question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Does all frequency of light travel with the same speed in a particular material like glass?</p>
<p>Since by cauchy's relation refractive index change with wavelength which implies the speed also changes.</p>
<p>But as derived from maxwells equation, the speed of light should only depent on medium through which it ... | g16479 | [
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<p>Let's say I have two distinguishable charged particles interacting electrostatically. In Fermi's golden rule, the two particles can change state at a rate proportional to:
$$|\langle \psi_f | H_{int} | \psi_i \rangle|^2 = \left| \int d^3 r_1 d^3 r_2 \; \psi_{1f}^*(r_1) \psi_{2f}^*(r_2) \frac{q_1q_2}{|r_1 - r_2|} \ps... | g16480 | [
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<p>I have a question. How come that the flight from Toronto to Moscow takes the same time as the flight from Moscow to Toronto. Should it take much longer because of the earth rotation?</p>
<p>One direction we travel in direction or an orbit and traveling back we are going against the Earth orbit...</p>
<p>From Toron... | g162 | [
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<p>I was reading this <a href="http://arxiv.org/abs/hep-th/9708067" rel="nofollow">article</a>(<em>On domain shapes and processes in supersymmetric
theories</em>). In the paragraph about domain walls intersection (paragraph $4$, page $7$) the authors say:</p>
<blockquote>
<p>In a one-field theory it is known that an... | g16481 | [
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<p>In my textbook, it is given:</p>
<blockquote>
<p>1 <a href="http://en.wikipedia.org/wiki/Atomic_mass_unit" rel="nofollow">atomic mass unit</a> equals $1/12$th mass of one carbon 12-atom. Since mass of $6.02 * 10^{26}$ atoms of carbon-12 is $12\space\text{kg}$. Thus, </p>
<p>$$1 \text{ a.m.u (or u)} = \frac{1... | g16482 | [
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<p>Can Bremsstrahlung radiation produced by the electron-electron interaction as e-e interaction can result acceleration due to coulomb repulsive force? If yes, how the energy of bremsstrahlung radiation produced by e-nucleus and e-e interaction can be compared?</p> | g16483 | [
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<p>The simplest equation expressing mass–energy equivalence is the famous $E=mc^2$ where $c$ represents the speed of light. Compare this with $E_K = \frac{1}{2}mv^2$. </p>
<p>Since $E=mc^2$ can be applied to rest mass ($m_0$) and rest energy ($E_0$) to show their proportionality as $E_0=m_0c^2$, I ask whether this re... | g16484 | [
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<p>I have a quick question about the equation of motion for a falling rod (with one end touching a frictionless surface). The end touching the surface is not fixed. I am given the moment of inertia about the center of mass. Only gravity is acting on the rod. The rod begins at an angle $\theta$ above the ground.</p>
<p... | g16485 | [
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<p>In my experiment, I have to obtain a relation between magnetic field of a solenoid and the applied Vp-p.
The setup is as follows.</p>
<hr>
<p><a href="http://www.teachspin.com/instruments/faraday/" rel="nofollow">http://www.teachspin.com/instruments/faraday/</a></p>
<hr>
<p>Does my choice of reference frequency... | g16486 | [
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<p>I was looking at the Wikipedia entries on Time Travel and the Grandfather paradox and noticed a paragraph on the so-called <a href="http://en.wikipedia.org/wiki/Grandfather_paradox#Huggins_Displacement_Theory" rel="nofollow">Huggins Displacement Theory</a>. I haven't been able to find the source although I assume it... | g16487 | [
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<p>Consider Euler equation for continuum body:</p>
<p>$$\frac{\partial u^i}{\partial t}+\mathbf u\cdot \nabla u^i=- \frac{1}{\rho} \frac{\partial p}{\partial x^i} $$</p>
<p>where $\rho$ is the mass density, $p$ is the pressure and $\mathbf u (t, \mathbf x)$ is the velocity field.
