question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I was reading upon Faraday effect when it said </p>
<blockquote>
<p>Faraday effect causes a rotation of the plane of polarization</p>
</blockquote>
<p>That in mind, does this mean the light can be bent around or does the light loose energy when its waves rotate? Can someone explain more about this effect simply ... | 1,400 |
<p>The mass of a nucleus if less than the mass of the protons and nucleus. The difference is knows as binding energy of the nucleus. This nuclear binding energy is derived from the strong nuclear force. </p>
<p>Now my question is that does the strong nuclear force provide this energy? How does the mass decrease if th... | 1,401 |
<p>If we are to believe that holographic principle holds over a wide number of dimensions, and gravitational theories, but specially, those that are relevant to our universe, then there must be some 3D QFT that is the dual description of our current 4D General relativity, over what it seems to be asymptotically flat de... | 1,402 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/15/what-experiment-would-disprove-string-theory">What experiment would disprove string theory?</a> </p>
</blockquote>
<p>We carefully observe things, observe patterns and then build theories that predict... | 19 |
<p>I have heard before that the 4th dimension is time, however, another theory makes a lot more sense to me. This is that the 4th dimension is the third dimension stacked on top of each other in a similar in which 3d objects are just many 2d planes.</p>
<p>I have seen many articles related to the 4thdimension being ti... | 1,403 |
<p>Reading this question and its answer</p>
<p><a href="http://physics.stackexchange.com/questions/130121/seesaw-type-1-and-integrating-out-heavy-fields">Seesaw type-1 and integrating out heavy fields</a></p>
<p>The diagonalization of the see-saw is described as going from "<em>interaction basis" right (and left) han... | 1,404 |
<p>There was a <a href="http://www.redorbit.com/news/science/1112700495/perpetual-clock-uses-4-dimensional-crystals-092512/" rel="nofollow">recent article</a> about the <a href="http://arxiv.org/abs/1206.4772" rel="nofollow">creation of 4D spacetime crystals</a> based on recent theory proposed by Frank Wilczek. This t... | 1,405 |
<p>I'm currently studying the operator methods in Quantum Mechanics, but I can't figure out the general procedure and its relations with the diagonalization problem.</p> | 1,406 |
<p>When ever i look this up all I get is sites saying how its because general relativity says "-" why does it do it though? it is because there is more motion near gravity than further away? Or is it something completely different?</p> | 1,407 |
<p>Why is <a href="http://en.wikipedia.org/wiki/Metallic_hydrogen" rel="nofollow">metallic hydrogen</a> considered a form of degenerate matter, akin to neutronium and electron-degenerate matter? I can understand that for the other two, degeneracy pressure is the only force countering inward gravity for very massive sta... | 1,408 |
<p>When I searched the net about magnetic field lines, <a href="http://en.wikipedia.org/wiki/Magnetic_field#Magnetic_field_lines" rel="nofollow">Wikipedia</a> told something about contour lines and that magnetic materials placed along a magnetic field has some specific loci, which i did not understand. Can someone expl... | 423 |
<p>In string theory, consistency with Weyl invariance imposes dynamics on the background fields through the vanishing of the beta functions. Those dynamics can also be derived from the so-called <em>low energy effective action</em>:
$$S = \frac{1}{2\kappa_0^2}\int d^{26} X\; \sqrt{-G}\; \mathrm{e}^{-2\Phi}\,(R-\frac{1}... | 1,409 |
<p>Reading a french article talking about a <em>recycling unit of rare earth from energy saving light bulbs</em> near Lyon - France (here is the <a href="http://www.solvay.com/EN/NewsPress/20120927_Coleopterre.aspx" rel="nofollow">official press release of the Salvay company</a>), I was wondering :</p>
<ul>
<li>where ... | 1,410 |
<p>In <a href="http://en.wikipedia.org/wiki/Homebrewing" rel="nofollow">homebrewing</a> on of the key steps when brewing with <a href="http://brewwiki.com/index.php/Extract_Brewing" rel="nofollow">extract</a> is to rapidly chill the wort from boiling temperatures to about 80F in 30 min. This is needed to reduce risk of... | 1,411 |
<p>Show that the Hamiltonian operator $\hat{H}= (\hat{p}^2/2m)+\hat{V}$ commutes with all three components of $\vec{L}$, provided that $V$ depends only on $r$. (Thus $H$,$L^2$, $L_z$ are mutually compatible observables).
