question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>I am trying to represent the result of a dimensional analysis calculation and I can't find an official document that lists the order that unit symbols should appear.</p>
<p>For example, when I google $5\text{ m}\times 2\text{ kg}$ or $2\text{ kg}\times 5\text{ m}$ the result is always meters first, or $10\text{ m k... | 4,369 |
<p>Kane and Fu proposed a few geometries how to create Majorana zero modes using a s-wave superconductor in proximity to a 3D topological insulator (TI).</p>
<p>-> <a href="http://www.physics.upenn.edu/~kane/pubs/p56.pdf" rel="nofollow">http://www.physics.upenn.edu/~kane/pubs/p56.pdf</a></p>
<p>I understand that we n... | 4,370 |
<p>I often read about s-wave and p-wave superconductors. In particular a $p_x + i p_y$
superconductor - often mentioned in combination with topological superconductors.</p>
<p>I understand that the overall Cooper pair wavefunction may have orbital momentum = 0 (s-wave)
or orbital momentum = 1 (p-wave) where the first ... | 4,371 |
<p>This is a homework question, so please don't give me the answer outright. I just need help conceptually.</p>
<p>"A cylindrical shell of length 190 m and radius 4 cm carries a uniform surface charge density of σ = 12 nC/m2.</p>
<p>(a) What is the total charge on the shell? </p>
<p>Find the electric field at the en... | 4,372 |
<p>In a laboratory course we had to perform an experiment with a pendulum (just an iron weight on a wire) and play around for some time with its wire's length and so on. </p>
<p>This was quite boring and we decided to make something more interesting:</p>
<p>We took two magnets (like <a href="http://www.artec-educatio... | 4,373 |
<p>How can a light passed though a single slit produce a similar interference pattern to the double-slit experiment? How does the diffracted wave produce the points of cancellation and reinforcement, if there is only one wave?</p> | 689 |
<p>Thomas Young used a single slit between the light source and the double slits. I can't understand why did he used the single slit, since the light from only one source is coherent already or isn't it? Does the narrow single slit make incoherent source coherent? </p> | 4,374 |
<p>From Wikipedia:</p>
<blockquote>
<p><a href="https://en.wikipedia.org/wiki/Bremsstrahlung" rel="nofollow">Bremsstrahlung</a> is electromagnetic radiation produced by the
deceleration of a charged particle when deflected by another charged
particle, typically an electron by an atomic nucleus. The moving
part... | 4,375 |
<p>In classical mechanics the motion of a particle is bounded if it is trapped in a potential well. In quantum mechanics this is no longer the case and there is a non zero probability of the particle to escape the potential through a process call quantum tunneling. </p>
<p>This seems extraordinary from the point of cl... | 4,376 |
<p>My <a href="http://en.wikipedia.org/wiki/Incandescent_light_bulb" rel="nofollow">light bulb</a> cast a clear light toward adjacent wall and I can clearly see, that <a href="http://en.wikipedia.org/wiki/Incandescent_light_bulb#Filament" rel="nofollow">wire filament</a> inside bulb shakes, though lamp itself does not ... | 4,377 |
<p>It is known fact, that boiling point of water decreases by decreasing of pressure. So there is a pressure at which water boils at room temperature.
Would it be possible to cook e.g. pasta at room temperature in vacuum chamber with low enough pressure?</p>
<p>Or "magic" of cooking pasta is not in boiling and we woul... | 4,378 |
<p>In expanding the classical Klein-Gordon field in Fourier space to write it in terms of $\phi(\mathbf{p})$ instead of $\phi(\mathbf{x})$, I reached the following result.