Under the effect of a boost $(t=t',R... | g16488 | [
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<p>Consider the simplistic case of two identical mass particles colliding elastically with the second particle initially stationary and the first particle travelling with energy $E$. By conservation of 4-momentum we have:</p>
<p>$$p_{1}^{\mu}+p_{2}^{\mu}=p_{1}'^{\mu}+p_{2}'^{\mu}$$</p>
<p>Taking the inner product of ... | g16489 | [
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<p>This is something I have wondered for a long time. Why are some materials like steel, diamond, and even light materials like graphene stronger than others? Is it due to the strength of the electromagnetic/static fields that repel two binding atoms? Or is it something else?</p> | g16490 | [
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<p>I understand that photons, even when traveling at the speed of light, cannot escape the event horizon of a black hole. Are gravitons and other virtual particles traveling at the speed of light also confined by event horizons?</p>
<p>If so, it seems that the gravitational field created by the black hole would resul... | g16491 | [
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<p><strong>Context</strong>: Solid state state physics, lattice dynamics.</p>
<p><strong>Question</strong>: I'd like to derive the condition for the wave vector $\boldsymbol{q}$ in order for the lattice to be periodic and infinite. My lecture notes state that the condition is $q_i = \frac{n_i}{N^{1/3}}$, where $n_i$ t... | g16492 | [
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<p>Since neutrons have no electric charge will an anti-neutron annihilate when it comes into contact with a regular neutron as protons and anti-protons do? if so what causes it to annihilate?</p> | g16493 | [
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<p>My question is the following:</p>
<p><strong>What causes graphite to have either a cubic lattice structure or a hexagonal lattice structure? Does it depend on how it is grown? Or is it a random process?</strong></p>
<p>I would also like to know if anyone has any good reading on the solid state physics of graphite.... | g16494 | [
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<p><img src="http://i.stack.imgur.com/vMfu0.png" alt="enter image description here"></p>
<blockquote>
<p><em>A small particle of mass $m$ is atop of a semi-sphere as shown in the figure. A little push was given to the particle. Prove that the particle will leave the spherical surface at a height of (2/3)$R$.</em></p... | g16495 | [
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<p>I am interested in trying to understand the meaning of the integral of power with respect to distance.</p>
<p>In the case of force, we have the two formulae: $\int F \, \operatorname{d}\!t = \Delta p$ and $\int F \, \operatorname{d}\!x = \Delta E_k$.</p>
<p>I understand that power is closely linked to time and wor... | g16496 | [
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<p>Some green tea requires to pour water at 70°C. I have no thermal sensor or kettle with adjustable temperature with me. </p>
<p>Do you know a way to get water at roughly 70°C like “boil water and wait for <em>x</em> minutes” or “mix <em>x</em> part of boiling water with 1-<em>x</em> part of fresh water” ?</p> | g16497 | [
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<p><a href="http://www.fisme.uu.nl/nno/opgaven/bestanden/Ronde1-Theorie-2009.pdf" rel="nofollow">http://www.fisme.uu.nl/nno/opgaven/bestanden/Ronde1-Theorie-2009.pdf</a>, question 5: </p>
<p><img src="http://i.stack.imgur.com/1kNED.png" alt="enter image description here"></p>
<blockquote>
<p>You have to calculate ... | g16498 | [
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<p>I read about an order paramater that describes a Bose-Einstein condensate. But I don't understand, the classification into "scalar" condensate and "spinor" one. Is it linked with spin of atoms that take part in condensation? Or is it a property of the condensate?</p>
<p>Does anyone have a good explanation? </p> | g16499 | [
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<p>Early in <a href="http://susy2013.ictp.it/video/05_Friday/2013_08_30_Arkani-Hamed_4-3.html">this talk</a> by Nima Arkani-Hamed, he describes what locality means for scattering amplitudes. "Locality tells you that the only poles in the scattering amplitude occur when the sum of a subset of the momenta of the particl... | g16500 | [
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<p>By using <a href="http://en.wikipedia.org/wiki/Dyson_series" rel="nofollow">Dyson series</a> for the representation of the $S$-matrix, it's expression can be written in a form
$$
\hat {S}(\infty , -\infty) = \sum_{n = 0}^{\infty}\frac{(-i)^{n}}{n!}\int \limits_{-\infty}^{\infty}d^{4}x_{1}...\int \limits_{-\infty}^{\... | g16501 | [
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<p>I'm not sure this is the good place to ask those questions. Sorry if it isn't.</p>
