question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Consider this figure
<img src="http://i.stack.imgur.com/epLm6.jpg" alt="A charge $e$ moves with certain velocity $\mathbf v_e$"></p>
<p>Now, when I measure a field produced by the charge $e$ at the point $\mathbf r$, at the time $t=t_1$, it means that the charge sent the signal field at the time $t=t_r$, where $t_1... | g10838 | [
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<p>I am trying to find a book on electromagnetism for mathematician (so it has to be rigorous).
Preferably a book that extensively uses Stoke's theorem for Maxwell's equations
(unlike other books that on point source charge, they take Stoke's theorem on
$B-\{0\}$ with $B$ being closed ball of radius 1, but this does no... | g10839 | [
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<p>The traditional physics career is an academic job at some university, with the eventual goal of becoming a tenured professor. Is it possible for a mostly self-educated outsider working outside academia to come up with significant results in physics? Let's take significant to mean accepted in a high ranking peer revi... | g10840 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/44967/mass-points-of-a-mass-spring-model">Mass points of a Mass-spring model</a> </p>
</blockquote>
<p>Say I have a spring like the one in the picture below:</p>
<p><img src="http://i.stack.imgur.com/8k... | g350 | [
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<p>$\alpha$ radiation consist of positive charged helium nuclei, $\beta$ radiation of negative charged electrons. So why don't the $\alpha$ particles take those electrons to get neutral?</p> | g10841 | [
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<p>I am spending some time reading about Bose-Einstein condensation. I want to know if it is possible to use atom lasers to realize the kind of holography traditionally associated with nano-fabrication.</p>
<p>Many papers say that the motivation for BEC is the aforementioned holography, but I can't find if they were a... | g10842 | [
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<p>How would you explain string theory to non physicists such as myself? I'm specially interested on how plausible is it and what is needed to successfully prove it?</p> | g10843 | [
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<p>I've been looking for a textbook in classical mechanics that's readily available (like can be found in the library of James Cook University of Townsville, Australia) and full of fully-answered questions in the Lagrangian/Hamiltonian formalisms yet I can't find any. My first port of call was the Schaum's Outlines and... | g12 | [
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<p>I'm trying to understand how to correctly think about a change of reference frames for a conducting rod moving sideways through a uniform magnetic field.</p>
<p>Thinking of the rod in motion through a uniform B field is easy. The Lorentz force explains the charge separation in the rod and I'm fine with that.</p>
... | g10844 | [
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<p>I read in <a href="http://rads.stackoverflow.com/amzn/click/0030839939" rel="nofollow">Ashcroft & Mermin's Solid State text</a> that for the <a href="http://en.wikipedia.org/wiki/Thomas%E2%80%93Fermi_model" rel="nofollow">Thomas-Fermi approximation</a> to be applicable, the external potential needs to be "slowly... | g10845 | [
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<p>Firstly I would like to know if this is valid for every kind of wave, or are there any conditions/exceptions where this is not valid.</p>
<p>But the main question is, is it possible to prove this fact for a general wave intuitively, rather than taking specific waves and deriving equations and showing it?</p> | g351 | [
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<p>In the textbooks that I read (namely Ashcroft/Mermin , Marder, etc.) it seems that a distinction is made between the correlations in electron gas and a Couloumb interaction between the electrons. What is exactly meant by the concept of correlations? How is that connected to the interactions in electron gas, and how ... | g10846 | [
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<p>Consider a body released from a height $h$ and assume a drag force is linearly proportional to the velocity. Then by Newton's Second Law, $$m\mathbf{\dot{v}} = \mathbf{F_g} + \mathbf{F_{drag}} = m\mathbf{g} -\mu \mathbf{v} $$ Take the positive $x$ axis upwards, then we can write $$m \mathbf{\dot{v}} = -mg \hat{x} ... | g10847 | [
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<p>Does <a href="http://en.wikipedia.org/wiki/String_theory">string theory</a> have a notion of vacuum? If yes, what is known about it?</p> | g10848 | [
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<p>Consider the space-time domain Klein-Gordon propagator:</p>
<p>$$G_F(x)=\int\frac{d^4p}{(2\pi)^4}e^{ipx}\frac{1}{p^2-m^2+i\epsilon}$$</p>