($\vec{L}$ is $\langle L_x, L_y, L_z\rangle$.)</p> | 1,412 |
<p>Before the discovery of neutrino mass, how did people aware electron and muon neutrinos are different?</p> | 1,413 |
<p>We've been using EMF to transmit energy (information) for over a century.
I was wondering is there any other way to send a message on long distances, even faster than EMF waves can travel? For example there are particles that travel faster than C. Or as another example I have heard the Quantum Entanglement can be us... | 1,414 |
<p>It is said <a href="http://en.wikipedia.org/wiki/Introduction_to_general_relativity#Experimental_tests" rel="nofollow">in this wikipedia article</a> (in the 7th paragraph) that where there exists huge masses and very large gravitational forces (like around binary pulsars), general relativistic effects can be observ... | 1,415 |
<p>Up to now, nothing else than one Standard Model (SM) Higgs boson-like resonance has been found at the LHC while many predictions based on effective theories using supersymmetry require several Higgs scalars and needs an entourage of sparticles close in mass to tame its quantum instabilities (I borrow more or less fr... | 1,416 |
<p>In Feynman diagrams, fermionic loops are drawn like this:</p>
<p><img src="http://i.stack.imgur.com/JkPkc.png" alt="enter image description here"></p>
<p>While scalar loops are drawn as tadpoles:</p>
<p><img src="http://i.stack.imgur.com/kOKCX.png" alt="enter image description here"></p>
<p>I assume the differen... | 1,417 |
<p>Suppose to have a system $S$ immersed in an enviroment; the pure states are elements of $H_S \otimes H_E$, where $H_S$ is the hilbert space of the system and $H_E$ is the hilbert space of the enviroment.</p>
<p>The density matrix for the total system $\rho_{S+E}$ evolves according to the Von Neumann equation
$$
i \... | 1,418 |
<p>Can a negative charge ionize air? Adding to this question, I have studied that positive charge ionizes air but never studied that negative charge ionize air. If possible, please explain how does it ionize air?</p> | 1,419 |
<p>Is there a database (or any other source) of graphs of average transparency of various materials (cardboard, concrete, gypsum etc.) as a function of wavelength?</p> | 1,420 |
<p>I am interested in understanding how and whether the transformation properties of a (classical or quantum) field under rotations or boosts relate in a simple way to the directional dependence of the radiation from an oscillating dipole. </p>
<p>For example, the EM field from an oscillating electric dipole $\mathbf{... | 1,421 |
<p>Here is a small experiment my tutor once told us for just amusement. It works for myopic people at least, and can be a good check to see if you have myopia. </p>
<blockquote>
<p>With your naked eye, ("remove the spectacles" for myopic spectacle
wearers) see a considerably distant object (a few meters). It sho... | 1,422 |
<p>The invariance under translation leads to the conserved energy-momentum tensor $\Theta_{\mu\nu}$ satisfying $\partial^\mu\Theta_{\mu\nu}=0$, from which we get the conserved quantity$$P^\nu=\int d^3\mathbf x\Theta^{0\nu}(x)$$But I cannot see explicitly <strong>how this quantity is a four-vector</strong> covariant und... | 1,423 |
<p>It is known that for perfect blackbodies,
$$\lambda T= c$$
where $\lambda= \text{peak wavelength}$<br>
$T= \text{Absolute temperature}$<br>
$c= \text{Wien's constant}$ </p>
<p>But this is for perfect blackbodies only, which have no theoretical existence.... | 1,424 |
<p>In Bose-Einstein condensate (BEC), people often say there is a well defined macroscopic phase. What exactly the macroscopic phase is? (a phase factor $\mathrm{e} ^{i\phi}$ in a many-body wavefuction?) Is the macroscopic phase the same as the coherent phase?</p> | 1,425 |
<p>Would a rocket burn more fuel to get from Earth's surface to Low Earth Orbit, or to get from LEO to Geosynchronous Earth Orbit?</p> | 1,426 |
<p>I am working on a simple force problem involving inclines. I found a reference of $48^\circ$, in the third quadrant; now, to find the obtuse angle, do I subtract that value from $270^\circ$, or do I add it to $180^\circ$?</p> | 1,427 |
<p>I'm trying to understand tension. So here it goes:</p>
<p>I'll start from the beginning.</p>
<p>Let's assume I'm in space and can move around and apply forces.</p>
<p>Let's say a rope is attached to a body(which is in space).</p>
<p>1) Let's say the body is immovable.