$$\int \mathrm{d}^3p\exp({i\mathbf{p}\cdot\mathbf{x}})\left[\frac{\partial^2}{\partial \mathrm{t}^2}+|\mathbf{p}|^2 + m^2\right]\phi(\mathbf{p},t) ... | 4,379 |
<p>If I understand this correctly, accelerating charges lose energy in the form of EM waves because they change the electric and magnetic fields, which "costs" energy. Does that mean that accelerating masses lose energy too, because they change the gravitational field (i.e. curve spacetime)?</p> | 4,380 |
<p>Measuring temperature in joules instead in the artificial units of Kelvin would render entropy as a dimensionless quantity. This is quite appealing since entropy has always been quite a misterious quantity: it is used a measure of the disorder in a system but its units are J/K, which makes it really hard to interpre... | 4,381 |
<p>I was working out the minimum tangential velocity required for a swing to complete a full revolution and assumed the centripetal force is equal to the centrifugal force, so that I could set the weight force equal to the formula for centripetal (i.e. net force 0 at the top so swing won't fall). I'm pretty sure the an... | 4,382 |
<p>I have a couple of different LED flashlights. One of them has three different "modes" of brightness, and the way it controls it is via pulse width modulation (PWM). Here is a picture that illustrates how it works: </p>
<p><img src="http://i.stack.imgur.com/GF3LQ.gif" alt="enter image description here"></p>
<p>I kn... | 4,383 |
<p>Terminal Velocity depends on two things- surface area and speed. These are inversely proportionate.</p>
<p>If both these variables affect terminal velocity, why do parachutes slow you down? Initially you had a small surface area but a fast speed- with the parachute you have a larger surface area but lower speed. Yo... | 4,384 |
<p>As it is.</p>
<p>As I study through classical mechanics and quantum mechanics, I began to wonder whether there is a relationship between classical electromagnetic wave frequency and quantum wave function and de broglie frequency).</p>
<p>I think this is somehow related to quantum electrodynamics...but anyway.</p> | 4,385 |
<p>Some explanations of the device base it on a simple echo of light: "The camera transmits invisible near-infrared light and measures its “time of flight” after it reflects off the objects. Time-of-flight works like sonar: If you know how long the light takes to return, you know how far away an object is." (<a href="h... | 4,386 |
<p>Consider a spherical body of uniform density $\rho$ and initial radius R. You can imagine this body containing another sphere of radius R/2 which touches the center and the periphery of the larger sphere. The smaller sphere has 8 times less mass, since the mass goes as the radius cubed.</p>
<p>If you let the big sp... | 4,387 |
<p>My book says a capacitor is two conducts being connected by an insulator. Now let's take a parallel plate capacitor to simplify the problem I have.</p>
<p>Suppose I got two parallel plate capacitor in series and I hook the circuit up with a battery. </p>
<p><img src="http://i.stack.imgur.com/YWnG8.jpg" alt="enter ... | 4,388 |
<p>I'm just struggling a little with this question:</p>
<p>A uniform sphere, of radius $R$, contains a spherical cavity of radius $R/4$, whose centre is $3R/8$ from the surface. The diameter passing through the centres of the sphere and cavity meets the surface at points $X$ and $Y$. Find the ratio of the gravitationa... | 4,389 |
<p>Assuming a solid rectangular plate, hinged along one edge. How does one calculate the mass of the plate if the force necessary to lift the opposite edge is known?</p> | 4,390 |
<p>Can an Electric Field with field lines Like So Exist:</p>
<p><img src="http://puu.sh/tWkJ" alt=""></p>
<p>One Of my friends said it couldn't as the field lines here are not conservative ; so it cannot exist ; Is he right?</p>
<p>Or can it be made to exist</p> | 4,391 |
<p><a href="http://en.wikipedia.org/wiki/Bell_test_experiments#Conduct_of_optical_Bell_test_experiments" rel="nofollow">Wiki</a> tells us that <em>In practice most actual experiments have used light, assumed to be emitted in the form of particle-like photons (produced by atomic cascade or spontaneous parametric down co... | 4,392 |
<p><img src="http://i.stack.imgur.com/zubVb.jpg" alt="enter image description here"></p>
<p>I have seen in <a href="http://books.google.fr/books/about/Molecular_theory_of_capillarity.html?id=_ydSF_XUVeEC&redir_esc=y" rel="nofollow">http://books.google.fr/books/about/Molecular_theory_of_capillarity.html?id=_ydSF_XU... | 4,393 |
<p>It is known that electromagnetic (EM) fields action on particles is limited to the Lorentz force action. In terms of spinors and currents, the EM field:</p>
<p>(i) rotates the Dirac current around the direction of the field $B$ to the angle proportional to the magnitude of $B$, and</p>
<p>(ii) "accelerates" the Di... | 4,394 |
<p>Is the universe finite, both in the sense of being a closed spacetime manifold, as viewed from the macro level, but also in the sense of being fully discrete and finite in all of its intricate quantum level construction?</p>
<p>The most popular current research, i.e. string theory, builds a machinery on top of a co... | 4,395 |
<p>In this experiment, a number of coins are put into a cup <em>full</em> of water, without spilling it.</p>
<p><a href="http://www.youtube.com/watch?v=N2mKpZHnEzw" rel="nofollow">http://www.youtube.com/watch?v=N2mKpZHnEzw</a></p>
<p>Firstly, let me clarify one thing. </p>
<blockquote>
<p>If you fill up a cup of ... | 4,396 |
<p>Some months ago, an ArXiv paper mentioned in passing that Maxwell's Equations were invariant under reciprocating the variables, or at least this results in a dual set of Maxwell Equations. (Actually I think "inverting" may have been the word the author used.)</p>
<p>The paper was in one of the endorsed groups (not ... | 4,397 |
<p>While reading Stanislaw Lem's essays on advanced civilizations, I had a question: When did the earliest generation of <a href="http://en.wikipedia.org/wiki/Population_1_star#Population_I_stars" rel="nofollow">population 1 star</a> systems <a href="http://en.wikipedia.org/wiki/Star_formation" rel="nofollow">form</a>?... | 4,398 |
<p>Let's say we are building Nd:YAG laser.
