<p>General relativity assumes that spacetime is a $4$-dimensional manifold. Ultimately, I know that physicists deal with Cala... | 1,089 |
<p>As I've stated in a prior question of mine, I am a mathematician with very little knowledge of Physics, and I ask here things I'm curious about/things that will help me learn.</p>
<p>This falls into the category of things I'm curious about. Have people considered whether spacetime is <a href="http://mathworld.wolfr... | 503 |
<p>Almost every book on physics that I read have some weird and non-clear explanations regarding the potential energy. Ok, I do understand that if we integrate a force over some path, we'll get a difference in some origin-function values ($\int_{A}^{B} Fdx = U(B) - U(A)$). This function is the potential energy. Of cour... | 1,090 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2175/is-it-possible-for-information-to-be-transmitted-faster-than-light">Is it possible for information to be transmitted faster than light?</a> </p>
</blockquote>
<p>Consider the following thought exper... | 4 |
<p>What is relativistic canonical transformation? I need every piece of information about it.
Does anyone know a reference or an article about relativistic canonical transformation?
For example, in classical mechanics, under one and only one condition, you can say that a transformation is canonical and that is:</p>
<... | 1,091 |
<p>I have read that it's not possible.</p> | 5 |
<p>In classical physics if one reverses time then energy does not change sign. For example in the formula for kinetic energy one has:</p>
<p>$$E = \frac{1}{2}m v^2$$</p>
<p>If you reverse time the velocity $v$ changes to $-v$ but $E$ stays the same.</p>
<p>What happens in quantum mechanics?</p>
<p>In QM one has the... | 1,092 |
<p>Up to which precision has the coulomb law proven to be true?
I.e. if you have two electrons in a vacuum chamber, 5 meters appart, have the third order terms been ruled out? Are there any theoretical limits to measure the precision ( Planck's constant?). Obviously there are practical limitations ( imperfect vacuum, ... | 1,093 |
<p>Does this photograph depict surface plasmon resonance? </p>
<p><img src="http://i.stack.imgur.com/RRN4e.jpg" alt="PHOTO 1 - Ellipsometric style photograph produces blue-green and purple resonance waves encircle nanogold-like tubule.">
PHOTO 1 - Ellipsometric style photograph produces blue-green and purple resonance... | 1,094 |
<p>I'm working on this problem; however, I cannot seem to get anywhere.</p>
<p>Given information:</p>
<p>The rectangular loop in the figure has 2.1x10^-2 ohm resistance.
What is the induced current in the loop at this instant?</p>
<p><img src="http://i.stack.imgur.com/IAVF7.jpg" alt="[Picture of Problem](http://sess... | 1,095 |
<p>Suppose you have a theory of maps
$\phi: {\cal T} \to M$
with $M$ some Riemannian manifold,
Lagrangian
$$L~=~ \frac12 g_{ij}\dot\phi^i\dot\phi^j + \frac{i}{2}g_{ij}(\overline{\psi}^i D_t\psi^j-D_t\overline{\psi}^i\psi^j) -\frac{1}{4}R_{ijkl}\psi^i\psi^j\overline{\psi}^k\overline{\psi}^l,$$</p>
<p>where $g_{ij}=g_{... | 1,096 |
<p>I came across many recommendations for both of these books, but I'm not sure which one should I use to study calculus...</p>
<p>I know most of the methods used in calculus and I use them frequently, but I'm shooting for mathematical physics and I was wondering which of these books would be better for someone aiming... | 1,097 |
<p>if it takes a 4 door sedan x amount of feet to go from 65 mph to 45 mph (and i don't know how many feet that is) on a dry straight road,
how many feet would it take for a large Mack truck transporting a full load of fluid, which would be most likely twice as heavy, to slow down from 65 to 45?