Then the force with which the rope is pulled... | 1,428 |
<p>Here is an argument that I have with regard to entropic forces and how it can be linked to the other forces in nature. </p>
<ul>
<li><p>Gravitational: This is debated: whether gravity is entropic or not. I am going for the paper that says gravity is entropic. <a href="http://physics.stackexchange.com/questions/4289... | 1,429 |
<p>Do the interiors of black-holes create gravitational waves and if so do these waves cause the radius of the event horizon to fluctuate as the waves pass the horizon ?</p> | 1,430 |
<p>Will the event horizons of a two black holes be perturbed or bent before a collision? What will the shape of the event horizon appear to be immediately after first contact?</p> | 1,431 |
<p>Does space have an elastic quality?</p>
<p>What I was thinking about was if space is expanding, is it being 'stretched', like a balloon being blown up, and if so, is this causing gravity to weaken? Imagine space as a 2 dimensional sheet (got this from one of Brian Greene's books) with planetary bodies resting on it... | 1,432 |
<p>I just don't understand how a object with 2 ends can be unidimensional.</p> | 1,433 |
<p>How do surfaces reflect certain colours and absorb the others?</p> | 1,434 |
<p>Consider infinitely many distinguishable observers, no two of whom ever meet; and who generally "keep sight of each other", but not necessarily "each keeping sight of all others".<br>
How should they determine whether or not they can be described as being "defined on a Lorentzian manifold"?</p>
<p>[This question re... | 1,435 |
<p>If I'm running at say $400\: \mathrm{m/s}$ and a bullet travels at $400\: \mathrm{m/s}$ and I fire the gun, will I see the bullet leave the barrel? </p>
<p>I either see it stay in the barrel floating because we are moving at the same speed.
-- Or --
The bullet would move and have a speed of $800\: \mathrm{m/s}$. <... | 1,436 |
<p>We speak of locality or non-locality of an equation in QM, depending on whether
it has no differential operators of order higher than two.</p>
<p>My question is, how could one tell from looking at the concrete solutions of the equation whether the equ. was local or not...or, to put it another way, what would it me... | 1,437 |
<p>Where can I find the base data for computing the energy release of nuclear decays and the spectra of the decay products?</p>
<hr>
<p>My immediate need is to find the energy release by the beta decay of Thorium to Protactinum upon receiving a neutron:</p>
<p>$$\mathrm{Th}02 + n \to \mathrm{Th}03 \to \mathrm{Pa} 13... | 1,438 |
<p><strong>Problem/Solution</strong></p>
<p><img src="http://img832.imageshack.us/img832/1313/88791065.jpg" alt="">!</p>
<p><strong>Question</strong></p>
<p>What happened to the work done by friction BEFORE it touched the spring? Why was that neglected? Also they say there is no physical meaning behind the negative ... | 1,439 |
<p>I'm quite perplexed by the notion of 'observation' in regards to the collapse of a particle's probability wave. Does a particle's wave only collapse when it is involved in a strong interaction (such as a collision with another particle, like bouncing a photon off another particle to determine the other particle's po... | 1,440 |
<p>I am curious whether the current <a href="http://en.wikipedia.org/wiki/Lambda-CDM_model" rel="nofollow">Lambda-CDM model</a> of cosmology matches well with observational data, especially expansion of the universe.</p>
<p>How well does Lambda-CDM defend its established status from other models, such as <a href="http... | 1,441 |
<p>Some of us have been to those amusement park/carnival/theme park rides where you enter some capsule/machine, and you will float, etc.</p>
<p>There is also some other thing where you go inside a big room with normal gravity, and you are closed in and you start to float (i.e. no gravity), and the amount of gravity ca... | 1,442 |
<p>Recently I heard that there is some "alternate" equation for the Dirac one. It can be introduced if we refuse some properties of the theory describes the electron, which Dirac used in <a href="https://www.dropbox.com/s/vw8fa1s4rr32o85/Proc.%20R.%20Soc.%20Lond.%20A-1928-Dirac-610-24.pdf" rel="nofollow">his original a... | 1,443 |