<p>Are there studies that evaluated the resistance of buildings against tsunami ? What kind of buildings could manage a tsunami with waves of 30 meters ? or a mega tsunami with waves of 100 meters ?</p>
<p>Are underground buildings ... | g16502 | [
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<p>Suppose there's a box with one face cold, and the opposite face hot. So when the air molecules hit the cooler face, it will transfer its momentum and energy to the wall, bouncing back with less momentum. And when molecules hit the hotter face, it will bounce back faster. And the hotter side will be hit more frequent... | g16503 | [
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<p>I was told that objects with the same mass but different sizes (or densities) will have a different gravitational pull. Is this true? If so, why?</p> | g16504 | [
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<p>I have a past exam question that I am stuck on.</p>
<blockquote>
<p>$200$m$^3/s$ of air is entering a shaft of $5m$ diameter, the density is $1.18$kg/m$^3$, and I have shock loss of factor $X=.5$</p>
</blockquote>
<p>I want static, total and velocity pressure at the starting point.</p>
<p>Now I know that Shock ... | g16505 | [
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<p>How is it possible to have negative mass for negative mass means something that has less mass even than nothing ? Does nothing has mass? And how is nothing a reference.</p> | g343 | [
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<p>I have recently watched a video about a powerful Octa-copter that uses 30,000 Volt brushless motors to propell, the batteries however look quite small about a 19v laptop battery. How is the voltage increased to suffice the voltage requirements? where does the extra electrical energy come from or what is the tradeoff... | g16506 | [
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0.048... |
<p>If the speed of an electromagnetic wave in a particular medium is such that $v = c$, the speed of light, does this mean that the permeability $\mu = \mu_0$, i.e. that of a vacuum and the index of refraction is also $n = \frac{c}{v} = 1$? Also $\epsilon = \epsilon_0$?</p> | g16507 | [
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... |
<p>According to a <a href="http://www.cambridge-news.co.uk/Home/Aliens-could-become-part-of-grand-design-07092012.htm">recently published article</a>, a <a href="http://en.wikipedia.org/wiki/Martin_Rees,_Baron_Rees_of_Ludlow">well-established Cambridge astrophysicist</a> stated that:</p>
<blockquote>
<p>the “origin ... | g16508 | [
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0.03235619515180588,
0.09910213202238083,
0.015... |
<p>Do temporarily accelerated particles experience the <a href="http://en.wikipedia.org/wiki/Unruh_effect" rel="nofollow">Unruh effect</a>?
I think, they don't, because they don't see an apparent event horizon.</p>
<p>On the other hand, if the duration of the acceleration is long enough, this case should be approximat... | g16509 | [
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<p>A lot of known quantum gates are in the Pauli group (I,X,Z,Y) or in the Clifford group (H,P,Cnot). I need examples of the quantum gates that aren't in this groups. Also, are there are matlab functions to check if a quantum gate (2x2 or 4x4) is in any of these groups? Or maybe there are matlab routines that generate ... | g16510 | [
-0.01371265109628439,
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<p>I first recall the Dirac's quantization rule, derived under the hypothesis that there would exit somewhere a magnetic charge: $\frac{gq}{4\pi} = \frac{n\hbar}{2} $ with $n$ natural.</p>
<p>I am wondering how the quantization of electric charge can be deduced from it. The quantization of the product $gq$ is certainl... | g16511 | [
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... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/27847/why-is-there-a-frac-1-2-in-frac-1-2-mv2">Why is there a $\frac 1 2$ in $\frac 1 2 mv^2$?</a> </p>
</blockquote>
<p>Hèllo, I have a question about kinetic energy formula.</p>
<p>As you know, in kin... | g501 | [
0.07282515615224838,
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0.023045282810926437,
0.017651... |
<p>Does anybody give a good textbook description of a quantum computer algorithm and how its different from an ordinary algorithm?</p> | g16512 | [
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<p>The second postulate of Special Relativity states:</p>
<blockquote>
<p>The speed of light in a vacuum is the same for all observers,
regardless of their motion relative to the source.</p>
</blockquote>
<p>Now imagine the observer that is looking at the light which is traveling away from him in a direction he i... | g16513 | [
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0.017... |
<p>Ok this is a really silly question, but I was really curious as to why this wouldnt work. I'm just starting my electricity and magnetism course, so I really dont know much about electricity. I know this is not possible, but why?