<p>I understand this as the amplitude at location $x$ created by a source located at spacetime event $(0,0)$. I also see it as plane waves propagating with momentum $p$ weighted... | g10849 | [
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<p><strong>Review and hystorical background:</strong></p>
<p><a href="http://en.wikipedia.org/wiki/Gravitomagnetism" rel="nofollow">Gravitomagnetism</a> (GM), refers to a set of formal analogies between <strong><em>Maxwell's field equations</em></strong> and an approximation, valid under certain conditions, to the <st... | g10850 | [
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<p>I realise the question of why this sky is blue is considered reasonably often here, one way or another. You can take that knowledge as given. What I'm wondering is, given that the spectrum of Rayleigh scattering goes like $\omega^4$, <em>why is the sky not purple, rather than blue</em>? </p>
<p>I think this is a... | g601 | [
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<p>I have had a question since childhood. Why do we always get circular waves (ripples) in water even when we throw irregularly shaped object in it? </p> | g10851 | [
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<p>I am thinking of a (greatly simplified) computer simulation of a universe that followed something like Newtonian rules. Inside the simulation are A.I.s that are made from those same rules, and can only use those rules interact the world around them. Would there be some fundamental limits on what those A.I.s could ... | g10852 | [
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<p><strong>Context:</strong> There have been a few papers out recently which mention how photosynthesis in plants might have connections to entanglement, or even perhaps that entanglement is causing photosynthetic complexes to capture the sunlight and go through the conversion stages. Here are two papers worth mentioni... | g10853 | [
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<p>This was explained to me many years ago, by a physics teacher, with the following analogy:</p>
<p>"If someone on the beach wants to reach someone else that is in the water, they will try to travel as much as they can on the beach and as little as possible on the water, because this way they will get there faster."<... | g10854 | [
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<p>In odd number of space-time dimensions, the Fermions are not reducible (<em>i.e.</em> do not have left-chiral and right-chiral counterparts).</p>
<p>Does this mean that there is no such thing as 'chiral' anomalies in odd number of space-time dimensions, when these fermions are coupled to gauge fields?</p> | g10855 | [
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<p>A recent joke on the comedy panel show <em>8 out of 10 cats</em> prompted this question. I'm pretty sure the answer's no, but hopefully someone can surprise me.</p>
<p>If you put a person in a balloon, such that the balloon ascended to the upper levels of the atmosphere, is it theoretically possible that an orbiti... | g10856 | [
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<p>In most nuclear fission examples and exercises, the products of a nuclear fission of Uranium-235 are two light nuclei of Krypton and Barium:</p>
<p>$$\mathrm{ _0^1n + U \longmapsto Kr + Ba + energy }$$</p>
<p>Is there some fission reaction that produces more stable nuclei instead of Krypton and Barium?</p>
<p>Ple... | g10857 | [
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<p>This happens in Peskin and Schroeder, <em>An Introduction to QFT,</em> on page 285. They set out to calculate correlation functions for the free <strong>real</strong>-valued Klein-Gordon field $\phi(x)\in \mathbb{R}$. They define a 4D space-time lattice with lattice spacing $\epsilon$, and define</p>
<p>$$\mathcal{... | g10858 | [
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<p>I am on a boat docked at Cape Charles, VA, about 30 or 40 miles from the center of Hurricane Irene. This understandably got me thinking about the force of wind on the boat. Since air friction is proportional to the speed squared (except for some friction types I'm sure someone will be kind enough to remind me of), i... | g10859 | [
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<p>Assume you start with a car at rest. Then you accelerate the car to 100 kilometers per hour. In terms of the energy needed, does it matter how fast you accelerated the car? </p>
<p>In other words, do you need to provide the same amount of energy to accelerate a car from 0 to 100 kilometers per hour whether you do i... | g10860 | [
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<p>I know the flavor and mass eigenstates are different, but are they related? What I mean is, in a process like fusion where electron neutrinos are created, do they start in the 1 mass eigenstate? My knowledge of QFT is nonexistent, so I've never really seen a Neutrino field written out mathematically, so I don't real... | g10861 | [
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<p>My question arises from two ideas that seem to be contradictory. </p>