It is optically pumped by some linear xenon flash lamps, it absorbs light around 750nm and 800nm, and emitted light is at 1064nm.</p>
<p>The question is why doesn't 1064nm emission from the flash lamps interfere with laser operation?</p>
<p>Why doesn't 1064nm photons emitted... | 4,399 |
<p>I wish to study supersymmetry in field theory(sometime in december). However, I am quite not sure what is needed for its study. In supersymmetry, I just want to get the mathematical idea, such as its algebra. I will finish a course in QM this semester. I have studied some lie algebra (Cahn, Georgi). I also have some... | 4,400 |
<p>I want to know from the smallest possible originating structures how the light I see generated from heat is made by atoms themselves.</p> | 4,401 |
<p>I know a family that grows fruit such as blueberries in a climate that frosts on occasion. When this happens, they turn on sprinklers which covers the buds and fruit with a layer of water which turns to ice.</p>
<p>Why would this layer of ice prevent damage to the plants/fruit? Perhaps it insulates them, keeping te... | 4,402 |
<p>At CMB recombination (z=1090), what is the radial extent of the last scattering "shell"?
a) Delta(z) = ....
b) Delta(comoving angular distance)= ....Mpc</p>
<p>The WMAP first-year parameters give
Delta(z) = 195. Is this still correct?</p> | 4,403 |
<p>The models/depictions I've seen of warp bubbles show space compressed ahead of the bubble and expanded behind, so that the space inside the bubble moves with respect to the space outside. If that is so, then what is happening at the sides? It would seem that there is some sort of shear taking place between the space... | 4,404 |
<p>I am currently finishing my undegraduate degree in physics and would like to do PhD in Theory of Condensed Matter field. Could you give advice on which are good groups/supervisors in the field. Please, justify by adding citations to important research papers they have produced, any awards received etc.</p> | 4,405 |
<p>Is there any way in which a bound state could consist only of massless particles? If yes, would this "atom" of massless particles travel on a light-like trajectory, or would the interaction energy cause it to travel on a time-like trajectory?</p> | 4,406 |
<p>If water is flowing through big pipe is branched into 4 branches of small pipe. Lets say the flow is around 4 m/sec. </p>
<p>I have the following questions:<br/></p>
<ol>
<li><p>What will be the flow rate in each of the pipes? I would be knowing diameter, height of the pipes. Considering all pipes are rigid.<br/><... | 4,407 |
<p>In my research, I found that the speed of light is not fixed. IS it true?</p>
<p>Namely, We know that light refracts when the medium it travels through changes. Actually, light travels in the same medium without refraction . This is a relative motion in two dimension. </p>
<p>However, in the medium light up to ‘’(... | 4,408 |
<p>I guess this is more of a chemistry question, but whatever. I think it's interesting.</p>
<p>Suppose you had two bare atomic nuclei. For concreteness, lets assume the nuclei are the same with atomic number $Z$. Lets bring in a single electron and focus on the ground states of the nuclei.</p>
<p>When the nuclei ... | 4,409 |
<p>What experiments could provide observable "stringy" effects.</p>
<p>All valid experiments are acceptable (also theoretical experiments).</p> | 4,410 |
<p>I am wondering if it makes sense to state that the upper limit is roughly 10<sup>12</sup> eV (up to know the physics probed by the LHC seems to be pretty consistent with the SM) and the lower one is ... the upper bound for the photon mass (somewhere between 10<sup>-14</sup> and 10<sup>-26</sup> eV according to <a hr... | 4,411 |
<p>What methods could be used to determine (<em>or</em> estimate within a <em>reasonable</em> margin of error) the mass of a living human's limbs, short of cutting them off? And more interestingly, how can this be done without any high tech equipment, just with the means commonly found in households?</p>
<p>A scale fo... | 4,412 |
<p>Leonard Suskind gives the following formulation of the energy-momentum tensor in his Stanford lectures on GR (#10, I believe):</p>
<p>$$T_{\mu \nu}=\partial_{\mu}\phi \partial_{\nu}\phi-\frac{1}{2}g_{\mu \nu}\partial_{\sigma}\phi \partial^{\sigma}\phi$$</p>