<img src="http://i.stack.imgur.com/k2HD5.jpg" alt="alt text"></p> | g16514 | [
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<p>The Standard Model gives non-zero mass to the electron via the coupling to the Higgs field. Issues of renormalizability aside, this is fundamentally unrelated to the fact that the electron couples to the EM field. However, if the Higgs mechanism did not operate - that is, if there were no vacuum symmetry breaking, t... | g16515 | [
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<blockquote>
<p>Two 60W-lightbulbs are connected on 220 V AC-voltage - how much electric power is spent by each lightbulb?</p>
</blockquote>
<p>There are two scenarios:</p>
<p>In one, these two lighbulbs are connected serially, and in the other parallelly. The trouble is, no resistance value is given, so I don't kn... | g16516 | [
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... |
<p>Did some of the aplha particles back trace their path after hitting the gold foil ? (Turn by 180 degrees.)</p>
<p>If so, how were they detected ?</p> | g16517 | [
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<ol>
<li><p>I understand that star is in Plasma state (all nucleus and electrons are not bound to each other and moving around freely)</p></li>
<li><p>Photon is emitted when an excited electron moves back to lower orbit.</p></li>
<li><p>So in a star if electrons are not in any orbit then how can photons be produced?</p... | g16518 | [
-0.011869595386087894,
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-0.... |
<p>Some time ago, I read something like this about the issue of "a final theory" in Physics:</p>
<p>"Concerning the physical laws, we have several positions as scientists</p>
<ol>
<li><p>There are no fundamental physical laws. At the most elementary level, the Universe/Multiverse is essentially chaotic and anarchical... | g16519 | [
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<p>In the undergraduate text of physics, the equation for velocity and displacement at constant acceleration are given in scalar form. For example, my text reads</p>
<p>$$v^2 = v_0^2 + 2a(x-x_0)$$</p>
<p>But today, I am reading another text which gives the vector form for displacement. I am trying to write above equa... | g16520 | [
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0.0583561435341835,
-0.01556... |
<p>I have recently studied <a href="http://en.wikipedia.org/wiki/Fourier_transform" rel="nofollow">Fourier</a> and Laplace transformation in maths. I wanted to understand the utility in physics with some examples that requires this change in dimension and the reason why. </p> | g16521 | [
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<p>I would like to explore some ideas with different geometries exchanging energy mainly by radiation.
This means solving Laplace equation for the steady state.