<blockquote>
<p>Before answering, please see <a href="http://meta.physics.stackexchange.com/a/4698"><strong>our policy</strong></a> on
resource recommendation questions. Please try to give substantial answers that detail the
<strong>style, content, and prerequisites</strong> of the book or paper (or other resourc... | 1,444 |
<p>The length contraction means that an object is the longest in the frame in which it is at rest. </p>
<p>Lets assume i have a meter stick with length $\Delta x$ in my rest frame which is $x,ct$ and i want to know how long my meter stick seems to an observer moving with a frame $x',ct'$.</p>
<p><strong>1st:</strong>... | 1,445 |
<p>This is a quantum mechanics question, I don't quite understand what it's getting at...</p>
<blockquote>
<p>Suppose the we have a state described by $|1\,\,\, m\rangle$. Let its matrix representation be $\vec u$. The angular momentum measured in $(0, \sin\theta, \cos\theta)$ direction is $+1$. What are the compo... | 1,446 |
<p>I am having some trouble interpreting a Hamiltonian in terms of "hopping" operators. The <a href="http://www.google.com/search?q=huckel+model+graphene" rel="nofollow">Huckel model</a> for nearest neighbour interaction in graphene is given by </p>
<p>$$H=-t\sum_\vec{R}|\vec R\rangle\langle \vec R+\vec \tau|+|\vec R\... | 1,447 |
<p>Suppose we place a Hertzian dipole (short, ends loaded with capacitance) in a time varying electric field $\vec{E}\left(t\right)$, with magniture $E\left(t\right)$ and direction as shown in this figure. What will be the (steady state) current $I\left(t\right)$ flowing through the resistance $R$?</p>
<p><img src="h... | 1,448 |
<p>Classical thermodynamics leads one to believe that if energy is transferred, and the universe is heading for maximum entropy, then back extrapolating to moments before the big bang, one could find a definitive answer of the total amount of energy of the system(universe) contains.</p>
<p>However I can't find this qu... | 1,449 |
<p>I recently found out about the discovery of 13 beautiful periodic solutions to the three-body problem, described in the paper</p>
<blockquote>
<p>Three Classes of Newtonian Three-Body Planar Periodic Orbits. Milovan Šuvakov and V. Dmitrašinović. <a href="http://dx.doi.org/10.1103/PhysRevLett.110.114301"><em>Phys.... | 1,450 |
<p>This video ( <a href="http://www.youtube.com/watch?v=Vs3afgStVy4" rel="nofollow">http://www.youtube.com/watch?v=Vs3afgStVy4</a> ) demonstrates lenz's law, if the current produced by the magnet fall induces an opposing magnetic field , after many tries , can this field demagnetize the magnet? or decrease its magnetiz... | 1,451 |
<p><img src="http://i.stack.imgur.com/ORjPY.png" alt="enter image description here"></p>
<p>Let me explain the picture just to make sure. Object with mass 2 kg is being pulled with a force of F = 14.4 N. The whole system has an acceleration of a = 2.8 m/s^2. The friction coefficient between the objects and the ground ... | 1,452 |
<p>For the wave function of a scattered particle when finding the scattering aptitude we have:</p>
<p>$$\psi(r)=Ae^{ik_0∙r}+\frac{2\mu}{\hbar^2} ∫G(r-r')V(r')\psi(r')d^3r'$$</p>
<p>I was wondering what the variables $r$ and $r'$ represent. I think r just represents the position of the particle and $r'$ the size of th... | 1,453 |
<p>I have heard that when a sailboat is sailing against the wind, it operates on the principle of 'lift'. I am unable to understand the explanation, based on Bernoulli principle, completely. My question is, when it says 'lift', it literally means that the boat is being 'lifted' out of the water? Like when we throw a st... | 1,454 |
<p>Suppose you have a state described by the wave function $\psi(x) = \phi_1(x)+2\phi_2(x)+3\phi_3(x)$ , where the $\phi$s are normalised eigenfunctions of a Hermitian operator $\hat{O}$ with eigenvalues $\lambda_1 = 1, \lambda_2 = 5, \lambda_3 = 9$.</p>
<p><strong>What happens to the wave function if you measure $\ha... | 1,455 |
<p>I know people will say it violates many laws of motion and conservation but could anyone explain why it is so?