<p>In an intro to GR book I find this formulation of the ... | 4,413 |
<p>A properly oriented calcite crystal will separate an unpolarized beam into two beams, one vertically polarized and one horizontally polarized. Other polarizers pass just one polarization and absorb the perpendicular one.<br>
Is there a device that splits an unpolarized light beam into a right circulaly polarized on... | 4,414 |
<p>Approaching the following question:</p>
<blockquote>
<p>Consider two experiments in which 2 moles of a monatomic ideal gas are
heated from temperature $T$ to temperature $T + \Delta T$: in the
first experiment the volume $V$ is kept constant, in the second
experiment the pressure $p$ is kept constant. How m... | 4,415 |
<p>I'm looking around the net to find good resources on how to compute total radiation flux from a given star at a given orbiting distance.</p>
<p>Ideally I'd like to get not just the $W/m^2$ of the star, but also the expected high-energy particles, EM, thermal, solar wind pressure.. well, the works.</p>
<p>Everywher... | 4,416 |
<p>In cosmology, we have two quantities and I want to understand the physical relation between these two :</p>
<p>$\chi = \int_{t_e}^{t_0}c\frac{dt'}{a(t')}$ : the comoving distance with $t_e$ the time at emission and $t_0$ the current cosmic time</p>
<p>$\eta_0 = \int_{0}^{t_0}\frac{dt'}{a(t')}$ : the conformal time... | 4,417 |
<p>Picture yourself standing on a ball that is expanding at such a rate that it makes you stick to the ball.
Everything in the universe is expanding at this same rate.
To escape the earths gravitational pull we would need to jet upward faster than the expansion of the earth.
Each object expands at a different rate on i... | 4,418 |
<p>In Fick's first law, the diffusion coefficient is velocity, but I do not understand the two-dimensional concept of this velocity. Imagine that solutes are diffusing from one side of a tube to another (this would be the same as persons running from one side of a street) to unify the concentration across the tube.</p>... | 4,419 |
<p>While hammering a nail (before it is in the wall) it is pretty evident that the tip of the nail is going to be applying a force directed along th axis of the nail, then why is it said that pressure is always non directional ?</p> | 138 |
<p>In our quantum mechanics script, it states that $[L^2, X^2] = 0$ and $[L^2, P^2] = 0$, therefore for the following Hamiltonan</p>
<p>$$H = \frac{P^2}{2m} + V(X^2)$$</p>
<p>it is that $[H, L^2] = 0$ therefore $H$ and $L^2$ have the same eigenvectors, and then it continues to calculate orbitals of the hydrogen atom.... | 4,420 |
<blockquote>
<p>Due to application of force tow blocks of mass 1Kg and 0.5Kg move together. Each block exerts a force of 6N on each other. What is the acceleration by which both the blocks move?</p>
</blockquote> | 4,421 |
<p>It seems that a common statistical model for the count numbers of a photomultiplier is a Poisson distribution whose parameter $\lambda$ equals to the square-root of the number of counts.(e.g. <a href="http://www.sciencedirect.com/science/article/pii/S1350448711005750" rel="nofollow">http://www.sciencedirect.com/scie... | 4,422 |
<p>Consider the Hamiltonian $H = -J_\text{F}S^{(1)}_zS^{(2)}_z + J_{AF}S^{(1)}_zS^{(2)}_z$, describing the graph</p>
<p><img src="http://i.stack.imgur.com/3lg1R.png" alt="enter image description here"></p>
<p>Here, F means ferromagnetic and AF means antiferromagnetic interactions. I am having problem with the value o... | 4,423 |
<p>Object A can move at 50km/h, wants to intercept object B (currently $15^{\circ}$, east of north from A) moving at 26km/h, $40^{\circ}$ east of north. What angle should A take to intercept B? AB is 20km apart</p>
<p><img src="http://i.stack.imgur.com/Kcm8I.png" alt="enter image description here"></p>
<p>The provide... | 4,424 |
<p>A ball rocks around an arc. In the following illustration, the ball reaches the end of the arc (its velocity magnitude is zero at that particular moment).</p>
<p><img src="http://i45.tinypic.com/16ixldw.png" alt="Illustration"></p>
<p>Now, I want to know which forces are acting on that ball at that particular mome... | 4,425 |
<p>By Carnot Theorem, the efficiency of Carnot cycle is$$\eta=1-\frac{T_C}{T_H}$$</p>