However the boundary conditions are always Neumann's because the only constraints are fluxes. After many questions and attempts, I realized that Mathematica ca... | g16522 | [
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0.015... |
<p>The dynamics of a type of physical system I am currently working on are modeled in most of the literature by replacing the moving parts of that system with an equivalent set of pendulums. Parameters and initial conditions for this approximate pendulum model are chosen such that the total mass and the center of mass ... | g16523 | [
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0.013713689520955086,
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0.011436530388891697,
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... |
<p>In the context of particle diffusion, I am trying to understand the equations that describe Brownian motion as a macroscopic process.</p>
<p>Assume $N(x,t)$ is a number concentration and $D$ is a diffusion constant, then we can write:</p>
<p>$$\frac{\partial N(x,t)}{\partial t} = D \frac{\partial^2}{\partial x^2} ... | g16524 | [
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0.01... |
<p>I know this is a basic question, but question:</p>
<p>A rock is connected to one end of string and is in circular motion with the center being the other end of the string. Now the string gets released at some point. How do we know the direction in which the rock is going to fly?</p> | g16525 | [
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<p>I'm in the process of working on a physics related game. I'm looking to find the maximum velocity of an object given it's mass and the force acting on it when it is traveling horizontally. I believe there must be a method of calculating this but I'm unaware of it. Is there a formula for this scenario? I'm unawar... | g16526 | [
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0.06251005828380585,
0.00712... |
<p>Suppose I know that Selenium has electron configuration $[Ar] 4s^2 3d^{10} 4p^4$.</p>
<p>How can I use this information to then come to the conclusion that its possible oxidation states are 6, 4, 2, 1 and -2?</p>
<p>I understand the 6: Give up all s electrons to reach $Ar$ configuration
I also understand the -2: O... | g16527 | [
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0.... |
<p>In Feynmans book, "Quantum mechanics and Path Integrals" he writes in the conclusions (chapter 12-10)</p>
<blockquote>
<p>With regards to quantum mechanics, path integrals suffer most grievously from a serious defect. They do not permit a discussion of spin operators or other such operators in a simple and lucid ... | g16528 | [
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0.0... |
<p>Just a quick question, </p>
<p>When a force on an object is equal to its static coefficient * normal force , would the object move or would it stay stationary? Or does the force always need to be greater than this value for the object to move?</p>
<p>My guess is that it need to be greater but im not completely cer... | g16529 | [
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... |
<p>Static electricity is caused by the transfer of electrons between substances right? For example, take a balloon and your hair. Both are stable and electrically neutral. So why would electrons jump from the balloon to your hair?</p> | g16530 | [
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<p>As of recent, I've been doing a bit of self education in GR, equipped with a working knowledge of the key elements of the differential geometry in GR, and in looking at the Einstein-Rosen bridge, <img src="http://i.stack.imgur.com/bMT6L.jpg" alt="Einstein-Rosen Bridge"></p>
<p>I see that geometrically it is a hyper... | g16531 | [
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<p>I am trying to understand where the Boltzmann distribution comes from. I recently learned some interesting things of which my interpretation follows below. Did I interpret correctly? If so, is this all there is to it, or is this only part of the story?</p>
<p>When sampling coordinates in a high-dimensional Euclidea... | g16532 | [
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<p>I'm having some trouble trying to find the irreversible work done by a perfect gas when expanding. I know that the reversible work is greater than the irreversible one, but how can I find the irreversible work for an isothermal process?</p>
<p>The exercise asks me to find the irreversible work for the expansion of ... | g16533 | [
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<p>Cars, like sedans, with slanted rear windows never seem to have windshield wipers on them. On the other hand cars, like mini-vans, with vertical rear windows generally do have windshield wipers on them. Yet it seems to me that the vertical rear windows would need them less than the slanted windows. Is my intuitio... | g16534 | [
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<p>In an essay I am reading on celestial mechanics the equations of motion for a 2 body problem is given as:</p>
<p>$$\mathbf{r}''=\nabla(\frac{\mu}{r})=-\frac{\mu \mathbf{r}}{r^3}$$</p>
<p>Fine. Then it says the "associated scalar equation" is:</p>
<p>$$r''=-\frac{\mu}{r^2}+\frac{c^2}{r^3}$$</p>
<p>I've never hea... | g16535 | [
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0.025068... |
<p>How does temperature affect the specific optical rotation of sugar solution at constant concentration and why?