It's NOT a question about free energy.</p>
<p>Imagine a motor in space. It has an arm (rod) attached to it. At the end of the arm there's a ball (weight) attached to it. The motor produces a circular motio... | 1,456 |
<p>I know that one of the dangers of a nuclear attack is the shockwave which compresses the air and can cause a pulmonary embolism in creatures in the area of effect. Is the shockwave directional in effect?</p>
<p>In other words, lets say your building is on the outskirts of a city and is built so that all the windows... | 1,457 |
<p>I was unable to answer this question from my daughter. Is it just a coincidence or is there a connection between the following two observations: (1) the core of the earth is made of an iron (-nickel alloy) as well as the existence of iron meteorites with the fact that (2) the heaviest element that can be produced by... | 1,458 |
<p>A particle of mass $m$ is at a very large distance $p$ from origin $O$ and is moving with velocity $\vec{V}$ which is perpendicular to $\vec{OP}$. I have to calculate angular momentum $L$ of the particle. </p>
<p>I know that $\vec{L}=\vec{r}\times m\vec{\dot r}$.<br>
Since $|\vec{r}|=p$ and $|\dot r|=V$ and $\alph... | 1,459 |
<p>Let's have the system of point-like non-interacting particles and it's own angular momentum
$$
\mathbf L_{1} = \mathbf L - [\mathbf R_{E} \times \mathbf P],
$$
where $\mathbf R_{E}$ - center of energy of the system, $\mathbf P $ - impulse of center of energy,</p>
<p>and it's operator,</p>
<p>$$
\hat {\mathbf L}_{1... | 1,460 |
<p>I was watching a video on Youtube which deduce Einstein's relation $E=mc^2$ and the process of deduction used the relation between <a href="http://en.wikipedia.org/wiki/Mass_in_special_relativity" rel="nofollow">relativistic mass and rest mass</a>, which is</p>
<p>$$m= \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}.$$ </p>
... | 20 |
<p>Given a stream of random binary numbers(*)</p>
<p>Is there any way to differentiate if they came from a Truly Random or from a formula/algorithm ? how?</p>
<p>if there is no way to decide this, then, I can't find any basis, to keep denying that behind the "truly random" of quantum mechanics can be a hidden algorit... | 1,461 |
<p>I recently bought some <a href="http://www.getbuckyballs.com/" rel="nofollow">buckyballs</a>, considered to be the world's best selling desk toy. Essentially, they are little, spherical magnets that can form interesting shapes when a bunch of them are used together.</p>
<p>After playing around with these buckyballs... | 1,462 |
<p><em>I've read the following question:</em> <a href="http://physics.stackexchange.com/q/27303/">Negative probabilities in quantum physics</a>
<em>and I'm not sure I understand all the details about my actual question. I think mine is more direct.</em></p>
<p>It is known that the <a href="https://en.wikipedia.org/wik... | 1,463 |
<p>I am reading a <a href="http://www.cambridge.org/us/academic/subjects/physics/particle-physics-and-nuclear-physics/foundations-perturbative-qcd" rel="nofollow">book</a> on perturbative QCD by John Collins. In Chapter 5, the terms <strong><em>reduced graph</em></strong> and <strong><em>pinch-singular surface</em></st... | 1,464 |
<p>Is there a manageable formula or set of formulas or simple algorithms that approximate stellar luminosity and effective temperature (or radius) as a function of stellar age?</p>
<p>I'm aware that accurate modeling of these attributes is complex and is determined by many factors; what I'm looking for is something th... | 604 |
<p>String theory false vacua can be described by effective Lagrangians at low energy. Is there generally a correspondence between these effective Lagrangians and SU(N) gauge theories? Or do the effective Lagrangians often not respect local invariance with respect to some or any gauge groups? </p> | 1,465 |
<p>I took a bucket, drilled 2 different sized holes on the side near the bottom and filled it with water. The stream of water the proceeded from the larger hole traveled further than the stream from the smaller one. How does the size of the hole affect the distance that the water travels?</p>
<p>See also: <a href="htt... | 1,466 |
<p>My teacher mentioned that field line density = no. of lines / area and the total area of a sphere is $4\pi r^2$ and so an electric force is inversely proportional to $r^2$. Actually, why can the total area of the sphere be applied to this case and is this true? How does one come up with the Coulomb's law?</p> | 1,467 |
<p>I apologize if this question is not up to par.