<p>Idea One: Wheeler's Delayed Choice experiment is an interesting variation of the double slit experiment.</p>
<p>Idea Two: In the "reference frame" for a photon, it is emitted and absorbed in the same instant; it 'experiences' no time.</p>
<p... | g10862 | [
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<p>If we pass current through a gas, like in the discharge tube, the electrons will accelerate in the electric field. The accelerated electrons will collide with gas molecules, and transfer some of their energy to them. Thus, producing gas molecules in the excited state. The excited molecule can come to ground state by... | g10863 | [
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<p>When physicists say energy is conserved, do they mean that energy satisfies the continuity equation:</p>
<p>$$\triangledown \cdot j+\dot{\rho}=0$$</p>
<p>On the internet there is plenty of talk of how the continuity equation applies to conservation of charge, fluid dynamics, and so forth, but I can't find any ment... | g10864 | [
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<p>The inverted pyramid puzzle has the following premises:</p>
<blockquote>
<p>A giant inverted steel pyramid is perfectly balanced on its point.
Any movement of the pyramid will cause it to topple over. Underneath
the pyramid is a $100 bill. How do you remove the bill without
disturbing the pyramid?</p>
</... | g10865 | [
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<p>My new question here: has string theory been analyzed somewhere in the context of various quantization prescriptions formulated in a mathematically sound way? I mean something like geometric quantization, Klauder Quantization, Brownian quantization etc. It is important to know if string theory ever passed through al... | g10866 | [
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<p>This is a question on gauge invariance in quantum mechanics. I do some simple math on a 1D wave-function with periodic boundary conditions, and get that gauge invariance is violated. What am I doing wrong?</p>
<p>Consider one coordinate dimension configured as a ring. The gauge dependent momentum operator can be ... | g10867 | [
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<p>Please please help me out with this. I am trying to find a software/program that I could use the simulate the scattering effect of light when it strikes gas particles moving at supersonic speeds? Please help me as I have no idea what to use. I have googled several searches but I could find nothing. Please help. than... | g10868 | [
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<p>This is a thought I asked myself often, but never did real efforts
to get an answer. Barsmonsters question about number of fans of a
wind turbine made me think of it again</p>
<p>Why do blades of aircraft propellers or wind turbines cover only a small fraction of the area they circle? Propellers of ships or Kapl... | g10869 | [
0.05949058383703232,
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<p>I would like to understand what is meant when one introduces a generator $G(z)$ as the superpartner of the energy-momentum tensor $T(z)$.</p>
<ul>
<li><p>How does one decide that this $G(z)$ should have a "conformal weight" of $\frac{3}{2}$ ?</p></li>
<li><p>How are the following OPEs for it derived ?</p></li>
</ul... | g10870 | [
0.03174520283937454,
0.03778274357318878,
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<p>I have been looking around to figure out how superconductors are made. What ways are there to create a superconductor that don't involve a coolant like liquid nitrogen? Is it possible to cause a material to become a superconductor by running electric current through it? How practical is it to create a superconductor... | g10871 | [
0.05263455584645271,
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0.008503138087689877,
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0.04... |
<p>Electronic aiming systems use automated rangefinders that can sometimes be based on lasers. Obviously a projectile itself will be subject to the Coriolis Force (among others) and deviate from its course slightly and this can be accounted for/calculated. Was doing some work on the accuracy of these when I reached thi... | g10872 | [
0.014559757895767689,
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<p>In the derivation of the Boltzmann distribution they consider a system $A$, enclosed by a diathermal wall in a heat reservoir $R$. Then they calculate the probability that the system $A$ is in an energy state $E_r$, given that the reservoir has a temperature $T$ and energy $E_0$ and the two systems are in thermal eq... | g10873 | [
0.03855067864060402,
0.04095103219151497,
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<p>In Quantum Optics and Quantum Mechanics, the time evolution operator </p>
<p>$$U(t,t_i) = \exp\left[\frac{-i}{\hbar}H(t-t_i)\right]$$ </p>
<p>is used quite a lot. </p>
<p>Suppose $t_i =0$ for simplicity, and say the eigenvalue and eigenvectors of the hamiltionian are $\lambda_i, \left|\lambda_i\right>$.