If, for example, the temperature is increased, will the optical rotation for a given path length and concentration increase or decrease, and why?</p> | g16536 | [
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0.05925631523132324,
-0.0... |
<p>How do you define a <a href="http://www.google.com/search?as_q=non+perturbative+qft" rel="nofollow">non-perturbative Quantum field theory</a>. What does it mean? I was just digging around some math about the meaning of $Z_1$, and such in terms of probabilities. It turns out these and associated counter terms are der... | g16537 | [
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... |
<p>could anyone show me the first couple of steps in taking the trace of something like this, im not sure how to start.</p>
<p>'Tr[$\gamma($$\gamma k + $$\gamma p + $$\gamma q + m) $$\gamma ($$\gamma k + $$\gamma p+ $m)]'</p> | g16538 | [
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<p>When one defines the path integral propagator, there is the need to normalize the propagator (since it would give you a probability density). There are two formulas which are used.</p>
<p>1) <strong>Original (v1+v2)</strong>: The first formula (which I can intuitively agree with) says that:</p>
<p>$$\tag{1} \int_{... | g16539 | [
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0.012065730057656765,
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0.03801529109477997,
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0.0434... |
<p>Something very basic which I don't get no matter how much I read.</p>
<ul>
<li>circuit A: only a resistor and power supply - the resistor will burn.</li>
<li>circuit B: only a LED and power supply - the LED will damaged.</li>
</ul>
<p>As far as I understand these are the facts.</p>
<ul>
<li>in circuit B LED will ... | g16540 | [
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<p>in one MOOC I am taking, the professor had a slide stating "when squeezed into a narrow space wave is amplified". I am not sure I understand what he meant by that, and I am trying to think into terms of wave equations. Could anyone explain it to me? Thank you.</p> | g16541 | [
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<p>Let's have the action
$$
S = \int (\partial_{\mu}h^{\mu \sigma}\partial^{\nu}h_{\nu \sigma} - \Lambda h^{\mu \nu}T_{\mu \nu}) d^{4}x.
$$
For definiteness,
$$
h_{\mu \nu} = h_{\nu \mu} , \quad T_{\mu \nu} = T_{\nu \mu} \neq f(h_{\mu \nu}), \quad h^{\mu \nu} = \eta^{\mu \alpha}\eta^{\nu \beta}h_{\alpha \beta}, \quad ... | g16542 | [
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<p>Recently I was told of a job offer to analyse astronomical data. The job offer states that they want somebody with knowledge of astronomical data analysis software and it will be a plus somebody who has experience with programming languages, giving as examples: IDL and Fortran.
My first question is:</p>
<ol>
<li><p... | g16543 | [
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<p>I'm interested in giving The Geometry of Physics a read, and I was wondering what the mathematical and (more importantly) physical prerequisites are. My background is a bit stronger on the mathematical side, and I'm worried that if heavy (or even moderate) exposure to physics is required that I'll miss out on a lot... | g201 | [
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<p>Imagine I have two plates that form a capacitor, so the magnitude of the charge in each plate is, let's say, $Q$. So, the force, in respect to the distance $d$, is gonna be:
$$F(d) = k\frac{Q^2}{d^2}$$
So, in order to calculate the <strong>energy</strong> stored in the capacitor, since it's equal the work needed to ... | g16544 | [
0.04141131415963173,
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<p>thanks for any help.</p>
<p>I'm trying to show that in a 2body problem, angular momentum is conserved given that $\dfrac{dp}{dt}=\dfrac{-GMm(rv)}{r³}$, where p is momentum, t time, G gravitational constant, M mass of 1 object, m mass of the other, (rv) is the vector between them and r is the magnitude of the vector... | g478 | [
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<p>The Casmir force is explained by wave exclusion: Two parallel plates create a reduction in the possible modes of vacuum oscillations between them, reducing the energy of the vacuum. Since we define vacuum far from any plates as "zero" energy, a reduction of energy creates a negative energy. However, these sources al... | g16545 | [
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<p>I know that silicon and even black plastic bags are transparent to infrared light. What about light-colored silicone polymers (take white or green colors)? Are they transparent to infrared light too? And why?</p> | g16546 | [
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<p>The Feynman propagator is non-vanishing outside the light cone, but still manages to be in accord with causality. How is this achieved? What does the $i\epsilon$-prescription have to do with this?</p> | g16547 | [
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<p>My questions mostly concern the history of physics. Who found the formula for kinetic energy
$E_k =\frac{1}{2}mv^{2}$
and how was this formula actually discovered? I've recently watched Leonard Susskind's lecture where he proves that if you define kinetic and potential energy in this way, then you can show that the... | g16548 | [
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<p>We know that in an inelastic collision that total momentum of the system before collision equals the total momentum after collision. But total kinetic energy before collision is not equal to total kinetic energy after collision. </p>