Also, as the truck slo... | 1,098 |
<p>In the classic bicycle wheel gyroscopic precession, using the right hand coordinate system of xyz and right hand rule of rotation,</p>
<p>Such as
<img src="http://i.stack.imgur.com/0ERpO.jpg" alt="bicycle wheel"></p>
<p>X axis is in the longitudinal direction (spin axis)
z axis pointing in the direction of gravit... | 1,099 |
<p>I'm working my way through <a href="http://cua.mit.edu/8.422_S05/PHYSICS-henry-glotzer-a-squeezed-state-primer-am-j-phys-v56-p318-1988-AJP000318.pdf" rel="nofollow">A Squeezed State Primer</a>, filling in details along the way.</p>
<p>Let $a$ and $a^\dagger$ be the usual annihilation and creation operators with $[a... | 1,100 |
<p>Is there a fundamental way to look at the universal constants ? can their orders of magnitude be explained from a general points of view like stability, causality, information theory, uncertainty? </p>
<p>for example, what sets the relative magnitudes of Planck's constant compared to say charge of electron or is it... | 1,101 |
<p>I'm trying to follow the steps in Eq. 2.60 of said book.</p>
<p>What I cant seem to figure out is how to change the integration variables from 'k' to 'E', as they state.</p>
<p>The equation is</p>
<p>$$\int \frac{d\textbf{k}}{4\pi^3} F(\epsilon(\textbf{k})) = \int_0^\infty \frac{k^2 dk}{\pi^2} F(\epsilon(k)) = \i... | 1,102 |
<p>What defines the <a href="http://en.wikipedia.org/wiki/Adiabatic_flame_temperature" rel="nofollow">adiabatic flame temperature</a>?</p>
<p>In a case I have to solve, I need to describe the combustion of natural gas (Groningen natural gas, to be specific). However, I am having some problems understanding the adiabat... | 1,103 |
<p>Air at 20 degrees Celsius is compressed adiabatically from 1 bar to 10 bar, what will its temperature be?</p>
<p>With
$$P_1 = 1,$$ $$P_2 = 10$$
$$T_1 = 293K,$$ $$T_2 = unknown$$
using $$\dfrac{P_1}{P_2}=\dfrac{T_1}{T_2}$$
my solution was
$$\dfrac{1}{10}=\dfrac{293}{T_2}$$
giving
$$T_2 = 2930$$</p>
<p>My physics... | 1,104 |
<p>In the MSUGRA breaking scenario, the stop particle typically appears at energies reachable at the LHC. Other sfermions, notably the partners of up, down, strange and charm are assumed to be degenerate in mass, and also heavier than the stop. Something similar holds for the stau.</p>
<p>Why is the third generation d... | 1,105 |
<p>I know that if one astronaut falls into a black hole, then a distant observer will see him take an infinite amount of time to reach the event horizon (provided the observer can see light of arbitrarily large wavelengths).</p>
<p>But the falling astronaut will only take a finite amount of time to reach the horizon.<... | 1,106 |
<p>According to my calculations, it is a lot skinnier than Airy’s photon, but still a whole lot fatter than a straight line.</p>
<p>So, how does a photon get from point A to Point B?
The ray optics approximation treats a photon as an infinitely skinny straight line. Feynman, on the other hand, says a photon takes ever... | 1,107 |
<p>Why is equal time commutation relation used in canonical quantization of free fields?</p> | 1,108 |
<p>I'm a software developer, and I need to calculate the estimated amount of force expended typing stored text. Preferrably in some interesting way. (i.e. the force exerted on keys thus far is enough to push a car 5 miles) (or: equivalent to 100 kg of TNT)</p>
<p>Assumptions:</p>
<ul>
<li>We're not going to worry ab... | 1,109 |
<p>We know that a point charge $q$ located at the origin $r=0$ produces a potential $\sim \frac{q}{r}$, and this is consistent with the fact that the Laplacian of $\frac{q}{r}$ is </p>
<p>$$\nabla^2\frac{q}{r}=-4\pi q\cdot \delta^3(\vec{r}).$$ </p>
<p>My question is, what is the Laplacian of $\frac{1}{r^2}$ (at the o... | 1,110 |
<p>In my poor understanding of quantum physics, quantum entanglement means that certain properties of one of two 'entangled' quantum particles can lead to change over infinitely large distances when the other particles' properties are changed.</p>
<p>Disregarding this already mind-boggling event taking place over say ... | 1,111 |
<p>When looking at the wave function of a particle, I usually prefer to write</p>
<p>$$
\Psi(x,t) = A \exp(i(kx - \omega t))
$$</p>