Now, n... | g10874 | [
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0.015573146753013134,
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<p>I'm trying to determine if going through the trouble of ingesting ice is worth the hassle versus ingesting ice-cold <em>water</em>, but my physics skills are rusty.</p>
<p>If I drink a gram of ice <em>water</em> at ~0C, my body has to heat the water to 37C.</p>
<p><a href="http://en.wikipedia.org/wiki/Heat_capacit... | g10875 | [
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<p>I have a problem set due tomorrow, and the last problem is driving me nuts. Been combing through griffiths trying to find similar examples to no avail, so it'd be greatly appreciated if stackexchange could help me out =)</p>
<p>Suppose that a quantum system has 4 independent states. The unperturbed energy of stat... | g10876 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/27909/why-is-exhaling-more-forceful-than-inhaling">Why is exhaling more forceful than inhaling?</a> </p>
</blockquote>
<p>If I put my hand behind my computer's system block, I can feel a very strong flux... | g659 | [
0.03425988927483559,
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0.020876824855804443,
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0.057... |
<p><a href="http://www.usatoday.com/tech/science/columnists/vergano/story/2012-01-02/international-linear-collider/52324768/1" rel="nofollow">USA Today</a> has an article on Japan's interest as the site for the $10 billion future International Linear Collider. This accelerator will utilize electron/positron collisions ... | g10877 | [
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<p>What happens when two D-branes annihilate? Do we get a radiation of strings?</p>
<p>Thanks in advance</p> | g10878 | [
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0.015169902704656124,
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<p>In Physics ordinary terms often acquire a strange meaning, action is one of them. Most people I talk to about the term action just respond with "its dimension is energy*time". But what is its historial origin?</p>
<p><a href="http://en.wikipedia.org/wiki/Action_(physics)#History">http://en.wikipedia.org/wiki/Action... | g10879 | [
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<p>Has a system where conducting sites can percolate by hopping over/tunnelling through a non-conducting site been described? If so what are the characteristics, and where can I find more details (such as a paper on the subject)?</p>
<p>In the image below, if the edge of a black square touches the edge of another blac... | g10880 | [
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0.021593645215034485,
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<p>In a lot of laymen explanations of general relativity it is implied that the four dimensions of the space-time are equivalent, and we perceive time as different only because it is embedded in our human perception to do so.</p>
<p>My question is: is that really how general relativity treats the 4 dimensions?</p>
<p... | g10881 | [
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0.02584335394203663,
0.022894... |
<p>What direction is the angular momentum of right hand polarized light points to? Is it vertical to its propagating direction? I want to recognize this in quantum theory.</p> | g10882 | [
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0.004342189524322748,
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<p>Light hits a charge coupled element. The wavelength of the light somehow is translated into a color picture. Where can I learn about methods (algorithms) to decompose light hitting a CCD into frequency spectrum? </p> | g10883 | [
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<p>So from learning Band theory, and PN Junction and such, I've learned that photons are created when "holes" are filled in a band, and this is what can create light (Isn't this how LEDs work?)</p>
<p>Anyways, my question is - How come when Electrons move between conduction bands light isn't produced? Or is it and it'... | g10884 | [