<p>where $T_C$,$T_H$ are the absolute temperature of the cold reservoir and hot reservoir respectively. Since $T_C > 0$, that means $\eta < 1$, so it concludes the Kelvin statement:
"no process is possible in which the sole r... | 4,426 |
<p>I am calculating the buoyancy flux ($B$) for a stratified fluid as follows:
$$
B=\frac{g\alpha S}{C_{pw}\rho_0}
$$</p>
<p>where $g = 9.81$ $m/s$; $\alpha = 1.6 t\times10^{-5} + 9.6\times10^{-6} \times (20 \text{ degC})$; $S = 100\text{ }Wm^{-2}$, $\rho_0 = 1000$ $kg/m^3$, and $C_{pw}$ is the specific heat of water.... | 4,427 |
<p>So I was recently wondering what happens to the excess charge when it is placed on an insulator or conductor e.g. rubbing two objects together. I know in the conductor the electrons are free to move whereas in the insulator they in general are not very mobile so the charge stays in a small region. But why does this ... | 4,428 |
<p>When introducing the 't Hooft diagrams from Feynman diagrams on a torus has there been a classification in terms of knots and <a href="http://en.wikipedia.org/wiki/Seifert_surface" rel="nofollow">Seifert surfaces</a>?</p> | 4,429 |
<p>I read in various places <a href="http://en.wikipedia.org/wiki/Geon_%28physics%29">geons</a> are "generally considered unstable." Why? How solid is this reasoning? </p>
<p>Is the reason geons are not studied much anymore because we can't make more progress without better GR solutions or a better theory of quantum g... | 4,430 |
<p>I've wondered how far would be able to send a concentrated beam of electrons in space. The reason is would we be able to launch a magnetic ring with an electron absorbing material on one side and just fire electrons through the ring to create a push? </p> | 4,431 |
<p>If I lift a book of mass $m$ from the ground and put it at height $h$,then initial and final energies with respect to ground are 0 and $mgh$ respectively. </p>
<p>So how energy is conserved here?</p> | 4,432 |
<p>One of the main sources of subtlety in the AdS/CFT correspondence is the role played by boundary terms in the action. For example, for a scalar field in AdS there is range of masses just above the Breitenlohner-Freedman bound where there are two possible quantizations and which one you get depends on what boundary t... | 4,433 |
<p>i was reading a specific book on quantum mechanics, partiicularly on the tunnel effect section. I am trying to understand how the probability of an eletron passing a barrier of energy V0 is calculated for both $E>V0$ and $E<V0$, i.e., the electron having more energy and less energy, respectively.</p>
<p>For ... | 4,434 |
<p>Is it correct to say that 9.0 is one order of magnitude smaller than 10.0? </p>
<p>Has anyone a link/source about confronting order of magnitudes, apart from wikipedia?</p> | 4,435 |
<p>Perhaps I am completely wrong, but as I understand it our observation of a system can affect the outcome. The example I remember is the double slit experiment where electrons behave as a wave at first, but when observing it behaves as a particle. The conclusion, as I remember hearing, is that <strong>observing</st... | 139 |
<p>I don't know how to explain the issues at hand in a way that nonphysicists are certain to understand. Can anyone point me to some resource (book, video, it doesn't really matter) that will help me?</p> | 140 |
<p>Sound can be a destructive force. However, could it be used to separate say the Hydrogen atom from the Oxygen atoms?</p> | 4,436 |
<p>How can one go from the 3D compressible <a href="http://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations" rel="nofollow">Navier-Stokes equations</a> to the simpler <a href="http://en.wikipedia.org/wiki/Euler_equations_%28fluid_dynamics%29" rel="nofollow">Euler equations</a>, <a href="http://en.wikipedia.org/wik... | 4,437 |
<p>There have been several Phys.SE questions on the topic of <a href="http://en.wikipedia.org/wiki/Zero_mode">zero modes</a>. Such as, e.g., </p>
<ul>
<li><p><strong>zero-modes</strong> (<a href="http://physics.stackexchange.com/q/2951/">What are zero modes?</a>, <a href="http://physics.stackexchange.com/q/68706/">Can... | 4,438 |
<p>Suppose there is an entangled state of two electrons, the spin part is
$$| \downarrow \uparrow \rangle - | \uparrow \downarrow \rangle \tag{1} $$.