<p>since it reminds me of classical waves for which I have an intuition ($k$ tells me how it moves through space ($x$) and $\omega$ tells me how it moves through time ($t$), roughly ... | 1,112 |
<p>I have, for instance, a problem with a spherically symmetric charge distribution. I deduce here, in order to solve the problem easily, that the corresponding electric field must be symmetric. How is this type of deduction rigorously justified?</p> | 911 |
<p>Say I hook a 1KW steam engine to the steam heat in my apartment, and generate 1KW of electricity (the engine is 1KW mechanical, not 1KW thermal) from it, so I don't have to pay ConEd. </p>
<p>That means I am getting 1KW less heating power for the same amount of steam. Does it take the landlord's heating plant 1KW m... | 1,113 |
<p>I have a question about tidal forces on the far side of a body experiencing gravitational attraction from another body. </p>
<p>Let's assume we have two spherical bodies $A$ and $B$ whose centers are $D$ apart, and who have radiuses $R_{A}$ and $R_{B}$, much smaller than $D$. </p>
<p>Gravitation force has a law in... | 1,114 |
<p>Suppose a light wave with wavelength 3m. What happens if one tries to contain that wave within a 1m container? If I'm going about this entirely the wrong way or have wrong conceptions about light (which might be the case because I'm not a professional physicist), please tell me that instead.</p> | 1,115 |
<p>What is imaginary (or complex) time? I was reading about Hawking's wave function of the universe and this topic came up. If imaginary mass and similar imaginary quantities do not make sense in physics, why should imaginary (or complex) time make sense?</p>
<hr>
<p>By imaginary I mean a multiple of $i$, and by comp... | 77 |
<blockquote>
<p>Related: <a href="http://physics.stackexchange.com/questions/21456/tubelightspower-lines-pictures/21513#comment50077_21513">Tubelights+power lines pictures?</a></p>
</blockquote>
<p>I would've edited this into the above question, but I realized that there' enough to it to qualify as a new one. Plus t... | 1,116 |
<p>I'm working on a homework problem in Mathematica. We have to graph the height and the velocity of a function given an initial height and initial velocity. However, when I do the graph for the <a href="http://en.wikipedia.org/wiki/Velocity" rel="nofollow">velocity</a> with an initial velocity of 0 and an initial heig... | 1,117 |
<p>Currently I am working on my masters thesis about dualities in QFT and their geometric realizations.
As of now, I am trying to understand the article 'N=2 Dualities" by Davide Gaiotto. On the internet I found some exercises related to the article (<a href="http://www.sns.ias.edu/pitp2/2010files/Gaiotto-Problems.pdf... | 1,118 |
<p>ever since I begun calculating thermodynamical cycles, I've had problems with determining the sign of the work along a particular bit of the cycle. Of course, I guess that an arbitrary cycle is 'bendy' and the sign of the work differential depends strongly on the coordinates, but usually the cycles I deal with consi... | 1,119 |
<p>I need assistance (or experience feedback) in estimating if a Venturi pump would work at low pressure.
A boiler under vacuum (10% atmosphere) will produce steam (at a given speed depending on the boiler power) and the steam flow will be used to suck water at the same temperature (of boiling water under this vacuum, ... | 1,120 |
<p>Classically, black holes can merge, becoming a single black hole with an horizon area greater than the sum of both merged components.</p>
<p>Is it thermodynamically / statistically possible to split a black hole in multiple black holes? If the sum of the areas of the product black holes would exceed the area of the... | 5 |
<p>Does anybody know a good reference that works out the <a href="http://www.google.com/search?q=chargino+neutralino+production+cross+section+susy+equations" rel="nofollow">equations</a> for the Chargino/Neutralino production cross section in SUSY? I'm trying to understand if there are any tricks for boosting the produ... | 1,121 |
<p>The Hamiltonian of tight binding model reads $H=-|t|\sum\limits_{<i,j>}c_i^{\dagger}c_j+h.c.$, why is there a negative sign in the hopping term?</p> | 1,122 |
<p>In nucleon-nucleon interactions of n-n, p-p, n-p how do you determine which pion is the mediator?</p> | 1,123 |
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