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<p>How does a state vector change under an exchange of a boson and a fermion ? That's how is $\Psi_{\alpha,\beta}$ related to $\Psi_{\beta,\alpha}$ where $\alpha$ and $\beta$ are a boson and a fermion respectively?</p> | g10885 | [
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... |
<p><img src="http://i.stack.imgur.com/RbNrA.png" alt="my poor attempt @ FBD..."><img src="http://i.stack.imgur.com/Pd2Sf.png" alt="enter image description here"></p>
<p>I did the FBD, and I found too many variables which are not eliminating...Moreover, I believe this question is based on kinetic and static friction. B... | g10886 | [
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<p><strong>Motivation</strong>: The neutral pion decays to 2 photons ($\pi^0\to\gamma\gamma$) most of the time. For the decay of the neutral to 3 photons ($\pi^0\to 3\gamma$) we have an upper limit on the branching ratio of $3.1 \cdot 10^{-8}$ in the Particle Data Book (2012). The explanation is that this decay would... | g10887 | [
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<p>If <strong>the position of some charge Q is known</strong>, the boundary condition is <strong>u=0</strong> on some parabolic surface, and we <strong>know the image charge has its electric volume of Q'</strong>, then <strong>how can I determine the position of the image charge</strong>?</p>
<p><strong>Same questions... | g10888 | [
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0.006795772351324558,
0.026662107557058334,
0.0... |
<p>My book "Concepts of Physics (Satish K. Gupta)" says: </p>
<blockquote>
<p>The electric field of a charge is the space property by virtue of which the charge modifies the space around itself. As a result, if any charge is brought in the space around the charge, it experiences electrostatic force. <em>It may be p... | g10889 | [
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0.009128489531576633,
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<p>Since gravity is three dimensional why planets are rotating only in one plane around sun.</p> | g231 | [
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<p>For a massless scalar field the equation of motion in a general curved Space time is $\frac{1}{\sqrt{g}}\partial_\mu(\sqrt{g}g^{\mu\nu}\partial_\nu\phi)=0$. Though, in the action, we can by hand include a term $\xi R\phi^2$ as the only possible local, dimensionally correct term which has the physical significance of... | g10890 | [
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<p>My understanding is that QCD has three color charges that are conserved as a result of global SU(3) invariance. What about SU(2) weak? Does it have two types of charges? What I'm getting at is:</p>
<p>U(1) --> 1 type of charge</p>
<p>SU(2) --> ?</p>
<p>SU(3) --> 3 types of charge</p>
<p>Does SU(2) have two types... | g10891 | [
0.053658679127693176,
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... |
<p>I want to prove that the reflectancy of an Electromagnetic wave in a medium with $\sigma$ $\ne$ 0 is:</p>
<p>\begin{align*}
R_{\|}=R_{\perp}=\frac{(n-1)^2+k^2}{(n+1)^2+k^2}
\end{align*}</p>
<p>any advice, please?</p> | g10892 | [
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<p>I've got several questions regarding the so called second quantization of the Schroedinger equation.</p>
<p>My professor introduced the field operators for the Schroedinger field by simply stating them as follows:
$$
\hat\psi (\vec{r},\xi)=\sum\limits _i \psi_i(\vec{r},\xi) \hat a_i\\
\hat\psi^\dagger (\vec{r},\xi)... | g10893 | [
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<p>Note: My question is duplicate of <a href="http://physics.stackexchange.com/questions/16561/why-doesnt-water-come-out-of-tap-faucet-at-high-pressure-when-i-turn-it-on">Why doesn't water come out of tap/faucet at high pressure when I turn it on?</a>. None of the answers given there explains how the continuity equatio... | g10894 | [
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0.03319062292575836,
-0.03180569037795067,
0.01531299203634262,
-0.0072756060399115086,