If I add the spatial part of the wavefunction as two Gaussians, it should be something like
$$ ( e^{- (r_1-R_a)^2- (r_2-R_b)^2} + e^{- (r_1-R_b)^2- (r_2-R_a)^2})( | \do... | 4,439 |
<p>As postulated by Stuart Hameroff in his article "quantum consciousness",that it is one of the reasons for reduction of quantum superposition.
Roger Penrose suggested that consciousness is not necessary for reduction but a system can undergo self reduction or objective reduction due to intrinsic feature of spacetime... | 4,440 |
<p>In the book <em>physical foundations of cosmology</em>, it saids that Hubble law is unique and a problem seems to be a hint of proving that.</p>
<blockquote>
<p>In order for a general expansion law,<strong>v</strong>=f(<strong>r</strong>,t), to be the same for all observers, the function f must satisfy the relati... | 4,441 |
<p>In "String Theory and M-Theory" by K. Becker, M. Becker and J.H. Schwarz, page 222, they give a brief introduction about the (space-filling) Orientifold Plane $O9$ as an object needs to be add in the theory to make the it consistence (or at least, that what I thought). However, I still don't really get their argumen... | 4,442 |
<p>Negative probabilities are naturally found in the Wigner function (both the original one and its discrete variants), the Klein paradox (where it is an artifact of using a one-particle theory) and the Klein-Gordon equation.</p>
<p>The question is if there is a general treatment of quasi-probability distributions, be... | 4,443 |
<p>I am covering the classic literature on predictions of Cabibbo angle or other relationships in the mass matrix. As you may remember, this research was a rage in the late seventies, after noticing that $\tan^2 \theta_c \approx m_d/m_s$. A typical paper of that age was Wilczek and Zee <a href="http://dx.doi.org/10.101... | 4,444 |
<p>I'm interested in the pure gauge (no matter fields) case on Minkowski spacetime with simple gauge groups.
It would be nice if someone can find a review article discussing all such solutions</p>
<p>EDIT: I think these are relevant to the physics of corresponding QFTs in the high energy / small scale regime. This is... | 4,445 |
<p>Say we have a two star system with both stars of equal mass $M$. The center of mass of this system is by definition in the center of the two stars. </p>
<p>There is a small asteroid with mass m in orbit around the center of mass of the two stars. (What is known as a halo orbit apparently)
The orbital distance is x... | 4,446 |
<p>Point charges q1=− 5.00nC and q2=+ 5.00nC are separated by a distance of 3.50mm , forming an electric dipole. The torque exerted on the dipole has a magnitude of 7.60*10^-9 N*m at an angle of 37∘ with the horizontal.
Using this information, I calculated that the magnitude of the electric dipole moment would be 1.75... | 4,447 |
<p>There are several online services that let you control a large
telescope (eg, lightbuckets.com and slooh.com), even some that are
free (eg, telescope.org). </p>
<p>Unfortunately, the pay services are expensive, and you get very little
reserved time on the scopes. The free services are painfully slow: I
had to w... | 4,448 |
<p>If I put my feet into a pool of water that contains a live wire, why do i get shocked? For electrons to flow through my body, there has to be a E-field/wave that passes through my body along a certain path, that motivates the electrons to flow through me. Now given that the live-wire is in the water and on the groun... | 4,449 |
<p>I have read somewhere that the best/easiest way to watch meteor showers is to lie on the ground or other horizontal surface with your feet oriented towards the "apparent point of origin" (what was that called again?) of the shower and just relax while having eyes open to the heavens.</p>
<p>Last November I actually... | 4,450 |
<p>If a particle is totally localized at $x=0$, its wave function $\Psi(x,t)$ should be a Dirac delta function $\delta(x)$. Accordingly, its Fourier transform $\Phi(p,t)$ would be a constant for all $p$, thus the particle's momentum is totally uncertain. I guess this is what the Uncertainty Principle told us.</p>
<p>B... | 4,451 |
<p><br/>
This is <a href="http://en.wikipedia.org/wiki/Logistic_map" rel="nofollow">the logistic map</a>:<br/>.