<p>How is possible given that the formula of momentum is $mv$ and the formula of k... | g16549 | [
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<p>When I jump out of a plane and begin to fall and accelerate, I feel no force whatsoever. When I stand on the earth, I feel only the force of the Earth pushing me outwards.</p>
<p>I contend the accelerating condition is a natural state brought about by a local curvature of space towards the center of mass of the Ea... | g16550 | [
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0.03512... |
<p>I am trying to understand the effects of gravity in the Cosmos without complications of Dark Matter/Dark energy issues. So my question is, assuming that a galaxy (for example, the Milky Way) does not contain any dark matter, does anyone know the equation that would explain how long it would take for the galaxy to c... | g16551 | [
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0.... |
<p>I have got a very interesting question. A car is driving this way on the picture down. In the looping is a missing part. The radius of the looping is r = 40cm. The car starts at the height h = 3r. If the car jumps from the interruption of the looping it flys and lands an the other side of the interruption and goes a... | g16552 | [
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0.01664106734097004,
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0.02122... |
<p>Some time ago, I happened to have found one problem:</p>
<blockquote>
<p>The refractive index of the planet's atmosphere decreases with height above the surface under the following law: </p>
<p>$$n=n_0-\alpha h$$ </p>
<p>with condition $\frac{\alpha h}{n_0}\ll1$</p>
<p>Find the altitude $H$ abov... | g16553 | [
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0.01032425370067358,
0.023340292274951935,
0.06693760305643082,
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0.00523... |
<p>Ampère's law states that</p>
<p>$$ \nabla \times \mathbf{B} = \mu_0 \mathbf{J} \tag{1}$$</p>
<p>Simultaneously, from Ohm's law, we know that</p>
<p>$$\mathbf{J}=\sigma\left(\mathbf{E}+\mathbf{u}\times\mathbf{B}\right)\tag{2}$$</p>
<p>When equating both currents $\mathbf{J}$, and applying Faraday's law, and knowi... | g16554 | [
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<p>I would like to understand how to create an active noise canceling system to reduce the noise coming from a street road bump. The advantage is that the area the noise is coming from is very small.</p> | g16555 | [
0.06440507620573044,
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<p>If, for some reason, the sun were to suddenly disappear altogether, I would like to know the following:</p>
<ul>
<li>would we "feel" it first (i.e. being thrown into outer space due to no longer having anything to orbit);</li>
<li>would we see the sun disappear at precisely the same moment that we "feel" it?; or</l... | g4 | [
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0.04137482... |
<p>What is the electrical potential difference and why we have to talk about a difference and not about the electrical potential itself? What is the electrical potential difference in practical terms (can you explain it using concrete example?)
Please help me with a very clear explanation. (sorry for the numerous quest... | g16556 | [
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<p>This is an extract from the astrophysics chapter in my book:</p>
<blockquote>
<p>Hydrogen atoms fuse to form helium. At the same time, lots of of gamma photons and neutrinos are produced. The photons take thousands of years to "fight" their way to the surface of the Sun, but then escape into space as visible or ... | g16557 | [
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0.011... |
<p>I am new to this site. Please help me figure out this problem.</p>
<p>Is it possible to lift oneself like shown in schematic?</p>
<p>Waiting for good suggestions.</p>
<p>Chirag<img src="http://i.stack.imgur.com/W0jHx.jpg" alt="Reference Schematic"></p> | g502 | [
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0.013996030203998089,
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<p>When observing clouds from a geostationary satellite, they appear displaced because of the parallax effect. The satellite looks at the clouds "at an angle" and it projects them on a point of the earth that is not exactly "under" the cloud.</p>
<p>This image shows the Normalized Cloud Offset as a function of the Ang... | g16558 | [
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<p>I've heard in a lecture that a star like the sun would burn 3% of its Hydrogen before expiring.</p>
<p>I would have thought it would be much more.</p> | g16559 | [
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<p>Suppose for example that a person like me likes his water in-between. A bit colder than the room temperature but not very cold. If you have a water dispenser that pours rtp water and cold water, which one to pour in the cup first to ensure the temperature I'm looking for? </p>
<p>I was just thinking of it as I was ... | g16560 | [
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... |
<p>A standard phrase in popular discussions of the Higgs boson is that "it gives particles mass". To what extent is this a reasonable, pop-science, level of description of the Higgs boson and it's relationship to particles' masses?</p>
<p>Is this phrasing completely misleading?