0.0... |
<p>I read about the geometrical limit of wave theory. The source from where I read had a slightly different explanation to provide than <a href="http://physics.stackexchange.com/questions/65237/if-light-rays-obey-to-the-wave-equation-why-can-they-be-thought-as-straight-lin">here</a>(The more rigorous answer is too comp... | g10895 | [
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-0.04453161358833313,
0.011927628889679909,
0.013331474736332893,
0.05330200865864754,
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<p>If the application of the <a href="http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_statistics" rel="nofollow">Bose-Einstein distribution</a> is in <a href="http://en.wikipedia.org/wiki/Black-body_radiation" rel="nofollow">blackbody radiation</a>, then what is <a href="http://en.wikipedia.org/wiki/Planck%27s_law" ... | g10896 | [
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<p>I work currently on the calculation of magnetic resistance for a air-gap of an electrical machine. For this I am using conformal transformations. I am doing this on a 2D slice. As the machine is obviously round I first use a logarithmic transformation to convert it to a polygonal shape. After that I use a Schwarz-Ch... | g10897 | [
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<p>To understand the phenomenon of diffraction as an interference effects of several dipole oscillators (like in case of several symmetrical, not sawtooth, scratches in a diffraction grating), we consider a linear array of $N$ particles, each of which acts as a source of EM wave, and their interference produces the dif... | g10898 | [
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<p>Currently I am stuck, trying to derive the self-inductance of a long wire. According to literature it should be </p>
<p>$$L=\frac{\mu_r\mu_0l}{8\pi}$$</p>
<p>and in literature its derived by looking at the energy of the magnetic field. I tried to derive this formula via the magnetic flux and I am getting $4\pi$ in... | g10899 | [
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<p>Here is the sketch:</p>
<p><img src="http://i.stack.imgur.com/0s1is.jpg" alt="Sketch for the problem"></p>
<p>The sketch is supposed to be side-view of the path of the object.</p>
<p>The following values are known:</p>
<ul>
<li>$r$ - radius of the circle that describes the path AB of the object</li>
<li>$a$ - an... | g591 | [
0.07083907723426819,
0.030009333044290543,
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<p>As stated according to Newton laws of gravity, every object with mass attracts all other object with a force which produces acceleration. Basically there are several forces in the universe which affects our planet as well.</p>
<p>My question: can an inertial frame (which has net force zero) can exist in these cond... | g10900 | [
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0.0082885... |
<p>Consider a metal surface which is being continuously irradiated with a light with frequency greater than the threshold frequency. After some time, all the electrons should have been emitted from the atoms of the metal on the surface. </p>
<p>Now since an electron has been removed from the valence shell, the ionisat... | g10901 | [
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<p>What the theta in schwinger function and what is theta formula?</p>
<p>is theta formula general solution of klein gordon equation? if so, what is its coefficient of $\exp\left(-ipx\right)$?</p> | g10902 | [
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<p>It is known that when a beam of lineary polarized light falls perpendicularly on a linear polarizer, the intensity of polarization changes according to Malus' law and the direction of polarization changes as cosine of angle between polarization vector and polarizer vector.</p>
<p>My question is: is anyone familiar ... | g10903 | [
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<p>I have stress tensors direct product of the form $T^{ab}(x)T^{cd}(y)$. I want to write this in terms of a tensor $I^{abcd}$ in the form.
$T^{ab}(x)T^{cd}(y)= I^{abcd}$.