When I was doing exercises in basic mechanics I checked the answers and I can't seem to find what I'm doing wrong.
Suppose we have a ball with mass $m$ and radius $r$ on an inclined plane with height $h$. At the end of the inclined plane is a loop with a radius of $R$ a... | 1,468 |
<p>While tossing a coin, it is commonly experienced that you get a head, if you toss it up with the head side up, and a tails if you toss with the tails side up. Is there a mathematical proof of this using classical mechanics? I would like to see a simple model of the coin as a symmetric top, and consider the precision... | 1,469 |
<p>I want to simulate the path of an electron through the anode of an electron gun. I therefore need to calculate the force on the electron due to the electric field from the anode and apply that to its existing velocity. The electron can start at any arbitrary point $p$ with velocity $v$ (both vectors).</p>
<p>I gues... | 1,470 |
<p>He is CORRECT. I use $\mathbf{B}=\left(0,0,B_{\perp}\right)$ and he use $\mathbf{B}=\left(0,0,-B_{\perp}\right)$. $B_{\perp}>0$.</p>
<h1>Nov.28.2012</h1>
<p>Basically I got mad with conventions.</p>
<p>1.Here is the link of the book (second edition): </p>
<p><a href="http://books.google.fr/books/about/Quantum... | 1,471 |
<p>Hi I'm calculating a problem, and I think it ought to be correct - but the result I get isn't.</p>
<p>The problem is described as follow:</p>
<blockquote>
<p>A spacecraft is traveling from Earth to Venus in an elliptical, but
NON-Hohman transfer orbit, starting at the apocentre at 1 AU. The
semi-major axis o... | 1,472 |
<p>I just went through <a href="http://www.nature.com/nature/journal/v505/n7485/full/nature12954.html">Observation of Dirac monopoles in a synthetic magnetic field</a>.</p>
<p>What exactly has been observed?</p>
<p>More importantly, are these monopoles localized inside the apparatus (no stray monopole field lines com... | 1,473 |
<p>I want some explanation of fields and <a href="http://en.wikipedia.org/wiki/Superfield" rel="nofollow">superfields</a> (types and components), and what the relationship between them and representation of a group. </p> | 1,474 |
<p>I am currently studying electrodynamics with all the fields and the like. Now, as I understand it, in a more modern viewpoint there is a duality between electromagnetic fields and photons, with photons being the particles that are exchanged in the process of interaction.</p>
<p>My question is, what is the current e... | 21 |
<p>In gas metal arc welding, an electric arc forms between the work piece and a consumable wire, heating the work piece and also melting the tip of this consumable wire, which is continually fed into the weld.</p>
<p>I recently found out that it is important to use the correct polarity when welding with direct current... | 1,475 |
<p>I wonder if there is a measure of how long a piece of metal takes to reach electrostatic equilibrium. </p>
<p>Does it depend on piece's size? Does it depend on the amount of imbalance?</p>
<p>Lots of websites and textbooks report "after a very short time". But how much short?</p>
<p>Thanks a lot</p> | 1,476 |
<p>Electricity: I was wondering, whether we can pass electricity through air over a distance of 100 meters or so as electricity means the flow of electrons and we have seen the discharge or movement of electrons in a cathode ray tube</p> | 1,477 |
<p>In Griffiths's <em>Introduction to Quantum Mechanics</em>, he says that the time dependence of an expectation value is
$$\frac{d\langle Q\rangle}{dt}=\frac{i}{\hbar}\langle [H,Q]\rangle+\langle \frac{\partial Q}{\partial t}\rangle$$
And I also saw a lecture note saying that time dependence of an expectation value is... | 1,478 |
<p>Note 1: This is probably as much a maths question as physics.