If not, what would be the next level dow... | g16561 | [
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0.0211... |
<p>I know someone that wants to buy a 60cm (1.5 inch) refractor and I thought about recommending what to look at the <a href="http://en.wikipedia.org/wiki/Messier_object" rel="nofollow">Messier objects</a>. And I was wondering, can he see all these objects with that refractor ? what about with a 10x magnification binoc... | g16562 | [
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0.062207117676734924,
... |
<p>If we fall into <a href="http://en.wikipedia.org/wiki/Saturn">Saturn</a> or <a href="http://en.wikipedia.org/wiki/Jupiter">Jupiter</a>, would we pass through it until we hit the nucleus?</p>
<p>Or would we hit the surface and stop there?</p> | g16563 | [
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-0.... |
<p>The reason why two independent bulbs cannot be used to create the young's two slit interference pattern is that the phase difference between those two sources varies very rapidly and therefore, the interference pattern cannot be sustained and shifts rapidly producing general illuminance. But by using a single source... | g16564 | [
-0.01937904953956604,
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<p>I'm confused between them. Can someone explain the difference between them? Is $\vec H$ field ONLY relevant during magnetization or demagnetization? $\vec H$ is just that value needed to magnetize/demagnetize or what is it useful for? </p>
<p>Is $\vec H$ only relevant to solenoids or magnets as well? Does it make s... | g16565 | [
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<p>I read that quantum decoherence is subjective, in the sense that two observers may not have the same "environment" and after each one has traced over those degrees of freedom they will end up with a different density matrix for the couple system-apparatus. </p>
<p>I kind of understand the idea, but has an example o... | g16566 | [
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<p>Neutrino is one of the most mysterious particles in todays physics. Even when values of some parameters like for example mass associated with it are not known (or there is great range of possible values), its existence is not questioned. There is a field of research named neutrino astronomy. Because neutrino interac... | g16567 | [
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<p><a href="http://en.wikipedia.org/wiki/Waterskiing" rel="nofollow">Water skiing</a> is a sport where an individual is pulled behind a boat or a cable ski installation on a body of water, skimming the surface.</p>
<p>Consider an idealized case where the boat is moving at a constant velocity $\overrightarrow v_0=\text... | g16568 | [
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<p>What would the result of a vertical variation of the Michelson-Morley experiment be? I.e., if one were to compare light traveling along a horizontal arm with light traveling along a vertical arm (perpendicular to the surface of the Earth), what would the result be?</p>
<p>My understanding is that light traveling a... | g16569 | [
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<p>IN this <a href="http://arxiv.org/abs/0802.3525" rel="nofollow">article</a> the author written a nonlinear equation as
$$-\frac{\partial^2 \phi}{\partial t^2}+ \nabla \phi= \phi+ \sum_{k=2}^\infty g_k \phi^k$$</p>
<p>They have scaled the time as,
$$\tau=\omega(\varepsilon) t$$
they have said in equation (8) is $\o... | g16570 | [
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<p>I've been working on this problem for a while now, but I still don't know how to solve it. It involves 2D kinematics, which aren't in themselves hard, but this one threw me for a loop.</p>
<p>A ball is thrown straight up from the edge of the roof of a building. A second ball is dropped from the roof 1.00 seconds la... | g16571 | [
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0.025244459... |
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