This is like decomposing the direct product of the Rank 2 symmetric tensor into its irreps. How can I do a decomposition like this for $T\otimes T\o... | g10904 | [
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<p>I am attempting to settle a friendly bet. Would a pendulum swing indefinitely in a hypothetical vacuum (i.e. no air resistance) having a hypothetical frictionless bearing (i.e. no energy lost due to friction) assuming the following</p>
<ol>
<li><p>The frictionless vacuum is on Earth (9.8 m/s^2).</p></li>
<li><p>Th... | g301 | [
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<p>I just have a question concerning the third law of thermodynamics. </p>
<p>The third law describes that the entropy should be a well defined constant if the system reaches the ground state which depends only on the temperature. Beside this fact we now that the temperature is independent on the measurement system we... | g10905 | [
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<p>I have to develop a physical model for a certain type of biological oscillation that can be built upon periodic sequences.</p>
<p>From earlier <a href="http://en.wikipedia.org/wiki/Periodic_sequence" rel="nofollow">questions</a> I know that any periodic sequence (containing $0$s and $1$s) can be developed based on ... | g10906 | [
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<p>Given a charge distribution $\rho(\vec{r})$ where $\vec{r}$ is the position vector and that $\rho$ is a function of only $|x|$, Why is it that the corresponding electric field $E$ is necessarily of the form $(E(x),0,0)$ and $E(x)$ is antisymmetric ? </p> | g10907 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/25254/why-does-the-moon-sometimes-appear-giant-and-a-orange-red-color-near-the-horizon">Why does the moon sometimes appear giant and a orange red color near the horizon?</a> </p>
</blockquote>
<p>I made ... | g106 | [
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0.03... |
<p>I understand that a 1.5 V cell will not deliver as much energy per coulomb as a 150 V power supply will.</p>
<p>What I do not understand is that why it is so.</p>
<p>I am digressing now. If we place two point charges at a distance r, then to increase the force between them, we need to increase their charges. This... | g10908 | [
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<p>Conventional physics as is usually presented in textbooks deals with the evolution of states in phase space parameterized by sharp instances in time, a real parameter. However, quantum fluctuations seem to suggest we have to smear a little over time to average over vacuum fluctuations and the like. What implications... | g10909 | [
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<p>For infinisesimal bispinor transformations we have
$$
\delta \Psi = \frac{1}{2}\omega^{\mu \nu}\eta_{\mu \nu}\Psi , \quad \delta \bar {\Psi} = -\frac{1}{2}\omega^{\mu \nu}\bar {\Psi}\eta_{\mu \nu}, \quad \eta_{\mu \nu} = -\frac{1}{4}(\gamma_{\mu}\gamma_{\nu} - \gamma_{\nu}\gamma_{\mu}). \qquad (.1)
$$
Then, by comp... | g10910 | [
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<p>I'm quoting the definition of Resultant of two forces acting in the same line from the book "A FIRST COURSE IN PHYSICS" one of whose authors is Robert Andrews Millikan:</p>
<blockquote>
<p><em>The resultant of two forces is defined as that single force which will produce the same effect upon a body as is produced... | g10911 | [
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<p>This is a question I would like to have an explanation with: It's in <a href="http://www.fisme.uu.nl/nno/opgaven/bestanden/Ronde1-Theorie-2013.pdf" rel="nofollow">this PDF</a>, question 9. </p>
<p><img src="http://i.stack.imgur.com/euGXK.png" alt="circuit"></p>
<blockquote>
<p>In that circuit, if switch 1 is clo... | g10912 | [
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0.0082... |
<p>How do you find a metric tensor given a coordinate transformation, $(t', x', y', z') \rightarrow (t, x, y, z)$? Our textbook gives a somewhat vague example as it skips some steps making it difficult to understand. What's the general definition for a metric tensor of a given transformation? The close... | g10913 | [
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<p>Up to my knowledge an electrified (charged) body can attract a non-electrified (neutral) body. I thought this because, when we bring a charged (suppose negatively charged) body near a neutral one. Electrified body can attract a non-electrified body by the opposite charge induced on neutral body due to electrostatic ... | g10914 | [
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0.01320854... |
<p>Generically an Abelian Fractional Quantum Hall Systems is described by chiral scalar fields $\hat{\Phi}^{\ }_{i}(t,x)$ with $i=1,\ldots,N$ and a Hamiltonian of the form
$
\hat{H}^{\ }_{0}:=
\int\limits_{0}^{L}
\mathrm{d}x\,
\frac{1}{4\pi}
\partial^{\ }_{x}\hat{\Phi}^{\mathsf{T}}
\;V\;