Note 2: I am not sure if my use of the the term conductance is correct.</p>
<p>I want to make a kiln. The walls will be thick. I can come to two figures for the conductivity of a kiln of given dimensions, between which the actual conductivity will lie. ... | 1,479 |
<p>Consider general state of a system with spin-$1/2$</p>
<p>$$ \psi = \frac{1}{\sqrt{2}}\left[\phi_{+1/2}(x) \left( \begin{array}{cc} 1 \\ 0 \\ \end{array} \right) + \phi_{-1/2}(x) \left( \begin{array}{cc} 0 \\ 1 \\ \end{array} \right)\right]. $$</p>
<p>If I created an apparatus which measures <em>only spin</em> wou... | 1,480 |
<p>Are there any hamiltonian systems without a periodic orbit? Can anyone give me an example?</p>
<p>If such a system exists, does this fact have any implication on its quantum version?</p> | 1,481 |
<p>Suppose a body is moving in a circle about a fixed point. In the frame of reference of the body, is the centripetal force felt or is only the centrifugal force felt? </p>
<p>More generally, does a body only feel the effect of pseudo forces in an accelerated reference frame?</p> | 1,482 |
<p>Let's suppose I have a point charge moving arbitrarily in space. As far I know, Maxwell's equations don't determine a unique electric and magnetic field, they only determine a family of electric and magnetic fields. What other information do I need in order to know uniquely the electric and magnetic field produced b... | 1,483 |
<p>I'm supposed to use law of cosines on $S_1S_2P$ in the following diagram that relates to a lens:</p>
<p><img src="http://puu.sh/5zDtv.jpg" alt="triangle diagram"></p>
<p>To arrive at the following equation:</p>
<p>$$
\frac{r_2}{r_1} = [1 - 2(\frac{a}{r_1})sin(\theta) + (\frac{a}{r_1})^2]^\frac{1}{2}
$$</p>
<p>I ... | 1,484 |
<p>It's been a while, and I'm trying to verify my understanding. I remember reasoning (but never being taught) that the sum of the (normalized) electric and magnetic waves in a single electromagnetic wave at any single point in time is always one. Like so:</p>
<pre><code>Given A of em-wave is normalized (max = 1, min ... | 1,485 |
<p>Many years ego, Earth was hot. Over time, it has lost energy and has become colder. Is it now in equilibrium or is its total energy changing?</p> | 1,486 |
<p>From my limited experience with ham radio when I was a kid, I expect transmitting and receiving antennas to have lengths that are on the same order of magnitude as the wavelength, and in fact I recall having to mess around to compensate for the fact that a given antenna wouldn't be properly resonant over an entire f... | 1,487 |
<p>When quantizing a system, what is the more (physically) fundamental commutation relation, $[q,p]$ or $[a,a^\dagger]$? (or are they completely equivalent?)</p>
<p>For instance, in Peskin & Schroeder's QFT, section 3.5, when trying to quantize the Dirac field, they first say what commutation relation they <em>exp... | 1,488 |
<p>If we imagine ourselves to be a civilization capable of manipulating very heavy masses in arbitrary spatial and momentum configurations (because we have access to large amounts of motive force, for example), then we can imagine building ponderous rings such that light, pointed in a particular direction, will be grav... | 1,489 |
<p>When we shoot a single photon out into space, the chance that it will eventually return to our vicinity from a different direction is vanishingly small, even though spatial curvature exists due to the gravitational influence of the distribution of mass energy throughout the universe. It is hard to imagine any regula... | 1,490 |
<p>Regarding the Bremsstrahlung Radiation emitted when a charged particle curves inside a uniform magnetic field; Is there a way of calculating the angle through which the charged particle will precess before emitting the first quantum of radiation? Also, is there a way of determining the angle through which the charge... | 1,491 |
<p>Let's say two objects are sitting adjacent (in contact) to each other. If we start pushing one of them, we know that both the objects move, remaining in contact to each other. But let's now consider imparting an impulse to one of the objects, instead of a steady force. I expect the two objects to start moving, but t... | 1,492 |
<p>Apparently (first paragraph of <a href="http://en.wikipedia.org/wiki/Second_harmonic_generation">this article</a>) the lack of <em>inversion symmetry</em> is some crystals allows all sort of nonlinear optic phenomena. </p>
<p>Now. Does anyone know of an intuitive or just physical explanation as to <em>why</em> this... | 1,493 |
<p>How do <a href="http://simple.wikipedia.org/wiki/String_theory" rel="nofollow">strings</a> present in particles give mass to them? Is it only by vibrating? I have been trying to find the answer but could not find it anywhere, can this question be answered?</p> | 1,494 |
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