<img src="http://i.stack.imgur.com/ooYe8.png" alt="Image of bifurcation diagram of the logistic map"><br/>
It is a fractal, as some might know here.<br/>
It has a <a href="http://en.wikipedia.org/wiki/List_of... | 4,452 |
<p>I am struggling with a derivation that calculates the cross sections for Mie scattering and since the incident light is considered to be a x-polarized plane wave I thought that we would have $$I_i = \frac{1}{2} \sqrt{\frac{\epsilon}{\mu}} \vert E_0 \vert^2$$, but I do not understand this derivation then, since a fac... | 4,453 |
<p>Hypothetical brain teaser here, no real kittens involved! - </p>
<p>For some bizarre reason I have a sack of kittens, I need to find the total weight of the kittens and the sack but I'm only allowed to use a spring scale and I'm only allowed use my arms to hold the scale. My arms are unsteady and the kittens are co... | 4,454 |
<p>IS there any quantum analogy where a three state (or three body) system shows chaotic dynamics as three body problem in classical mechanics?</p> | 4,455 |
<p>Can classical mechanics be derived from quantum mechanics as the same way thermodynamics derived from statistical mechanics?</p> | 141 |
<p>As far as I understand it, the first principle of thermodynamics is a mere definition of the quantity “Heat”: $$\text d Q: = \text d L + \text d U.$$
This is somewhat the point of view taken in Fermi's introductory book "Thermodynamics": </p>
<blockquote>
<p>[...] $$\Delta U + L=0$$If the system is not thermally ... | 4,456 |
<p>In n-body simulation you need to know the positions of the particles in order to calculate the force between them. The new velocity of each particle can then be calculated given a simulation timestep dt.</p>
<p>If the gravitational interaction propagates at the speed of light, do we need to specify the force betwee... | 4,457 |
<p>I was wondering if anyone knew the formula to calculate how much force is required to lift a tire or any object by the edge. </p>
<p>For example if a tire weighs 500 lbs (or has a mass of 226.8 kg). I would just like to know the formula how to calculate how much of that 500 lbs we are actually lifting since it is o... | 4,458 |
<p>Recent results from the BICEP2 experiment have produced a lot of talk about the primordial gravitational waves produced during the inflationary period.</p>
<p>I would like to have some explanation about how inflationary models predict the generation of these gravitational waves. Have these gravitational waves been ... | 4,459 |
<p>I got one more stupid question in Polchinski's string theory book. In p. 44, it is said</p>
<blockquote>
<p><em>The currents</em>
$$j(z)=i v(z) T(z), \tilde{j}(\bar{z}) = i v(z)^* \tilde{T}(\bar{z}) \tag{2.4.5}$$
<em>are conserved for any holomorphic $v(z)$.</em></p>
</blockquote>
<p>Did he mean
$$\part... | 4,460 |
<p>I am wondering about a specific question regarding the speed at which an electrical current traverses through salt-water / saline. </p>
<p>By this I do <em>not</em> mean the electron drift speed - I mean, at what speed would a current travelling from an anode to a cathode immersed in salt water be? </p>
<p>A ball ... | 4,461 |
<p>If the sinusoidal electric component of a light wave were off-set to one side of the magnetic component and then the smaller "lobe" were to cancel out with much of the larger side, then where would the energy go? Would it not form a closed loop much like a mass-bearing string? Could the electrical energy not be conv... | 4,462 |
<p>If a conductor - a long rod - moves at constant speed across the "lines" of a uniform magnetic field, is there an EMF within this conductor? Or, if a conducting rod rotates at uniform rate, pivoted in the middle or at one of its ends in a uniform magnetic field perpendicular to the plane of rotation, is there an EM... | 142 |
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