\partial^{\ }_{x}\hat{\Phi}
\;
... | g10915 | [
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0.08814749866724014,
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-0.00630... |
<p>A <a href="http://en.wikipedia.org/wiki/Zener_diode" rel="nofollow">Zener diode</a> is used as a voltage stabilizer. The graph of current vs voltage of Zener diode clearly shows that there is a constant voltage across Zener after the breakdown voltage as the current increases rapidly.</p>
<p>But, I would like to kn... | g10916 | [
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0.006... |
<p>I have two questions on mirrors.</p>
<ol>
<li>I’ve read that in the past quality mirrors were coated with silver but that today vacuum evaporated coatings of aluminum are the accepted standard. When I look at the <a href="http://en.wikipedia.org/wiki/Reflectivity">reflectance vs. wavelength plot</a>,</li>
</ol>
<p... | g10917 | [
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0.... |
<p>Can someone explain with a concrete example of how can I can check whether a quantum mechanical operator is bounded or <a href="http://en.wikipedia.org/wiki/Unbounded_operator" rel="nofollow">unbounded</a>?</p>
<p>EDIT: For example., I would like to check whether $\hat p=-i\hbar\frac{\partial}{\partial x}$ is bound... | g10918 | [
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0.... |
<p>Is it possible to find out the generic eigenvalue spectrum of the non-Hermitian operator $L_x+iL_y$, without using any representation?</p> | g10919 | [
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... |
<p>I am introducing myself to fluids through some physics textbooks. Most of them start with <a href="http://en.wikipedia.org/wiki/Pascal%27s_law" rel="nofollow">Pascal's principle</a>.:</p>
<blockquote>
<p>If an external pressure is applied to a confined fluid, the pressure at every point within the fluid increases... | g10920 | [
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-... |
<p>Given, $M_4 = \Sigma \times C$,
How do you get an effective theory by studying maps
$\Sigma \rightarrow M_4$ .
Technically, the physics in one manifold is supposed to gossip about the overall affairs of people in the entire manifold at least up to a certain limit.
To be direct I am trying to know how ... | g10921 | [
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0.0016095144674181938,
-0.007593441288918257... |
<p>From Michael on <a href="http://skeptics.stackexchange.com/questions/1664/it-is-not-the-voltage-that-kills-you-it-is-the-current/1677#1677">Skeptics Stackexchange</a>:</p>
<blockquote>
<p>How about a wire that's grounded?
Safe to touch, right? WRONG.</p>
<blockquote>
<pre><code> ________________ 30 am... | g10922 | [
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<p>Searching for this on google proved to be quite tedious, but I reckon that someone working with crystals a lot might know this off the top of his head:</p>
<p>Is there a good source that lists the Madelung constants for a variety of geometries? I'd be particularly interested in that for a NaCl-type 110 surface.</p> | g10923 | [
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<p>During solar system formation, many bodies achieved hydrostatic equilibrium, a spherical shape where their self gravitational force was balanced by internal pressure. Many also achieved differentiation, where a body is seperated into layers of different density (core, mantle and crust). Differentiation was mainly th... | g10924 | [
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<p>Can ${g}^{\mu\sigma}{\Gamma}^{\rho}_{\sigma\nu}$ be written as ${\Gamma}^{\mu\rho}_{\nu}$? If so how come this symbol never appears in any GR book?</p> | g10925 | [
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<p>Shlomo Sternberg (math professor at Harvard) wrote a book called "Group theory and physics". On p156 (<a href="http://books.google.com/books?id=k2Fp3JA93oYC&pg=PA156" rel="nofollow">link</a>) there's a strange offhand comment:</p>
<p>"Experiments done in 1964 by Fitch and Cronin seem to indicate that CP is not ... | g10926 | [
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<p>In <a href="http://en.wikipedia.org/wiki/Gravity" rel="nofollow">Wikipedia</a> it's stated that <em>"[..] gravity, is the natural phenomenon by which physical bodies appear to attract each other with a force proportional to their masses"</em>.</p>
<p>Then I found many examples regarding free fall and gravity, such ... | g10927 | [
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<p>This is a follow-up question to "<a href="http://physics.stackexchange.com/questions/7922/in-quantum-mechanics-why-do-the-probabilities-of-the-possible-outcomes-of-a-meas">In QM, why do the probabilities ... add up to 1?</a>".</p>
<p>No actual measurement is perfect. While theorists may ignore this, experimenters k... | g10928 | [
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0.010... |
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